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1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) is highly effective in nucleation of the &alpha, form of isotactic polypropylene (iPP). However, its role in high-pressure crystallization of iPP, facilitating the formation of the &gamma, polymorph, has not been explored. The present paper focuses on the influence of DMDBS on nucleation of high-pressure crystallization of iPP. iPP with 0.2&ndash, 1.0 wt.% of the DMDBS was crystallized under elevated pressure, up to 300 MPa, in various thermal conditions, and then analyzed by PLM, WAXD, SEM, and DSC. During cooling, crystallization temperatures (Tc) were determined. It was found that under high-pressure DMDBS nucleated crystallization of iPP in the orthorhombic &gamma, form. As a consequence, Tc and the &gamma, form content increased for the nucleated iPP, while the size of polycrystalline aggregates decreased, although the effects depended on DMDBS content. The significant increase of Tc and the decrease of grain size under high pressure of 200&ndash, 300 MPa required higher content of DMDBS than the nucleation of the &alpha, form under lower pressure, possibly due to the effect of pressure on crystallization of DMDBS itself, which is a prerequisite for its nucleating activity.

It is well known in practice that the shape and dimensions of injected parts are highly dependent on the packing-holding stage. A major problem in semi-crystalline polymers is the prediction of the solidified layer, whose thickness has an important effect on shrinkage and warpage. We propose a pragmatic approach based on the concept of no-flow temperature. This temperature should be related to crystallization temperature, but the choice is not easy because it depends on cooling rate and pressure which are functions of time and position. The objective of the work is to evaluate the sensitivity of an injection molding computation to the no-flow temperature and to evaluate the relevance of its choice. The crystallization temperature of an isotactic polypropylene is determined as a function of cooling rate and pressure in laboratory experiments. The pressure dependence is measured using the original Cristapress cell. As a case study, we simulate the filling and post-filling of a plate mold using Rem3D, a 3D code for injection molding. Three no-flow temperatures and two sets of parameters for temperature dependence of viscosity are tested. Their respective influences on the pressure evolution are shown, and the crystallization temperature calculated a posteriori using the experimental material data is compared to the “arbitrary” no-flow temperature.

International audience; Poly(ethylene 2,5-furandicarboxylate), referred to as PEF, was uni-axially stretched for temperatures above glass transition temperature. This bio-based polymer is considered as a serious competitor for the petroleum analogous poly(ethylene terephthalate), named PET. To replace PET in bottle forming, PEF has to be deformed to large strains which are only reachable when it is in its rubbery state. In the present work, the stretching conditions have been chosen by determining precisely the range of temperature and strain rate where PEF exhibits a rubbery-like state. This was feasible through the building of a master curve at a reference temperature. Local strain field measurements allow the description of PEF intrinsic mechanical behaviour. Above a draw ratio of around 6 to 8, the mechanical response presents an impressive strain hardening whereas a well-defined crystalline phase with a high orientation is formed. Diffraction peaks were indexed and compared to previous papers. Only one crystalline phase was observed either under mechanical loading or during static crystallization. Mechanical loading significantly speeds up crystallization.

International audience; The crystallization of 3 polyamides 66 has been studied by optical microscopy and differential scanning calorimetry (DSC). Nonisothermal crystallization kinetics has been analyzed using Oza-wa's equation. Two polymers have close behaviors with a crystallization mainly spherulitic. The third one, which has the highest molar mass, is subject to intense transcrystallinity, which disturbs the crystallization kinetics (shoulder on the DSC curves and low Avrami exponent). For this polymer, original methods based on a detailed analysis of transcrystallinity have been applied to measure crystal growth rate and to determine the "intrinsic" crystallization kinetics, that is, not polluted by transcrystallinity

International audience; Interest in graphite fillers has grown since the separation of graphene from graphite by micromechanical cleavage. The object of the paper is to understand the influence of graphene nanoplatelets (GNPs) with different sizes on the crystallization behavior of a polyolefin matrix such as polypropylene (PP), after elaboration by melt mixing and compression molding. Composites with volume fractions of graphene nanoplatelets ranging from 0.3 to 2 vol% were prepared. The particle dispersion states in the composites were characterized at different scales using Scanning and Transmission Electron Microscopies (SEM and TEM). Polypropylene crystallization and orientation were investigated using optical microscopy, Differential Scanning Calorimetry (DSC) and X-ray diffraction. This paper discusses the strong acceleration of crystallization kinetics due to the presence of GNPs. The micrometric flake-shaped GNPs act as nucleating agent and induce an epitaxial growth of alpha (α) crystalline phase of PP. The nucleating effect is related to the surface of the particles available for heterogeneous nucleation. Radial spherulitic growths are observed from the smallest micrometric particles. The coarsest GNPs, easily oriented by flow, favor PP transcrystallinity, in such a way that (010) plane of PP is parallel to (001) plane of graphene nanoplatelets.

Nucleating agents used for the monoclinic α-form of isotactic polypropylene (PP), commonly occurring under atmospheric pressure, are able to nucleate its crystallization in the orthorhombic γ-form under high pressure. Nucleation of γ-lamellae is possible through epitaxy involving (001)γ crystallographic plane on substrates nucleating the α-form through epitaxy engaging (010)α plane because of equivalency of both planes. Another possibility is nucleation of α-lamellae through epitaxy involving either (010)α or (110)α plane, and formation of the γ-phase through γ/α epitaxy. The study focuses on the structure and mechanism of nucleation of high pressure crystallization of PP with selected nucleating agents: poly(tetrafluoroethylene) particles, commercial Hyperform HPN-20E and ADK Stab NA11UH. The nucleated PP was isothermally crystallized in the γ-form under pressure of 200 and 300 MPa and studied ex-situ by WAXD, PLM and SEM. Analysis of lamellar structure provided insight into the nucleation mechanism of high pressure crystallization of PP. In all the materials the α-lamellae were nucleated first and served as seeds for the γ-form.

International audience; In this paper, a general numerical method to simulate polymer crystallization under various conditions is proposed. This method is first validated comparing its predictions with well-validated analytical models in infinite volumes. Then, it is compared to Billon et al. validated model for thin films, without or in presence of transcrystallinity on the films surfaces. It is also compared with Chenot et al. model for thin films, proposed in a conference in 2005 and never yet compared with other methods. Finally, it is also compared with an extension of this model for the transcrystalline case. These models are valid for general nucleation cases (not only sporadic or instantaneous), and can be used for any thermal conditions. All the numerical and analytical results are consistent, except in a case which is shown to be out of the validity domain of the transcrystalline case extension of Chenot et al. model.

In polymer processing, crystallization generally occurs in complex, inhomogeneous and coupled mechanical (flow, pressure), thermal (cooling rate, temperature gradient) and geometrical (surface of processing tools) conditions. A first route to understand crystallization in processing conditions is to design model experiments to isolate the specific influence of a given parameter. The emphasis will be laid here on the influence of: (i) shear flow through rheo-optical measurements using the commercial RheoScope module, (ii) high cooling rates obtained with the modified hot stage Cristaspeed (up to 2 000 °C min−1) and (iii) high pressures in the original Cristapress cell (up to 200 MPa). Numerical simulation is also a useful tool to understand and predict the coupled phenomena involved in crystallization. Based on Avrami's ideas and equations, a general differential formulation of overall crystallization kinetics has been proposed by Haudin and Chenot (2004). It is able to treat both isothermal and non-isothermal cases, and has been extended to crystallization in a limited volume without and with surface nucleation inducing transcrystallinity.

International audience; Natural fillers composed of cellulose, lignin and fillers with a varying lignin/cellulose ratio (flax, jute, curauà fibers and miscanthus stem fragments) were used to prepare composites with polypropylene using the same procedure, with or without a maleic anhydride–grafted polypropylene (MA-g-PP) coupling agent. A clear acceleration of the crystallization kinetics was observed in the presence of miscanthus stem fragments. For non-coupled composites, the size and aspect ratio of fragments had no significant influence onto the crystallization kinetics of polypropylene. The presence of the MA-g-PP coupling agent increased even more the kinetics. A clear effect of the nature of the polymers present in the filler was observed. There is a direct relationship between the values of the Avrami kinetic constant k for the six fillers and their lignin content, the more effective to enhance crystallization kinetics being pure cellulose. Lignin has no effect onto the crystallization kinetics of polypropylene.

A comprehensive understanding of the inherent link between in-situ growth kinetics of a polymer spherulite and high-pressure constraints under controlled temperature is concerned. As a matter of fact, while the link with temperature is well illustrated, little comprehensive study has been conducted to quantify the effect of pressure. This is yet required to model ‘extreme’ polymer processing conditions.Mainly, the experimental set-ups developed to reproduce the pressure effect can be classified into four families: “simple” cells, dilatometric set-ups, differential thermal analysis and diamond anvil plus in-situ measurement. In this context, an original model experiment, named CRISTAPRESS, has been constructed. The cell design exploits the optical properties of semi-crystalline spherulites. Time-resolved light depolarizing microscopic observations are conducted concomitantly with a fine PVT control, for high pressure up to 200 MPa and temperature up to 300 °C. The physical analysis of isothermal and isobaric holding of a model polymer shows the influence of temperature and pressure on the key kinetic parameters of crystallization, i.e., the growth rate and the number of activated nuclei, as well as on the subsequent morphologies. Simple modeling dealing with the Avrami equation and the Hoffman & Lauritzen theory is established.

International audience; The crystallization of isotactic polypropylene (PP) in γ-modification, which forms under high pressure but also at high temperature, can be nucleated by nucleating agents used for PP α-modification crystallizing under atmospheric pressure, like poly(tetrafluoroethylene) (PTFE) particles and commercial Hyperform HPN-20E. The study focuses on answering the question whether these nucleants are sufficiently active under high pressure to nucleate crystallization of PP during cooling in the temperature range of crystallization of the γ-form. To this aim, neat PP and PP with 0.2 wt% of nucleating agents were annealed at 250 °C for 5 min and subsequently cooled under a pressure ranging from 1.3 to 300 MPa. After releasing pressure, the specimens were analyzed by DSC, WAXD and PLM to have an insight into morphology, crystallinity and content of crystallographic forms. Both, Hyperform HPN-20E and PTFE, nucleated the crystallization of PP during cooling under high pressure in the γ-form causing an increase of crystallization temperature, the γ-form content and a decrease of grain size, although the first nucleant was more efficient. Calcium pimelate, a known nucleant of the β-form, studied for comparison, was ineffective.

The growing interest for continuous fiber-reinforced polymer composites leads to the development of new processes such as resin transfer molding for thermoplastics (RTM-TP) or tape placement. In the aim of optimization, their simulations are required and have to include all involved physical phenomena and the associated couplings. During the consolidation step, the crystallization of the semicrystalline matrix occurs between the fibers of the multiscale reinforcement. A tricky task is to provide a realistic model able to describe the crystallization kinetics, which includes the effect of fibers on the polymer phase change and avoiding large computation time. In 2004, Haudin and Chenot proposed a generalization of the Avrami model, written in a differential form to compute the evolution of the crystallization of a neat thermoplastic in an infinite volume. In the present article, new extensions are proposed to predict the crystallization in long-fiber thermoplastic composites, without or in the presence of transcrystallinity on fiber surfaces. In both cases, they are compared to three-dimensional numerical simulations using a previously validated numerical method. All the numerical and analytical results are consistent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44508.

International audience; A prototype hot-stage termed "Polymer High Cooling - Optics" was especially designed to follow on-line the nucleation and growth of crystallizing entities at constant cooling rates. The optically transparent hot-stage receives a gaseous flow at a constant temperature, which passes over the sample. Quiescent crystallization is monitored in real-time at relatively moderate (from 30 to 500 degrees C/min) and even at high (from 500 to 2000 degrees C/min) constant cooling rates. As a first application of this new set-up, two relevant parameters of the cc-modification of isotactic polypropylene, i.e., the crystallization temperature and the spherulite growth rate, were successfully captured for different constant cooling rates in a reproducible way. The superposition of these newly-collected growth rate data with those compiled by Janeschitz-Kriegl (2006) demonstrates the reliability of our experimental determination.

International audience; Shear-induced isothermal crystallization in iPP based nanocomposites with organo-modified montmorillonite was followed by light depolarization technique. Prior to the crystallization, samples were sheared at 1 or 2 s(-1) for 10s in a plate-plate system at crystallization temperature of 136 degrees C. Structure of the solidified specimens was investigated by light microscopy and electron microscopy, X-ray techniques and IR spectroscopy. Strong enhancement of the nucleation and crystallization after shearing was observed in the compatibilized nanocomposites with the clay. Clay exfoliation was found to accelerate strongly the shear-induced nucleation and overall crystallization. However, the sheared samples exhibited only weak orientation of alpha crystals with (040) crystallographic planes parallel to shearing direction that resulted probably from a small population of oriented crystals that formed due to shear-induced orientation of iPP chains and served as nuclei for further nearly isotropic growth.

In packaging industry, many structures are produced by extrusion coating. In this process, a polymer film is extruded through a slit die, then stretched in air, coated on a substrate (paper, aluminium or steel foil) between a chill roll and a flexible pressure roll, and finally cooled on successive chill rolls. Due to their non-polar character, polypropylenes are not suitable for extrusion coating on metallic surfaces. Adhesive properties can be improved by grafting on the polymer chain a polar group like maleic anhydride which may react with the aluminium surface. Our purpose was to develop a general model in order to predict the temperature field in the thickness of the multilayered structure along the stretching, laminating and cooling steps, and especially near the polymer/metal interface. This model includes crystallization kinetics and accounts carefully for the heat transfer coefficient with the successive rolls and surrounding air. Its predictions have been successfully compared to experimental temperature measurements along the coating line for various processing conditions (velocity, roll temperature, etc). Moreover, thermal history has a real impact on structure and morphology in the film. All these aspects are revealed by microscopic observations of thin microtomed sections of the film and X-ray diffraction experiments. Finally, adhesion properties of the laminate have been tested for the same process conditions. A good correlation has been established between adhesion properties and the thermal history experienced by the grafted polypropylene near the interface with aluminium before crystallization.

The widely applied approaches to the description of the conversion of melt into spherulites are reviewed and critically assessed. The attention is focused on the polymer crystallization in quiescent conditions. Both isothermal and nonisothermal crystallization processes are considered, including also the crystallization in a temperature gradient. In addition, the approaches to the description of the influence of spatial confinement and additional nucleation processes on surfaces confining the material on the conversion of melt into spherulites are discussed. Since similar phenomena occur also in fiber-reinforced systems, the theoretical predictions of the overall crystallization kinetics in these systems are also included in the present review. The possible reasons of discrepancies between the theoretical predictions and the experimental data are analyzed.

The purpose of the present work is to introduce a crystallization law into Rem3D, a 3D code written in C++ and dedicated to the injection molding of polymers. We kept the basic hypotheses of Avrami's model and cast the kinetic equations into a differential system that is solved numerically. The variation of the density of potential nuclei with temperature is taken into account. Furthermore, the distribution of mean spherulite sizes can be deduced from the calculations. The second part of the paper is an experimental study of crystallization in well-controlled conditions (2D, isothermal or constant cooling-rate). It establishes a procedure for the determination of the nucleation and growth parameters used in the theoretical model, and gives a first validation of this model. Finally, the crystallization equations are introduced into Rem3D, in order to assess the feasibility of our new approach. Some typical results concerning the evolution of the transformed volume fraction in injection-molded parts are presented.

Crystallization of thin polypropylene films was performed in isothermal, constant cooling-rate and mixed conditions. The experiments were first analyzed using the classical procedures based on simplified forms (Avrami, Ozawa) of the general Kolmogoroff-Avrami-Evans (KAE) theory. These analyses, which can be applied over an unusually wide transformation range, show that the crystallizations are actually 2 D. Then, a procedure has been established for the determination of the nucleation and growth parameters involved in the theoretical model presented in the first paper of this series. These parameters have been introduced into the model in order to predict the crystallization behavior in isothermal, constant-cooling-rate and mixed-conditions: transformed fraction, number of activated nuclei, final size distribution of semi-crystalline entities. A very good agreement is generally found between predictions and experimental results.

The crystallization of nanocomposites of isotactic polypropylenes with organo modified montmorillonite compatibilized by maleic anhydride grafted polypropylene was studied by light microscopy in isothermal conditions in quiescent state and in shear. The isothermal and nonisothermal crystallization of the composites was also investigated by DSC method. Only weak nucleation activity of montmorillonite was observed during crystallization in static conditions. The clay nucleation activity was greatly enhanced in shear-induced crystallization and resulted in a drastic decrease of spherulite sizes. In nanocomposite films crystallized isothermally the intense nucleation of isotactic polypropylene spherulites was observed when the polymer was forced to flow to compensate the volume shrinkage due to crystallization. It was also found that the presence of a glass support enhances spherulite nucleation in nanocomposites which is caused possibly by shear due to a difference in thermal shrinkage of a polymer matrix and a glass support.

International audience; Polymer crystallization often occurs in the presence of foreign bodies, such as walls of processing tools. In such cases, there is a competition between nucleation in the bulk polymer and nucleation on well-identified surfaces. If many nuclei are activated at the surfaces, their proximity imposes that entities emanating from these nuclei grow preferentially normal to the surfaces, leading to transcrystalline zones. The competition between surface and bulk nucleation can be studied through crystallizations of thin polymer films in contact with pan surfaces in a DSC apparatus. These experiments show that in thin samples transcrystallinity is limited by sample thickness. When thickness increases, the transcrystalline zones can grow, but up to a limiting value, because at a certain stage their development is stopped by the growth of bulk spherulites. A specific analysis of these DSC experiments gives access to crystallization parameters such as the number of nuclei per unit surface or the growth rate, and makes it possible to determine the crystallization kinetics of the polymer not disturbed by transcrystallinity.

International audience; Crystallization under shear of many different polypropylenes has been studied using a fiber pull-out device. It appears that growth can be considerably enhanced by flow. The best correlation is obtained with weight average molecular weight. Modeling the flow pattern gives access to the mechanical parameters at the growth front (shear rate and shear stress) as well as to the total strain applied to the polymer. The residual strain can be calculated taking into account relaxation processes.

International audience; Nucleation of the γ-form in isotactic polypropylene (PP) under high pressure was investigated. Three nucleating agents were used to nucleate crystallization of PP under atmospheric pressure: commercial Hyperform HPN-20E from Milliken Chemical, poly(tetrafluoroethylene) particles nucleating the α-form, and calcium pimelate nucleating the β-form. Crystallization of neat PP and PP with addition of 0.2 wt% of the nucleating agents was studied. Specimens were either kept at 200 °C under pressure of 200 MPa for time ranging from 2 min to 4 h or for 15 min under pressure ranging from 1.3 to 300 MPa. After cooling to ambient temperature and releasing the pressure, the specimens were analyzed by DSC, WAXD, and PLM to have an insight into the structure and to determine a crystallinity level and contents of crystallographic forms. Both α-nucleating agents strongly nucleated crystallization of PP under high pressure in the γ-form, whereas the β-nucleating agent had only a slight effect. The results show the possibility to use nucleating agents to nucleate the γ-form of PP under high pressure.

Three series of isotactic polypropylene characterized by different molecular weights and the same isotactic index have been studied during crystallization under static and shearing conditions. The shear is induced by the displacement of a glass fiber in the molten polymer. The monoclinic α-phase is here formed under shear with a columnar organization at the surface of the glass fiber, and does not appear under static condition. The growth-rate, constant during the shear-induced crystallization experiment, is compared with the result obtained from static crystallization. An important increase of the growth-rate due to the shear flow is observed. This increase depends on the molecular structure. The average molecular weights ―Mw and ―Mz seem to be the most important molecular parameters, for which an excellent correlation is obtained. The increase of these parameters ―Mw and ―Mz leads to a significant enhancement of the growth-rate, which can be multiplied by a factor of 10 in the present conditions.

The isothermal crystallization of isotactic polypropylenes has been studied under static conditions and under shear flow. The shear was induced by displacement of a glass fibre in the molten polymer. An α-monoclinic crystalline phase was formed with a columnar organization at the surface of the glass fibre, which did not appear under static conditions. The growth rate, constant during shear-induced crystallization experiments, is compared with the results obtained from static crystallizations. An important increase of the growth rate due to the shear flow is observed. This increase depends on the molecular weight and the tacticity of the polypropylene. Actually, the molecular weight and the isotactic index seem to be the most important molecular parameters. Their augmentation leads to a significant increase of the growth rate, which can be increased by a factor of seven, under the present conditions.

An erratum has been published for this content. Erratum: "CRISTAPRESS: An optical cell for structure development in high-pressure crystallization" Review of Scientific Instruments, 85 (2) art. no. 029902; International audience; An original optical high-pressure cell, named CRISTAPRESS, has been especially designed to investigate phase transitions of complex liquids, i.e., polymers, polymer blends, nano-composites, etc. The design of the cell is based on the optical properties of morphological entities through in situ light depolarizing microscopic observations. Pressure up to 200 MPa with a fine temperature control up to 300 °C can be applied. A striking advantage of this cell is the possibility to select the pressure transmitting medium that can be water, silicone oil, a fluid in the supercritical state, etc. The potential of the novel technique was demonstrated by carrying out time-resolved measurements during polymer crystallization induced by water pressure. These preliminary experimental investigations permit to discriminate the role of the barometric and thermal histories on the kinetics of polymer growth, as well as on the subsequent morphologies. It should lead to new reliable crystallization kinetics models.

The plane-strain compression test provides quantitative data on the polymer rheology in homogeneous large deformation at constant strain-rate, and on the friction shear stress between the film and the dies. Thin HDPE films with a homogeneous morphology were formed by quenching or isothermal crystallization. The structure was modified by varying the crystallization temperature over a wide range: 118°C ≤ T C ≤ 130°C. A mechanical model with a pressure-dependent rheology and two friction laws was tested. The rheological parameters are different in tension and in compression. The occurrence of brittle fracture under compression depends on the crystallization temperature, but the rheological parameters are almost independent of the crystallization conditions.

International audience; A combined effect of organo-modified montmorillonite (o-MMT) and shear flow on nonisothermal crystallization and emerging structure of isotactic polypropylene (iPP) was studied. Composite materials of iPP with 3 wt.% of o-MMT, nanocomposite compatibilized with maleic anhydride grafted iPP and non-compatibilized composite, blend of iPP with the compatibilizer and neat iPP were sheared for 10 s at a rate ranging from 1 to 40 s−1 during cooling at 10 °C min−1, beginning at different temperatures: 143, 153 and 163 °C. The crystallization behavior of all the materials studied did not differ under quiescent conditions. However, the effects of flow, that is an increase of crystallization temperature, enhancement of nucleation and decrease of grain size, and also orientation of crystals, although dependent on shear temperature and rate, were amplified by the presence of o-MMT. The strongest effects were observed for the compatibilized nanocomposite with exfoliated clay. In the nanocomposite sheared at 143 °C crystallization temperature increased by 16 °C, more than 12 °C achieved for the blend and the non-compatibilized composite. However, even in the latter case the increase was larger than 7 °C measured for neat iPP. The sheared nanocomposite exhibited the orientation of α-phase crystals with (0 4 0) crystallographic planes parallel to the shearing direction and (1 1 0) planes bimodally oriented, parallel and normal to the shearing direction.

International audience; Introduction, General Effects of Processing Conditions on Crystallization, Effects of Flow, Effects of Pressure, Effects of Cooling Rate, Effects of a Temperature Gradient, Effects of Surfaces, Modeling, General Framework, 2 Simplified Expressions, General Systems of Differential Equations, Crystallization in Some Selected Processes, Cast Film Extrusion, Fiber Spinning, Film Blowing, Injection Molding, Conclusion

International audience; The crystallization kinetics of polypropylene was observed during shear and after shear experiments under isothermal condition. The crystallizations were performed in a plate-plate and a fiber pull-out device. The nucleation density, the crystalline growth and the overall kinetics were measured and compared with data obtained in a similar way but during static experiments. The morphologies are spherulitic and formed from nuclei which seem to be randomly distributed, α-phase spherulites are always observed but with a nucleation density and a growth rate which depend on shearrate. The nucleation density is strongly enhanced by shear and acts as the main factor on the overall kinetics. The overall kinetics can be analyzed with a two-step Avrami model, where an Avrami exponent n1 with a very high value is always observed first after shear and a more usual parameter n2 for the subsequent crystallization period. This high value of n1 seems to be related to the strong enhancement of nucleation density. The growth rate increases with the shear-rate, but the basic growth mechanisms do not seem to be modified. For crystallizations after shear the growth rate decreases with a long-time delay after shear but not down to the static value. The effect is characteristic of a partial relaxation of chain orientation after shear but with a very unusual time constant.

International audience; The growth kinetics of a polymer spherulite is function of temperature and pressure. While the link with temperature is well understood, little comprehensive study has been conducted to quantify the effect of pressure. This is yet required for polymer processing. An original experiment has been constructed for pressure and temperature controls up to 200 MPa and 300°C, respectively. The cell design takes advantage from the optical properties of the semi-crystalline spherulites to conduct in-situ real time light depolarizing microscopic observations. Preliminary analyses of isothermal isobaric holding of a model polymer shows the influence of temperature and pressure on nucleation and growth kinetics of spherulites, as well as on the crystallization morphology. Simple modeling dealing with the Avrami equation and the Hoffman and Lauritzen theory is introduced.

This article was presented at the 4th International Conference on Polymer Behavior, International Union of Pure and Applied Chemistry, Lodz, Poland, September 20-23, 2010.; International audience; The use of three different calorimeters made it possible to measure the overall kinetics of isotactic polypropylene in the α-phase in a wide temperature range. Original results concerning the growth rate of α spherulites were also obtained by optical microscopy by using a prototype hot stage developed in our laboratory. A new growth regime seems to exist at low crystallization temperature. The number of nuclei shows a smooth evolution with temperature with no rupture in the nucleation behavior in the low-temperature range. Combination of experimental results and an appropriate extrapolation procedure lead to an overall kinetics law valid in the whole domain of existence of the α-phase. This law is based on Ozawa's formalism. It will be used in polymer processing.

Intense parasitic nucleation has been observed at the surface of differential scanning calorimetry samples for various polymers, whereas their crystallization traces exhibit complex shapes. Revisited overall kinetics theories and computer simulation, taking into account small thickness of samples and transcrystallinity effects, allow to explain and reproduce experimental ‘double peaks’, currently observed with polyamide 6-6. The beginning of the transformation and the main peak are attributed to surface and bulk nucleations, respectively. As a consequence, any DSC experiment should be followed by a microscopic observation and more accurate models including thermal gradients and resistances should be developed for their interpretation.

An experimental and theoretical investigation of the overall crystallization kinetics of thin polymer films containing transcrystalline regions on their surfaces is presented. DSC experiments on polyamide 6-6 show that typical features of crystallization curves can be associated with the occurrence of transcrystallinity. In order to interpret these experimental results, a theoretical model is built within the frame of overall crystallization kinetics theories. It makes it possible to correlate the thickness of transcrystalline zone both to the crystallization temperature, the shape of the peak and the density of nuclei within the polymer. Computer simulation is also used to describe the different steps of structure development within a thin film containing transcrystalline regions.

We are grateful to InTech the publisher of the book "Thermodynamics - Interaction Studies - Solids, Liquids and Gases", for letting this publication being archived in this Open Access repository. The publication is available from Intech Open Access Publisher: http://www.intechopen.com/articles/show/title/thermodynamics-and-thermokinetics-to-model-phase-transitions-of-polymers-over-extended-temperature-a; International audience; A scientific understanding of the behaviour of polymers under extreme conditions of temperature and pressure becomes inevitably of the utmost importance when the objective is to produce materials with well-defined final in-use properties and to prevent the damage of materials during on-duty conditions. The proper properties as well as the observed damages are related to the phase transitions together with intimate pattern organization of the materials. Thermodynamic and thermokinetic issues directly result from the thermodynamic independent variables as temperature, pressure and volume that can stay constant or be scanned as a function of time. Concomitantly, these variables can be coupled with a mechanical stress, the diffusion of a solvent, and/or a chemically reactive environment. A mechanical stress can be illustrated in a chemically inert environment by an elongation and/or a shear. Diffusion is typically described by the sorption of a solvent. A chemical environment is illustrated by the presence of a reactive environment as carbon dioxide or hydrogen for example. Challenging aspects are polymer pattern multi scale organizations, from the nanometric to the macrometric scale, and their importance regarding industrial and technological problems, as described in the state of the art in Part 2. New horizons and opportunities are at hands through pertinent approaches, including advanced ad hoc experimental techniques with improved modelling and simulation. Four striking illustrations, from the interactions between a solvent and a polymer to the growth patterns, are illustrated in Part 3.

Within the frame of overall kinetics of crystallization, polymer crystallization is characterized by only three parameters: the initial density of potential nucleiN0, their activation frequencyq and the growth rateG. The growth rateG is rather easy to measure, whereas the nucleation parameters are generally unknown. Our purpose is to determine bothN0 andq using experimental isothermal two-dimensional crystallizations and computer simulation. Both these parameters are deduced from the rate of appearance of spherulites expressed as a function of the transformed surface fraction. The activation times of the spherulites are deduced from the shape of the boundaries between spherulites at the end of the transformation. When the growth rateG is known, the evolution of the transformed surface fraction is rebuilt using a computer simulation, so that only one observation of the final stage of the crystallization is needed.

International audience; This article reports on the impact of shear on crystallization upon cooling of palm oil. Samples were cooled down under shear from 70 to 10 degrees C, then kept at this temperature, while performing rheological measurements using a controlled shear rate rheometer and rheo-optical observations using optical microscopy and small-angle light scattering. Shear rates between 1 and 300 s(-1) were investigated. Two crystallization steps were observed, characterized by associated viscosity increases. The effect of shear on these 2 crystallization processes was investigated. Shear was shown to influence almost all of the steps of the structuring process of the crystallizing palm oil. The spherulite size and growth rate during the 1st crystallization are affected by shear. The onset time of the 2nd crystallization process strongly depends on the extent of shear. The steady state structures after the 1st and 2nd crystallization processes constituted of a suspension of aggregates of spherulites are controlled by the applied shear rate. Practical Application: The texture of crystallized vegetal fats and subsequent end product properties depend on the structure developed during the crystallization process. This structuring process is strongly influenced by the thermo-mechanical history applied to the product (cooling rate, degree of undercooling, annealing time, application of flow). This article shows how the shear rate as well as extent of shear affects the different steps of the crystallization and aggregation processes in the case of palm oil after the 1st crystallization.

International audience; Recently obtained results on gas-polymer interactions and associated molecular organizations are reported. As a matter of fact, they are of interest for several applications from petroleum industry to nano-science and polymer processing. They constitute an incursion into the thermodynamics and kinetics of solid polymer/gas interactions and liquid polymer/gas interactions as well as solid to liquid (polymer) transitions. Experimental and theoretical studies have been conducted to better understand the competition between the effects of solubility/plasticization and of hydrostatic pressure of a gas in the polymer-rich phase and also the importance of the interface in block copolymers. A relation characterizing the global isobaric thermal expansion of thermoplastic semi-crystalline polymers saturated in gas has been developed. In addition, it has been shown that the control of the supercritical conditions of the gas enabled to successfully monitor the size of nano-structures appearing by self-assembling in di-block copolymers. The overall kinetics of the liquid to solid transition, that is crystallization, of a semi-crystalline polymer has been described within the framework of Avrami general assumptions. A system of differential equations has been derived for quiescent crystallization and extended to flow-induced crystallization which can be used to predict the formation of microstructures.

International audience; In the context of polymer crystallization under high and constant cooling rates, a new survey is presented. The growth kinetics of spherulites from the molten state and the corresponding temperature of crystallization under similar cooling rates are considered. An industrial grade of isotactic polypropylene (iPP) is investigated in the range of slow (from 1 to 10°C/min), of relatively moderate (from 30 to 500°C/min) and of high (from 500 to 1600°C/min) constant cooling rates. The growth kinetics for the α-modification of iPP versus the temperature of crystallization is in agreement with the data published by Janeschitz-Kriegl [Macromolecules, 2006]. To understand the growth mechanism, the Hoffman equation is used and then extrapolated to lower temperatures of crystallization. Finally, to describe the non-isothermal crystallization, the equation of Ozawa is used. The benefits to use the spherulitic growth kinetics to extrapolate data from alternative methods, i.e., differential scanning calorimetry (DSC), are briefly discussed.

Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. A, 2008, Vol. 50, No. 5, pp. 827–840.; International audience; The general context of this paper is introduction of a crystallization model into 3D software dedicated to a thermomechanical description of the injection-molding process. From the Kolmogoroff-Avrami-Evans equation for overall kinetics and from additional assumptions on nucleation, a system of differential equations is derived for quiescent crystallization and extended to flow-induced crystallization. The experiments done to identify the relevant crystallization parameters are then described, and the values of these parameters are optimized using the Genetic Algorithm inverse method. To check the validity of the theoretical model and the accuracy of our experimental characterization, the curves calculated for the evolutions of the transformed volume fraction and of the number of spherulites are compared to the experimental ones. Finally, the crystallization model is implemented in the Rem3D® code and some typical calculations are presented.

International audience; To understand the relationship between 'polymers-processing conditions-structures-properties', crystallization is one of the major concerned phenomena. A general crystallization model derived from Avrami's work has been developed at CEMEF and implemented into a 3D finite element code for injection-molding named Rem3D®. It gives a precise description of the crystallization event, allows the determination of morphological features, but it requires a reliable determination of the crystallization parameters. The experimental procedures adopted to capture relevant experimental parameters are presented. The determination of overall kinetics, density of potential nuclei with activation frequency of nuclei into crystalline entities, and growth rate is carried out with polarized optical microscopy (POM) and is supplemented by small angle light scattering (SALS). The treatment of data is performed by a classical method or using an inverse genetic algorithm method to extract the parameters necessary to our model. The 2D simulation of the crystallization, illustrated with Rem3D®, reproduces the experimental reality quite accurately, in the case of an isothermal and static crystallization. This is applied to two polymers, an isotactic homopolymer polypropylene iPP and a polyether-block amide PEBAX®.

International audience; The paper first presents the experimental set-ups designed to produce flow-induced crystallization and the techniques used to analyze structure development. Then, the general effects of flow are discussed in terms of crystallization thermodynamics (nucleation, growth, overall kinetics), with the consequences on morphologies (from spherulites to shish-kebab morphologies). Finally, some open questions are presented, which shows that many things are not yet explained, especially the nucleation event.

PurposeThis paper sets out to show the feasibility of the genetic algorithm inverse method for the determination of the parameters of crystallization kinetics laws in isothermal and non‐isothermal conditions, using multiple experiments.Design/methodology/approachThe mathematical model for crystallization kinetics determination and the numerical methods of its resolution are introduced. Crystallization kinetic parameters determined by approximate physical analysis and the inverse genetic algorithm method are presented. Injection molding simulations taking into account crystallization are performed using the finite element method.FindingsIt is necessary to perform the optimization on two parameters, transformed volume fraction and number of spherulites to obtain correct results. It is possible to use results from different samples, in spite of the dispersion of some values.Research limitations/implicationsExperimental data for isothermal and non‐isothermal conditions were used and obtained good results for the parameters of crystallization kinetics laws from which the evolutions of overall crystallization kinetics and crystalline microstructure were deduced. Nevertheless, the dispersion of the experimental data concerning the number of spherulites obtained with different samples is important. The evolution of the number of spherulites is required for the optimization to get correct results.Practical implicationsAn important result of this work is that the genetic algorithm optimization can be applied to this problem where the experiments cannot be performed with a single sample and the experimental data for the number of spherulites have low precision. Even if only the crystallization kinetics was considered, the feasibility in molding simulation has been shown.Originality/valueSimulation of crystallization in injection molding is very important for a later prediction of the end‐use properties.

This paper is devoted to the formation of a spherulitic pattern in polymers that are spatially confined. The nucleation at sample boundaries influences the spherulitic structure and accelerates the local conversion of melt into spherulites. A model of the spherulitic pattern formation in narrow strips of polymer based on the probability theory was developed to account for the effect of spherulite nucleation at sample borders. The model allows us to predict the rates of formation of the interspherulitic boundaries and also the distributions of distances from spherulite centers to the boundaries for an isothermal as well as a nonisothermal crystallization. The final length of interspherulitic lines and the final number of triple points between spherulites can also be calculated. The predictions of the model were verified by computer simulation, which reproduces spherulitic patterns observed experimentally in strips of thin films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2319–2329, 2005

The influence of pre-shearing on the crystallisation of a conventional Ziegler–Natta catalysed and a metallocene catalysed linear low-density polyethylene (LLDPE) samples was studied by a rheo-optical method, coupling light scattering and steady shear flow. Experiments were performed on a high-temperature shearing cell, with a pair of parallel quartz plate windows. The polymers were sheared at a melt temperature Ts (ranging from 190 to 150 °C) at a constant shear rate ( γ ) for a duration time ts. After cessation of shear (at a given deformation of γ t s unit), the sample was maintained at the selected melt temperature for a waiting time tw (ranging from 0 to 10 min) before it was cooled down to 90 °C. Small-angle light scattering (SALS) patterns were recorded during the whole process. It was shown that the pre-shear history thus investigated has no measurable influence on crystallisation of the linear metallocene LLDPE. For the Ziegler–Natta sample, the influence of pre-shear on its crystallisation is larger when the shear rate ( γ ) and strain ( γ t s ) are large, the waiting time tw is smaller or the temperature Ts is lower. The consequence of shear is giving ellipsoidally deformed spherulites, elongated in the flow gradient direction, which originate from oriented nuclei. Crystallisation, following flow in particular, is shown to be a very good probe of chain orientation and it turns out to be more sensitive than classical linear rheological methods. It can detect if the sheared sample is in a steady state or if all chains have relaxed after a flow. For example, it is surprisingly shown that chain orientation for the Ziegler–Natta sample requires a large amount of shear deformation, in the order of 1000 strain units, to reach a steady state.

International audience; Transcrystallinity may occur during differential scanning calorimetry analysis at the surfaces of the samples. In such a case, measurements may be unsuitable. We propose simple methods for the determination of intrinsic crystallization data that are accurate for the polymer and for the determination of the nucleating ability of the surfaces. These methods are based on the experimental analysis of the crystallization of samples with different and calibrated thicknesses during experiments at different constant cooling rates. Analysis of thin samples allowed the characterization of transcrystallinity, whereas analysis of at least three samples of different thicknesses allowed us to determine the true crystallization kinetics of the bulk material. These two techniques were independent of each other and were successfully applied to the case of a high-density polyethylene. The determinations were verified with simple analytical models. A further extension could be the study of the nucleating ability of different substrates.

International audience; The crystallization of a high-density polyethylene was analyzed with differential scanning calorimetry (DSC) measurements. An intense transcrystallinity was observed at the contact between the polymer and the DSC pans. The modification of the crystallization kinetics induced by this phenomenon was studied as a function of cooling rate and sample thickness. We point out that most of the theoretical predictions of our previous model could be checked. The crystallization temperature was a function of the sample thickness and could be also correlated with the thickness of the transcrystalline zones. The shapes of the DSC traces were complex and correlated with the amount of transcrystallization. The usual interpretations of such DSC curves were not accurate. We conclude that specific experimental procedures must be proposed to understand and correctly use such measurements.

International audience; Strain induced crystallisation of poly(ethylene terephthalate) (PET) designed for stretch-blow moulding is studied combining well-controlled tensile tests, different quenching protocols and X-ray diffraction technique. As well known [Polymer, 33 (1992) 3182; Polymer, 33 (1992) 3189], crystallisation begins when a minimum strain has been reached. However, crystallisation is a progressive phenomenon that could involve intermediate stages or phases as suggested by some recent papers [Macromolecules, 31 (1998) 7562; Polymer, 41 (2000) 1217]. In this study, first evidence for the crystallisation is the appearance, parallel to the tensile direction, of zones having the crystal lateral order. The spreading out of the diffraction dots suggests that these zones are small in comparison to usual lamella thickness or that the order is imperfect. Longitudinal order appears later, progressively leading to fibre-texture. At low strain, before this texture is totally developed, cooling influences the final microstructure superposing steps in which crystallisation and relaxation compete illustrating the relative importance of cooling protocol when strain induced crystallisation of PET is studied. Nevertheless, strain hardening can be observed before the crystalline microstructure is totally developed, emphasising the fact that strain hardening is mainly controlled by first stages of crystallisation and that actual crystallisation,occur during a following relaxation step..

The growth rate of an ethylene-propylene random copolymer with a 2.8% w/w ethylene content was studied in a similar manner to polypropylene. A growth regime transition associated with a birefringence change was observed at 130‡C, while the same phenomena appeared at 138‡C in isotactic polypropylene. In both polymers positive birefringence corresponds to Regime III, whereas negative birefringence of spherulites is associated with Regime II. The birefringence change is attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae at low temperature (Regime III) and preferentially radiating lamellae at higher temperature (Regime II). We confirm that such a morphological change can be interpreted using the concept of “non-adjacent re-entry” introduced in Hoffman's kinetic theory. Thus, quadritic morphology seems to have a partly kinetic origin. The shift of the transition temperature in the copolymer is due to the rejection of ethylene segments at the surface of crystalline lamellae of polypropylene.

A differential scanning calorimetric study of barium stearate has been undertaken. Four transitions have been found: two crystal-crystal at 70 and 117°C, a crystal-mesomorphic phase transition at 150°C, and a second-order transition at 220°C. The correspondence between heating and cooling peaks has been established. The enthalpies have been determined.