Mariano Pracella, graduate in Chemistry cum laude at the University of Naples (Italy), is Senior Researcher of the Italian National Research Council (CNR) and responsible of the Institute of Composite and Biomedical Materials (IMCB), section of Pisa - c/o Department of Chemical Engineering & Materials Science, University of Pisa (Italy). His research activity has been focused on the study of morphology, functional modification, reactive compatibilization and physical/mechanical properties of polymer blends and composites with natural and inorganic fillers. He is responsible of CNR research projects, international cooperation projects with Polish and Bulgarian Academies of Sciences, CONICET (Argentina), and collaboration programmes with Venezuela and Egypt. He has been the co-ordinator of an European Project on recycling of post-consumer plastic materials. Presently, he is adj. prof. of Chemistry and Applied Chemistry at the Dept. of Energetic Engineering, Univ. of Pisa.
Abstract: A comparative study of the preparation and properties of composites of PCL with cellulose microfibres (CFs) containing butanoic-acid-modified cellulose (CB) or PCL grafted with maleic anhydride/glycidyl methacrylate as compatibilizers, is reported. The composites are obtained by melt mixing and analyzed using SEM, DSC, TGA, XRD, FT-IR, NMR and tensile tests. An improved interfacial adhesion is observed in all compatibilized composites, as compared to PCL/CF. The crystallization behavior and crystallinity of PCL is largely affected
by CF and CB content. Composites with PCL-g-MAGMA display higher values of tensile modulus, tensile
strength and elongation at break.
Abstract: Ternary composites of a biodegradable thermoplastic matrix, Mater-Bi (MB), with various polyolefins
(PP, HDPE and PS) and hemp fibres (H) were obtained by melt mixing and characterized by SEM, OM,
DSC, TGA and tensile tests. The properties of composites were compared with those of MB/polyolefin
and MB/H blends. Maleic anhydride functionalized polyolefins were employed as compatibilizers. Crystallization behaviour and morphology of the composites were found to be affected by the composition,
phase dispersion and compatibilizer. Thermogravimetric analysis indicated that the thermal stability
of the polyolefin phase and fibres was influenced by the composition and phase structure. A significant
improvement of tensile modulus and strength was recorded for composites of MB with PE and PS as compared to MB/H composites. The results indicate that incorporation of polyolefins in the biodegradable
matrix, compared to binary matrix/fibre system, may have significant advantages in terms of properties,
processability and cost.
Abstract: Composites of polystyrene (PS) with cellulose microfibres and oat particles, obtained by melt mixing,
were examined. The compatibilization of the composites was carried out by addition of maleic anhydride-functionalized copolymers (SEBS-g-MA, PS-co-MA) and poly(ethylene glycol) to improve the fibre–matrix interfacialinteractions. The plain components and their composites were characterised by FT-IR, DSC, TGA, SEM microscopy and mechanical tests. The properties of the various systems were analysed as a function of both fibre and compatibilizer amount. The compatibilized PS composites showed enhanced fibre dispersion and interfacial adhesion as a consequence of chemical interactions between the anhydride groups on the polymer chains and the hydroxyl groups on the fibres, as demonstrated by FTIR
spectroscopy. DSC analysis pointed out a neat increase of Tg of composites on addition of SEBS-g-MA, as compared to PS-co-MA. The thermal stability of composites was also influenced by the type and amount of fibres, as well as by the structure and concentration of compatibilizer. The effect of the reactive copolymers on the composites properties was accounted for on the basis of the polymer–polymer miscibility and chemical interactions at the matrix/filler interface.
Abstract: A novel composite material containing 2 wt% of cellulose nanofibers well dispersed in PLA matrix, both 23
materials being biodegradable, was prepared and studied. Biodegradable composites with 2 and 20 wt% 24
of cellulose fibers with standard diameters were also obtained and examined for comparison. The nano- 25
composite exhibited markedly higher storage modulus as compared to neat PLA and the composite with 26
the same content of cellulose standard fibers. In addition, strength of the nanocomposite was improved 27
in comparison with neat PLA, especially at elevated temperature of 45 C, at which it was higher by 50%. 28
No negative effect of standard fibers and nanofibers onmolarmass of PLAmatrixwas observed.Moreover, 29
the composite materials, including the nanocomposite, did not show weight loss up to 300 C.
Abstract: Composites based on ethylene-vinyl acetate copolymers (EVA) functionalised with reactive groups (maleic anhydride, glycidyl methacrylate) and cellulose fibres (Cell) of different type were obtained by melt mixing, in the composition range 0-50 wt% Cell. The phase behaviour, the morphology and matrix-fibre interactions of the composites were analysed by DSC, DMTA, TGA, SEM and FT-IR spectroscopy. FT-IR analysis indicated the chemical interactions between the functional groups (MA, GMA) of EVA and the hydroxyl groups of cellulose. Accordingly, SEM microscopy pointed out an improved adhesion between cellulose and matrix in both EVA-MA/Cell and EVA-GMA/Cell composites, as compared to EVA/Cell composites. Glass transition behaviour and filler effectiveness (CFE) were analysed by DMTA. Tg of EVA and EVA-GMA changed markedly by the incorporation of cellulose. Cellulose was found to be more effective filler for EVA-GMA (CFE= 0.02) than EVA-MA (CFE = 0.22). Thermal resistance and tensile properties were significantly improved for GMA functionalised systems.
Abstract: Cellulose microfibres were modified with two different bi-functional monomers, namely maleic anhydride (MA) and glycidyl methacrylate (GMA). Composites of EVA copolymer with modified and unmodified cellulose were prepared in the presence of radical initiator by melt mixing in Brabender mixer. The samples were analyzed by SEM, WAXS, FT-IR, DSC, TGA, DMTA and tensile mechanical tests. SEM analysis pointed out that the presence of reactive groups on cellulose surface enhanced the compatibility, improving the fibre/matrix interfacial adhesion as compared to unmodified composites. This was correlated with the occurrence of chemical reactions between the double bond of functional groups onto cellulose and the polymer chains, as demonstrated by FT-IR analysis. The incorporation of fibres affected the crystallization behaviour and crystallinity of the polymer matrix. Composites with GMA modified cellulose displayed better compatibility, higher thermal stability, elongation at break and tensile strength as compared to EVA/Cell.
Abstract: The article is focused on analyzing the effect of functionalization and reactive processing on the morphological, thermal, rheological and mechanical properties of composites of isotactic polypropylene (PP), polystyrene (PS), poly(ethylene-vinyl acetate) (EVA), with cellulose fibers, hemp or oat as natural fillers. Both polymers and fibers were modified with bi-functional monomers (glycidyl methacrylate, GMA; maleic anhydride, MA) capable of facilitating chemical reactions between the components during melt mixing. Polyolefin copolymers containing reactive groups (PP-g-GMA, SEBS-g-MA, PS-co-MA, etc.) were used as compatibilizers. Optical and SEM microscopy, FTIR, RX, DSC, TGA, DMTA, rheological and mechanical tests were employed for the composites characterization. The properties of binary and ternary systems have been analyzed as a function of both fiber and compatibilizer content. All compatibilized systems showed enhanced fiber dispersion and interfacial adhesion. The phase behavior and the thermal stability of the composites were affected by the chemical modification of the fibers. Marked changes in the overall crystallization processes and crystal morphology of PP composites were observed owing to the nucleating effect of the fibers. The tensile mechanical behavior of the compatibilized composites generally resulted in a higher stiffness, depending on the fiber amount and the structure and concentration of compatibilizer.
Abstract: Morphology, thermal properties, and microhardness of ethylene-glycidyl methacrylate copolymer (EGMA)/clay and ethylene-acrylic ester-glycidyl methacrylate terpolymer (EAGMA)/clay nanocomposites with different clay concentrations have been studied. The results have shown that EGMA and EAGMA are highly compatible with the organoclays Cloisite120A (Cl20A) andCloisite130B (Cl30B). Intercalated structures are formed in the whole range of Cl20A loadings investigated, whereas partial degradation of the Cl30B organoclay was observed. The thermal characteristics and microhardness of EGMA/clay nanocomposites suggest that the filler dispersion deteriorates at high concentration. The concentrated EGMA/Cl20A nanocomposites have been used as masterbatches to prepare ternary high density polyethylene (HDPE)/Cl20A and low density polyethylene (LDPE)/Cl20A nanocomposites. Diffractometric characterization and scanning electron microscopy observations of these materials have shown that the intercalated structure of the starting EGMA/Cl20A masterbatches is preserved after dilution with the polyolefins. The results suggest that the silicate platelets remain localized within the EGMA droplets in the diluted nanocomposites. The latter display improved microhardness, whereas the mechanical properties, including elongation at break, are comparable with those of the neat polyolefins. Considerable enhancement of the flame retardant properties has been observed for the ternary nanocomposites.
Abstract: The calorimetric characteristics, the flammability, the thermal stability and the microhardness
of polyethylene high density/clay nanocomposites (HDPE/clay) have been
studied by differential scanning calorimetry, thermogravimetry, determination of limiting
oxygen index and microhardness tests. The nanocomposites have been compatibilized by
ethylene–acrylic acid copolymer (EAA), acrylic acid grafted HDPE (HDAA) and maleic
anhydride grafted HDPE (HDMA). The clay was montmorillonite Cloisite 15A. The influence
of the presence and the type of the compatibilizers on the properties of the nanocomposites
has been evaluated. The results have shown that the thermal stability, the
reduction of the flammability and the microhardness of HDPE/clay nanocomposites,
compatibilized by HDAA and HDMA are higher than those for nanocomposite compatibilized
by EAA. Moreover, the presence and the type of compatibilizer have negligible
effect on the characteristics of the HDPE phase transitions. These results have been
interpreted by the better clay dispersion and higher level of clay exfoliation in the presence
of compatibilizers HDAA and HDMA, than those in the presence of EAA compatibilizer.
Abstract: Green composites of PLA with micropowders derived from agricultural by-products such as oat husks, cocoa shells, and apple solids that remain after pressing have been prepared by melt mixing. The thermal and mechanical properties of the composites, including the effect of matrix crystallization and plasticization with poly(propylene glycol), have been studied. All fillers nucleated PLA crystallization and decreased the cold-crystallization temperature. They also affected the mechanical properties of the compositions, increasing the modulus of elasticity but decreasing the elongation at break and tensile impact strength although with few exceptions. Plasticization of the PLA matrix improved the ductility of the composites.
Abstract: Composites Of poly(L-lactide) (PLA) with hemp fibers (Cannabis sativa), prepared by batch mixing and plasticized with poly(ethylene glycol) (PEG; weight-average molecular weight = 600 g/mol), were examined by polarized optical microscopy, scanning electron microscopy, wide-angle X-ray scattering, differential scanning calorimetry, thermogravimetric analysis, and mechanical tests. The properties of both fully amorphous and semicrystalline samples of PLA/hemp and PLA-PEG/hemp composites were analyzed as a function of the fiber amount. The cold-crystallization kinetics of PLA in amorphous composites were investigated under isothermal conditions within the range of 70-130 degrees C. For PLA/hemp samples, the bulk crystallization rate displayed a maximum near 110 degrees C, whereas for plasticized samples, a higher and almost constant crystallization rate was observed over the entire temperature range, independently of the hemp amount. The kinetics were then analyzed on the basis of the Avrami model. The effect of fibers on the growth morphology of PLA spherulites, as well as the influence of the plasticizer on the melting behavior of PLA crystals and their reorganization during heating, was also examined. The thermogravimetric analysis of the composites, carried out in both nitrogen and air, showed that the degradation process of fiber-filled systems started earlier than that of plain PLA, independently of the presence of the plasticizer. Mechanical tests showed that the modulus of elasticity of the composites markedly increased with the hemp content, reaching 5.2 GPa in the case of crystallized PLA reinforced with 20 wt % hemp, whereas the elongation and stress at break decreased with an increasing amount of fiber for all examined systems. Plasticization with PEG did not improve the tensile properties of the composites. (C) 2007 Wiley Periodicals, Inc.
Abstract: The co-polymerization of ethylene with 1-hexene has been performed with titanium precursors based on carboxylato ligands in the presence of organoaluminium compounds as activators to afford linear low-density polyethylenes (LLDPEs). The influence of the polymerization parameters was studied with particular reference to the type and amount of catalyst components, solvent, temperature, ethylene pressure, 1-hexene concentration. The chloro-substituted bis-carboxylato titanium complex resulted the most active precursor in the co-polymerization, allowing to obtain copolymers with modulable composition in the 1-5 mol% range of 1-hexene units. The obtained copolymers were characterized by thermal analysis, X-ray diffraction spectroscopy, FTIR and NMR techniques. (c) 2007 Elsevier Ltd. All rights reserved.
Abstract: Ethylene/1-hexene random copolymers with 1-hexene content in the range of 1-5 mol-%, synthesised in the presence of new heterogeneous catalyst systems based on bis-carboxylato and -bis-chloro-carboxylato titanium chelate complexes, have been characterised by FTIR microspectroscopy (FTIR-M), DSC calorimetry and X-ray scattering. The co-monomer content and sequence distribution in the various samples were determined by means of both FTIR-M and C-13 NMR spectroscopy. The deformation bands of methyl groups in the region of 1400-1330 cm(-1) were used for the structural analysis of these copolymers. The effect of composition on the crystallinity and phase transitions of copolymers was analysed both in 1500-1300 and 760-690 cm(-1) frequency ranges as a function of the annealing temperature. A neat variation of the absorbance ratio of methyl band at 1378 cm-1 was recorded between 110 and 130 degrees C corresponding to the melting range of the copolymer crystals. The crystallisation behaviour of the copolymers was examined by DSC in dynamic and isothermal conditions; the isothermal kinetics were analysed according to the Avrami model. A marked decrease in the bulk crystallisation rate, accompanied by changes in the nucleation and growth of crystals, was found with an increase in the co-monomer content. The melting behaviour of isothermally crystallised samples was also investigated and the melting temperatures of the copolymers at equilibrium conditions were related to the composition; the experimental data were consistent with the Flory exclusion model of side branches from the crystalline phase. The lowering of crystal growth rate in the copolymers has been accounted for by an increase in the free energy of formation of critical size nuclei due to the effect of the side branches.
Abstract: Composites Of poly(L-lactide) (PLA) with hemp fibers (Cannabis sativa), prepared by batch mixing and plasticized with poly(ethylene glycol) (PEG; weight-average molecular weight = 600 g/mol), were examined by polarized optical microscopy, scanning electron microscopy, wide-angle X-ray scattering, differential scanning calorimetry, thermogravimetric analysis, and mechanical tests. The properties of both fully amorphous and semicrystalline samples of PLA/hemp and PLA-PEG/hemp composites were analyzed as a function of the fiber amount. The cold-crystallization kinetics of PLA in amorphous composites were investigated under isothermal conditions within the range of 70-130 degrees C. For PLA/hemp samples, the bulk crystallization rate displayed a maximum near 110 degrees C, whereas for plasticized samples, a higher and almost constant crystallization rate was observed over the entire temperature range, independently of the hemp amount. The kinetics were then analyzed on the basis of the Avrami model. The effect of fibers on the growth morphology of PLA spherulites, as well as the influence of the plasticizer on the melting behavior of PLA crystals and their reorganization during heating, was also examined. The thermogravimetric analysis of the composites, carried out in both nitrogen and air, showed that the degradation process of fiber-filled systems started earlier than that of plain PLA, independently of the presence of the plasticizer. Mechanical tests showed that the modulus of elasticity of the composites markedly increased with the hemp content, reaching 5.2 GPa in the case of crystallized PLA reinforced with 20 wt % hemp, whereas the elongation and stress at break decreased with an increasing amount of fiber for all examined systems. Plasticization with PEG did not improve the tensile properties of the composites. (C) 2007 Wiley Periodicals, Inc.
Abstract: Nanocomposites of isotactic polypropylene (PP) with polyhedral oligomeric silsesquioxanes (POSS) [RSiO1,5](8) having different alkyl substituents (R = methyl, isobutyl, isooctyl) were obtained by melt blending and analysed with electron microscopy, optical microscopy and DSC calorimetry. The influence of POSS structure on the morphological characteristics, the crystallization and melting behaviour of PP/POSS composites was investigated with varying the filler amount. The crystallization kinetics of the composites from the melt, examined both in isothermal and non-isothermal conditions, demonstrated that the nucleation activity of the examined POSS can be related to the length of alkyl substituents which, depending on the loading amount, affect the filler dispersion in the PP matrix and the growth of polymer crystals.
Abstract: Composites of isotactic polypropylene (PP) with Hemp fibres (Cannabis sativa), functionalized by means of melt grafting reactions with glycidyl methacrylate (GMA) and prepared by batch mixing, were examined. Either the modification of fibres (Hemp-GMA) and polyolefin matrix (PP-g-GMA), as well as the addition of various compatibilizers (PP-g-GMA, SEBS, SEBS-g-GMA) were carried out to improve the fibre-matrix interactions. The modified components and their composites were characterised by FT-IR analysis, POM and SEM microscopy, RX, DSC, TGA and mechanical tests. The properties of binary (PP/Hemp, PP/Hemp-GMA, PP-g-GMA/Hemp) and ternary (PP/Hemp/compatibilizer) composites were analysed as a function of the fibre amount and compatibilizer content. All modified composites showed improved fibre dispersion in the polyolefin matrix and higher interfacial adhesion when compared to the unmodified system (PP/Hemp) as a consequence of chemical bonding between fibre and polymer. The thermal stability and phase behaviour of the composites resulted to be largely affected by the fibre and matrix modification. Changes in the spherulitic morphology and crystallisation behaviour of PP were observed in the composites due to the nucleating effect of Hemp fibres. Moreover, a marked increase of PP isothermal crystallisation rate (in the range 120-138 degrees C) was recorded with increasing the Hernp-GMA content. All composites displayed higher tensile modulus (about 2.9 GPa) and lower elongation at break as compared to plain PP; compatibilization with PP-g-GMA (10 phr) resulted in an increased stiffness of the composites as consequence of an improved fibre-matrix interfacial adhesion. (c) 2005 Elsevier Ltd. All rights reserved.
Abstract: Bioartificial blends of poly-(epsilon-caprolactone) (PCL) with a polysaccharide (starch, S; dextran, D; or gellan, G) (PCL/S, PCL/D, PCL/G 90.9/9.1 wt ratio) were prepared by a solution-precipitation technique and widely characterized by differential scanning calorimetry analysis (DSC), Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATR), optical microscopy (OM), wide-angle X-ray diffraction analysis (WAXD), and thermogravimetry (TGA). DSC showed that the polysaccharide reduced the crystallinity of PCL and had a nucleation effect, which was also confirmed by OM analysis. Hoffman-Weeks analysis was performed on PCL and blend samples allowing calculation of their equilibrium melting temperatures (). WAXD showed that the crystalline unit cell type was the same for PCL and blends. FTIR-ATR did not evidence interactions between blend components. Thermal stability was affected by the type of polysaccharide. Microparticles (<125 microm) were produced from blends by cryogenical milling and characterized by scanning electron microscopy analysis (SEM). Selective laser sintering (SLS), a new rapid prototyping technology for scaffold fabrication, was applied to sinter blend microparticles according to a PC-designed two-dimensional geometry (strips and 2 x 2 mm(2) square-meshed grids). The optimal experimental conditions for sintering were established and laser beam parameters (beam speed, BS, and power, P) were found for each blend composition. Morphology of sintered objects was analyzed by SEM and found to be dependent on the morphology of the sintered powders. Sintered samples were analyzed by chemical imaging (CI), FTIR-ATR, DSC, and contact angle analysis. No evidence of the occurrence of degradation phenomena was found by FTIR-ATR for sintered samples, whereas DSC parameters of PCL and blends showed changes which could be attributed to some molecular weight decrease of PCL during sintering. CI of sintered samples showed that the polysaccharide phase was homogeneously dispersed within the PCL matrix, with the only exception being the PCL/D blend. The contact angle analysis showed that all samples were hydrophilic. Fibroblasts were then seeded on scaffolds to evaluate the rate and the extent of cell adhesion and the effect of the polysaccharides (S, D, G) on the bioactivity of the PCL-based blends.
Abstract: Precipitated CaCO3 (PCC)/High Density Polyethylene (HDPE) composites were prepared on a twin screw mixer-single screw extruder with a particle content of 10 vol%. The average particle size was 70 nm. The influence of surface treatment of the particles, with and without stearic acid (SA), on the physico-mechanical and rheological properties was studied. The experiments included tensile tests, impact tests, differential scanning calorimetry (DSC), microscopy and rheology experiments. The addition of 10 vol% calcium carbonate to HDPE causes a rise in Young's modulus and yield stress of its composites and is accompanied by a sharp drop in impact strength. The addition of SA has the effect of slightly decreasing both Young's modulus and yield stress of the composites compared to the uncoated PCC composites, while the impact strength progressively increases. During the tensile test filled HDPE composites showed stress whitening zones appear and develop along the gauge length. Volume measurements during tensile tests showed an increase in volume strain with deformation, due to the matrix-particle debonding phenomenon, while pure HDPE showed actually a decrease in volume with elongation. At constant deformation, for the composites with coated PCC, it can be observed that an increase in the SA content leads to a slight decrease in volume change. The microscopical evaluation showed cavities and voids due to debonding and deformation bands in the stress whitened areas. DSC experiments have shown that uncoated PCC particles have a very small nucleating effect on HDPE. (C) 2004 Published by Elsevier Ltd.
Abstract: Blends of polyamide-6 (PA6) and low density polyethylene (LDPE) were compatibilized by melt mixing with various polyolefins functionalized with glycidyl methacrylate (GMA), i.e., GMA grafted LDPE (LDPE-g-GMA), GMA grafted styrene-ethylenelbutylene-styrene block copolymer (SEBS-g-GMA) and ethylene-co-glycidyl methacrylate copolymer (E-GMA). Blends with PA6/LDPE composition ratios of 25/75 and 75/25 wt.-%/wt.-% were prepared in a Brabender internal mixer and their properties were evaluated by SEM, theological measurements and DSC. Morphological investigation by SEM showed a neat improvement of phase dispersion and interfacial adhesion in all compatibilized blends when compared to PA6/LDPE binary blends. The variation of the dispersed phase size was analyzed as a function of blend composition, compatibilizer concentration and GMA content. The emulsification curves of compatibilized blends showed that the equilibrium size of dispersed particles at the saturation concentration of copolymer was lower when PA6 was the major component. The finest dispersion of the LDPE phase (< 0.25 mu m) was observed in the presence of SEBS-g-GMA copolymer. LDPE-g-GMA and E-GMA displayed a similar compatibilizing efficiency. In all cases, the blends with a polyamide matrix presented a marked rise in torque and melt viscosity with increasing compatibilizer content, These effects were accounted for by a reaction between the epoxide groups of LDPE-g-GMA and the carboxyl/amine end-groups of PA6, leading to the formation of an interchain graft copolymer. The phase transition processes of PA6 in the blends were influenced by the compatibilizer content and the interfacial interactions between the polymer components, suggesting a different role for the compatibilizer at the PA6/LDPE interface.
Abstract: Styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) and styrene-b-(ethylene-co-propylene) (SEP, SEPSEP) block copolymers with different styrene contents and different numbers of blocks in the copolymer chain were functionalized by melt radical grafting with glycidyl methacrylate (GMA) and employed as compatibilizers for PET-based blends. Binary blends of PET with both functionalized (SEBS-g-GMA, SEP-g-GMA, SEPSEP-g-GMA) and neat (SEBS, SEP, SEPSEP) copolymers (75 : 25 w/w) and ternary blends of PET and PP (75 : 25 w/w) with various amounts (2.5-10 phr) of both modified and unmodified copolymers were prepared in an internal mixer, and their properties were evaluated by SEM, DSC, melt viscosimetry, and tensile and impact tests. The roles of the chemical structure, grafting degree, and concentration of the various copolymers on blend compatibilization was investigated. The blends with the grafted copolymers showed a neat improvement of phase dispersion and interfacial adhesion compared to the blends with nonfunctionalized copolymers. The addition of grafted copolymers resulted in a marked increase in melt viscosity, which was accounted for by the occurrence of chemical reactions between the epoxide groups of GMA and the carboxyl/hydroxyl end groups of PET during melt mixing. Blends with SEPSEP-g-GMA and SEBS-g-GMA, at concentrations of 5-10 phr, showed a higher compatibilizing effect with enhanced elongation at break and impact resistance. The effectiveness of GMA-functionalized SEBS was then compared to that of maleic anhydride-grafted SEBS. (c) 2005 Wiley Periodicals, Inc.
Abstract: Samples of propylene-ethylene (EP) and propylene-(1-butene) (BP) random copolymers with various comonomer content (2-3.1 wt% ethylene, 9.9 wt% 1-butene), were melt-mixed in Brabender internal mixer at various compositions (25/75, 50/50, 75/25). Films of copolymers and blends, as well as of a homopolymer sample (iPP), obtained by compression moulding and with different thermal history were characterized by optical and scanning electron microscopy (OM, SEM), small-angle light scattering (SALS), small- and wide angle X-ray scattering (SAXS, WAXS) and differential scanning calorimetry (DSC). It was found that all copolymers and blends studied crystallized exclusively in monoclinic alpha-modification forming spherulitic structure in a very broad undercooling range. The average size of spherulites is smaller in the copolymer containing 1-butene as compared to those containing ethylene or to iPP homopolymer, due to enhanced heterogeneous nucleation in BP copolymer. SEM microscopic observations demonstrated that EP and BP copolymers were miscible at all examined compositions and form homogeneous blends. Structural and morphological analysis indicated that the comonomer units are incorporated into growing crystallites in both EP and BP copolymers, while the non-crystallizing material is rejected out of the crystallites. For small concentrations of comonomer some of non-crystallizing species are pushed ahead of the front of growing spherulite into interspherulitic regions. For higher comonomer concentration these species are mostly trapped in intraspherulitic regions. Melting behavior of copolymers reflects the incorporation of comonomer into crystalline phase: melting temperature and crystallinity degree decrease in copolymers and blends as compared to plain iPP. (C) 2004 Elsevier Ltd. All rights reserved.
Abstract: Results concerning the compatibilization and the chemical-physical characterisation of blends of PET and polyolefins (HDPE, PP) obtained from postconsumer packaging materials are presented. The blend compatibilization was carried out by melt mixing and extrusion processes in the presence of a variety of polyolefins functionalized with reactive groups, such as maleic anhydride, acrylic acid, and glycidyl methacrylate. The effect of the type and concentration of compatibilizer, as well as the mixing conditions on the morphology, crystallization behavior, thermal stability, rheological, and dynamic-mechanical properties of the blends was investigated by various techniques, such as scanning electron microscopy, rheometry, differential calorimetry, thermogravimetry, FTIR, NMR, and mechanical analysis.
Abstract: The mechanical and thermal behaviour and the morphology of High-Density Polyethylene (HDPE), filled with different types of Barium Sulfate (BaSO4) submicron particles have been examined. Composites with a fitter content in the range 5-15 vol% were obtained with a twin screw mixer-single screw extruder and then analyzed by means of DSC, SEM and tensile and Charpy impact tests. The effect of different surface treatments of filler particles on the composite properties has been studied. The results indicate that the addition of BaSO4 particles leads to slight increase in Young's modulus and to a decrease in the yield stress independently of surface treatment. The fracture resistance tests demonstrated a strong influence of filler content and surface agents on impact parameters. The use of BaSO4 filler appears to induce a good toughening of HDPE, especially at low volume content, while surface agents reduce particle agglomeration and decrease the adhesion between filler and polymer matrix.
Abstract: Blocks copolymers styrene-b-(etliylene-co-butylene)-b-styrene (SEBS) and styrene-b-(ethylene-co-propylene) (SEP, SEPSEP), with different styrene content and number of blocks in the chain, were functionalized with glycidyl methacrylate (GMA) by melt radical grafting. The influence of monomer concentration. radical initiator and copolymer structure on the grafting degree Was examined. The grafted copolymers were characterised by DSC and capillary rheometry. Blends of PET With functionalized SEBS and SEPSEP showed a marked improvement of phase morphology and elongation at break when compared to blends With unfunctionalized copolymers.
Abstract: Low-density polyethylene (LDPE) was functionalized by melt radical grafting with glycidyl methacrylate (GMA) and employed for reactive blending with polyamide-6 (PA6). The effect of the reaction procedure on the grafting degree of LDPE-g-GMA samples (0.5-12.5 wt.-% GMA) was analyzed as a function of the concentration of GMA monomer, radical initiator (BTP), and addition of styrene as co-monomer. Optimized grafting conditions were obtained when the amount of the monomer is below 10 wt.-% and that of peroxide in the range 0.2-0.4 wt.-%. Binary blends of PA6 with LDPE-g-GMA (3.5 wt.-% GMA) and with LDPE at various compositions (80/20, 67/33, 50/50 wt.-%) were prepared in an internal mixer and their properties were evaluated by torque, SEM and DSC analyses. Morphological examination by SEM showed a large improvement of phase dispersion and interfacial adhesion in PA6/LDPE-g-GMA blends as compared with PA6/LDPE blends. The average diameter of dispersed polyolefin particles was about 0.4 mum for LDPE-g-GMA contents <50 wt.-%. A marked increase of melt viscosity was observed for the compatibilized blends depending on the concentration of grafted polyolefin, and it was accounted for by the reaction between the epoxy groups of GMA and the carboxyl/amine end-groups of PA6. The variation of torque was thus related to the molar ratio of reactive group concentration. The analysis of crystallization and melting behavior pointed out marked differences in the phase structure of the blends due to the presence of the functionalized polyolefin. Finally, the in situ formation of a graft copolymer between LDPE-g-GMA and PA6 was investigated by means of a selective dissolution method (Molau test) and by FT-IR and DSC analyses.
Abstract: The melt radical grafting of glycidyl methacrylate (GMA) onto isotactic polypropylene (PP) was carried out in Brabender internal mixer and the influence of reaction procedure, radical initiator concentration and addition of co-monomer (styrene) on the grafting efficiency was examined. The viscosity, the thermal behaviour and melt rheology of PP-g-GMA samples was then analysed as a function of grafted GMA content. Blends of poly(ethylene terephthalate) (PET) with PP and PP-g-GMA (5.2 wt% GMA), prepared in internal mixer, were characterised by SEM, DSC and melt viscosimetry. The morphological analysis of PET/PP-g-GMA blends (80/20, 50/50 w/w) pointed out a marked improvement of phase dispersion (with particle size of about 0.6 mum for 80/20 blend) and interfacial adhesion, as compared to non-compatibilized PET/PP blend. The results of mixing torque and thermal analysis supported the occurrence of in-situ compatibilization reaction between epoxy groups of GMA modified PP and carboxyl end-groups of PET in the melt.
Abstract: Low-density polyethylene (LDPE) was functionalized by melt radical grafting with glycidyl methacrylate (GMA) and employed for reactive blending with polyamide-6 (PA6). The effect of the reaction procedure on the grafting degree of LDPE-g-GMA samples (0.5-12.5 wt.-% GMA) was analyzed as a function of the concentration of GMA monomer, radical initiator (BTP), and addition of styrene as co-monomer. Optimized grafting conditions were obtained when the amount of the monomer is below 10 wt.-% and that of peroxide in the range 0.2-0.4 wt.-%. Binary blends of PA6 with LDPE-g-GMA (3.5 wt.-% GMA) and with LDPE at various compositions (80/20, 67/33, 50/50 wt.-%) were prepared in an internal mixer and their properties were evaluated by torque, SEM and DSC analyses. Morphological examination by SEM showed a large improvement of phase dispersion and interfacial adhesion in PA6/LDPE-g-GMA blends as compared with PA6/LDPE blends. The average diameter of dispersed polyolefin particles was about 0.4 mum for LDPE-g-GMA contents <50 wt.-%. A marked increase of melt viscosity was observed for the compatibilized blends depending on the concentration of grafted polyolefin, and it was accounted for by the reaction between the epoxy groups of GMA and the carboxyl/amine end-groups of PA6. The variation of torque was thus related to the molar ratio of reactive group concentration. The analysis of crystallization and melting behavior pointed out marked differences in the phase structure of the blends due to the presence of the functionalized polyolefin. Finally, the in situ formation of a graft copolymer between LDPE-g-GMA and PA6 was investigated by means of a selective dissolution method (Molau test) and by FT-IR and DSC analyses.
Abstract: The process for the compatibilized blending of recycled poly(ethylene terephthalate) and recycled high-density polyethylene with ethylene/glycidyl methacrylate copolymer was enlarged to the scale of a pilot plant. The addition of a compatibilizer effectively reduced the size of dispersed inclusions with better bonding to the matrix. The optimum contents of the compatibilizer were found to be around 4 pph. The extrusion and orientation of films from the blend were developed on an industrial scale, and the structure and properties of the obtained films were characterized. The crystalline phase of poly(ethylene terephthalate) in oriented films assumed a strong texture resulting from the plane-strain state of the deformation of the films on the industrial machinery. The origin of the texture was mostly strain-induced crystallization. The chain segments in the amorphous phase were oriented along the machine direction, but there was significant anisotropy of the chain packing in the amorphous phase in the plane perpendicular to the drawing direction, the pseudohexagonal packing of chain fragments being in register over the whole film. Such a texture of an oriented amorphous phase of poly(ethylene terephthalate) is reported here for the first time. The nonoriented and oriented films obtained with the industrial machinery showed good mechanical properties, with strengths up to 120 MPa and elongations to break of 40%. (C) 2002 Wiley Periodicals, Inc.
Abstract: Two ways of recovering the properties of the scrap plastics poly(ethylene terephthalate) (PET) and high-density polyethylene (HDPE) were analyzed: (1) blending incompletely segregated polymers with a compatibilizer and (2) blending nonsegregated polymers with a small amount (2 pph) of another compatibilizer. The advancement of the compatibilization reaction in a twin-screw extruder depended on the residence time and intensity of mixing according to melt viscosity measurements and scanning electron microscopy observations. The acceptable mechanical properties for systems with different PET contents were obtained in blends compatibilized with ethylene- glycidyl methacrylate (EGMA) and styrene-ethylene-butylene-styrene grafted with maleic anhydride. For a blend with 75% PET and 25% HDPE, the optimum content of EGMA was determined to be about 4 pph, and a film was produced with this composition. Admixtures present in recycled HDPE migrated to PET during blending and accelerated the hydrolysis of PET. As a result of migration, differences in the mechanical properties of the blends were observed, depending on the brand of recycled HDPE used. EGMA was also successfully used for the improvement of mechanical properties of a nonsegregated mixture based on PET. Tensile properties of two compatibilized PET-rich and HDPE-rich commingled scraps indicated the possibility of using these blends for film extrusion, with potential applications in the packaging of technical products. (C) 2002 Wiley Periodicals, Inc.
Abstract: Blends of recycled poly(ethylene terephthalate) (R-PET) and high-density polyethylene (R-PE), obtained from post-consumer packaging materials, were prepared both by melt mixing and extrusion processes and compatibilized by addition of various copolymers containing functional reactive groups, such as maleic anhydride, acrylic acid and glycidyl methacrylate. The effect of the type and concentration of compatibilizer, as well as the mixing conditions, on the phase morphology, thermal behaviour, theological and mechanical properties of the blends was investigated. The results indicated that addition (5divided by10 pph) of ethylene-co-glycidyl methacrylate copolymer (E-GMA) allows for a marked improvement of processability and physical/mechanical performances of R-PET/R-PE blends.
Abstract: The morphology and physical/mechanical properties of non-compatibilized and compatibilized blends of poly(ethylene terephthalate) (PET) and polyethylene (HDPE) obtained from virgin and post-consumer packaging materials were investigated. The blend compatibilization was carried in the presence of various polyolefins functionalized with reactive groups (HDPE-g-MA, EPR-g-MA, E-AA, E-GMA, SEBS-g-MA). The effect of the type and concentration of compatibilizer, as well as the mixing conditions on the phase morphology, crystallization behaviour, chemical interactions and melt rheology of the blends was then examined by means of electron microscopy (SEM), scanning calorimetry (DSC), FTIR and NMR spectroscopy, and capillary rheometry. The results pointed out that ethylene-co-glycidyl methacrylate copolymer (E-GMA) displayed a higher compatibilizing efficiency giving rise to a neat improvement of phase dispersion and interfacial adhesion in the blends, as compared to the other compatibilizers examined. This was accounted for by a high reactivity of epoxy groups with the chain end-groups of PET during melt-mixing and the effect of in situ formed graft copolymer on the interfacial properties (reduction of coalescence, interpenetration with homopolymer phases). Tensile mechanical tests showed that elongation at break of recycled PET/HDPE (75/25) blends was markedly enhanced upon addition of E-GMA amount lower than 5 wt.-%.
Abstract: Immiscible blends of recycled polyethylene terephthalate) (R-PET), containing some amount of polymeric impurities, and high-density polyethylene (R-PE), containing admixture of other polyolefins, in weight compositions of 75 : 25 and 25 : 75 were compatibilized with selected compatibilizers: maleated styrene- ethylene/butylene-styrene block copolymer (SEBS-g-MA) and ethylene-glycidyl methacrylate copolymer (EGMA). The efficiency of compatibilization was investigated as a function of the compatibilizer content. The rheological properties, phase structure, thermal, and viscoelastic behavior for compatibilized and binary blends were studied. The results are discussed in terms of phase morphology and interfacial adhesion among components. It was shown that the addition of the compatibilizer to R-PET-rich blends and R-PE-rich blends increases the melt viscosity of these systems above the level characteristic for the respective binary blends. The dispersion of the minor phase improved with increasing compatibilizer content, and the largest effects were observed for blends compatibilized with EGMA. Calorimetric studies indicated that the presence of a compatibilizer had a slight affect on the crystallization behavior of the blends. The dynamic mechanical analysis provided evidence that the occurrence of interactions of the compatibilizer with blend components occurs through temperature shift and intensity change of a P-relaxation process of the PET component. An analysis of the loss spectra behavior suggests that the optimal concentration of the compatibilizers in the considered blends is close to 5 wt %. (C) 2001 John Wiley & Sons Inc.
Abstract: In order to study the compatibility promoted in polyamide 6 (PA6) and ultra low-density polyethylene (ULDPE) blends by grafting polar groups into the ULDPE, several blend compositions were prepared in a twin screw extruder. The grafting agent was diethylmaleate (DEM), and the blend compositions prepared were 0, 20, 50, 80 and 100 wt.-% of PA6. The compatibility was evaluated by studying the rheological, thermal, morphological, and spectroscopic (infrared and dielectric) properties of the blends. The formation of a copolymer was observed by infrared spectroscopy after selective extraction of the components, presumably by the interaction of terminal NH2 groups of PA6 and carbonyl groups of ULDPE-graft-DEM. Thermal properties showed changes due to compatibilization. For instance, fractionated crsytallization of the PA6 component was observed when it formed the dispersed phase in reactive blends in view of the enhanced dispersion. Nucleation of the ULDPE component by the PA6 component was observed for reactive and non-reactive blends. The DSC melting results showed the presence of two crystalline forms of the PA6 in the blends. These were the less stable gamma -form, predominant over the more stable alpha -form, in reactive blends, especially for the 20/80 and 50/50 wt.-% blend compositions. Dynamic rheological experiments provided data for fitting the Carreau viscosity model; the results revealed that longer characteristic times are obtained for compatibilized systems. This was reinforced by the more elastic behavior that such systems presented in G ' -G " plots, as compared to the non-reactive ones. Dielectric spectroscopy revealed a noticeable shifting of the alpha -mode of the PA6 to lower temperatures for the 50/50-g, together with an enhancement of the beta over the gamma -made which indicates the presence of tightly bound water. The T-g depression could be due to the plasticization effect resulting from the substitution of intramolecular PA6 H-bonds by either water molecules or physical interactions across the interphases.
Abstract: The melt free radical grafting of glycidyl methacrylate (GMA) onto high-density polyethylene (HDPE) was carried out in Brabender internal mixer. The GMA content of the grafted HDPE (HDPE-g-GMA) was determined through FTIR by means of a calibration curve. The influence of reaction procedure, radical initiator concentration and addition of a co-monomer (styrene) on the grafting efficiency was examined. Blends of poly(ethylene terephthalate) (PET) with HDPE and HDPE-g-GMA (75/25 w/w) were prepared by melt mixing in internal mixer. The morphology of the blends was then analysed by SEM microscopy. PET/HDPE-g-GMA blends displayed improved phase dispersion and interfacial adhesion as compared to unfunctionalized PET/HDPE blend.
Abstract: The goals of the investigation were: to indicate the methods of characterization of recycled polymers, to show general tendencies in properties deterioration and characterize recyclates on Central Europe and European Community markets. The properties and composition of scrap poly(ethylene terephthalate) from several sources were characterized by: TGA, DSC, FTIR, tensile properties, dynamic viscosity, intrinsic viscosity and thermooxidative stability. We found that all PET regrinds contained admixture of other polymers (0.1-5 wt%). The presence of more than 50 ppm PVC makes PET worthless for advanced application as film forming, because it catalyzes the hydrolysis and reduces the strength of material. Although the individual flakes of recycled PET show almost unchanged molecular characteristics and properties, the processed regrinds always exhibit worse properties. Partial restoration of recycled PET properties can be achieved by careful working, removing the dust fraction and by proper drying. The difference between studied PET's results from different applied recycling procedure. Admixtures of polymers without compatibilizer always deteriorate tensile properties. Various levels of stability of polymer viscous flow during film and tape extrusion were observed, depending on composition of recycled PET from various sources. Microgels were observed in all samples during film extrusion. (C) 2000 Elsevier Science Ltd. All rights reserved.
Abstract: Two means of plastic deformation were applied to the polyamide 6/polypropylene-g-acrylic acid blends (in two composition 8:2 and 2:8): drawing and plane strain compression in a channel die. X-ray diffraction pole figures,density measurements, SEM, DMTA were applied for studying the structure and properties of oriented blends. It is concluded that interfaces between blends components are weak elements of the blends even in presence of compatibilizing action of PP-g-AA.
Abstract: Blends of Nylon 6 (Ny6) and polyolefins functionalized with acrylic acid (polyethylene-PE-AA, polypropylene-PP-AA) were investigated in terms of crystallization behavior and resulting Ny6 crystalline structure. Thermal analysis showed that in the case of blends with functionalized polyolefin as a matrix: (a) Ny6 crystallization is spread and dramatically shifted toward lower temperatures, approaching that of the polyolefin component 125-132 degrees C; (b) Ny6 gamma crystal polymorph is the major phase present; confirmed and quantitatively evaluated by use of deconvolution computations performed on WAXS spectra of the blends. When Ny6 is dispersed in functionalized polyolefin matrix, the weight content of Ny6 gamma crystals increases up to three times with respect to analogous, non-compatibilized blends and up to approximate to 16 times with respect to Ny6 homopolymer. These phenomena are explained by the reduction of size of Ny6 dispersed particles, caused by the interactions between the functional groups of polyolefin and the polar groups in polyamide chain. The nucleation mechanism is changed due to the lack of heterogeneous nuclei in most small Ny6 droplets, which results in the enhanced gamma crystal formation. (C) 2000 Elsevier Science Ltd. All rights reserved.
Abstract: A physical and mechanical characterization of blends of Nylon 6 (PA6) and very low density polyethylene (VLDPE), functionalized with maleic anhydride (MA) or diethylmaleate (DEM) is reported. The functionalization of VLDPE with MA and DEM was performed by reactive extrusion in a twin-screw (Berstoff) extruder in the presence of dicumylperoxide. The PA6/VLDPE, PA6/VLDPE-g-MA, and PA6/VLDPE-g-DEM blends with composition ratio of 80 : 20 (wt %) were obtained by using a twin-screw Werner & Pfleiderer extruder. An industrial-type blend based on PA6 and MA-grafted ultra low density polyethylene (ULDPE-g-MA) was also tested for comparison. All blends were then characterized by optical and scanning electron microscopy, differential scanning calorimetry, and dynamic mechanical thermal analysis. The results of slow fracture and impact tests showed that the ductile-brittle transition temperature of the examined blends depends on the type of functional group and test speed. (C) 1999 John Wiley & Sons, Inc.
Abstract: Films of blends of poly(vinylidene fluoride) (PVDF) with isotactic and syndiotactic poly(methyl methacrylate) (i-PMMA and s-PMMA), obtained by casting tetrahydrofuran (THF) and dimethyl sulphoxide (DMSO) solutions onto BaF2 windows, have been investigated by means of FTIR-microspectroscopy (FTIR-M), optical microscopy and differential scanning calorimetry (DSC). The study of the effect of the PMMA tacticity on the intermolecular interaction between the two components, as well as on the structure, morphology and thermal behaviour of these blends, is the object of this paper. On the basis of the major shift of the carbonyl band of i-PMMA in the mixtures, the occurrence of stronger interactions for PVDF/i-PMMA compared with PVDF/s-PMMA blends can be suggested. (C) 1998 SCI.
Abstract: The objective of the present work was to study the effect of interfacial interactions on the thermal stability of blends of Nylon 6 with: polypropylene (iPP), polypropylene grafted with 6% by weight acrylic acid (iPP-AA), and a random copolymer of ethylene and acrylic acid with 8% by weight acrylic acid (PE-AA). Thermogravimetrical analysis (TGA) was performed on all the samples and both qualitative and quantitative analysis were made in order to evaluate the thermal stability of the materials under investigation. The results indicate that when there are strong intermolecular interactions between the polymers to be mixed land therefore strong interfacial activity), the thermal stability in the blends can be increased with respect to the values expected in view of a simple additive rule of mixing and synergistic effects can be produced. (C) 1998 Elsevier Science Ltd. All rights reserved.
Abstract: Blends of nylon 6 (Ny6) with ethylene-co-vinyl alcohol (EVOH) and EVOH modified with the introduction of carboxyl groups (EVOH-COOH) have been studied by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, and dynamic-mechanical thermal analysis. The thermal and thermomechanical analyses of the blends show that the melting, crystallization, and relaxational behavior are affected by the blend composition and the presence of carboxyl groups on the EVOH chains. Nevertheless, microscopic and thermal investigations demonstrate the biphasic nature of the two-blend systems. Selective solvent extraction of the EVOH or EVOH-COOH phase in their blends and Fourier transform infrared analysis of the residual products indicates the occurrence of ionic linkages between the amino groups of the polyamide and the carboxyl groups of the modified EVOH, whereas specific interactions are evidenced for Ny6/EVOH blends. Tests performed on extruded Ny6/EVOH films show that the addition of EVOH effectively reduces the gas permeability of Nylon, whereas the addition of small amounts of EVOH-COOH helps to control and stabilize melt theology. (C) 1998 John Wiley & Sons, Inc.
Abstract: The aim of this work was the synthesis of new graft copolymers consisting of polypropylene (PP) backbones and liquid crystalline polymer (LCP) branches, to be used as compatibilizing agents for PP/LCP blends. The PP-g-LCP copolymers have been prepared by polycondensation of the monomers of a semiflexible liquid crystalline polyester (SBH 1 : 1 : 2), that is, sebacic acid (S), 4,4'-dihydroxybiphenyl (B), and 4-hydroxybenzoic acid (H) in the mole ratio of 1 : 1 : 2, carried out in the presence of appropriate amounts of a commercial acrylic-acid-functionalized polypropylene (PPAA). The polycondensation products, referred to as COPP50 and COPP70, having a calculated PPAA concentration of 50 and 70 wt %, respectively, have been fractionated with boiling toluene and xylene, and the soluble and insoluble fractions have been characterized by Fourier transform infrared and nuclear magnetic resonance spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry, and X-ray diffraction. All analytical characterizations have concordantly shown that the products are formed by intricate mixtures of unreacted PPAA and SBH together with PP-g-SBH copolymers of different composition. Exploratory experiments carried out by adding small amounts of COPP50 or COPP70 into binary mixtures of isotactic polypropylene (iPP) and SBH while blending have demonstrated that this practice leads to an appreciable improvement of the dispersion of the minor LCP phase, as well as to an increase of the crystallization rate of iPP. (C) 1998 John Wiley & Sons, Inc.
Abstract: Poly(vinylidene fluoride) (PVDF) samples, obtained by casting from tetrahydrofuran solutions and submitted to various thermal treatments, have been examined by Fourier transform-infrared microspectroscopy (FTIR-M) and differential scanning calorimetry (DSC). This kind of analysis allowed us to examine microdomains of samples with different morphological characteristics and to obtain an indication of the polymorphism of PVDF. In some cases the simultaneous presence of two or three forms has been evidenced thanks to the comparison of FTIR-M spectra and DSC traces. Vibrational spectra of single crystalline forms can be recorded by FTIR-M on phase homogeneous microdomains.
Abstract: The phase behaviour of two polymer/liquid crystal blends has been investigated by DSC and optical microscopy. In one case, blends of poly(octadecylethylene) (POE) and p-azoxyanisole (PAA) are found almost immiscible below the isotropization temperature of the liquid crystal. The crystallization process of PAA in the blends takes place with a sporadic growth of dendritic structures determined by the dispersion of the nematic phase in the molten polymer. In the other case, blends of Poly(biphenylyloxyexylacrylate) (PBHA) and PAA display a different phase behaviour indicating partial miscibility of the two components at temperatures above the melting point of the polymer. At high concentrations of PAA a nematic phase dispersed in a isotropic liquid mixture of polymer and Liquid crystal is observed. These results are accounted for by the different side-chain structure of the polymer components.
Abstract: Due to the apolarity of the aliphatic backbones, unmodified polyolefins are scarcely miscible with most of other polymers. The functionalization of preformed polyolefins is a way which has been successfully followed to improve the polymer miscibility. The functionalization of linear low density polyethylene (LLDPE) and ethylene-propylene copolymers (EP), with diethyl maleate (DEM) and dicumyl peroxide (DCP) as radical initiator, gives products containing up to 2-5 mol % of well defined functional groups (2-diethyl succinate). Intermolecular interactions of these functional groups ate characterized by comparison with suitable low-molecular-weight structural models in the presence of different solvents containing acidic hydrogen atoms. On the basis of these indication evidences of interface molecular interactions in blends with halogenated polymers are described between the functionalized polyolefins and poly(vinyl chloride) (PVC), poly(vinylidene fluoride) (PVDF) or vinylidene fluoride-hexafluoropropene copolymer obtained in semiindustrial Brabender mixers. It is shown that a smooth functionalization of the polyolefins can modify the phase behaviour and structure of these systems. The FT-IR microanalysis supports the occurrence of partial miscibility phenomena which can be accounted for by specific intermolecular interactions involving the inserted functional groups and occurring mainly at the interfaces between domains of polyolefins and of the halogen-containing polymers.
Abstract: The phase morphology and the influence of composition on the primary nucleation of isotactic polypropylene in isotactic polypropylene/isotactic poly(butene-1) (iPP/iPB) blends were investigated by electron and light microscopy and small-angle light scattering. It was found that iPP and iPB are miscible but the thermal treatment induces partial phase separation of components and the formation of iPP-rich and iPB-rich phases. The complete phase separation needs high temperatures and/or a long time of melt annealing. In samples crystallized isothermally at low undercooling the heterogeneous primary nucleation in blends is depressed as compared to plain iPP. In blends the less active heterogeneities lose their activity because of an increase of the energy barrier for critical size nucleus formation due to phase separation of blend components during crystallization. For the same reason the rate of homogeneous nucleation in blends decreases, as observed in samples crystallized at very high undercooling. At very high undercooling IPP and iPB are able to crystallize with similar rates, which results in the formation of a fraction of iPB spherulites in addition to iPP spherulites. Consequently the number of spherulites in the blend is larger than that in plain iPP, in spite of the decrease in the homogeneous nucleation rate of iPP in the blend. (C) 1994 John Wiley and Sons, Inc.
Abstract: The crystallization and melting behaviour of two sets of ethylene/1-butene copolymers have been analysed by DSC. The samples, with comonomer content in the range from 0 to 21.5 mol %, were obtained by industrial processes using both Mg/Ti-based and Ti/V-based catalyst systems. The composition dependences of melting and crystallization temperatures were found to be strictly affected by the catalyst type. Moreover, logarithmic plots of the melting and crystallization enthalpy as a function of the ethylene content (mol%) in the copolymers fitted linear relationships whose slopes have been related to the critical sequence length of crystallizable ethylene units, depending on the catalytic system. These results are compared with those reported in the literature for ethylene/1-butene copolymers synthesized by other catalysts and are accounted for by a different distribution of the comonomer units in the macromolecules of the two sets of samples.
Abstract: The phase behaviour of blends of poly(ethylene oxide) (PEO) with the liquid crystal p-azoxyanisole (PAA) has been studied by differential scanning calorimetry and optical microscopy. This system exhibits partial miscibility of the components in the molten state (at temperatures above 337 K). The melting temperature and enthalpy of the PAA phase has been found to depend on the blend composition, whereas the melting behaviour of the polymer phase remains quite unaltered. The occurrence of the PAA nematic phase, dispersed within an isotropic liquid phase, has been observed at high concentrations of liquid crystal. The morphology of the blends in the solid state changes largely with the PAA content, depending on the solubility of the components in the liquid phase.
Abstract: Blends of polyphenylene sulfide (PPS) with a commercial, wholly aromatic, liquid crystal copolyesteramide (Vectra-B950) have been prepared by melt-blending. The crystallization behavior of neat and blended PPS has been studied by differential scanning calorimetry (DSC), under both non-isothermal and isothermal conditions. It has been found that blending PPS with Vectra-B leads to an increase of the temperature of non-isothermal crystallization and to a pronounced acceleration of the isothermal crystallization, without any reduction of the degree of crystallinity. All these effects have been found to occur independent of the Vectra-B concentration, within the investigated range (2 to 20%, w/w). The results have been interpreted in terms of an increased nucleation density of the blends, probably due to heterogeneous substances, initially present in the Vectra-B bulk, which dissolve to saturation in the PPS phase, during melt-blending.
Abstract: The thermal behaviour, morphology, molecular interactions and phase structure of blends based on polyolefins functionalised with diethylmaleate and commercial polymers (poly(vinyl chloride), polystyrene, poly(vinyliden fluoride)) were analysed by means of DSC, FT-IR, optical and electron microscopy. It is shown that the occurrence of partial miscibility phenomena is favoured by specific molecular interactions between the polymer components and is affected by the structure of the functionalised polyolefins, degree of functionalisation and thermal history.
Abstract: PLA composites with nanocellulose filled poli(vinyl acetate) (PVAc/NC), were prepared by mixing aqueous PVAc emulsion with NC suspension and melt blending with PLA. The nanocomposites were analysed by SEM, AFM, TGA, DMTA and tensile mechanical tests, and the properties were compared with those of PLA/NC composites. Functionalization of PLA and NC by glycidyl methacrylate (GMA) was also applied to improve the nanofibre dispersion and interfacial interactions in the composites. PLA/PVAc/NC composites showed better dispersion of nanofibres into the polyester matrix, good thermal stability and higher tensile modulus and strength, as compared to PLA/NC.
Abstract: Polylactide (PLA) nanocomposites containing inorganic nanofillers, either 3 wt.% montmorillonite (MMT) or 5 wt.% nano-sizes calcium carbonate (NCC), and 15 wt.% cellulose fibres were prepared and studied. Good dispersion of nanoparticles in the PLA matrix was obtained. X-ray analysis and TEM examination evidenced that exfoliation of MMT was achieved. Dynamic mechanical response, thermal and mechanical properties, and also thermal stability of the composite materials were investigated with various methods. All the fillers, especially MMT, enhanced cold crystallization of PLA matrix, possibly by augmenting nucleation.
Abstract: The lecture is aimed at analysing the effect of functionalization and reactive mixing processes in the melt of composites of polylactide (PLA), polycaprolactone (PCL), Mater-Bi (MB), ethylene vinyl acetate (EVA) copolymers - and their blends - with natural fibres (cellulose, hemp, etc.) on the morphological, thermal and mechanical properties. Polymer matrices and fibres were modified by means of grafting with bi-functional reactive monomers, such as glycidyl methacrylate (GMA), maleic anhydride (MA) and acetic anhydride. Both binary and ternary composite systems, containing modified components or compatibilized with functionalized copolymers, were obtained by using different mixing procedures. The effect of polymer and/or fibre functionalization, compatibilizer addition and composition on the composite properties was analysed by SEM, OM, RX, FT-IR, DMTA, DSC, TGA, rheological and tensile mechanical tests.
Abstract: The structure and phase behaviour of PP/POSS nanocomposites obtained by reactive blending of maleic anhydride grafted PP and amino functionalized POSS, have been investigated. SEM, EDS, WAXS and DSC analyses showed marked changes in the crystallization behaviour and properties of the samples supporting a molecular dispersion of POSS in the polymer matrix.
Abstract: Composites of isotactic polypropylene (PP) and polylactide (PLA) with hemp fibres (cannabis sativa), and composites of polystyrene (PS) with cellulose fibres, oat (avena sativa) and CaCO3 particles respectively, obtained by melt mixing, were examined by FT-IR analysis, optical and SEM microscopy, EDS, WAXS, DSC, TGA and mechanical tests. For PP/hemp composites, grafting of glycidyl methacrylate (GMA) either onto fibres (Hemp-GMA) and polymer chains (PP-g-GMA) was carried out to improve the fibre–matrix interfacial interactions. For composites with PS matrix the effect of
addition of maleic anhidride functionalized copolymers (SEBS-g-MA, PS-co-MA, PP-g-MA) and oligomers (PEG, PPG) was investigated. The properties of binary and ternary systems were analysed as function of fibre characteristics, compatibilizer concentration and mixing parameters.
Abstract: Composites of isotactic polypropylene (PP) with hemp fibres and of polystyrene (PS) with cellulose, oat and CaCO3 respectively, obtained by batch mixing, were examined. Either the modification of fibres with glycidyl methacrylate (Hemp-GMA) and the addition of various compatibilizers containing reactive groups (PP-g-GMA, SEBS-g-MA, PS-co-MA) were carried out to improve the fibre–matrix interfacial interactions. The modified components and their composites were characterised by FT-IR analysis, POM and SEM microscopy, WAXS, DSC, TGA and mechanical tests. The properties of binary and ternary composites were analysed as a function of the fibre amount and compatibilizer. The compatibilized systems showed enhanced fibre dispersion and interfacial adhesion as a consequence of chemical interactions between the functional groups on the polymer chains and the polar groups of the fibres. The thermal stability and phase behaviour of the composites resulted to be affected by the chemical modification of the fibres. Changes in the spherulitic morphology and overall crystallisation rate of PP were also observed in PP/Hemp composites due to the nucleating effect of the fibres. The mechanical properties of both PP and PS composites were found to depend at large extent on the fibre amount and on the structure and concentration of compatibilizer. Generally, higher tensile modulus and lower elongation at break were observed with increasing the fibre content; the addition of PP-g-GMA and PS-co-MA in PP/Hemp and PS/Cell composites, respectively, resulted in a higher stiffness as consequence of the improved fibre–matrix adhesion.
