José I Velasco

Abstract: The rejected fraction of plastics from different sorting plants has been studied in terms of composition, processability and enhancement potential. This waste stream consists of a coarse range of plastics families, polyethylene constituting the most abundant one. Blends with two recycled polyethylenes in different proportions were analyzed. The results showed that the mixed fraction was easy to process although it showed a brittle behavior. The addition of recycled polyethylene caused limited ductility improvements, although acceptable levels were achieved in certain mixing ratios. This work demonstrates that mixed plastic wastes can be transformed into a useful material. © 2013 Copyright Taylor and Francis Group, LLC.

Abstract: In this work we have studied the effect of different flame retardants on the fire behavior and mechanical properties of epoxy mortars. Flame retardants acting under different mechanisms of action have been compared: phosphate flame retardants as well as magnesium hydroxides and carbonates. Besides the commercial flame retardants we have also used a magnesium basic carbonate obtained from an industrial by-product. The use of an alternative based on an industrial by-product combines an economic and sustainable solution. Different formulations of flame retarded epoxy mortars have been prepared and characterized. The obtained results prove the effectiveness of the tested flame retardants on the improvement of the fire properties of the epoxy mortars without a significant decrease on their mechanical properties. © 2012 Elsevier Ltd. All rights reserved.

Abstract: Investigation of the flexed plate impact of polymers requires the study of the local plate reaction during the contact between the hemispherical tip and the specimen. The current work investigates the low energy impact indentation with a hemispherical indenter applied to a polymer sheet with a ductile behavior. The samples were freely supported on a very rigid steel plate and transversely collided by the instrumented dart. The restitution coefficients are calculated, and a lumped mass-spring model based on the Hertz law, which agrees with the experimental contact forces, restitution coefficients, indenter depth of penetration and permanent deformations is developed. This is an indirect method to estimate the Young's modulus at these relatively high strain rates. The influence of the geometrical parameters of the test such as target thickness, drop mass, indenter diameter, along with impact velocity are analyzed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 Copyright © 2012 Wiley Periodicals, Inc.

Abstract: This work considers the preparation and characterization of polypropylene foams with variable concentrations of graphene and carbon nanofibres, focussing on the influence of the foaming process and the nanofillers on the microstructural and dynamic-mechanical-thermal properties of the foams. Great differences were found in terms of foam morphology depending on the type of foaming process, with foams prepared by physical foaming showing a vertically deformed cell structure, while chemical foams presented an isotropic-like cellular structure. The addition of graphene resulted in foams with higher cell densities and more uniform cellular structures when compared to the ones with nanofibres. Direct result of the combination of their particular cellular structure and higher expansion, polypropylene foams obtained by physical foaming presented a higher orientation of the α-monoclinic polypropylene crystal perpendicular to the foam's surface and higher exfoliation of the nanofillers, resulting in foams with improved mechanical properties. All these considerations are of extreme importance, as some of the most promising applications of these polymer foams require a good electromagnetic interference shielding efficiency, which greatly depends on the developed foam morphology. © 2013 The Author(s).

Abstract: In this paper LDPE/silica nanocomposites are foamed by two different processes. First one is the pressure quench method which is based on the use of a physical blowing agent and second one is the improved compression moulding technique. As the latter process uses a chemical blowing agent, both types of foamed nanocomposites will provide very useful information about the relationship between foaming process-microstructure and macroscopic properties. Results have revealed how silica nanoparticles are able to act as nucleating sites during foaming step in both processes; however, the optimum amount of particles strongly depends on the foaming route. Thermal and mechanical properties of solid and foamed nanocomposites have been analyzed by means of thermogravimetric analysis and compression tests. Results have revealed that nanosilica particles act as effective nucleating agents, not only reducing cell size and increasing cell density but also achieving more homogeneous cellular structures. Thermal and mechanical properties are improved due to the presence of silica nanoparticles. It has been found that the improvement degree reached for samples produced using chemical blowing agents is greater than that achieved for samples produced using physical blowing agents. © 2013 Elsevier Ltd. All rights reserved.

Abstract: Different relative density polypropylene foams were prepared by means of two foaming processes: chemical foaming by compression moulding and physical foaming by high pressure CO 2 dissolution. By controlling the foaming parameters, such as blowing agent concentration, foaming temperature, pressure drop and pressure drop rate, it was possible to regulate the cellular structure, foams showing from markedly isotropic-like cellular structures to ones with highly-elongated cells in the vertical foam growth direction (honeycomb-like cell orientation). The thermal conductivity was measured using the transient plane source method. Using this technique, it was possible to measure the global conductivity and the thermal conductivity in both the axial and radial directions of a given sample. Results show that the global thermal conductivity of foams was mainly regulated by their relative density. In addition, the honeycomb-like cell orientation of the CO 2 dissolution foams resulted in considerably higher values in axial direction when compared to radial, demonstrating that there was a direct influence of cellular structure on the thermal conduction behaviour of these foams, enabling the development of new polypropylene foams with direction-dependent thermal properties. Highlights: We study the thermal anisotropy of polypropylene foams using a transient method. Cellular structure influences the thermal conductivity of CO 2 dissolution foams. Thermal anisotropy increases with reducing density due to a stretched cell structure. The lowest density CO 2 dissolution foams show axial conductivity similar to solid PP. By separating axial and radial components we show the importance of cell orientation. © 2012 Elsevier B.V.

Abstract: Polypropylene (PP) foams have become essential items due to their excellent properties. Nevertheless, obtaining net-shaped PP foams with medium relative densities is a complicated issue. In this article, two processes able to produce moulded PP foams in this density range are presented. One of them is based on a modification of the pressure quench foaming method and therefore uses a physical blowing agent (CO 2). The second one is the improved compression moulding technique which uses a chemical blowing agent (azodicarbonamide). PP foams with relative densities in the range between 0.25 and 0.6 and cylindrical shape were prepared using these foaming techniques. A common PP grade (instead a highly branched one) was used to obtain the samples, showing, that by combining the appropriate foaming technique, the adequate moulds, suitable blowing agent and proper foaming parameters, net-shaped PP foams with excellent properties can be produced starting from a conventional PP grade. Samples were characterized by analyzing their cellular structure and their mechanical properties. Results have showed that depending on the chosen foaming route isotropic or anisotropic structures with cell sizes ranging from 40 to 350 μm and open cell content in the range between 0 and 65% can be obtained. Moreover, mechanical properties are highly influenced by the production route and chemical composition of the foams. For instance, the stiffer materials at relative densities higher than 0.4 are the ones produced using the chemical blowing agent while at relative densities lower than 0.4 are the ones produced using the physical blowing agent. © Springer Science+Business Media, LLC 2012.

Abstract: Novel lightweight composite foams based on recycled polypropylene reinforced with cellulosic fibres obtained from agricultural residues were prepared and characterized. These composites, initially prepared by melt-mixing recycled polypropylene with variable fibre concentrations (10-25wt.%), were foamed by high-pressure CO 2 dissolution, a clean process which avoids the use of chemical blowing agents. With the aim of studying the influence of the fibre characteristics on the resultant foams, two chemical treatments were applied to the barley straw in order to increase the α-cellulose content of the fibres. The chemical composition, morphology and thermal stability of the fibres and composites were analyzed. Results indicate that fibre chemical treatment and later foaming of the composites resulted in foams with characteristic closed-cell microcellular structures, their specific storage modulus significantly increasing due to the higher stiffness of the fibres. The addition of the fibres also resulted in an increase in the glass transition temperature of PP in both the solid composites and more significantly in the foams. © 2011 Elsevier Ltd.

Abstract: In this paper, polymer foams based on a benzoxazine resin have been successfully prepared using azodicarbonamide (ADC) as a chemical blowing agent and have been characterized regarding their foaming behavior, cellular structure, and physical properties. The effect of the ADC on the curing process of the resin was analyzed using differential scanning calorimetry and blowing agent decomposition was followed by thermogravitmetric analysis (TGA). The characterization of the cellular structure of the foamed samples was done using scanning electron microscopy. The mechanical properties of the foams were determined using compression tests and the thermal conductivity was assessed using the transient plane source method. The results indicated that the curing process and gas release took place in a similar time interval. The foams showed an isotropic cellular structure with relative densities in the range 0.35-0.60, and showed compressive strengths and compressive moduli in the range of 10-70MPa and 400-1100MPa, respectively. Thermal conductivities were in the range of 0.06-0.12Wm -1K -1. The findings in this paper demonstrate the possibility of producing polybenzoxazine foams using a simple process in which curing and foaming take place simultaneously. In addition, the mechanical characterization of these materials indicates that they are suitable for structural applications. © 2011 John Wiley & Sons, Ltd.

Abstract: A novel technique to determine in situ the free expansion kinetics of chemically foamed thermoplastic foams, so-called optical expandometry, is presented in this work. This technique is based on the camera monitoring of a free-foaming material placed inside a furnace. Images are acquired under special illumination conditions to facilitate the later image processing. The present article explains the experimental set-up and the image processing methods used to determine the free volumetric expansion of different polyolefin-based foams. The results are compared with those obtained using thermo-mechanical analysis. In addition, several possible applications of this method are detailed, such as studying the effect of polymer rheology, foaming temperature, blowing agent content and the anisotropy of the expansion. Copyright © 2011 Wiley Periodicals, Inc.

Abstract: A thermogravimetric study in both nitrogen and air atmospheres has been carried out on unfilled and graphene-reinforced solid and foamed polycarbonate. Polycarbonate foams were prepared using a supercritical CO 2 dissolution one-step batch foaming process. Results showed that polycarbonate displayed a characteristic one-step decomposition under nitrogen, while three-step degradation was observed in air. In addition, as-received pristine graphene nanoplatelets displayed a three-step degradation in air, compared to a mild degradation under nitrogen. It was found that the thermal stability remarkably improved for the foamed composites, related to a combination of a heat transfer reduction promoted by the insulating cellular structure and the presence of the platelet-like graphene, which helped create a physical barrier effect, delaying the escape of volatile products generated during decomposition. © 2012 Elsevier Ltd. All rights reserved.

Abstract: Two types of commercial low density polypropylene based flexible foams produced by extrusion foaming were characterized in terms of their fracture behaviour using the concept of the Essential Work of Fracture (EWF), focusing on the influence of the foam's relative density and cellular structure on the values of the fracture parameters. With that in mind, correction procedures based on the expansion ratio of the foams and their cellular structure were proposed, with the objective of taking the complexity of these materials into account in the obtained fracture parameters. Significant differences were found between the fracture parameters of the two foams related to differences in their cellular structure, particularly cell size, cell aspect ratio and preferential cell orientation. Generally speaking, the specific fracture elastic contribution in the two considered extrusion directions increased with increase of the cell aspect ratio, especially in the case of the foams with a marked cell orientation in the direction of the extrusion flow. In any case, the fracture parameters for all foams were considerably lower in the direction perpendicular to the extrusion flow, hence demonstrating the highly anisotropic fracture behaviour of these foams due to the anisotropic cellular structure induced during foaming. © 2012 Elsevier Ltd. All rights reserved.

Abstract: The properties of polypropylene (PP) foams can be extended by controlling the cellular structure and adding functional fillers. PP-based microcellular foams having an interesting combination of mechanical and transport properties were prepared by two different batch foaming processes. The batch processes employed were a semisolid state CO 2 dissolution physical foaming process and a chemical one based on the dissolution of the gases generated by the thermal decomposition of a chemical blowing agent in the molten state. The role of the cellular structure and nanofillers (5 wt% of organoclay and 10-20 wt% of cellulosic fibers) on the foam properties and CO 2 diffusion rate was discussed. Foams with expansion ratios around 3 but different cell structures were prepared and studied concerning their structural characteristics. For unfilled foams prepared by CO 2 dissolution, the microcellular structure resulted in the highest values of the specific storage modulus. A fraction of organically-treated montmorillonite dispersed into the PP matrix resulted in superior mechanical properties due to the combined effect of a finer cell structure and inherent higher stiffness of the silicate layers. Despite displaying an open-cell structure, foams reinforced with high contents of cellulosic fibers showed increased specific storage moduli with respect to the unfilled foams. POLYM. ENG. SCI., 2011. Copyright © 2011 Society of Plastics Engineers.

Abstract: In the present work polyurethane foams containing variable concentrations of nano-sized clay and esparto wool were prepared and studied, with the objective of developing new multi-scalar rigid foams. The addition of montmorillonite clay favoured foaming and the formation of finer and homogeneous cellular structures, resulting in foams with compressive elastic moduli and collapse stresses lower than that of the polyurethane foams. Nevertheless, a comparative analysis versus the foams' relative density demonstrated that both properties follow one single trend for the two materials. The combination of esparto and montmorillonite further reduced the cell size of foams, at the same time promoting higher open cell contents, resulting in the foams with the lowest mechanical properties. Although no important differences in thermal conductivity were found with adding montmorillonite, its value decreasing with reducing the relative density, the incorporation of esparto led to higher thermal conductivities, independently of the relative density. The combination of esparto and montmorillonite resulted in foams with thermal conductivities halfway between the esparto-reinforced and the montmorillonite-reinforced foams, related to a higher open cell content. © 2011 Elsevier B.V.

Abstract: One of the actual trends in polymer foams consists in the development of new materials by combining density reduction through foaming with the incorporation of functional fillers. This would enable to obtain materials with improved specific properties and added functionalities. There is also a growing interest in the use of environmentally-friendly materials obtained from renewable sources, thus coming as a logical step to combine both in order to create novel biocomposite foams. This work presents an overview of our recent results regarding the preparation and structural and thermo-mechanical characterizations of rigid polypropylene-based composite foams, with the main goal of developing new lightweight materials with tailor-made properties (multifunctional foams). Several reinforcements have been considered, from renewable cellulose fibres to nanometric-sized reinforcements such as silicate-layered nanoclays and carbon nanofibres. © Smithers Rapra Technology, 2011.

Abstract: This study assesses the processing behaviour and mechanical properties of different thermoplastic polymers filled with Electric Arc Furnace Dust (EAFD). Design of Experiments (DoE) approach enabled the evaluation of the influence of each component and the interactions between them. There were prepared different composite formulations varying the content of EAFD. The mechanical properties and the melt flow index (MFI) of composites were selected as output responses and the effect of CaCO 3, BaSO 4 and EAFD fillers as well as different polymer matrixes were evaluated. It was observed that slight variations in the formulation yield to a broad range of response values. Polyethylene-co-vinyl acetate (EVA) concentration showed a significant effect on all responses. It was found that the presence of EAFD increased fluidity and decreased the elasticity modulus and the elongation at break. In addition, when added with barite, the presence of EAFD caused an increase of the tensile strength. © 2011 Elsevier B.V.

Abstract: Microcellular foams of polystyrene (PS), poly(styrene-co-acrylonitrile) (SAN), and poly(methyl methacrylate) (PMMA) having organically modified layered double hydroxides (LDH) were prepared using a high-pressure CO 2 dissolution foaming process and characterized both structurally and thermo-mechanically. The saturation concentration of CO 2 was found to increase with the incorporation of LDH nanoparticles into the PMMA, while the opposite effect was observed in the PS and SAN nanocomposites with respect to the pure polymers. The CO 2 desorption diffusion coefficient substantially decreased in the nanocomposites comparatively to the respective pure polymers. The incorporation of hydrotalcite (HT) into the polymers and subsequent foaming resulted in foams with finer and more isotropic cellular structures, related to a cell nucleation effect promoted by the particles. No significant differences were found among the several foamed nanocomposites. Both PS and SAN nanocomposite foams displayed higher glass transition temperatures than the respective unfilled ones, related to a higher amount of residual CO 2 in the last, favoring plasticization. The contrary effect was observed in PMMA, attributed to a combined plasticizing effect promoted by the higher affinity of PMMA for CO 2 and greater interaction with the organically modified HT platelets. Although no significant differences were found among the several nanocomposite foams and respective unfilled counterparts, the incorporation of HT limited the reduction observed in the specific storage moduli with foaming, related to a finer cellular structure induced by the HT particles. © 2010 American Chemical Society.

Abstract: Magnesium hydroxide-filled polypropylene foams were prepared by a compressionmolding chemical foaming process and studied considering the effects of foaming and the presence of the particles on the microstructure (cellular structure and induced particle and polymer orientations), dynamic mechanical, and flame retardancy of the polypropylene composites. Two magnesium hydroxide concentrations, 50 and 70 wt%, as well as different foam densities, were considered. Results are discussed in terms of the observed anisotropy-induced cellular and particle and crystal orientations and their effects on the direction-dependent dynamic mechanical and flame behavior results. Preliminary flame retardancy characterization of the several solid and foamed composites showed interesting results due to foaming, foams globally exhibiting a higher extinguishability than the respective solid composites. © The Author(s) 2011.

Abstract: The influence of foaming a semi-crystalline polymer reinforced with different concentrations of carbon nanofibres (0-20 wt.%) on the formation of an electrically conductive network was studied at room temperature using an impedance analyzer over a wide interval of frequencies (from 10 -2 to 10 6 Hz). Composites were prepared by melt-compounding using a twin-screw extruder, and later chemically foamed. Although composite materials displayed lower conductivities than expected, assuming a percolative behavior, foaming promoted a tunnel-like conduction at lower CNF concentrations than in the solids. At higher CNF concentrations, no great improvements were achieved as tunneling conduction decreased with increasing local crystallinity. Foams showed electrical conduction characteristics typical of a conductive random-distributed fibre-like system, while the behavior of the solids was closer to a system of spherical particles, related to CNF aggregation. The anisotropic cellular structure of the 20 wt.% CNF composite foamed by a physical foaming process disrupted the preferential in-plane CNF orientation attained during solid preparation, with these foams showing higher through-plane conductivity and more isotropic electrical properties than the chemically-foamed ones. It has been demonstrated that foaming PP-CNF composites resulted in the formation of a conductive network at lower CNF concentrations than in the solids, with foams showing the potential for use in conductive high-performance lightweight composite systems. © 2010 Elsevier Ltd. All rights reserved.

Abstract: Layered Double Hydroxide (LDH) particles intercalated with dodecylsulfate anions were prepared following different methods and analysed by thermogravimetry (TGA) and X-ray diffraction (XRD). Two commercial grades of MgAl LDH particles were used as LDH precursors. Two-step reconstitution was found to be the most effective route to prepare dodecylsulfate intercalated LDH particles. The obtained particles were melt blended with polypropylene at a 10. wt.% loading. The thermal stability and flame retardant behaviour of the resultant nanocomposites were studied with TGA and limiting oxygen index tests. The mechanical properties were also characterized. The experimental results reveal the potential of these organic modified LDH particles to improve both the thermal stability of polypropylene matrix and the mechanical properties. © 2010 Elsevier B.V.

Abstract: Microcellular foams of poly(methyl methacrylate) with variable concentrations of an organically modified montmorillonite, oMMT (2.5-10 wt %), were prepared using a supercritical CO 2 dissolution physical foaming process. Particular importance was given to the analysis of the influence of the montmorillonite on the CO 2 desorption behavior out of the several nanocomposites. The saturation concentration of CO 2 was found to be two times higher in the nanocomposites when compared to the pure PMMA and a comparative analysis of the desorption curves showed that a higher concentration of CO 2 remained in the nanocomposites for long times when compared to PMMA, except for the 10 wt % oMMT nanocomposite. Also, the incorporation of oMMT promoted the formation of submicrometric foams with much lower cell sizes and higher cell densities. With increasing the amount of oMMT, the glass transition temperature of PMMA decreased in both the solids and foams and important improvements were observed regarding the specific elastic moduli of the foams, demonstrating the mechanical reinforcement effect of oMMT. © 2011 American Chemical Society.

Abstract: The impact event involves the motion of the specimen, the motion of the striker and the local indentation in the contact zone. In order to study the effect of the local indentation, epoxy-carbon fiber laminate specimens supported on a very rigid steel plate, were subjected to low energy impacts in an instrumented falling weight dotted with an instrumented striker with an hemispherical head. The obtained restitution coefficients show that the energy absorption by indentation is not negligible. It has been developed a lumped mass spring model based in the Hertz law which agrees with the experimental contact forces, indenter displacements and restitution coefficient, which give a very good fitting. This non-conservative model allowed assessment of the Young's modulus at these relatively high strain rates. © Smithers Rapra Technology, 2011.

Abstract: This work presents the preparation and characterization of compression-moulded montmorillonite and carbon nanofibre-polypropylene foams. The influence of these nanofillers on the foaming behaviour was analyzed in terms of the foaming parameters and final cellular structure and morphology of the foams. Both nanofillers induced the formation of a more isometric-like cellular structure in the foams, mainly observed for the MMT-filled nanocomposite foams. Alongside their crystalline characteristics, the nanocomposite foams were also characterized and compared with the unfilled ones regarding their dynamic-mechanical thermal behaviour. The nanocomposite foams showed higher specific storage moduli due to the reinforcement effect of the nanofillers and higher cell density isometric cellular structure. Particularly, the carbon nanofibre foams showed an increasingly higher electrical conductivity with increasing the amount of nanofibres, thus showing promising results as to produce electrically improved lightweight materials for applications such as electrostatic painting. Copyright © 2010 M. Antunes et al.

Abstract: This article presents the preparation of microcellular polypropylene foams produced by a CO2 batch-foaming process and their characterization regarding the influence of the pressure drop rate on the foaming behavior and dynamic-mechanical properties. A polypropylene-based material was prepared by melt-mixing in a twin-screw extruder, cooled, and pelletized and later compression-molded in a hot-plate press to solid discs. These discs were finally foamed inside a high pressure vessel by dissolving CO2 and carefully controlling its sudden decompression drop. The dynamic-mechanical properties of the different expansion ratio-produced PP foams were studied, analyzing the influence of the pressure drop rate and residual pressures on the cellular structure and subsequent dynamic-mechanical behavior of the foams. With increasing the sudden pressure drop by reducing the residual pressure value, higher expansion ratio PP foams were obtained, reaching a maximum value of 3. Only slight differences were observed between foams regarding the cell size (maximum cell size - 100 m), the foams presenting slightly lower specific storage moduli than that of the solid material, indicating the efficiency of this process in nucleating and generating relatively high expansion ratio foams with a closed-cell type of structure and cell sizes in the micrometer range. © 2010 The Author(s).

Abstract: The Essential Work of Fracture (EWF) technique has been used for the ductile materials characterization, where yielding phenomenon occurs before crack propagation. The EWF method characterizes the post-yielding fracture, determining two parameters: the specific essential work of fracture, w e related with the real fracture process area, and the specific non-essential work of fracture, w p that corresponds with the work done in the outer region of the crack tip. The EWF technique has been successfully employed especially with polymers, allowing the study of the influence of many variables on the fracture behavior, unavailable using other techniques such as J integral. In this work, the fundamentals of the technique and examples of application are reviewed, presenting a brief summary of the most relevant contributions of our group to the EWF method. © 2010 Universidad Simón Bolívar (Venezuela).

Abstract: Nanocomposites based on a sodium partially- neutralized ionomer of poly(ethylene-co-methacrylic acid) (EMAA) and MgAl layered double hydroxide (LDH) particles with and without organic modification were prepared from a melt mixing process. The structure was characterized using X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). Although TEM micrographies revealed the presence of agglomerates of LDH sheets, the achievement of an exfoliated structure was observed when dodecyl sulphate-modified LDH particles were used. The effects of the LDH particles on the thermomechanical properties of EMAA were analyzed using differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The thermal transition of the ionic aggregates and dynamic mechanical response of EMAA were found strongly modified by these particles, resulting in an increase on the storage modulus and a decrease on the loss factor values. Moreover, the alpha relaxation of the composites was visibly shifted to higher temperatures. © 2010 Wiley Periodicals, Inc.

Abstract: This article presents the study of the modification of the particle/matrix interface region and its effects on the structure and dynamic mechanical behavior of polypropylene (PP)/hydrotalcite nanocomposites prepared by melt extrusion. The interface modification was promoted by combinying the organophillization of the hydrotalcite particles with blending the PP with a maleic anhydride-grafted-PP (PP-g-MAH) or a maleic anhy-dride-grafted- poly(styrene-co-ethylenebutylene-co-styrene) (SEBS-g-MAH). Sodium dodecyl sulphate was used to promote the organophillization of the hydrotalcite particles. X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed a partially exfoliated hydrotalcite structure, with an increasing exfoliation being achieved by adding a compatibilizer and organo-modifying the particles. Values of the Young's modulus (E), storage modulus (E�), maximum tensile strength (�max), neck propagation strength (�neck), and elongation at break (εb) were found to depend both on the nature of the particle matrix interface as well as on the type of compatibilizer. Also, nanocomposites prepared with the organophillized particles showed lower Tg and loss factor values. © 2009 Society of Plastics Engineers.

Abstract: Hybrid nanocomposites formed with polyoxymethylene copolymer (POM) and different types of polyhedral oligomeric silsesquioxane (POSS) nanoparticles have been investigated. Four types of POSS have been studied in contents of 2.5% and 5% wt. The POSS were incorporated by direct melt-mixing. Traditionally copolymerization has been the preferred approach used to form polymer- POSS nanocomposites because the possibility of immiscibility with the polymer matrix is reduced. However, melt-blended POSS nanoparticles can also improve the thermo-mechanical properties of some polymers. Different morphologies were obtained depending on the type of POSS used. GI-POSS and O-POSS exhibit sub-micron or micron-sized inclusions which size increased with increasing percentages of POSS added. On the other hand, both G-POSS and T-POSS appeared to be uniformly dispersed in the POM matrix probably at a molecular level. This is a clear indication of miscibility between these systems and also that POSS solubility in POM is higher than 5 wt%. G-POSS improved the thermal stability of the systems. However, the melting temperature and the modulus of elasticity were found to slightly decrease. On the other hand, the O-POSS produced the opposite effect in the matrix. Finally T-POSS filled systems do not yield important variations in regard to polymethylene oxide properties although interaction between T-POSS and the matrix was detected. Copyright © 2010 American Scientific Publishers All rights reserved.

Abstract: In this paper, carbon-nanofibre-reinforced polypropylene foams were prepared and characterized regarding their foaming behaviour, cellular structure and both thermo-mechanical as well as electrical properties. Polypropylene (PP) nanocomposites containing 5, 10 and 20 wt% of carbon nanofibres (CNF) and a chemical blowing agent were prepared by melt-mixing inside a twin-screw extruder and subsequently water-cooled and pelletized. The extruded nanocomposites were later foamed using a one-step compression-moulding process. The thermo-mechanical properties of the CNF-reinforced PP foams were studied, analyzing the influence of the carbon nanofibres on the cellular structure and subsequent thermo-mechanical behaviour of the foams. Carbon nanofibres not only seemed to act as nucleating agents, reducing the average cell size of the foams and increasing their cell density for similar expansion ratios, but also helped produce mechanically-improved foams, even reaching for the 20 wt% CNF-reinforced ones a specific modulus around 1.2 GPa.cm3/g for densities as low as 300 kg/m3. An increasingly higher electrical conductivity was assessed for both the solids as well as the foams with increasing the amount of carbon nanofibres. Copyright © 2010 American Scientific Publishers. All rights reserved.

Abstract: In the present paper, the effects of nanoparticles' content and orientation were studied on the structure, phase morphology and thermo-mechanical properties of highly oriented montmorillonite/ poly(methyl methacrylate) moulded nanocomposites. The nanocomposites were compounded using a co-rotating high-shear twin-screw extruder. Square plates were prepared by a two-stage compression-moulding process from the previously extruded materials, with the test specimens being directly machined in both parallel and perpendicular directions with respect to the plate's surface. Wide-angle X-ray diffraction (WAXD) revealed a highly-ordered structure of silicate platelets parallel to the plate's surface. Observations by transmission electron microscopy (TEM) supported this analysis, demonstrating the high anisotropy degree of the nanocomposites. Dynamic mechanical thermal analysis (DMTA) showed that the perpendicular specimens were stiffer than the parallel ones, with the presence of the oriented nanoparticles decreasing PMMA's mobility during the glass transition, although no significant differences were registered in the T g temperatures with increasing the amount of clay content or with orientation. Remarkable improvements regarding the fracture energy were observed for the perpendicular specimens, with the 20 wt% oMMT nanocomposite showing a fracture energy almost 10 times that of pure PMMA. Copyright © 2010 American Scientific Publishers. All rights reserved.

Abstract: The aim of this work is to evaluate the use of Poly(lactic acid) (PLA) industrial waste as a source of raw material for certain applications, as well as to understand the effects of the annealing on the fracture behavior of PLA. PLA waste has been simulated by an initial step of extrusion in a single screw extruder and pelletizing. Specimens of virgin and reprocessed PLA were obtained by injection molding. An annealing treatment capable of increasing the percentage of crystallinity (determined by differential scanning calorimetry) was also analyzed in reprocessed and non reprocessed specimens. The fracture behavior was studied at slow and high testing speed, applying the linear elastic fracture mechanics (LEFM) on single edge notched bend (SENB) specimens. This study revealed that the fracture toughness of the reprocessed PLA was basically the same that the virgin PLA and also that the increase in the crystalline fraction produced an improvement on the fracture toughness, at slow loading rate. © 2010 Springer Science+Business Media, LLC.

Abstract: The Post-Yielding Fracture Mechanics describe the fracture behaviour of pre-cracked films and thin sheets that show yielding phenomenon at the crack tip during fracture. The Essential Work of Fracture method (EWF) has been used for this type of fracture characterization, determining two parameters: the specific work of fracture, we related with the real fracture process area, and the specific non-essential work of fracture, wp that corresponds with the work done in the outer region of the crack tip. The EWF technique has been successfully employed especially with polymers, allowing the study of the influence of many variables in fracture properties, unavailable using other techniques such us KIC or JIC determination. In this work, the fundamentals of the technique and examples of application are reviewed, presenting a brief summary of the most relevant contributions of our group to the EWF method. © 2009 Elsevier Ltd. All rights reserved.

Abstract: This article presents the analysis of the processing parameters influence on the foaming behavior and cellular structure of PP-montmorillonite foams. Polypropylene nanocomposites containing 5.0 phr of an organically-modified montmorillonite (MMT) were initially melt-compounded in a twin-screw extruder with azodi-carbonamide (ADC) and later foamed using a one-step compression-molding process. The cellular structure and morphology of the foams was assessed using both scanning and transmission electron microscopies. A time-dependant double-effect was observed during foaming: (1) first of all, the melt strength of the polymer, too high for shorter times, not allowing full cell growth, and too low for high foaming times due to thermal oxidation; (2) and polymer degradation, clearly observed for very high foaming times, directly affecting polymer's melt resistance. Comparatively, PP-MMT foams exhibited a broader foaming time processing window, a more isometric type of cellular structure and decreased open-cell contents, indicating an effective nucleation and cell wall stabilization induced by the exfoliated MMT particles. © 2009 Society of Plastics Engineers.

Abstract: Low-grade magnesium hydroxide (LG-MH) is a solid by-product that undergoes an endothermic decomposition in the temperature range of 300-750 °C. Due to its thermal behaviour and its lower cost relative to pure Mg(OH)2, it was studied as a non-halogenated flame retardant filler in a 28% vinyl acetate (VA) content poly(ethylene-co-vinyl acetate) matrix. The solid was characterized by XRF and the crystalline phases determined by XRD, composed predominantly of Mg(OH)2 and calcium and magnesium carbonates. Particle size reduction was performed by both mechanical as well as air jet milling in order to optimize the particle size distribution. Composites with different filler concentrations were prepared to evaluate the mechanical properties and flame retardancy by means of limiting oxygen index tests. LOI was also determined in specimens filled with commercial flame-retardants to analyse the effectiveness of this solid. © 2008.

Abstract: Composites of polystyrene (PS) and poly (styrene-co-acrylonitrile) (SAN) containing a fraction of a dodecylsulfate-modified Mg-Al layered double hydroxide (LDH) were prepared by means of a melt-extrusion process. The structure and morphology were analyzed with wide-angle X-ray scattering and transmission electron microscopy, respectively. The X-ray spectra of the PS matrix composite displayed the diffraction peak characteristic of the hybrid LDH basal plane at 2θ = 3.1 deg. The SAN matrix composite did not exhibit such a diffraction peak. Both PS and SAN composites displayed an intercalated type of morphology with respect to the LDH platelets, as assessed by transmission electron microscopy. A plasticizing effect due to the hybrid LDH particles was observed for all composites and was supported by a decrease in the glass-transition temperature values and by Fourier transform infrared spectra. Besides tensile properties, the fracture toughness of the composites was compared with that of the pure polymers through the linear elastic fracture mechanics parameters. They were determined from fracture tests under a three-point-bending configuration. The results indicated that the effect of adding a small fraction of modified LDH particles to SAN caused an improvement in fracture toughness of 50% with respect to that of the pure polymer. Moreover, the relative increase in the fracture energy was about 200%. For PS matrix composites, both tensile properties and linear elastic fracture mechanics fracture parameters remained unaffected. These results were explained on the basis of the different plasticities developed by both polymers around the particles. © 2008 Wiley Periodicals, Inc.

Abstract: Nanocomposites of recycled poly(ethylene terephthalate) (rPET) containing 2.5 wt% and 5.0 wt% of montmorillonite modified with organophilic quaternary ammonium salt (DELLITE 67G) were prepared by melt compounding using a co-rotating twin-screw type extruder with two organoclay contents were used: 2.5 wt% and 5.0 wt% and were prepared using two different rotation speeds: 150 and 250 rpm. Thermal characterization (analysis) of the nanocomposites was performed using differential scanning calorimetry (DSC) analysis. The results from DSC measurements showed that the addition of organoclay affects recycled PET's crystallization for two screw rotation speeds studies. The nucleating effect of organoclay was investigated. Morphological analysis using Transmission Electron Microscopy (TEM) revealed the presence of fully exfoliated clay platelets in samples prepared at 150 rpm. Copyright © 2009 American Scientific Publishers All rights reserved.

Abstract: This paper presents the characterization of the cellular structure and thermal conduction behaviour of polypropylene foams produced using different foaming processes, with the aim of selecting the best possible PP foam thermal insulator. Thermal conductivity results have shown that the global heat transfer behaviour is controlled by the relative density. For relative densities higher than 0.2, thermal conductivity differences were insignificant, the data being predicted by the mixture's rule and Russell's model. In the low density range, all of the proposed models underestimated the overall conductivity, the effect of the processing method being more significant, slight differences being observed between foams produced by extrusion and those produced by gas dissolution with higher cell sizes and anisotropies. Foams with finer cellular structures showed to be better insulating materials. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract: High-density polyethylene (HDPE)/hydrotalcite nanocomposites were prepared and characterized with a partially neutralized sodium ionomer of poly(ethylene-co-methacrylic acid) (EMAA) as a compatibilizer. Moreover, nanocomposites based on this ionomer were characterized as patterns to analyze the interactions between the hydrotalcite sheets and the methacrylic groups on the ionomer. Hydrotalcite particles were organically modified with sodium dodecyl sulfate ions. Their presence in the interlayer space was confirmed by means of Fourier transform infrared spectroscopy (FTIR) and X- ray diffraction (XRD). Morphological analysis carried out with XRD and transmission electron microscopy (TEM) revealed the partially exfoliated/intercalated structure achieved in the nanocomposites. The mechanical properties of the HDPE nanocomposites mainly depended on the nature of the polymer matrix. Higher values of the tensile strength and Young's modulus were found in the EMAA nanocomposites. Thermogravimetric analysis (TGA) showed that hydrotalcite particles improved the thermal stability and delayed the onset decomposition temperature of both HDPE and EMAA nanocomposites. © 2009 Wiley Periodicals, Inc.

Abstract: The non-isothermal crystallization behaviour of Mg-Al layered double hydroxide (LDH)/polypropylene (PP) nanocomposites prepared by melt-dispersion was investigated through differential scanning calorimetry and discussed in comparison with that of montmorillonite (MMT)/PP ones. Combined effects of the LDH interlamellar modification and blending the PP with maleic anhydride-grafted PP (PP-g-MAH) and maleic anhydride-grafted poly(styrene-co-ethylenebutylene-co-styrene) (SEBS-g-MAH) were analysed. Different approaches were applied to determinate the crystallization kinetic parameters. The nucleation activity parameter indicated that LDH particle resulted active for heterogeneous nucleation of PP. Overall; the crystallization rate constant of the PP increased in presence of LDH in a similar extension that in presence of MMT nanoparticles. By applying an isoconversional method to the calorimetric data it was found that the effective activation energy decreased because of the effect of the nanoparticles and its value displayed different growing trends with the crystallization degree depending of the nanocomposite composition. © 2008 Elsevier B.V. All rights reserved.

Abstract: The effects of extrusion conditions on the mechanical properties of recycled poly(ethylene terephthalate) (rPET)/clay nanocomposites were studied. Nanocomposites of recycled PET containing 2.5 and 5.0 wt % of montmorillonite modified with organophilic quaternary ammonium salt (DELLITE 67G) were prepared by melt compounding using a corotating twin-screw type extruder at two different screw rotation speeds: 250 and 150 rpm. The highest value of Young's modulus was found for low screw rotation speed (150 rpm). Morphological analysis using transmission electron microscopy (TEM) revealed the presence of fully exfoliated clay platelets in samples prepared at 150 rpm. It was concluded that the screw rotation speed should be optimized when preparing recycled PET /clay nanocomposites by melt compounding. © 2008 Wiley Periodicals, Inc.

Abstract: The combination of organophillised montmorillonite (MMT), synthetic hydromagnesite and aluminium hydroxide (ATH) as flame retardant system for polyethylene-based materials was studied and compared with a similar system with magnesium hydroxide, ATH and MMT. The thermal stability and the flame retardant properties were evaluated by thermogravimetric analysis (TGA), differential thermal analysis (DTA), limiting oxygen index (LOI) and cone calorimeter tests. The results indicated that the addition of montmorillonite makes it possible to reduce the total filler content to achieve the flame retardant requirements. The thermal stability of filled LDPE/EVA blends increases to a higher extent for the samples containing MMT. In the cone calorimeter tests we observed a reduction of the peak heat release rate for the sample containing montmorillonite in comparison with a sample with higher filler loading without this nanoclay. An increase of the stability of the char formed could be responsible for this favourable behaviour when montmorillonite is added. In addition, mechanical properties significantly improved for the composites containing montmorillonite both for the filler loading reduction and the reinforcement effect of the nanoclay. © 2007 Elsevier Ltd. All rights reserved.

Abstract: Hydromagnesite is a basic magnesium carbonate that undergoes an endothermic decomposition with water and carbon dioxide release in the temperature range of 200-550 °C. Due to this thermal behaviour it has been studied as flame retardant filler for polymers in cable applications. For this purpose the particle size distribution should be optimized, as it is in most cases responsible for decrease in final composite mechanical properties. This work describes the variations found in the thermal behaviour of hydromagnesite associated with the process of particle size reduction. Air jet micronization was compared with mechanical milling. Thermogravimetry and differential scanning calorimetry were used to study thermal decomposition. FTIR spectroscopy and XRD analysis of the solid residue after heating were used to follow structural changes. Decomposition behaviour of synthetic hydromagnesite was shown to be dependent of the applied particle size reduction process. A remarkable increase in the decomposition rate was observed for the milled sample, which was attributed to the introduction of defects in the crystalline structure during the mechanical milling. Therefore, it was concluded that the mechanical milling process may affect the thermal decomposition of hydromagnesite and therefore its characteristics as flame retardant. © 2006 Elsevier Ltd. All rights reserved.

Abstract: Recycled PET/organoclay nanocomposites were prepared by melt intercalation process with several amounts (1, 3, and 5 wt %) of clay modified with quaternary ammonium salt (DELLITE 67G) dispersed in a recycled poly (ethylene terephthalate) (rPET) matrix. The resultant mechanical properties (modulus and yield strength) of the nanocomposites were found to be different from those of rPET. Wide angle X-ray scattering (WAXS) and Transmission Electron Microscopy (TEM) measurements have shown that although complete exfoliation was not achieved, delaminated clay platelets could be observed. Thermal analysis did not show significant changes in the thermal properties from those of recycled PET. Mechanical testing showed that nanocomposite properties were superior to the recycled PET in terms of strength and elasticity modulus. This improvement was attributed to nanoscale effects and strong interaction between the rPET matrix and the clay interface, as revealed by WAXS and TEM. © 2007 Wiley Periodicals, Inc.

Abstract: The effect of modifying the particle/matrix interfacial region on the morphology and tensile behaviour of glass bead-filled polypropylene (PP) composites was studied. The interface modification was promoted by blending PP with a small concentration (5% by weight) of poly(ethylene terephthalate-co- isophthalate) (co-PET). Ten different PP/co-PET/glass beads ternary composites were prepared, characterized and compared with the homologous PP/glass beads binary ones. Maleic anhydride-grafted PP was added as a compatibilizing agent for PP and co-PET in some of the studied formulations, and its effect studied. Furthermore, four different silane-treated glass beads were used to prepare the composites (50 wt.%). Results showed that three different interfaces, corresponding to three different levels (low, middle and high) of particle/matrix adhesion, could be obtained in these composites by varying the matrix composition and the silane coupling agent on the glass bead surface, which resulted in a wide range of tensile properties, from ductile composites with low tensile strength and high elongation to brittle ones with high tensile strength. It was found that co-PET embeds glass bead surface independently of the silane coupling agent employed. Finally, the adhesion degree differences between the different composite phases seemed to be the main cause to explain the differences found in the sensitivity of the composite tensile characteristics to the strain rate. © Springer Science+Business Media, LLC 2007.

Abstract: The fracture behaviour of glass microsphere-filled polypropylene/ poly(ethylene terephthalate-co-isophthalate) blend-matrix composites was investigated in comparison with that of the glass microsphere-filled PP composites. Depending on the deformability displayed by the composite, it was carried out through the linear-elastic fracture mechanics or by applying the J-integral concept. The matrix ductility was regulated in the composite through the glass bead surface treatment applied with different silane-coupling agents, as well as with the addition of maleated PP as polymer compatibilizer. Whereas all the composites failed in a brittle manner at moderate impact speed, quasi-brittle fracture behaviour was only observed at low strain rate in composites having high and medium interfacial adhesion level. Results showed that composites containing both aminosilane-treated glass microspheres and maleated PP showed the highest values of fracture toughness. In composites with low adhesion level between matrix and glass beads, the critical J-integral value diminished due to the presence of PET. © Springer Science+Business Media, LLC 2007.

Abstract: This paper presents the compared analysis of the foaming behaviour and cellular structure of LDPE/hectorite nanocomposites and respective neat LDPE foams. To assess the influence of hectorite on the foaming behaviour and final foam morphology, nanocomposites containing 3 and 7 wt.% of a modified hectorite were first melt-compounded in a twin-screw extruder. Variables such as temperature, pressure and time were optimized to prepare foams in a second stage by a two-step compression-molding process. Crystallinity and crystal structure of the polymer matrix were determined using X-ray scattering (WAXS) and differential scanning calorimetry (DSC). Clay intercalation/exfoliation was analyzed by WAXS and transmission electron microscopy (TEM), with the results indicating that partial exfoliation of the particles was only reached with foaming but not during melt mixing. A quantitative characterization of the cellular structure and morphology of the foamed nanocomposites was done using both scanning (SEM) and transmission electron microscopies. The nanocomposite foams exhibited differences in the crosslinking degree, showing lower gel content values (from 35% of the neat LDPE to as low as 28% for the 7 wt.% hectorite foam), expansion behaviour, cell aspect ratio, with the foamed nanocomposites showing more isometric type of cells, and cell wall texture with regard to the neat LDPE foams. All these differences, analyzed and compared for the three composites, directly affect both the thermal and mechanical responses of the foams and due to that fact are of extreme importance. © 2007 Elsevier Ltd. All rights reserved.

Abstract: Novel polymer nanocomposite foams made by a two step compression molding method are analyzed in this article. Nanocomposites of low density polyethylene and an organo-modified hectorite were first melt compounded and then foamed using a compression molding method. To study the influence of the presence and the amount of hectorite in both mechanical and thermal properties, samples with 3% and 7% content of hectorite were prepared. Polyethylene crystalline characteristics and thermal stability of the samples were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. Mechanical properties of foams and solid nanocomposites were analyzed by using dynamical mechanical analysis (DMA). Thermal expansion of the samples was analyzed by thermomechanical analysis. The results indicate that the exfoliation of hectorite platelets was achieved after the foaming process, but not during the melt mixing step. Foams with hectorite nanoparticles exhibit improved thermal stability and mechanical properties when compared with neat polymeric foams. © 2007 Wiley Periodicals, Inc.

Abstract: The essential work of fracture (EWF) concept was successfully applied to the fracture toughness characterization of ductile glass microsphere-filled polypropylene (PP)-matrix composites. Injection-moulded PP and PP/poly(ethylene terephthalate-co-isophthalate) (PET) blend-matrix composites filled with both untreated and silane-treated glass beads (50 wt%) were studied to ascertain the influence of the material composition on the EWF parameters. In addition, the effect of the specimen thickness was also studied on deeply double-edge notched (DDENT) specimens of nominal thickness 1, 2 and 3 mm. The results indicated that the EWF methodology could be applied to this kind of particulate-filled composites whenever high plasticity is developed in the crack tip front before the fracture propagation. PET addition markedly reduced both fracture toughness and plastic work of fracture in untreated and mercaptosilane-treated glass beads, attributed to glass embedding by PET. Concerning specimen dimensions, a noticeable drop in fracture toughness was found in thicker samples, whereas plastic work of fracture showed the opposite trend. © 2007 Elsevier Ltd. All rights reserved.

Abstract: A new flame retardant (FR) system for ethylene-vinyl acetate, mainly based on the combination of hydromagnesite (HM, obtained from an industrial by-product) and organo-modified montmorillonite (oMMT) has been compared with a magnesium hydroxide (MDH) and oMMT flame retardant system. The presence of oMMT in association with both hydrated minerals gave a strong decrease of heat release rate in cone calorimeter tests. Moreover, the HM/oMMT combination leads to a better improvement of resistance to ignition and self-extinguishability in comparison with the MDH/oMMT one. The study of residues formed during thermal decomposition revealed the formation of forsterite (Mg2SiO4) when either MDH or HM was used in combination with oMMT. SEM observations of residues showed sintering of the mineral particles at high temperature particularly in the case of HM/oMMT composition. © 2006 Elsevier Ltd. All rights reserved.

Abstract: Combined effects of clay treatment and compatibilizer polymers on the structure and properties of polypropylene /clay nanocomposites were studied. Dynamic mechanical analysis was used to analyze comparatively the dynamic mechanical response of different nanocomposites prepared from polypropylene and montmorilloniterich bentonite, and to relate such response with the material microstructure. Two different bentonites were used: a purified Spanish natural bentonite was organophillized by means of 11-undecyl-ammonium ion and a commercial bentonite organophillized with dimethyl dehydrogenated tallow ammonium ion. Three different polar copolymers were employed as compatibilizer agents in some of the formulations: maleic anhydride-grafted polypropylene, maleic anhydride-grafted poly(styrene-co-ethylenebutylene-co-styrene), and poly(ethylene terephthalate-co-isophthalate) (PET). To ascertain the microstructure characteristics in the nanocomposites, wide angle X-ray diffraction, trans mission electron microscopy, and differential scanning calorimetry techniques were used. The nanocomposites containing both bentonite organophillized with 11-undecylammonium ion and PET, and maleated PP as compatibilizer system, were found to have the highest storage modulus and the smallest loss factor values, which was mainly due to the better clay platelets dispersion. The dynamic mechanical response of nanocomposites prepared with bentonite organophillized with dimethyl dehydrogenated tallow ammonium ion and maleated SEBS was strongly affected by the presence of this compatibilizer. The temperature of PP and α, β, and γ relaxations strongly depended on the interactions between the different phases in the nanocomposites. © 2006 Wiley Periodicals, Inc.

Abstract: Reused tyres powder was used as reinforcement in HDPE-reused tyre composites. In order to improve the compatibility between both components, several pre-treatments performed over the rubber tyres were applied: sulphuric acid etching, use of a silane coupling agent and chlorination with trichloroisocyanuric acid (TCI). Mechanical properties of the resulting materials (e.g. tensile strength, Young's Modulus, toughness and elongation at break) were studied and compared. Chemical modifications on the surface of reused tyres were monitored by FTIR and physical modifications and behaviour to fracture were followed by means of SEM. The influence of rubber pre-treatment was assessed by comparing the results of treated and untreated composites with those for neat HDPE. Reused tyre rubber, added to the HDPE in small quantities, acts as a filler, improving the stiffness and providing a more brittle behaviour. Pre-treatment with TCI gave poor results in terms of mechanical properties obtaining lower values than neat HDPE in some cases and always worst properties than sulphuric or silane coupling agent. Treatments with H2SO4 and silane coupling agent improve the ability of rubber to interact with the HDPE, increasing the material's stiffness and its tensile strength. Sulphuric acid modificates chemical and physically the particles' surface improving mainly mechanical adhesion, whereas silane acts as a compatibilizer developing chemical matrix-reinforcement interactions. © 2006 Elsevier Ltd. All rights reserved.

Abstract: Synthetic hydromagnesite obtained from an industrial by-product was evaluated as a non-halogenated flame retardant. It was used in combination with aluminium hydroxide (ATH) and compared with commercial flame retardants like magnesium hydroxide (MH) and natural hydromagnesite-huntite (U) in a polyolefin system of low-density polyethylene/poly(ethylene-co-vinyl acetate) (LDPE/EVA). The thermal stability and flame behaviour of the halogen free flame retarded composites were studied by thermogravimetric and differential thermal analysis (TG-DTA), limiting oxygen index (LOI), epiradiateur and cone calorimeter. It has been shown that synthetic hydromagnesite could be an alternative solution to the use of MH in non-halogenated flame retardant systems in EVA. © 2005 Elsevier Ltd. All rights reserved.

Abstract: The availability of scrap poly(ethylene terephthalate) (PET) from post-consumer bottles is increasing as the post-consumer collecting systems are becoming more usual in daily life. PET is well known as a high-performance engineering thermoplastic because of its good thermal stability, chemical resistance, and excellent mechanical properties. Many efforts have been carried out to use this material in housings of electronic applications. However, the flammability of PET is a shortcoming in some of these applications. In this study, our attempt is to incorporate a non-halogenated flame retardant, in form of a phosphorus-containing compound, together with a commercial glass fibre grade to achieve UL94 test V-0 rating for PET. An investigation of thermal stability and flammability (HDT, UL94 V-test) and mechanical (tensile, flexural and impact tests) properties of glass fibre filled PET samples is reported as a function of fraction of flame retardant. This work shows the influence of the filler content and the interfacial filler/matrix adhesion on the flame retardant and the mechanical properties. © 2004 WILEY-VCH Verlag GmbH & KGaA, Weinheim.

Abstract: PP/PET/MAPP blends have been filled with 50 wt% of glass beads. The orientation of the PP crystalline phase, the crystallization behavior and the dynamic mechanical response of these materials have been analyzed. The dynamic mechanical response is strongly affected by the presence of the glass beads, being possible to detect the effect of PET and MAPP on the storage modulus and loss factor values. Moreover, the alpha relaxation of the composites is visibly affected by thermal treatments. © 2004 WILEY-VCH Verlag GmbH & KGaA, Weinheim.

Abstract: A natural bentonite rich in calcium montmorillonite (CaMMT) was initially purified and ion-exchanged to obtain sodium montmorillonite (NaMMT). Both clays were organophillised by cationic exchange reaction with undecylammonium chloride, and characterized. Isotactic poly(propylene) (PP) was melt-compounded with both the unmodified and the organophilic montmorillonites. The hybrids produced have been characterized structurally, thermally and mechanically. Maleic anhydride-grafted PP (MAH-g-PP) was used as compatibilizer in some of the formulations. Homologous series of hybrids were also synthesized employing blends of PP/PET and compared with those of the pure PP to investigate possible beneficial effects due to the presence of small amounts of PET on the microstructure and properties of this kind of materials. The analysis of the results indicates some extension of both macromolecules intercalation and clay particles exfoliation in the hybrids prepared with the organophilic montmorillonite. The hybrids prepared with compatibilized PET/PP blends were found to have a better nanostructure. © 2004 WILEY-VCH Verlag GmbH & KGaA, Weinheim.

Abstract: Investigations of thermal and mechanical properties of recycled poly(ethylene terephthalate) (PET) reinforced with glass fibre have been carried out, focusing on the influence of two variables involved in the extrusion process: screw speed and torque. A Factorial Experimental Design of the processing conditions during extrusion (screw speed and torque) was done to get the best thermomechanical properties versus processing conditions. Mechanical properties such as Young's Modulus and Impact Resistance increased after the addition of glass fibre in recycled PET matrix. © 2005 Published by Elsevier Ltd.

Abstract: 1 mm sheets of polypropylene and ethylene-propylene block copolymers (EPBC) have been obtained using different processing methods in order to study the influence of processing induced morphology in the fracture properties of these materials. The processing methods employed were compression moulding (CM), extrusion-calendering (EC) and injection moulding (IM). Additionally, the sheets obtained by extrusion and injection were submitted to an annealing process with the aim to obtain more homogeneous morphologies that would ease their characterization. The morphology has been characterized by different techniques: Polarizing light microscopy (MLP), differential scanning calorimetry (DSC), wide-angle X-ray diffraction scattering (WAXS) and scanning electron microscopy (SEM). The fracture properties were determined by the essential work of fracture (EWF) method for deeply double edge notched specimens (DDENT), since these materials show ductile and post-yielding fracture behaviour. The EWF technique was applied in both the melt flow (MD) and the transversal (TD) directions in the sheets obtained by extrusion and injection moulding. Results show that the sensitivity of the technique allows examining the effect of morphological variations of thin sheets, as well as a better characterization of the orientation level (versus other parameters like yielding stress or elastic modulus obtained by tensile test). © 2005 Springer Science + Business Media, Inc.

Abstract: A synthetic hydromagnesite obtained from an industrial by-product rich in magnesium oxide was employed and evaluated as a non-halogenated flame retardant for poly(ethylene-co-vinyl acetate). The filler was characterized with different techniques (such as specific surface area, TGA, particle morphology and size measurements, WAXS). Significant differences were found between the synthetic hydromagnesite and the natural one. Synthetic hydromagnesite was coated with stearic acid and the effectiveness of the coating process was studied by the dye adsorption method and sedimentation volume measurements. The amount of coating agent ranged from 1 to 4.5%. This factor was found to have a significant effect on the thermal decomposition behaviour of the filler. A poly(ethylene-co-vinyl acetate) (27% of VA) was filled with the coated synthetic grades of hydromagnesite as well as with two commercial flame retardants and different physicochemical properties were evaluated, including their flame retardant effect. © 2004 WILEY-VCH Verlag GmbH & KGaA, Weinheim.

Abstract: The study of polymer and composite behavior under high strain rates is of fundamental relevance to determine the material suitability for a selected application. However, the impact phenomenon is a very complicated event, mainly due to the short duration, large deformation, and high stresses developed in the sample. In this work, we have performed impact tests over a carbon fiber reinforced epoxy using low-energy in the striker. A nonconservative and nonlineal spring-dashpot series model has been proposed to reproduce the material behavior. The model considers simultaneously both flexural and indentation phenomena accounting for energy losses by means of the restitution coefficient. Using this model, an excellent fit between the predicted and the experimental force-time trace has been obtained below the composite failure point, which was recognized by a separation of both mentioned curves. As the epoxy-fiber laminate has a very low viscoelasticity, the high strain rate Young's modulus obtained from the model was compared with that extracted from a conventional three point bending test, finding a very good match between the values. The study of the dashpot coefficients allows concluding that the dominant mechanism is the composite flexion, while the indentation effects contribution takes on importance at low impact velocities. © 2005 Wiley Periodicals, Inc.

Abstract: Blends of poly(propylene) (PP) and poly(ethylene terephthalate-co-isophthalate) (co-PET) (95/5) with and without compatibilizing agent (maleic anhydride PP), as well as composites of these blends with glass beads (50 wt%) with and without silane coupling agent surface-treatment, were prepared and studied on a basis of the material microstructure and thermomechanical properties. Infrared and Raman spectroscopy, as well as transmission electron microscopy, displayed evidence of MAPP compatibilizing action for the blend. Differential scanning calorimetry showed a remarkable effect of nucleation rate increase exerted by co-PET on the PP crystallization. Moreover, glass beads were found to increase the PP nucleation rate slightly. PP crystallinity hardly varied with the composition. Wide angle X-ray diffraction allowed determination of differences in the orientation of the poly(propylene) b-axis, with more homogeneous orientations in the presence of both co-PET and glass beads. MAPP promoted the PP b-axis orientation. Differences in PP αα relaxation could be analyzed through dynamic-mechanical thermal analysis (DMTA). © 2004 Wiley Periodicals, Inc.

Abstract: The present work propose is the polymer and composites mechanical proprieties evaluation, using low energy impact techniques in flexure plate configuration hitting by a semi spherical indenters and working with a non linear and non conservative model that involve the permanent deformations due to the impact flexure and indentation. Two systems arrayed in serial configuration, a flexion spring-dashpot and an indentation hertzian spring-dashpot, conform this model. Since this do not have analytical solutions, a 4rd order Runge-Kutta numeric model is used in order to solve it and is compared with experimental results measuring the global energy lost with the restitution coefficient. Different polystyrene (PS) matrix composites series with elastomeric and rigid dispersed phases were tested. A satisfactory model approach to the registered experimental curves is showed, allowing the elastic modulus calculus at high impact velocities and also the determination of the energy at the beginning of the specimen damage.

Abstract: PP/PET blends (95/5) filled with 50% by weight of glass beads were prepared and studied at morphological and mechanical level, and compared with its analogous samples of glass bead-filled PP. The influence of a compatibilizing agent (maleic anhydride grafted polypropylene) and different silane coupling agents was analysed. It has been found that PET embeds glass bead surface independently on the silane coupling agent employed. Addition of MAPP in PP/PET blends leaded to tensile strength values similar to those of unfilled PP, but rupture takes place in a brittle manner.

Abstract: Fracture and thermal behavior of injection-molded poly (ethylene terephthalate-co-isophthalate) filled with milled glass fiber has been studied as a function of fiber content in the range 0-40% by weight. Composite Young's modulus and tensile strength increased with fiber percentage, and good agreement was found with theoretical predictions. Low rate fracture tests were carried out on injection-molded SENB specimens. Fracture toughness (KIC) and fracture energy (GIC) could be obtained by applying Linear Elastic Fracture Mechanics (LEFM). Results seemed to indicate improved fracture toughness if compared with homopolymer poly (ethylene terephthalate) composites. The reason was attributed to a lower crystallinity developed in the matrix, which promoted higher plastic strain.

Abstract: Filled PA6 are important representatives of engineering plastics used in automotive components. Nowadays, the demand of plastic recycled grades is increasing in this branch of industry but polymer recycling can undergo thermomechanical degradation processes with the results of a poor secondary material, regarding its properties. In this paper an investigation of thermal, mechanical (tensile, flexural and impact tests) and rheological properties of a sample of recycled and filled PA6, is reported as a function of the number of reprocessing operations (3 times) and of the fraction of recycled material (15, 30 and 50%) added to the virgin material. Recycled PA6, used in this study, comes from fibre grade production waste. Material was filled with 20% glass beads and 10% glass fibre, according to the specifications of the application, mainly to obtain a lower shrinkage in the end product. This work also shows that the mineral fraction, not being degraded during the injection process, allows better recyclability to the filled material. The properties of the recycled material remain below the virgin, and the best combination of both appears to be the mixture with 30w.% recycled fraction, which shows a lost of properties similar to 3 reprocessing operations.

Abstract: Thermal and dynamic mechanical characteristics of injection-moulded discs of polypropylene (PP) filled with 40% by weight of magnesium and aluminium hydroxides have been studied by means of differential scanning calorimetry and dynamic mechanical thermal analysis, and have been related to the anisotropy and microstructure heterogeneity of the discs. The effect of filler type, particle morphology and surface coating has been analysed. The nucleation activity of filler particles on PP has been quantified and found to be reduced in coated grades of magnesium hydroxide. The employed coatings worked isolating and preserving particles surface from direct interaction with polymer chains. The different orientations of both filler particles and PP α crystals were found to be the main cause of the differences observed in mechanical properties. © 2002 Elsevier Science Ltd. All rights reserved.

Abstract: Investigation of thermal and mechanical characteristics of short glass fiber reinforced polyethylene terephthalate (PET) has been carried out, focusing on the influence of three of the variables involved in the injection-molding process: mold temperature, holding pressure time and closed mold time. Mold temperature plays a decisive role in controlling crystallinity development of PET matrix, which is directly correlated with the values of tensile strength and elongation at rupture. Holding pressure time acts improving piece compaction. Longer closed mold times lead to the highest values of developed crystallinity. Moreover, sodium benzoate, titanium dioxide and an ionomer have been added in order to study efficacy as nucleating agents.

Abstract: The influence of aluminium hydroxide particle morphology and magnesium hydroxide surface coating on the anisotropy and microstructure heterogeneity of injection-moulded discs of polypropylene (PP) filled with 40% by weight of these fillers has been studied through wide-angle X-ray diffraction measures. In general, the discs displayed an anisotropic structure due to different orientations of both filler particles and PP crystals through the part thickness. The samples also exhibited some degree of heterogeneity due to different levels of particle orientations in specimens far away and close to the disc mould entrance. © 2002 Elsevier Science Ltd. All rights reserved.

Abstract: The normalization method is applied to different magnesium hydroxide filled polypropylenes. As the load separation principle is the basis of the method, its validity is checked using the load separation criterion developed by Sharobeam and Landes. Load separability is checked for all the materials when the condition of stationary crack length is fulfilled. During the determination of the deformation function using the normalization method, the large decrease of the load value of highly filled materials make it impossible to describe the load normalization variation with plastic displacement by a power law equation. Nevertheless, for the lower-filled materials, i.e. up to 40 wt% with copolymer PP and 20 wt% with homopolymer PP, the J-R curve can be determined and high concordance is found with the J-R curve obtained by multiple specimen method. The applicability of the normalization method is discussed in terms of the geometry of the plastic deformation zone. It is found that the materials that are not suitable for normalization method application are characterized by a very small plastic zone, due to the restriction of plastic flow caused by mineral filler. © 2002 Kluwer Academic Publishers.

Abstract: The objectives of this work are to describe the fracture behaviour of a material model composed by polystyrene and different amounts of solid glass beads. Seven compositions with beads content ranging between 0 % and 40 % by weight, have been prepared. A morphology study has been carried out to examine the microstructure developed during injection moulding. Fracture parameters (KIC, GIC and JIC) were calculated at high and low strain rate as a function of particle content. The maximum reinforcement was found at middle levels of glass beads (6%-15%wt). The composite fracture behaviour at low strain rate was always brittle although it was found that beads tend to stabilize its propagation. At high strain rate, the particle reinforcement effect is lower, however a small increment in KIC and GIC was found.

Abstract: The influence of processing induced morphology, thickness and ethylene content (EC) of different ethylene-propylene block copolymers on fracture properties has been studied using the essential work of fracture (EWF) method. To analyse the influence of EC, four different materials were chosen with 0, 5.5, 7.8, and 8.4% in weight EC. Each material was injected in three different thicknesses (1, 2 and 3 mm). The resulting plaques were tested using the EWF method in both main orientations; the melt flow direction and transverse to melt flow direction. Different fracture behaviours have been observed, some of them preventing the applicability of the EWF method. Polarised light microscopy observations have revealed the existence of a skin/core structure, which is reduced with an increase in thickness and EC. © 2002 Elsevier Science Ltd. All rights reserved.

Abstract: The process parameters during injection molding of polypropylene Hostalen PPN 1060, affect the crystallinity and morphol. of crystal phases; as crystallinity increases, the rigidity, tensile strength, and flexural strength increase but the tenacity and impact strength decrease. The level of crystallinity is detd. by how effectively the pressure is applied and maintained across the process and is in turn dependent on the temp. at the point of injection.

Abstract: The Essential Work of Fracture (EWF) theory has been applied to study the fracture behaviour of untreated and silane-treated glass bead-filled EPDM composites. The experimental values of both Young's modulus and tensile strength have been compared with those predicted by the main theoretical and semiempirical models, and the influence of the composite processing temperature on the tensile properties has been studied, noticing a marked drop of stiffness and strength from a processing temperature of 200 °C. A good adhesion between EPDM matrix and glass beads was achieved with the silane Z-6032, resulting in higher tensile strength, and it has been observed that glass bead presence induces plasticity in the EPDM matrix. No differences of the specific essential work of fracture were found in the three filled samples, although results show that the higher adhesion degree between matrix and particles, the higher value of the specific plastic work of fracture, and also the higher final instability in crack propagation.

Abstract: In this paper the applicability of the load normalization method to determine J-R curves of polypropylene copolymers (PP) is analyzed. This method allows the determination of resistance curves ideally from a single fracture test, and it is based on the load separation principle, which assumes that load can be separated in two multiplicative functions, the geometry function, G(a/W), and the deformation function, H(νpl/W), which depend of the crack depth and the plastic displacement, respectively. The load separation validity has been checked for two different PP copolymers (block and random copolymers) and the load normalization method has been applied in order to determine and analyze the resistance curves, which have been compared, as a reference, with those obtained by the multiple specimen method. The applicability of the load normalization method to PP copolymers is analyzed by introducing some variations in the general procedure: Firstly, the deformation function is determined using either a power law fit or the so-called LMN function. With the power law, two different fitting methods have been tested: the usual "6 + 1" method and a "6 + 6" method proposed here for giving more weight to the final point of the curve. Secondly, the influence of the material crack tip blunting has been analyzed quantifying it through different values of the constriction factor (m) in the general expression of the blunting line. Finally, the effect of the separable blunting region extension on the J-R curve has been also analyzed by establishing different separable blunting zones.

Abstract: Two grades of isotactic polypropylene (homopolymer and block copolymer) were filled with magnesium and aluminium hydroxides, and studied focusing the mechanical and fracture characteristics of the composites. As expected, dispersion of such fillers in PP resulted in improved stiffness and reduced tensile yield strength. By one hand, the composites fracture resistance was characterised at low strain rate applying the J-integral concept; the resistance to crack growth initiation (J IC) was found decreasing as the Mg(OH) 2 concentration was raised in the copolymer PP matrix. By the other hand, the linear-elastic fracture mechanics (LEFM) parameters were determined by means of instrumented impact tests at 1 m/s on the homopolymer PP filled with uncoated Al(OH) 3 particles. The higher the Al(OH) 3 mean particle size, the lower the composite fracture energy (G IC). In the opposite, with commercial surface-coated filler grades it was not possible to achieve LEFM conditions to characterise the fracture toughness of filled PP at 1 m/s, because the Mg(OH) 2 surface coating, which is applied in practice to improve the melt processing, acts increasing the composite plasticity and reducing the tensile yield strength.

Abstract: The aim of this work is to study the influence of the filler fraction and that of the filler/matrix interfacial adhesion on the mechanical properties and on the fracture behaviour of a poly(methyl methacrylate) PMMA (for injection moulding). The variation of the tensile and flexural mechanical properties with the filler volume fraction was determined. The changes in the fracture behaviour produced by the fillers were studied by evaluating the K IC and G IC parameters of the LEFM (Linear Elastic Fracture Mechanics) by carrying out tests with SENB geometry at room temperature and low strain rates. After fracture surfaces examination by SEM (Scanning Electron Microscopy), it was found that the surface treatment had been rather effective and that the fracture toughening mechanism was multiple crazing.

Abstract: The activity of inorganic substrates in the catalysed nucleation of polymer melts was studied using a nonisothermal differential scanning calorimetry technique (DSC). The analysis of the results was made by using the method developed by Dobreva-Veleva et al. In this method the kinetics of nonisothermal overall crystallisation of polymers was analysed in terms of the general non steady state nucleation theory at small undercoolings. Two examples of the applicability of this method are presented.

Abstract: The anisotropy and microstructure heterogeneity induced by filler presence and processing has been studied on injection-moulded discs of poly(propylene) homopolymer (PP) filled with a wide range of concentration (0-60 wt.-%) of uncoated platy magnesium hydroxide. Differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) techniques were used to help state the microscopic structure and justify properties measured by dynamic mechanical thermal analysis (DMTA). On the one hand, the anisotropy has been analysed by measuring samples in the parallel and perpendicular directions to the discs surface. On the other hand, the heterogeneity has been characterised by testing samples cut from different zones of the discs. It has been found that the nucleation activity of magnesium hydroxide on the α-phase of poly(propylene) increases with the filler concentration up to the maximum level studied (60 wt.-%). The polymer crystalline β-phase was only detected in unfilled PP and in samples containing less than 20 wt.-% of magnesium hydroxide. Remarkable differences in the polymer (α-phase) and particle orientation degrees have been observed in the composites depending on whether the analysis was carried out over the disc skin or core. The anisotropy degree of poly(propylene) crystals in the composites was independent on that of the filler particles up to 10 wt.-% of Mg(OH)2 concentration; however, from 20 wt.-% of filler the orientation of magnesium hydroxide particles clearly influenced the orientation and anisotropy of the polymer. Moreover, the differences of orientation in the specimen skin were mainly responsible for the heterogeneity of the discs. Composites with lower magnesium hydroxide concentration exhibited the higher heterogeneity. These factors were found to be main causes of the different dynamic mechanical properties obtained for these materials when the experiments were performed in different zones and/or through different directions in the injection-moulded discs.

Abstract: Three different experimental techniques [compression experiments at low strain rates, instrumented falling-weight impact tests, and dynamic mechanical analysis (DMA)] have been used for the mechanical characterization of a collection of crosslinked closed-cell polyolefin foams of different chemical compositions, densities, and type of cellular structure. The experimental results that it is possible to obtain from each technique are shown, and related to the different applications of these materials. The relationships between the structure and the mechanical properties are also presented.

Abstract: The anisotropy and heterogeneity of injection-molded discs of polypropylene, talc-filled polypropylene composites, and silane-treated talc-filled polypropylene composites are studied by means of dynamic mechanical analysis and thermomechanical analysis. The aims of this work are to discover the relationships between the structure of the composites, their anisotropic properties, and the heterogeneity of the molded discs. The experimental results show that although the discs are almost homogeneous, they present a high degree of anisotropy.

Abstract: This paper presents the fracture behaviour of films of a bioriented poly(ethylene terephthalate) (BOPET), that was studied by the Essential Work of Fracture (EWF) method. The influence of specimen thickness and molecular orientation was investigated. The results show that this method is a useful alternative for studying the plane-stress fracture of this material, finding that the specific essential work of fracture is strongly affected by the orientation [we was smaller in the direction of extrusion (MD) than in the perpendicular one (TD)], but independent of the specimen thickness in a range from 50 to 250 μm. On the other hand, the plastic work item is sensitive to variations of thickness but does not depend on orientation.

Abstract: Low-energy instrumented falling dart impact techniques have been applied to characterize the rigidity of several series of polyolefinic flexible foams, at relatively high strain rates. Rebound tests were specially designed in order to determine the elastic modulus of the foams by application of a theoretical model that describes the indentation phenomena of a hemispherical element on a sample. A potential relationship between values of the determined elastic modulus and foam density was found and, as expected, the foams based in HDPE showed the higher values of the elastic modulus of all the studied foams, whereas the samples containing EVA resulted in the lower values. Moreover, the elastic modulus determined using hemispherical dart headstocks (indenters) with different diameter resulted in a constant value, as the indentation model applied establishes. The results presented in this paper show the utility of this test to characterize mechanically flexible foams, bemuse it is sensible to identify small differences of rigidity due to variable density, foaming process and chemical composition.

Abstract: The essential work of fracture concept (EWF) was applied to EPDM (Dutral TER4038) compds. with untreated and silane-treated glass beads. The silane coupling agents used are silane Z-6032, Dow Corning [(N-(2-vinylbenzylamine)-ethyl)-3-aminopropyl-trimethoxysilane], and a mixt. of vinyl silanes Ucarsil PC-1A and PC-1B, Union Carbide. The theory is not applicable to pure EPDM due to its high elasticity, but it is adequate when compounded with glass beads that confer certain plasticity. Improved adhesion between EPDM and glass beads, higher plastic work of fracture, and higher final instability of crack propagation were obsd. A marked drop in stiffness was obsd. when processing the compds. at 200. The improved adhesion between EPDM and glass beads achieved through surface treatment was confirmed by SEM. Indexing -- Section 39-14 (Synthetic Elastomers and Natural Rubber)

Abstract: The applicability of instrumental falling weight impact techniques in characterizing mechanically thermoplastic foams at relatively high strain rates is presented in this paper. In order to try simulating impact loading of foams against sharp elements, an instrumented dart having a hemispherical headstock was employed in the tests. Failure strength and toughness values were obtained from high-energy impact experiments, and the elastic modulus could be measured from both flexed plate and indentation low-energy impact tests. The results indicate a dependence of the failure strength, toughness, and the elastic modulus on the foam density, the foaming process, and the chemical composition. This influence was found to be similar to that of pure nonfoamed materials and also to that observed from low-rate compression tests. The results also indicate that the indentation low-energy impact tests were more accurate in obtaining right values of the elastic modulus than the flexed plate low-energy impact tests usually used to characterize rigid plastics. The foam indentation observed with this test configuration contributes to obtaining erroneous values of the elastic modulus if only a simple flexural analysis of plates is applied.

Abstract: Dynamic mechanical analysis (DMA) is used to study the dynamic mechanical properties of injection-moulded discs of polypropylene, talc- filled polypropylene composites and silane-treated talc-filled polypropylene composites. Silane addition in a very low proportion improves the adhesion between the filler and the polymer and enables composites to be used where otherwise they could not. Therefore, on the one hand, the composites have different properties due to the filler and the coupling agent, and on the other hand the injection processing induces a structure, resulting in inhomogeneity and anisotropy for the moulded discs. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X- ray diffraction (WAXD) techniques are used to help state the microscopic structure and justify the macroscopic properties measured with DMA. Dynamic mechanical analysis (DMA) is used to study the dynamic mechanical properties of injection-moulded discs of polypropylene, talc-filled polypropylene composites and silane-treated talc-filled polypropylene composites. Silane addition in a very low proportion improves the adhesion between the filler and the polymer and enables composites to be used where otherwise they could not. Therefore, on the one hand, the composites have different properties due to the filler and the coupling agent, and on the other hand the injection processing induces a structure, resulting in inhomogeneity and anisotropy for the moulded discs. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) techniques are used to help state the microscopic structure and justify the macroscopic properties measured with DMA.

Abstract: This paper presents the fracture behaviour of injection-moulded magnesium hydroxide filled polypropylene block copolymer (PP) as a function of the filler content, and it is compared to that of the unfilled PP. The J-integral concept was applied from tests carried out on SENB specimens according to the European Structural Integrity Society (ESIS) protocol for plastics. The results show lower fracture toughness (J IC) as the filler content increases in the composite, what is explained on the basis of morphological details.

Abstract: A fracture mechanics analysis of polypropylene and magnesium hydroxide filled polypropylene composites is presented in this article. The fracture mechanics analysis, based on the J-integral concept was carried out on three-point flexion specimens (SENB) at room temperature. The mechanical characterization was done using tensile tests. The results of the fracture mechanics analysis show that a fracture toughness reduction occurs as the filler volume fraction increases in the composite. The tensile tests show that magnesium hydroxide particles promote an increase of the polymer stiffness and a reduction of the yield stress. The results are analyzed in terms of the observed plastic deformation mechanisms in the polymer matrix.

Abstract: In this paper, the mechanical and fracture behavior of composite materials composed by a matrix of PMMA and glass beads, is analyzed. Three-point flexion specimens (SENB) and double torsion were used, determining some fracture parameters. Also, mechanical tensile and flexion tests have been performed, and the effect of volume fraction and surface treatment of the microspheres has been studied. The results are in agreement with some results reported in the literature.

Abstract: The efficiency of several halogen-free flame retardant on polypropylene has been determined, using vertical (UL 94) and horizontal (UL 94 HB) flammability tests. Polypropylene composites were produced by twin screw extrusion and their mechanical properties were evaluated. The results show that high concentration of flame retardant (over 50 wt%), are required to obtain a satisfactory flame retardation (V-O class). However, it was also found that such high concentrations of flame retardant affect the mechanical properties of the material, decreasing the yield stress and strain stress of the composites.

Abstract: The effect of filler particle size on the fracture behavior of PP/Al(OH)3 composites was investigated at a concn. level of 20 vol/vol% of filler. Two grades of Al(OH)3 having different av. particle sizes (1.5 and 60 .mu.m) were used as fillers in a polypropylene homopolymer, and the fracture characterization of the composites was based on LEFM anal. from impact data, which were obtained using an instrumented Charpy impact pendulum on injection-molded SENB specimens with a large range of initial crack lengths. It was shown that under the conditions applied the LEFM anal. seems to be valid to characterize the fracture toughness of these materials. The composite filled with the finest grade of Al(OH)3 showed higher stiffness, tensile strength, fracture toughness and fracture energy than the composite filled with coarser particles. Indexing -- Section 37-5 (Plastics Manufacture and Processing)

Abstract: In this work we have detd. the bending fracture parameters of polycarbonate (PC)/ABS resin blends in the PC-rich range, at low strain rate. The EPFM J-integral criterion standardized by ASTM and ESIS was applied following the Narisawa and Takemori methodol., and compared with an essential work of fracture (EWF) anal. with SENB geometry. An excellent correlation was obtained between the crit. J-value and the EWF crit. one. It was obsd. that the energy required to initiate crack growth increased up to 15 wt.% ABS in the blend, while the crack propagation resistance (dJ/da) rose until a level of 20% ABS was reached. Indexing -- Section 37-5 (Plastics Manufacture and Processing)

Abstract: The fracture mechanism and mech. properties were studied of composites of polystyrene (Lacqrene-1541, Elf-Atochem) contg. mineral oil as lubricant, and glass microspheres having median diam. of 27 .mu.m, Poisson coeff. 0.22, Young's modulus 69 Gpa, and sp. wt. of 2.46 g/cm3. The elastic modulus of the composites increased with glass microsphere content, while the flexural strength and tensile strength decreased slightly, compared to those of neat polystyrene. The fracture strength and deformation at break of the composites improved and the composites are pliable. A micro-deformation mechanism of multiple pseudo-cracking or multiple crazing is obsd., which result in multiple planes for crack propagation, thus increasing the toughness of the material. Indexing -- Section 37-5 (Plastics Manufacture and Processing) Section cross-reference(s): 57

Abstract: The reinforcing effect of talc particles on polypropylene was analyzed by measuring tensile characteristics of the composites as a function of mineral content (0-40%). The effect of surface treatment of talc particles with silane coupling agents was also taken into account, as was the strain rate. The Young's modulus and tensile strength were measured by tensile tests on injection-molded std. specimens. The values were compared with those predicted by the principal theor. and semi-empiric models for composites. The rigidity of polypropylene/talc composites increased with mineral content, and with silane surface treatment. The tensile strength is strongly dependent on the surface treatment of talc; the tensile strength could be adequately predicted by math. models for short-fiber composites where interface shearing mechanisms are present. Indexing -- Section 37-2 (Plastics Manufacture and Processing)

Abstract: Tensile fracture behavior of different thickness isotactic polypropylene (PP) films and sheets was studied using the essential work of fracture method following the ESIS protocol, as an alternative to LEFM and EPFM, which are not suitable for the characterization of ductile films. The specific essential work of fracture, we, and the plastic work of fracture, .beta.wp, were detd. The we value was considered as a toughness measurement, independent of the sample geometry. The influence of the thickness, t, and the rate of testing, v, on we and .beta.wp, was studied on PP films and sheets with a deep double edge notched tension geometry. Indexing -- Section 37-5 (Plastics Manufacture and Processing)

Abstract: Two different series of talc-polypropylene composites ranged between 0 and 40 wt % were prepared by extrusion. In one of the series, the talc surface was modified with silane coupling agents in order to improve the affinity relation between the filler and the PP matrix. By means of X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) techniques, the configuration of the PP crystalline phase and the nucleating activity of the mineral have been stated in both series. © 1997 Elsevier Science Ltd. All rights reserved.

Abstract: Fracture behaviour of injection-moulded polypropylene filled with silane-treated talc was studied as a function of filler volume fraction (0-20%) and compared to that of polypropylene filled with untreated talc. High-rate tests (0.57 m/s) on SENB specimens were carried out using an instrumented Charpy impact pendulum, and linear elastic fracture mechanics (LEFM) was applied to calculate the fracture parameters, Kc and Gc. It was found that moderate fractions of talc which were added to the polypropylene matrix increased the fracture toughness of the composite independent of the talc surface treatment. This general improvement seems to be due to the peculiar orientation of the talc platelets in the injection-moulded specimens. The fracture behaviour of the composites was also studied at low strain rate (1 mm/min) by tests on J-integral type specimens with the same SENB geometry. In this case, the composites with silane-treated talc presented poor J-integral values compared to those of the samples with untreated talc. This was attributed to a reduction of the plastic zone at the crack tip, since the improved coupling between the talc platelets and matrix increased the yield strength of the composite. All the results are explained on a basis of morphological and microstructural details.

Abstract: Talc-filled polypropylene (PP) composites were prepared by extrusion in a wide composition range (0-40 wt %). To improve the affinity relation between talc and the PP matrix, we modified the talc surface with silane coupling agents. Differential scanning calorimetry investigations on test samples, prepared by injection moulding, revealed that the talc content and its surface modification had a pronounced effect on the crystallization behavior of the filled PP composites. The experimental results indicate that a talc concentration of 2 wt % strongly affects the nonisothermal crystallization process of the PP, especially when talc is silane treated. Isothermal crystallization experiments on samples with minimum amounts of talc (2 wt %) revealed an improved nucleation activity with silane-treated talc. © 1996 John Wiley & Sons, Inc.

Abstract: To improve the affinity of talc and polypropylene matrix, the talc surface was modified with silane [Ucarsil PC-1A and PC-1B] coupling agents. DSC data of injection molded specimens showed a pronounced effect of talc content and surface modification on the crystn. behavior of filled PP composites. A talc content of 2% strongly affected nonisothermal crystn., specially when talc was silane-treated, by improving nucleation activity of talc. Indexing -- Section 37-2 (Plastics Manufacture and Processing)

Abstract: The fracture behavior of injection-molded talc-polypropylene (PP) was studied as a function of talc content and talc surface treatment. Untreated and silane-treated talc comprised up to 40% of the composites. The fracture toughness was measured by impact tests and linear elastic fracture mechanics was applied to calc. the fracture parameters. Moderate amts. of talc increased the fracture toughness of the composite, independently of surface treatment. This effect is attributed to the peculiar orientation of talc platelets in the injection-molded specimens. The fracture behavior of the composites was also studied at low strain rate by J-integral tests. Under conditions of ductile fracture, the composites with silane-treated talc presented poor fracture resistance, compared to that of PP filled with untreated talc. All tests were carried out according to the European structural integrity society (ESIS) testing protocols. The role of morphol. and microstructure on the fracture mechanisms is described in detail. Indexing -- Section 37-5 (Plastics Manufacture and Processing)

Abstract: Polycarbonate foams reinforced with 0,5 wt% of graphene were obtained by firstly melt-mixing the polycarbonate and graphene in an internal mixer, compression-moulding the melt-compounded grinded material and lastly dissolving CO 2 inside a high pressure vessel. The CO 2 desorption behaviour in the unfilled polycarbonate and nanocomposite was studied in terms of the CO 2 saturation concentration and desorption diffusion coefficient, with the graphene-filled nanocomposite displaying a higher CO 2 loss rate when compared to the neat polycarbonate. The cellular structure of the foams was found to be highly dependent on the saturation/foaming temperature, with smaller cell sizes being obtained with decreasing the temperature. Another parameter that had an important influence was the residual pressure, with higher residual pressure values resulting in foams with more uniform and regular cells.

Abstract: In this paper we prepared and characterized several polyurethane composite foams by combining variable concentrations of organophilic clay (montmorillonite) and metal reinforcement, with the objective of developing novel multi-scalar multifunctional rigid foams. The addition of montmorillonite clay promoted foaming and the formation of finer and more homogeneous cellular structures, resulting in foams with compressive elastic moduli and collapse stresses lower than that of the unfilled polyurethane foams. However, a comparative analysis versus the foams' relative density demonstrated that both mechanical properties follow one single trend for the two materials. The combination of montmorillonite and metal reinforcement further reduced the cell size of foams, ultimately resulting in foams with similar mechanical properties for considerably lower relative densities. Although no important differences in thermal conductivity were found for the polyurethane foams with adding montmorillonite, the incorporation of the metal reinforcement led to considerably higher thermal conductivities, its value increasing with increasing relative density.

Abstract: It is well known the growing industry interest in reducing the high flammability of polymers, as it limits their suitability in a wide variety of applications where fire retardancy is required, at the same time maintaining some of the advantages related to their lightness. With that in mind, this work presents the development of new rigid polypropylene composite foams filled with high amounts of flame-retardant systems based on hydrated magnesium carbonate. Particularly, interesting flameretardancy synergistic effects were observed in the polypropylene composite foams by means of cone calorimetry by combining the hydrated magnesium carbonate with an intumescent formulation and layered nanoparticles.

Abstract: In this paper, novel polymer foams based on a benzoxazine resin system developed by Henkel for aerospace applications were successfully prepared using azodicarbonamide as a foaming agent. The curing process of the resin was analyzed using differential scanning calorimetry (DSC) and the blowing agent decomposition followed by thermogravitmetric analysis (TGA). The cellular structure of the foamed samples was analyzed using scanning electron microscopy (SEM) and the mechanical properties determined using compression tests. The foams were predominantly open cell materials with relative densities in the range 0.35-0.60 showing compressive strengths and a compressive moduli in the range of 12 - 63 MPa and 465 - 1065 MPa respectively and thermal conductivities in the range of 0.06 - 0.12 W/mK. The findings in this paper, demonstrate the possibility of producing polybenzoxazine foams using a simple technique in which curing and foaming are performed simultaneously and that these materials are suitable for structural applications.

Abstract: This chapter is dedicated to the study of heat transfer in polyolefin-based foams, particularly thermal conductivity, as a function of their structure and chemical composition. A small review of the main experimental techniques used to measure the thermal conductivity of these materials is also given, focusing on the transient plane source method (TPS), as well as different theoretical models commonly used for estimating its value. Alongside cellular structure (cell size, anisotropy, etc) and composition considerations, particular importance is given to the analysis of the presence of micrometric and nanometric-sized fillers in the resulting cellular composite thermal properties. This is a novel research field of particular interest, thought to extend the application range of these lightweight materials by tailoring their conductivity. © Springer-Verlag Berlin Heidelberg 2010.

Abstract: The application of the essential work of fracture (EWF) methodology for the fracture behavior characterization of closed-cell low density polyethylene flexible foams is discussed in the present paper. The thickness of the foamed sheet and the relative orientation of the initial crack were the main parameters studied. The interpretation of the results is carried out on the basis of the material microstructure and the applicability of the testing method. © (2011) Trans Tech Publications.

Abstract: The thermal conductivity of unfilled polypropylene foams produced using different foaming processes has previously been demonstrated to be mainly affected by the foam's bulk density [1]. The influence of adding inorganic particles is now studied, with the thermal conductivity of the mineral-filled PP foams being determined using the Transient Plane Source Method (TPS). To this end, two different fillers were used. The incorporation of high amounts (50 and 70 wt.%) of magnesium hydroxide resulted in considerably higher thermally conductive foamed materials, with interesting thermal anisotropies being observed for the higher expansion ratio foams. On the contrary, adding montmorillonite (MMT) nanoparticles did not considerably alter the thermal conductivity of the foams, their value being mainly affected by the relative density. © (2010) Trans Tech Publications.

Abstract: The preparation and characterization of cellulosic fibre-reinforced polypropylene composite foams is presented. The cellulose fibres were isolated from a barley straw obtained from local sources. They were compounded with the polymer in the melt state to obtain composites with nominal concentrations of 10 and 20% by weight. After compression-moulding the composite samples were foamed in a high-pressure batch-process employing CO 2 as foaming agent. The effects of the fibre loading on the basics characteristics of the foams was investigated. © (2010) Trans Tech Publications.

Abstract: Carbon nanofibre-reinforced polypropylene nanocomposites containing from 5 to 20 wt.% of carbon nanofibres and a chemical blowing agent were melt-compounded and later foamed using compression-moulding. Alongside their foaming behaviour analysis and cellular characterization, foams showing an increasingly finer isometric cellular structure with increasing the amount of nanofibres, their thermal conductivity was determined using the Transient Plane Source Method (TPS). Contrarily to the electrical conductivity, which has previously been shown to rise with increasing the amount of carbon nanofibres [1], the addition of the nanofibres did not significantly alter the thermal conductivity of the PP foams, their value being mainly affected by the relative density, only slight differences being assessed for the higher expansion ratio PP-CNF foams. © (2010) Trans Tech Publications.