Dr. Gaetano Lamberti graduated in Chemical Engineering, summa cum laude, in 1997, then he gained the Ph.D. degree in Chemical Engineering in 2001. Then he obtained a post-doc grant at the Dep. of Chemical and Food Engineering, University of Salerno. In October 2003 he obtained a position as assistant professor in transport phenomena (S.S.D. ING-IND/24). His didactic activity consisted in seminars in the frame of Principles of Chemical Engineering and Fluid Dynamics courses. He gave assistance to the courses: Introduction to the Chemical Engineering, Thermodynamics of the Chemical Engineering and Principles of Chemical Engineering. He was/is responsible for courses: Principles of Environmental Chemical Engineering, for the Master Degree in Civil and Environmental Engineering. And Thermodynamics II, for the II level of Degree for Chemical Engineers. He was also advisor or co-advisor for about 40 thesis in Chemical Engineering. Research activities of dr. Lamberti was developed mainly at the University of Salerno on the modelling of the supercritical extraction and on issues related to film casting and to crystallization of polymers. From October 2002 to April 2003 he worked for a period at the Mechanical Engineering Department at the Technical University of Eindhoven (NL). Recently, dr. Gaetano Lamberti devoted his attention to the transport phenomena which take place in pharmacology, particularly to the hydration kinetics and to the release of bioactive molecules from pharmaceutical solid systems (tablets), made up of swelling hydrogels. As usual, his research activities were both experimental, to elucidate the transport phenomena, and modeling, to describe the observed phenomena. He was a referee for the more than ten international journals. He produced more than 100 papers, of which about 40 are published on international journals.
Abstract: To predict the drug hemeatic levels after administration is a goal of great interest in the design of novel pharmaceutical systems and in therapies management. The most reliable approach in pharmacokinetic modeling consists in analyzing the physiology of the living beings and in describing tissues and organs as different biochemical reactors. These models have been identified as physiologically based pharmacokinetic models (PBPK). They can be very detailed in the description, but, in this case, they also claim for the knowledge of an high number of parameters which are difficult to be determined by experiments. In this work, a review of the most complete PBPK models proposed in literature was performed, and a novel PBPK model was developed and validated by comparison with in vivo data available in the literature. The appeals of the novel model are its simplicity and the limited number of parameters required. Last but not least, it was proved able to predict the hemeatic drug levels after different kinds of administrations (intravenous injection, oral assumption of delayed release tablets).
Abstract: This paper describes the development of pH-sensitive poly(methyl methacrylate-acrylic acid) copolymers for the enteric coating of pharmaceutical products for oral administration. To obtain the dissolution at the desired pH level, different pH-sensitive polymers are available on the market. Usually, for each desired dissolution pH, an ad hoc polymer is designed. Thus, different dissolution pH values could ask for completely different polymers. Instead, the materials proposed in this work are copolymers of the same two monomers, and the different dissolution pH was obtained by changing the volume fraction of the hydrophobic methyl methacrylate monomer to the hydrophilic acrylic acid monomer. Increasing the volumetric percentage of methyl methacrylate causes the polymer to dissolve at increasing pH, until the dissolution does not take place at all, and it is replaced by a slow swelling phenomenon. The copolymers obtained were characterized by differential scanning calorimetry, in order to evaluate their glass transition temperature, and these latter were related to %MMA. The molecular weights of the pure polymers (PAA, PMMA) were measured by intrinsic viscosity, to further validate the glass transition temperatures observed. The dissolution of the copolymers was carefully tested in buffer solutions for a dense set of pH values. A linear relationship between dissolution pH and volumetric percentage of methyl methacrylate was obtained from these measurements. As a result, for any physiological compartment, the copolymer which dissolves at the pH of interest can be easily synthesized.
Abstract: The pharmacokinetic (PK) models predict the hematic concentration of drugs after the administration. In compartment modeling, the body is described by a set of interconnected "vessels'' or "compartments''; the modeling consisting of transient mass balances. Usually the orally administered drugs were considered as immediately available: this cannot describe the administration of extended-release systems. In this work we added to the traditional compartment models the ability to account for a delay in administration, relating this delay to in vitro data. Firstly, the method was validated, applying the model to the dosage of nicotine by chewing-gum; the model was tuned by in vitro/in vivo data of drugs (divalproex-sodium and diltiazem) with medium-rate release kinetics, then it was applied in describing in vivo evolutions due to the assumption of fast- and slow-release systems. The model reveals itself predictive, the same of a Level A in vitro/in vivo correlation, but being physically based, it is preferable to a purely statistical method.
Abstract: The water solutions of the block copolymers PEOn-PPOm-PEOn, known as pluronics, show a complex thermal behavior, since they are liquid at low temperature (5 degrees C), and they can give soft gel when heated at body temperature (37 degrees C). These properties are of great interest in biomedical applications. To properly design these applications, a prerequisite is the knowledge of the thermodynamics-how much-and of the kinetics-how fast-with which these transformations take place. In this work, solutions of F127 (the copolymer for which n = 100 and m = 65) were studied by varying the concentration and the temperature and analyzing their behavior when heated under several heating rates. The studies were performed by differential scanning calorimetry (DCS) and dielectric spectroscopy. The investigations carried out under equilibrium conditions allowed us to determine the thermodynamics of the phase transitions, whereas the investigations carried out wider varying conditions allowed us to quantify the kinetics of the phase transitions. Empirical models were also proposed to describe both the thermodynamics and the kinetics observed. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 688-695, 2009
Abstract: This work deals with the modeling of drug release from solid pharmaceutical systems (matrices) for oral delivery. The attention was paid to the behavior of matrices made of hydrogels and drug, and the modeling was devoted to reproduce all the relevant phenomena (water up-take, gel swelling, diffusivity increase, drug diffusion and polymer erosion). Thus, the transient mass balances (for both drug and water), with the proper initial and boundary conditions were written, and a generalized numerical code was formulated; it is able to describe several geometries (slab, sphere, infinite and finite cylinders; this latter was done by an approximation which reduces the 2D problem to an 1D scheme). The main phenomena observed in drug delivery from hydrogel-based matrix, i.e. polymer swelling and erosion, were taken into account. The code was validated by comparison with analytical solutions, available for some simplified situation, and then it was tested with some experimental data taken from literature. (c) 2008 Elsevier B.V. All rights reserved.
Abstract: In this work ultrasonic atomization process is applied to produce biopolymer microparticles with potential applications in pharmaceutical and nutraceutical fields. Natural polymer (alginate)/water solution is atomized by ultrasonic assisted process and the droplets spray is reticulated using a solution of copper sulfate, where the Cu2+ ions cause the formation of a network structure (hard porous gel). Several operating parameters (solution concentration, flow rate, atomization power) are changed to study their effects on the produced microparticles. Literature correlations able to predict the features of the droplets as functions of process parameters are optimized using a statistical approach. Furthermore, the energy requirement for the drops production is compared with the energy required by traditional techniques to evaluate the intensification effect of the ultrasonic on the atomization process. (C) 2009 Elsevier B.V. All rights reserved.
Abstract: Design of systems for oral controlled release of drug could take advantages from the knowledge of which phenomena take place. In this work matrices obtained by powders compression (50:50, hydroxypropyl methylcellulose, a swelling hydrogel, and theophylline, a model drug) were immersed in water at 37 degrees C, allowing the water uptake and the drug release by lateral surface, confining the cylindrical matrices between glass slides. The tablets, after given immersion times, were withdrawn, cut in several annuli, and subsequently analyzed for the drug and the water concentration radial profiles. The data confirmed the pseudo-diffusive nature of the process, allowing to give a deep insight into the drug release process from swellable hydrogel matrices. In particular, it was confirmed the presence of nonhomogeneous gel layer, rich in water and poor in drug, with a profile of drug concentration which agrees well with a pseudo-diffusion phenomenon. (C) 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4100-4110, 2009
Abstract: The water swellable hydrogels are commonly used in the production of solid pharmaceutical dosage systems for oral administration (matrices). Their use allows to obtain the controlled drug release. The key role is played by the transport phenomena which take place: water up-take, gel swelling and erosion, increase in diffusivity due to hydration. Thus, knowledge of these phenomena is fundamental in designing and realizing the pharmaceutical systems. In this work, tablets made of pure hydrogel, HydroxyPropyl-MethylCellulose (HPMC), were produced and immersed in a thermostatic bath filled with stirred distilled water (37 degrees C). The water up-take was allowed only by radial direction (from the lateral surface) by confining the tablet between two glass slides. Two distinct methods, an optical technique already described in a previous work, and a gravimetric procedure described here, were applied to measure the water concentration profiles along the radial direction in the tablets. The data obtained were used both to clarify the nature of the transport phenomena involved, and to perform a better tuning of a mathematical model previously proposed. (C) 2009 Elsevier Ltd. All rights reserved.
Abstract: The oral administration of pH-sensitive drugs requires protecting the drug molecules from the acidic pH in the stomach: the simplest way is to use polymers as coating, especially polymers which are insoluble at low pH (in the stomach) and soluble under neutral conditions (in the intestine). The Cellulose Acetate Phosphate, CAP, is one of these polymers, and it is one of the most used coating polymers. Studies related to the behavior of such pharmaceutical systems require fast and accurate methods to assay the released drug concentration in dissolution medium. However, both the drug and the coating polymer are present in the dissolution bulk with unknown concentration, and they can interfere each other in assaying. In this communication, a simple method to assay, by UV analysis, Theophylline (TP) and Cellulose Acetate Phosphate concentrations in a dissolution medium, phosphate buffer pH 7.0 (BP), is proposed and validated.
Abstract: Supercritical fluid technology has recently been proposed in literature to obtain drug controlled release systems as alternative to conventional techniques. In this work, the Supercritical Assisted Atomization (SAA) is proposed to produce hydroxypropyl methylcellulose (HPMC) based composite microparticles using ampicillin trihydrate as model drug. Successful micronization of HPMC alone and, then, coprecipitation of HPMC and ampicillin were obtained using a buffer solution as solvent. Well-defined micrometric particles with spherical or "doughnut-like" morphology were produced in both cases, with a sharp particle size distribution: diameters ranged between about 0.05 and 5.20 mu m. SAA composite microparticles were characterized by differential scanning calorimetry (DSC), Scanning electronic microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and UV-vis analysis. A solid solution of HPMC and ampicillin was produced; a stabilizing effect of the polymer on the drug was observed, resulting in the protection of ampicillin from thermal degradation. Coprecipitates were produced at different drug/polymer ratios and two kinds of formulations for oral drug delivery were explored to verify ampicillin controlled release from HPMC: tablets and gelatine capsules of coprecipitated microparticles. Tablets released 97% of AMP in more than 72 h, allowing a slower drug release than capsules, that released 100% of AMP in 8 h. Drug release mechanisms characteristic of swelling-controlled systems were observed, with ampicillin release rate dominated by the erosion of HPMC matrix. (c) 2008 Elsevier B.V. All rights reserved.
Abstract: In this work, the heat transfer phenomena taking place during the cooling of thin films of crystallizable polymers were analyzed. The thermal histories, as recorded during experimental cooling runs carried out at various cooling rates, were compared with the predictions of a general purpose numerical code, which was resulted able to capture all the main features of the process. Thus, the conditions which allow homogeneous cooling (negligible temperature gradient within the sample) or homogeneous cooling history (the same cooling history for all the positions within the sample) were predicted by the simulation code.
Abstract: This work is focused on the transport phenomena which take place during immersion in water of pure hydroxypropylmethylcellulose tablets. The water uptake, the swelling and the erosion during immersion were investigated in drug-free systems, as a preliminary task before to undertake the study of drug-loaded ones. The tablets, obtained by powder compression, were confined between glass slabs to allow water uptake only by lateral surface and then immersed in distilled water at 37 degrees C, with simultaneous video-recording. By image analysis the normalized light intensity profiles were obtained and taken as a measure of the water mass fraction. The time evolutions of the total tablet mass, of the water mass and of the erosion radius were measured, too. Thus a novel method to measure polymer and water masses during hydration was pointed out. Then, a model consisting in the transient mass balance, accounting for water diffusion, diffusivity change due to hydration, swelling and erosion, was found able to reproduce all experimental data. Even if the model was already used in literature, the novelty of our approach is to compare model predictions with a complete set of experimental data, confirming that the main phenomena were correctly identified and described. (C) 2007 Elsevier B.V. All rights reserved.
Abstract: The crystallization of a polymer melt, taking place during transformation processes, has a great impact on the process itself mainly because it causes a large increase in the viscosity (hardening). Knowledge of the hardening kinetics is important for modeling and controlling the transformation processes. In this work, first an overview is given of the experimental and modeling work on the hardening of crystallizing polymers. Next, we present isothermal crystallization experiments using differential scanning calorimetry (DSC) and rotational rheometry to measure the dynamic viscosity. The evolution of the relative crystallinity and normalized complex viscosity are correlated by a novel technique which allows simultaneous analysis of several runs, even if they are not carried out at same temperatures; the main requirement with the traditional technique. The technique, described in detail in this paper provides an experimental relationship between the crystallinity and the hardening, i. e. the increase in the viscosity. Moreover, by measuring the dynamic viscosity at different frequencies, surprisingly, a master curve is obtained which combines the effects of shear rate, temperature and the level of crystallinity.
Abstract: In this work, polymer film casting experiments have been performed using commercial isotactic poly(propylene) (iPP), under operating conditions such that the solidification takes place during the path in air. The experiments were carried out with and without the presence of two jets of cooling air impinging on both the sides of the film. The effects of the cooling air jets on the experimental profiles of the film width, axial velocity, and temperature are reported and briefly discussed.
Abstract: In this work constant cooling rate crystallization experiments were carried out by a DSC, working with an iPP and using a very little amount of material, to minimize the heat transfer resistance in the mass of the sample. The resulting data were corrected to take into account also for the external heat transfer resistance. The corrected data were compared with data produced in the past, working with larger amounts of the same resin in a less accurate DSC apparatus, confirming that in the field of polymer crystallization kinetics the calorimeter has to be used carefully. The data were also used to check a kinetic model previously tuned under isothermal conditions. Up to 10 degrees C/min (0.167 K/s) the isothermal model is accurate enough, but faster tests requires an improvement of the model.
Abstract: In this work the microwave absorbing properties of carbon black/silicone rubber blends were investigated in the frequency range 0.2+6.0 GHz, varying the carbon black contents. In particular, the permittivity of the samples was measured by a network analyzer and then the experimental data were fitted as function of microwave frequency and carbon black content, epsilon*=epsilon*(f,C). The reflection loss for a layer of blend attached on a metal plate, which is related to the shielding effectiveness, was simulated as function of frequencies and of layer thickness for some values of carbon black content, and the simulation results were summarized in contour plots. These plots can be used to select thickness and carbon black content necessary to achieve the desired shielding effectiveness for a given frequency.
Abstract: In this work, real-time measurements of temperature, width, velocity and crystallinity collected during film casting experiments on polypropylene were adopted as basis for the analysis of heat transfer phenomena taking place during the process. A model describing the heat exchange coefficient, which accounts for natural and forced convection and for radiating exchange between film and surrounding air, and the hot metal die was proposed and tested. (c) 2005 Elsevier B.V. All rights reserved.
Abstract: A study of light transmission through a crystallizing polymer has been carried out by graphic simulations, consisting of sporadic and pre-determinate nucleation and growth of disks (spherulites) in a rectangular area. Interaction between a light beam crossing a sample of polymer has been described by a series of simple graphical rules, accounting for both absorption and scattering. Results of the code well reproduce the experimental behavior observed in the literature of main beam light intensity emerging from a crystallizing polymer sample and allows a better understanding of the interaction between light and nucleating/growing units. Emerging light behavior calculated by the simulation has been adopted as the basis to suggest the dependence of the light scattering coefficient upon crystallization kinetic parameters. (c) 2005 Elsevier Ltd. All rights reserved.
Abstract: Polymer solidification occurring in many processes, like for instance injection molding, compression molding and extrusion, is a complex phenomenon, strongly influenced by the thermo-mechanical history experienced by the material during processing. From this point of view, characterization of polymer crystallization in the range of processing conditions, i.e. including high cooling rate, is of great technological and academic interest. Quiescent, non-isothermal crystallization kinetics of two polypropylene resins were investigated using a new method, based on fast cooling of thin samples with air/water sprays and optical detection of the crystallization phenomenon. The range of cooling rates attained in this experimental study is considerably larger than that achieved by traditional methods. Quiescent crystallization kinetics of the resins is also investigated by the means of DSC, operated under isothermal conditions with a limited degree of under-cooling and for constant cooling rates up to about 1 K s(-1). The results demonstrate the importance of performing fast cooling experiments to gather reliable crystallization kinetics data. (c) 2005 Elsevier Ltd. All rights reserved.
Abstract: In this work, an experimental set-up able to quench thin polymer films whilst recording the sample thermal history as well as the overall and depolarized light intensities of a laser beam emerging from the sample is described. The interactions between the light beam and the crystallizing material have been modeled accounting for absorption and scattering phenomena. The proposed model was found to be able to reproduce the experimentally observed behavior of light intensities and it was validated by comparison with conventional DSC analysis. On the basis of this model, a method to obtain crystallinity evolution is proposed and applied to some fast cooling runs. The method was applied to quenching runs of an iPP carried out under cooling conditions more than one order of magnitude faster than those allowed for the DSC technique. The crystallization temperature dependence upon cooling rate was obtained from these runs in a cooling rate range never before explored.
Abstract: Data from iPP film casting experiments served as a basis to model the effect of flow on polymer crystallization kinetics. These data describe the temperature, width, velocity and crystallinity distributions along the drawing direction under conditions permitting crystallization along the draw length. In order to model the effect of flow on crystallization kinetics, a modification of a previously defined quiescent kinetic model was adopted. This modification consisted in using a higher melting temperature than in the original quiescent model. The reason for the modification was to account for an increase of crystallization temperature due to entropy decrease of the flowing melt. This entropy decrease was calculated from the molecular orientation on the basis of rubber elasticity theory applied to the entangled and elongated melt. The evolution of molecular orientation (elongation) during the film casting experiments was calculated using a non-linear dumbbell model which considers the relaxation time, obtained from normal stress difference and viscosity functions, to be a function of the deformation rate. The comparison between experimental distributions and model based crystallinity distributions was satisfactory.
Abstract: In this work, solidification of semi-infinite polymer slabs was modelled accounting for heat transfer and phase change. Transient one-dimensional energy balance was numerically solved, coupled with a suitable crystallization kinetic model, coming from literature [ 1]. To this purpose a generalized code was adopted, which was proposed in a previous communication, together with its preliminary validation [ 2]. Solidi. cation runs were simulated both under isothermal conditions and under slow cooling rates, comparable to the ones attainable in standard differential scanning calorimetry (DSC). The output DSC signals were simulated, and it is shown that traditional analysis, usually performed on these signals in the frame of crystallization kinetics studies, can give correct results for isothermal tests, but can give suggestions consistently far from real material behaviour during cooling ramps.
Abstract: In the present work, a large number of growth rate data for alpha-phase isotactic polypropylene, taken from literature, have been described by the Lauritzen and Hoffmann equation. A general procedure to predict nuclei density by simple DSC measurements is described and applied successfully to a commercial iPP.
Abstract: A great number of heat transfer problems can be treated as transient heat transport phenomena within a body, often semi-infinite or symmetric in some directions, and in these cases a one-dimensional treatise is enough. Dielectric/microwave heating of cylinder and fast cooling of thin slabs are common examples. A numerical code was developed to simulate heat transfer phenomena in variable conditions. Model equations were based on transient. one-dimensional energy balance. Moreover, the different kinds of energy source terms, and the different kinds of boundary conditions can be implemented in the model. Aim of this communication is a preliminary validation of the numerical code, by comparison with several analytical solutions of the heat transfer problems coming from literature. The validation has been carried out, and here results are shown and briefly discussed.
Abstract: A method based on Fourier transform infrared (FTIR) transmission spectra is proposed to measure the crystallinity of isotactic polypropylene (iPP) samples. The method parameters were tuned as compared with wide-angle X-ray scattering measurements performed on test samples characterized by different crystallinity values obtained by solidification of thin iPP films under several cooling rates in a homemade device. The FTIR dichroic ratio measurements were adopted to measure crystalline and average Hermans' orientation factors of iPP samples obtained by film casting. The crystalline orientation measurement method was validated as compared with the birefringence measurement. The techniques were successfully used in real time during some film-casting runs with a suitably modified FTIR system made of a spectrometer equipped with two optical guidelines and an external detector. Real-time measurements are reported and discussed. (C) 2003 Wiley Periodicals, Inc.
Abstract: Film casting experiments were carried out with iPP under processing conditions causing the crystallization process to occur under orienting flow. Draw ratio and cooling rates were changed by varying mass flow rates and die thickness. The effect of processing conditions on film crystallinity was investigated by combining WAXS and FT-IR transmission methods, while orientation of both phases was measured by IR dichroism (according to Fraser's method) and successfully compared to birefringence measurements on final films. Crystallinity appears to be almost insensitive to draw ratio and cooling rate. Moreover the crystallinity profile turned out to be also constant along the transverse film direction. Phases orientation were found relatively low and no dependence on draw ratio was detected.
Abstract: Orientation and crystallinity of isotactic polypropylene moulded products have been investigated by means of infrared microscopy. The experimental techniques are described elsewhere [1-3]. The previous application to film casting products and the application in this work to injection-moulded products confirms their usefulness in polymer science. Orientation and crystallinity distributions obtained for different samples are reported and briefly discussed.
Abstract: In the case film process a polymer melt is extruded through a slit die, stretched in air and cooled on a chill roll. During the path in air the melt cools and a reduction of both thickness and width takes place; obviously, temperature distribution, thickness and width reductions are function of draw ratio and stretching distance. Temperature distribution along the draw direction was measured as function of flow rate during film casting experiments performed with an iPP resin. A non-contacting method of measurement, based on a narrow-band IR pyrometer, was adopted. A good qualitative agreement is shown between experimental temperature data and predictions of a model accounting of radiation emissivity dependence upon film thickness. Differences are consistent with discrepancies of film thickness evolution along draw direction, indeed the model slightly over predicts both film thickness reduction and, parallel, temperature decrease along the draw direction. (C) 2002 Elsevier Science Ltd. All rights reserved.
Abstract: In the cast film process a polymer melt is extruded through a slit die, stretched in air, and cooled on a chill roll. During the path in air the melt cools while being stretched. Film casting experiments were carried out with an isotactic polypropylene resin. The temperature and width distributions were measured along the draw direction. Further, the crystallinity and Hermans orientation factor were measured on the final film. The process was described by a simple thermomechanical model derived elsewhere. The evolution of the molecular orientation parameters was calculated on the basis of a dumbbell model coupled with velocity and temperature distributions provided by the thermomechanical model. The experimental crystalline orientations of the final films collapsed into a single step-shaped curve (from low to high orientation) if plotted versus the stress calculated by the model at the frozen line. The experimental values of the crystallinity and Hermans orientation factors are discussed on the basis of predictions of the dumbbell model for melt orientation at the frozen line and the crystallinity data obtained in quiescent conditions under the same cooling rate. (C) 2002 whey Periodicals, Inc.
Abstract: Detailed knowledge of polymer crystallization kinetics is a mandatory requirement in modeling of transformation processes. On the other hand, techniques for investigation of crystallization kinetics are limited to cooling rates much lower than those experienced by the materials in industrial processes. A method suitable to investigate crystallinity evolution during cooling procedures carried out adopting rates comparable with those experienced by the polymer during industrial processes is thus extremely attractive. In this work a method is proposed, based on fast cooling of thin samples by means of air/water sprays and optical detection of the crystallization phenomenon. Preliminary results of crystallization temperatures detected with a device based on such a method are presented and, in the low cooling rate range, are compared favorably with calorimetric results. The comparison of experimental crystallization temperature with results of a kinetics model previously developed leads to satisfactory agreement.
Abstract: Although many efforts have been spent on polymer crystallization kinetics, reliable results, if typical industrial processing conditions are applied, have been attained only in few cases. The main problem is related to the availability of data obtained under fast cooling conditions. Only those data can indeed discriminate between available models, or lead to the development of new ones. A new apparatus, able to provide real time crystallization data under high cooling rates, has been designed, built and tested. Description of apparatus and methods are discussed together with preliminary data obtained.
Abstract: Film casting experiments were carried out with an iPP resin supplied by Montell. Width, velocity, temperature, crystallinity and orientation profiles along draw direction were measured, respectively by image analysis (width and velocity), a dedicated infrared pyrometer (temperature) and a FT-IR transmission device (crystallinity and orientation). Temperature history of each particle along the draw direction was determined from velocity and temperature profiles. Experimental crystallinity distributions along draw direction were compared with crystallinity distributions calculated on the basis of the resin quiescent crystallization kinetics description and particle temperature histories. The comparison gives evidence of a relevant effect of the flow on the crystallization kinetics during the process. The effect is, however, consistent with a thermodynamic crystallization temperature increase of only 3 K.
Abstract: The model proposed by Ziabicki [1] [2] for non-isothermal crystallization kinetics was adopted in this work, to describe the crystallization kinetics of a commercial iPP under a very wide range of conditions (i.e. isothermal, slow-cooling rate and high-cooling rate (up to 200 degreesC/s) from the melt). A modification of the model was required in order to achieve a good agreement between model predictions and the whole set of experimental data.
Abstract: In the cast film process a polymer melt is extruded through a slit die, stretched in air and cooled on a chill roll. During the path in air, while the melt cools, a reduction of both thickness and width takes place; obviously, thickness and width reductions are functions of draw ratio and stretching distance. Width distribution along the draw direction was measured on a iPP resin supplied by Montell as function of both flow rate and take up velocity. Final film width was found to decrease as take up velocity increase and, surprisingly, as extrusion flow rate increases. Thus draw ratio increase, attained by either lowering extrusion flow rate or by rising take up velocity, can lead to either enlargement or reduction of final film width. The process of stretching in air was modelled with coupled one-dimensional equations of continuity and motion based on work of Barq, Haudin, Agassant, and Bourgin (Int. Poly. Process. 9 (1994) 350) the crystallinity generation term, according to the Nakamura non-isothermal model, was included in the equation of energy lumped along the thickness direction. The polymer was considered as a viscous fluid (non-Newtonian), the apparent viscosity being function of temperature and strain rate. Furthermore, the effect of crystallinity on viscosity was somehow accounted for. The model equations were solved numerically. A modified expression of heat transfer coefficient with respect to the model of Barq et at. (1994) was applied leading to a better agreement between model predictions and data with reference to width distribution along the draw direction and final film thickness. (C) 2001 Elsevier Science Ltd. All rights reserved.
Abstract: Supercritical CO2 extraction was used to post-process a semi-solid orange flower extract produced by liquid solvent extraction. The optimum process conditions to separate volatile oil were 90 bar and 40 degrees C. At these conditions no undesired compounds were co-extracted except waxes. Adopting a stage-wise separation procedure, consisting of two separators operated in series, these latter compounds were eliminated. The volatile oil yield was 53.6% by weight of the charged material. The volatile oil was considered to be a mixture of four different compound families (pseudo-components). A model based on the formation of 'shock concentration waves' was proposed and integrated with a numerical method. The results of modelling confirm that the hypothesis of volatile oil as formed by pseudo-components is sufficient to describe the behavior of monoterpenes (hydrocarbon and oxygenated), whereas a multi-pseudo-component simulation is required to describe the extraction kinetics of sesqui- and diterpenes. (C) 1999 Elsevier Science B.V. All rights reserved.
Abstract: Thirteen terpenes forming a mixture that is characteristic of peel essential oils have been simultaneously adsorbed on silica gel from supercritical CO2. They have been divided into four pseudo-components according to the similarity of their behavior during the adsorption process. An equilibrium model based on differential mass balances written for the fluid and the solid phase was proposed. The numerical integration of the four partial differential equations resulting from the model was performed using the Wendroff method. The computational molecule was modified with respect to the original method. A molecule of variable geometry was adopted to avoid numerical oscillatins in the solution of the problem. The breakthrough time and the maximum concentration of the four pseudo-components were fairly well modelled. The consecutive displacement of the various pseudo-components by those more strongly adsorbed was also well described by the proposed model when compared to the experimental data. The simulation of the concentration profiles of the pseudo-components along the adsorption bed at increasing processing times was also proposed. It was possible to describe the onset and the evolution of displacement waves of the pseudo-components along the bed. (C) 1998 Elsevier Science Ltd. All rights reserved.
