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The present work provides a unique insight to reveal the long chain branching (LCB) influence to the nano‐fillers, that is via analyzing the conductivity evolution during the thermal annealing, fast shear flow and melt to solid cooling process. Meanwhile the crystallization behavior is also discussed. A linear polypropylene (PPC) and a long chain branched polypropylene (PPH) are chosen as the two polymer matrices with carbon nanotubes (CNTs) as the nanofillers. During the thermal annealing process, a more obvious growth of electrical conductivity of linear PPC nanocomposites are observed compared with LCB PPH nanocomposites. The harder movement of CNTs inside LCB PPH matrix may be the main reason. This also can be reflected by the conductivity evolution during slow cooling process where a decrease‐then‐increase (DTI) phenomenon is found for PPC/CNTs systems due to the rebuilding of CNTs conductivity network after crystallization. By contrast, this does not happen for PPH/CNTs systems. [ABSTRACT FROM AUTHOR]

The incorporation of bioactive and biocompatible fillers improve the bone cell adhesion, proliferation and differentiation, thus facilitating new bone tissue formation upon implantation. During these last 20 years, those biocomposites have been explored for making complex geometry devices likes screws or 3D porous scaffolds for the repair of bone defects. This review provides an overview of the current development of manufacturing process with synthetic biodegradable poly(α-ester)s reinforced with bioactive fillers for bone tissue engineering applications. Firstly, the properties of poly(α-ester), bioactive fillers, as well as their composites will be defined. Then, the different works based on these biocomposites will be classified according to their manufacturing process. New processing techniques, particularly additive manufacturing processes, open up a new range of possibilities. These techniques have shown the possibility to customize bone implants for each patient and even create scaffolds with a complex structure similar to bone. At the end of this manuscript, a contextualization exercise will be performed to identify the main issues of process/resorbable biocomposites combination identified in the literature and especially for resorbable load-bearing applications. [ABSTRACT FROM AUTHOR]

The purpose of the present work was to gain a fundamental understanding of how the composition and physico-chemical properties affect the rheology, morphology, miscibility, and thermal stability of poly(lactic acid) (PLA)—poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) biopolymer blends obtained by melt mixing. First, restricted processing conditions were chosen, due to the inherent thermal degradation of PHBV, as proven by rheological dynamic time sweep (DTS) measurements and size-exclusion chromatography (SEC). Based on this, the composition dependence of the blends was investigated using small-amplitude oscillatory shear rheology (SAOS), and the results were confirmed by scanning electron microscopy (SEM) analysis. Subsequently, the changes in glass transition temperatures (Tgs) from the molten to the solid state, as observed by DMA and DSC, were verified by coupling SAOS to dielectric relaxation spectroscopy (DRS). Herein, the thermo-rheological complexity of PLA/PHBV blends in the melt was revealed, especially for PLA-rich blends. Irregularly structured morphologies, caused by highly mismatched viscoelastic properties, illustrated the degree of partial miscibility. Moreover, the thermo-rheological complexity appeared in the molten state of the asymmetric PLA-rich phases could be correlated to the crystal-amorphous interfacial MWS polarization, because of the locally-induced phase separation and heterogeneity, and owing to the differences in their crystallization properties during cooling. The miscibility also suffered from the lower thermal stability of PLA and the even more unstable PHBV. Nevertheless, the melt-induced degradation process of the PLA/PHBV blends seemed to be responsible for some of the in situ self-compatibilization and plasticization mechanisms. As a result, the miscibility and thermo-rheological simplicity were improved for the intermediate and PHBV-rich compositions at low temperatures, since their properties were, to a large extent, governed by the significant degradation of PHBV. The present findings should increase the understanding of morphological changes in PLA/PHBV blends and help control their micro/nanostructure. [ABSTRACT FROM AUTHOR]

Moreover, the modified mechanism of PSCTLCP on MH/LLDPE/PSCTLCP composites was investigated at different processing temperatures, rotation speeds and shear rates to guide the actual processing in industry. I am so glad to share with you our Special Issue entitled "Rheology and Processing of Polymers", which covers the latest developments in the field of rheology and polymer processing, highlighting cutting-edge research focusing on the processing of advanced polymers and their composites. The following keywords cover all related topics: polymer processing; rheology; polymers; natural polymers and biopolymers; biopolymers; polymer nanocomposites; advanced polymers; composites and biocomposites; biocomposites; modeling; numerical simulation; polymer physics; innovative processing; polymer melts; polymer engineering; recycling Bo Lu et al. [[1]] reviewed interfacial phenomena in multi-micro/nanolayered polymer coextrusion from fundamental and engineering aspects. 33050464 14 Guan X., Cao B., Cai J., Ye Z., Lu X., Huang H., Liu S., Zhao J. Design and Synthesis of Polysiloxane Based Side Chain Liquid Crystal Polymer for Improving the Processability and Toughness of Magnesium Hydrate/Linear Low-Density Polyethylene Composites. [Extracted from the article]

The objective of the present study was to investigate multiphase systems based on polylactic acid (PLA) and polyamide 11 (PA11) from blends to multilayers. Firstly, PLA/PA11 blends compatibilized with a multifunctionalized epoxide, Joncryl, were obtained through reactive extrusion, and the thermal, morphological, rheological, and mechanical behaviors of these materials were investigated. The role of Joncryl as a compatibilizer for the PLA/PA11 system was demonstrated by the significant decrease in particle size and interfacial tension as well as by the tensile properties exhibiting a ductile behavior. Based on these findings, we were able to further clarify the effects of interdiffusion and diffuse interphase formation on the structure, rheology, and mechanics of compatible multilayered systems fabricated with forced-assembly multilayer coextrusion. The results presented herein aim to provide a deeper understanding of the interfacial properties, including the rheological, mechanical, and morphological behaviors, towards the control of the interface and confinement in multilayer polymers resulting from coextrusion, and also to permit their use in advanced applications. [ABSTRACT FROM AUTHOR]

This paper investigates the biaxial stretchability of polylactic acid (PLA)/poly (butylene adipate co-terephthalate) (PBAT)/thermoplastic cereal flour (TCF) ternary blends with a PLA/PBAT ratio close to 60/40 and a constant TCF content. A twin-screw extrusion process was used to gelatinize the starch and devolatilize the water in order to obtain a water-free TCF, which was then blended into a compatibilized or non-compatibilized PLA/PBAT matrix, introduced in the molten state. These blends were subsequently cast into sheets and biaxially drawn using a biaxial laboratory stretcher. The prepared ternary blends were found to present a typical ductile behavior. Scanning electron micrography highlighted dispersion and adhesion properties in the PLA/PBAT/TCF blends, where two different phases were observed. Moreover, the addition of the thermoplastic cereal flour did not significantly affect the biaxial stretchability of the PLA/PBAT blends but was found to lower the maximum stress before breaking. The modification of the interfacial tension between PLA and PBAT with the compatibilizer Joncryl before mixing with TCF had no effect on the durability of the PLA/PBAT/TCF sheet. Still, it slightly increased the maximum of nominal stress before failure. [ABSTRACT FROM AUTHOR]

Abstract: This study has been dedicated to the foaming of modified poly (lactic acid) with supercritical CO2. The first part of this work consisted in a rheological modification of neat PLA through chain extension. Improvement of the melt viscosity and elasticity has been achieved by the use of an epoxy additive during a reactive extrusion process. Rheological characterizations confirmed an increase of the melt strength due to this chain extension process. Foaming was then performed on the neat and modified PLAs using a batch process with supercritical CO2 as blowing agent. The investigation of the foaming temperature revealed an enlarged processing window for modified PLAs compared to neat PLA. Depending on the foaming parameters, foams with a cellular structure ranging from macro scale to micro scale have been obtained. A concomitant effect of the CO2-plasticization and the crystallisation on the melt rheology could explain this wide range of cellular morphologies. [Copyright &y& Elsevier]

Short date palm tree lignocellulosic fibers were used as a reinforcing phase in a polyepoxy thermoset commodity resin. Unmodified fibers as well as counterparts chemically oxidized using TEMPO catalyst mediation were used as fillers for composite materials prepared in a Resin Transfer Molding process. The preparation was facilitated in the case of the composites based on oxidized fibers. During the process, the front displacement of injected resin was more regular, more homogeneous, and faster in the case of oxidized fibers. The morphology, thermal and mechanical properties of the resultant composites were characterized by SEM, DSC, DMA, as well as three-point bending and Charpy impact tests. An elevated reinforcing capability of the oxidized fibers as compared to their unmodified counterparts was demonstrated, particularly by a high strain test in the glassy state. This confirmed the enhanced filler/matrix interface observed in such materials during the process and in the final composite as analyzed by SEM. No significant difference in reinforcing capability of the two kinds of filler was observed in the DMA analysis [ABSTRACT FROM AUTHOR]

The focus of the present paper is the rheological study of poly(D,L-lactic-acid) (PDLLA) towards a modeling of their healing properties during 3D direct pellet printing extrusion (DPPE). The viscoelastic properties of PDLLA and the filament temperature during deposition are first characterized. The influence of DPPE processing conditions is investigated in terms of temperature, time, and printing speed. For this, we propose a modeling of the process-induced interphase thickness between two deposited layers considering the non-isothermal polymer relaxation and accounting for the contribution of entanglement rate through the Convective constraint release model. Hence, taking into account the induced chain orientation and mobility coming from filament deposition, this model quantifies the degree of healing between 3D-printed layers. Eventually, the proposed model is validated by comparing the theoretically calculated degree of healing with experimental tensile properties and lap shear results. [ABSTRACT FROM AUTHOR]

In a circular economy context with the dual problems of depletion of natural resources and the environmental impact of a growing volume of wastes, it is of great importance to focus on the recycling process of multilayered plastic films. This review is dedicated first to the general concepts and summary of plastic waste management in general, making emphasis on the multilayer films recycling process. Then, in the second part, the focus is dealing with multilayer films manufacturing process, including the most common materials used for agricultural applications, their processing, and the challenges of their recycling, recyclability, and reuse. Hitherto, some prospects are discussed from eco-design to mechanical or chemical recycling approaches. [ABSTRACT FROM AUTHOR]

For blending immiscible polymers, such as in the toughening modification of polylactide (PLA) via blending with rubbery materials, interfacial compatibilization is of great significance while the mechanism, especially the role of interfacial rheology, remains elusive. In this study, styrene-butadiene block copolymer elastomer (SBC) was employed to toughen PLA and a dumbbell-shaped Janus nanoparticle (JNP) consisting of polymethyl methacrylate and polystyrene spheres with equal size (∼80 nm) was used as the compatibilizer. Located at the interface, JNPs exhibited a great compatibilization efficiency in PLA/SBC blends, as demonstrated by the good morphology stabilization against droplet coalescence under static annealing and low shear flow conditions, as well as by the resistance against droplet breakup under high shear flow conditions. Moreover, as revealed from the linear viscoelasticity of JNP compatibilized blends, when JNP loading is more than 2 phr, aside from shape relaxation, an interfacial relaxation dominated by Marangoni stress was observed, indicating the possibility of particle redistribution on droplet surfaces. However, when loading is more than 4 phr, relaxations in the terminal zone no longer exist, implying the possible formation of a particle network on the droplet surface. This is consistent with the mechanical properties. The blend shows the greatest toughness at JNP loading around 3 phr, while the toughness is very poor when JNP loading is either too low or too high. This suggests interfacial relaxation to be crucial to guarantee a good toughening effect of SBC in PLA. [ABSTRACT FROM AUTHOR]

The present work explores the shear and extensional rheology of immiscible multi-micro/nanolayered systems comprising low-density polyethylene (LDPE) paired with polystyrene (PS) and polycarbonate (PC) obtained from forced-assembly multilayer coextrusion. Firstly, miscible multilayer references based on LDPE/LLDPE layers were prepared with their miscibility characterized by shear and elongational measurements. Their strain hardening behaviors were found to be intricately linked to the number of layers and confinement. Secondly, for immiscible LDPE/PS and LDPE/PC multilayers with symmetric (50/50) and asymmetric (10/90) compositions, negative deviation of complex viscosities from neat polymers was highlighted because of the heightened confinement of LDPE chains by PS or PC and reduced entanglements at polymer–polymer interfaces. Intriguingly, LDPE/PC systems exhibited no strain hardening irrespective of layer configuration, while the geometric confinement imposed by PS layers facilitated interactions between single chains with long-chain branching (LCB), leading to strain hardening under specific conditions. Furthermore, the extensional viscosities were predicted using the Macosko model (C.W. Macosko et al. Journal of Rheology. 63 2019), accurately describing the behavior of 1024 layered films for both asymmetric (10/90) LDPE/PS and LDPE/PC systems, but not for 32 layers due to a limited number of interfaces. This study provides insights into quantifying interfacial tension properties in micro/nano-layered systems with high mismatched viscoelastic polymers, shedding light on their strain hardening properties in the presence of increased interfacial area. [ABSTRACT FROM AUTHOR]

The colossal development of modern electronic devices has inevitably led to an increase in electromagnetic interference (EMI), which has gradually become the fourth most prevalent type of pollution in the world. It is therefore necessary to seek more effective EMI‐shielding materials to overcome the shortcomings of conventional metal‐based materials, which include high density, a lack of mechanical flexibility, low corrosion resistance and costly processing. Conductive polymer composites (CPCs) have attracted more and more attention due to their superiority in many aspects. However, their performances should be further enhanced for future applications. One polymer with only one type of filler often cannot meet this kind of requirement. In this paper, filled polymer materials for EMI shielding are reviewed in terms of their processing, rheological properties, conductivity, and shielding effectiveness. Moreover, the combination of different ingredients and fillers when fabricating multicomponent composites for EMI shielding is also highlighted. The coordination of various components in composites with different structures, including solid, segregated, layered/sandwiched, and foamed/porous structures, is then discussed. [ABSTRACT FROM AUTHOR]

Lattice structures nowadays have gained a peak in research. Inspired by the honeycomb structure and fishbone, this study investigated lattice structures that can provide auxetic behavior and store maximum energy absorption during deformation mode. From that, the study involved designing and producing different modified lattices based on the honeycomb's structure and the fishbone's perspective. The specimens were 3D printed within fused filament fabrication techniques within the additive manufacturing platform of Euromed University of Fes. The conception, production, mechanical testing, and simulation have been employed to get optimum data analysis of the mechanical properties of the designed structures. The results observed under quasi-dynamic compression did not show significant densification behavior; but, the auxetic behavior was seen in all structures, while some suddenly collapsed. The experimental and numerical analysis demonstrated similar deformation behavior and strong agreement in their respective results. Nevertheless, some discrepancies in mechanical values were observed, with a relative percentage error of approximately 1% for both methods. Consequently, owing to the enhanced energy absorption observed in the V2 and V3 structures, it is evident that these modifications hold promise for optimizing the performance of these metamaterials in various practical applications. [ABSTRACT FROM AUTHOR]

It is proverbial that the rheological properties of low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) are disparate because of their different molecular microstructures due to the unlike methods of polymerization. In this work, multiple characterizations including Size-Exclusion Chromatography (SEC) coupled with low-angle light scattering and viscosmeter, 13C Nuclear Magnetic Resonance, Crystallization Elution Fractionation (CEF) and Differential Scanning Calorimetry (DSC) were conducted to get detailed information of branching on different LDPEs and LLDPEs. It was found that, in our case, LDPEs possessed higher molecular weight and greater amounts of long-chain branching (LCB) in comparison with LLDPEs. The Chemical Composition Distribution (CCD) of each LLDPE sample depends strongly on the catalyst used. LLDPE produced by Z-N catalyst exhibited broad short-chain branching (SCB) distribution (less uniform composition distribution), whereas LLDPE obtained by metallocene catalyst showed more uniform microstructure. Unlikely, the two LDPEs displayed wider but unimodal distribution corresponding to the free-radical polymerization mechanism. Both linear and nonlinear rheological results were strongly influenced by the presence of LCB. LDPEs in this work exhibited higher zero shear-viscosity, higher values of storage modulus, longer relaxation times, and higher activation energy comparing to LLDPEs. The presence of LCB leads to more pronounced strain hardening behavior in the elongational flow which is neglected in LLDPE. The molecular structures of linear and branched PEs were consistent with the rheological properties. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of the present work is to develop a new biomaterial with suitable melt strength, stiffness‐to‐toughness balance, and the required thermal performance for food packaging applications. The study is dedicated to investigating a new physical compatibilization approach of biosourced materials as well poly (lactic acid) (PLA) and polyamide 11 (PA11) in comparison with the chemical compatibilization through addition of a multifunctionalized epoxide. For this reason, this paper deals with gaining better understanding physical compatibilization in the biosourced blend with the incorporation of an acrylic melt strength enhancer into PLA/PA11 blend. The main focus of this paper is studying how physical compatibilization improves melt strength in comparison with chemical approach. Hitherto, the chain extension–branching balance was demonstrated to be difficult to be controlled and decoupled from chemical compatibilization at the polymer–polymer interface. Hence, the physical approach is presented as an original route in this work to develop a PLA‐based blend with good film blown processability and engineering properties. Morphological, rheological and thermomechanical properties of the new obtained biosourced blends were studied. The physical compatibilization effect was confirmed by the tuning interfacial properties. The extensional rheology highlighted that melt strength for the physical blends was also improved without any pronounced strain hardening in comparison with reactive blends. Besides, a great enhancement of the blowing processing windows of physically PLA‐PA11 compatibilized blend was highlighted while higher blow‐up ratio and take‐up ratio values were obtained. Overall, a correlation between the obtained thermal and crystalline properties was performed for the optimal biosourced blown film. [ABSTRACT FROM AUTHOR]

In the industry of polymer coextrusion processing, efforts are being made toward a better control of multilayer flow stability that is governed by the interface/interphase between neighboring layers, the understanding of which is considerably inadequate. This study aims to explore the relaxation dynamics of polymer chains located in the interphase between two compatible polymer melts based on transient rheology in step shear experiments, an area that is often overlooked without justification. First, transient rheology was investigated based on pure polymers of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) melts, focusing on a feature of abrupt stress decline observed in the transient period after a large step shear. This feature is considered to be the phenomenological onset of rheological nonlinearity (e.g., stress damping) commonly observed in the long-time window of a relaxation for an entangled polymer. From the molecular viewpoint, the nonlinearity onset is a result of polymer chain disentanglement under a large flow as interpreted based on a refined version of the Doi–Edwards tube model and Wang’s force imbalance theory, etc. A decreased entanglement number of polymer chains, either by decreasing molar mass in the melts or by reducing polymer concentration in solutions, was demonstrated to accelerate the onset of the rheological nonlinearity. In particular, a noticeable stress break-off in the transient period can be observed upon large deformations in the solutions due to their very weak entanglements. Second, large step shears were given to PMMA/PVDF bilayer-structured melts and a new model has been developed to determine the relaxation behavior of the interphase triggered between the layered polymers. Similar to the solutions, an abrupt stress decline was observed in the transient period for the interphase upon a large step deformation, indicating an analogous entanglement weakness of the interphase to the solution. Hence, a close correlation can be established between the interphase and the pure melts and solutions based on their transient rheology and the concept that the polymer chain entanglements can be weakened either by solvent dilution or by blending with dissimilar chains. [ABSTRACT FROM AUTHOR]

Influence of an in situ reactive interphase composed of graft copolymer on the melt shear and extensional rheology was systematically studied with a model bilayer of polyamide-6 (PA6)/maleic anhydride grafted poly(vinylidene fluoride) (PVDF- g -MAH). Firstly, small-amplitude oscillatory shear was used in situ to probe the development of reactive interphase from the interfacial reactions by tracking the changes of viscoelastic responses. Secondly, shear (start-up shear, shear stress relaxation) and extensional rheology was comparatively performed on the healed bilayers to evaluate the effects of reactive interphase. Interestingly, shear stress relaxation and especially extensional rheology were pretty sensitive to the presence of reactive interphase, whereas start-up shear showed negligible sensitivity. Specifically, the reactive interphase retarded the stress relaxation of healed bilayers subjected to step strains. Particularly, extensional rheology provided a more direct and quantitative view of the contribution of reactive interphase to melt rheology in both linear and nonlinear regimes. The remarkable increase in transient extensional viscosity and enhanced strain hardening resulting from the interfacial reaction in bilayer were demonstrated in terms of the interfacial stress. Besides, effect of reaction extent on extensional rheology was further examined, where it was found that interfacial stress increased with reaction time. The observed changes in rheology were attributed to the in situ formed interphase with graft copolymers and the resulting increased entanglements between neighboring layers. This study highlights the remarkable sensitivity of shear stress relaxation and especially extensional rheology to a reactive interphase. [ABSTRACT FROM AUTHOR]

The objective of this study was to gain a deep understanding of composition and compatibilization effects on the properties of entirely sustainably sourced polymer blends based on polylactide (PLA) and polyamide 11 (PA11). Generally, PLA cannot challenge regular commodity polymers due to its weak thermo-mechanical properties and its poor elongation properties. With this work, however, we present a promising route to overcome these drawbacks in order to enhance the processability of PLA: blending the polymer with various compositions of other ductile biopolymers such as PA11, as well as mixing PLA/PA11 blends with various amounts of a chain extender, Joncryl ADR®-4368, containing reactive epoxy functions, in a laboratory-scale twin-screw extruder. The effects on the rheological, morphological and mechanical properties were investigated. Results showed that a "self compatibilization" between PLA and PA11 chains can occur but it was found to be insufficient, contrary to recent work reported in the literature. The role of Joncryl as a compatibilizer for the PLA/PA11 system has been demonstrated by the significant decrease of particle size and interfacial tension as well as the improvement of ductile properties. Moreover, a new relaxation peak appeared in the relaxation spectrum, indicating the generation of a copolymer at the polymer-polymer interface. [ABSTRACT FROM AUTHOR]

This work aims to examine whether or not interfacial failure can occur in a compatible polymer bilayer system under large shear and elongation deformations, as well as to probe the sensitivity of nonlinear transient rheology to the presence of interface/interphase at neighboring layers. For this, stress relaxation after a step strain and fast startup in simple shear and uniaxial extension experiments have been performed on healed and coextruded poly(methyl methacrylate)/poly(vinylidene fluoride) bilayers with the presence of a robust diffuse interphase as evaluated by energy dispersive X ray. For unhealed bilayers, interfacial failure occurred in shear flows at intermediate deformations, while for healed bilayers the interphase greatly delayed the onset of interfacial failure to larger deformation steps and to a higher deformation rate in the startup shear. Extensional rheology demonstrated that the presence of an interphase in the bilayers greatly enhanced the transient extensional viscosityηE+(t) as well as the tensile relaxation modulus E(t) of the structure, even though the entanglement density was relatively low. Moreover, models are presented to predict the nonlinear relaxation behavior of bilayers and to estimate the relaxation behavior of the interphase. Fitting of the tube model to the shear relaxation indicates a dilated tube diameter in the interphase, confirming its weak entanglement intensity and its readiness to flow-induced disentanglement under large external deformations. Finally, the physics of the interfacial failure was assessed based on some recent molecular dynamic theories. [ABSTRACT FROM AUTHOR]

This study was dedicated to the blown film extrusion of poly(lactic acid), which mainly presents poor shear and elongation viscosities, and its blends. In order to enhance its melt strength, two main routes were selected (i) a structural modification through chain extension and branching mechanisms by adding a reactive multifunctional epoxide (named Joncryl) and (ii) blending with poly(butylene adipate-co-terephtalate), named PBAT in presence (or not) of Joncryl. The effects of the reactive agent on the shear and elongation rheology, morphological, and interfacial properties of the blends were systematically investigated. A decrease of the interfacial tension has been also demonstrated according to the deformed drop retraction method (DDRM). Hence, the role of Joncryl as a compatibilizer was highlighted. Consequently, finer morphology of the dispersed phase was obtained. Furthermore, the impact of the two modification routes on the blown film extrusion ability of PLA has been studied. Based on the improved shear and elongational rheological properties, a great enlargement of the blowing processing window of PLA modified with Joncryl was demonstrated. Indeed, with the addition of Joncryl into PLA-PBAT blends, a reduction of the instability defects has been detected. Finally, the induced crystalline structure and the thermo-mechanical properties of blown films were shown to be improved. [ABSTRACT FROM AUTHOR]

Shear step strain experiments with various strain amplitudes have been performed on poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) melts using both stress-controlled and strain-controlled rheometers. Firstly, the onset of the rheological nonlinearity, i.e., nonlinear stress damping behavior, occurring after a large step strain is found to be a phenomenological consequence of an abrupt stress decline within the transient period of strain actuation. Such a feature, analogous to the stress overshoot in a fast startup shear with sufficiently high rates, is interpreted based on theoretical frameworks concerning chain disentanglement/re-entanglement arising from chain retraction. Furthermore, this work infers that full technical considerations in step strain experiments are indispensable for acquisition of accurate stress relaxation data, as some common but easily overlooked technical problems are influential, probably introducing errors. For instance, a too long finite rise time and a stress overload enable to hinder the nonlinearity onset in the transient period, resulting in inaccurate experimental data. In this sense, the stress-controlled rheometer is advantageous relative to the strain-controlled one, although the inertia in the stress-controlled mode incurs a strain overshoot effect. Nevertheless, the amplitude-dependent strain overshoot offers a very subtle effect on the stress damping behavior. Moreover, transducer compliance problems need to be taken into account, especially for high stiffness polymers. Overall, the effects of such technical factors are dictated by their ability to influence the chain stretching/retraction and the disentanglement. A well-considered experimental methodology is necessary to achieve confidence windows in step strain experiments for analysis accuracy. [ABSTRACT FROM AUTHOR]

Interfacial rheology has become a powerful tool to study the viscoelastic properties of interfaces in several multiphase polymer-based systems such as multilayer liquids containing surfactants, proteins or solid particles, and also in polymer blends, 3D printed multimaterials and coextruded multilayer films. During all these manufacturing processes, the elongational flow at interface is predominant. Nevertheless, direct interfacial rheological measurements in extension devoted to such polymer systems are not plentiful and are often based on indirect modelling methods. In the present work, interfacial dilational rheology testing based on the rising oscillating drop method was used to probe surface (and interfacial) properties of model Newtonian polymer melts: polydimethylsiloxane (PDMS)/polyisobutylene (PIB) systems. The interfacial properties in both oscillatory and static drop experiments were carefully corrected, considering the inertia and the contribution of the coexisting phase viscosities during the processing of the numerical data. The influence of molecular weight and temperature on the interfacial rheological responses was particularly examined. A new approach was developed to determine the dilational relaxation times (τ) of the studied polymer systems using a square pulse relaxation test. It was found that the evolution of τ with the temperature followed an Arrhenius behaviour. A comparison with capillary breakup extensional rheometry revealed similar overall values to those obtained with the pulse method. Finally, using interfacial shear rheology, we focused on the Trouton correlation between shear and dilational surface rheology, and a direct link between shear surface viscosities and elongational relaxation times was evidenced for the first time and over the entire viscosity range studied. [ABSTRACT FROM AUTHOR]

The study of the viscoelastic properties of polymer systems containing huge internal two-dimensional interfacial areas, such as blends, foams and multilayer films, is of growing interest and plays a significant role in a variety of industrial fields. Hence, interfacial rheology can represent a powerful tool to directly investigate these complex polymer–polymer interfaces. First, the current review summarizes the theoretical basics and fundamentals of interfacial shear rheology. Particular attention has been devoted to the double-wall ring (DWR), bicone, Du Noüy ring and oscillating needle (ISR) systems. The measurement of surface and interfacial rheological properties requires a consideration of the relative contributions of the surface stress arising from the bulk sub-phases. Here, the experimental procedures and methodologies used to correct the numerical data are described considering the viscoelastic nature of the interface. Second, the interfacial dilational rheology is discussed, starting with the theory and underlying principles. In particular, the Langmuir trough method, the oscillating spinning drop technique and the oscillating pendant drop technique are investigated. The major pioneering studies and latest innovations dedicated to interfacial rheology in both shear and dilatation–compression are highlighted. Finally, the major challenges and limits related to the development of high-temperature interfacial rheology at the molten state are presented. The latter shows great potential for assessing the interfaces of polymer systems encountered in many high-value applications. [ABSTRACT FROM AUTHOR]

The aim of this work was to highlight the presence of long chain branching, LCB, due to the incorporation of a multifunctional epoxide, named Joncryl ®, as a chain extender, into both poly (lactic acid) (PLA) and poly (butylene-adipate-co-terephtalate) (PBAT) polymers. The modified polymers were prepared using a twin-screw reactive extrusion system. It has been demonstrated through this study that these modified biopolymers are thermo-rheologically complex. This complexity may be attributed to the formation of covalent bonds between both polymer and chain extender and leads to a failure of the time-temperature superposition (TTS). The linear viscoelastic properties were predicated on the use of the so-called Van-Gurp-Palmen plots, from which the topology of the modified PLA and PBAT has been studied and analyzed. Indeed, they exhibited a typical feature of a mixture of linear and randomly branched polymers. Furthermore, the resulting linear and branched chains, due to the reactive highly functionalized epoxide, are discussed using rheological investigations (relaxation spectra, flow activation energy) coupled with solution viscometry (solution viscometry properties, hydrodynamic radius) and physico-chemical properties (size-exclusion chromatography). [ABSTRACT FROM AUTHOR]

The focus of this paper was to gain a true understanding of the impact of a multifunctional epoxide (Joncryl®;ADR-4368) on the interfacial properties of biopolymer blends based on poly(lactic acid) (PLA) and poly(butylene adipate- co-terephthalate) (PBAT). The effect of Joncryl on the shear rheological, morphological, and interfacial properties of the blends was systematically investigated. For the deformed drop retraction experiments, different sandwich model systems (droplet/matrix), representing various scenarios of compatibilization, were prepared, aiming to probe the role of the epoxy-functionalized chains on the interface. The decrease of the interfacial tension in the modified/compatibilized PLA_PBAT and the formation of the PLA-Joncryl-PBAT copolymer were highlighted. A new relaxation peak relative to this copolymer was detected by the relaxation spectrum. Transient start-up shear and nonlinear stress relaxation experiments were carried out and confirmed the obtained results. In addition, the interface contribution was demonstrated using the Lee and Park model. The relaxation time increased with the amount of added Joncryl. Hence, the coexistence of chain extension/branching chains coupled to the PLA-Joncryl-PBAT copolymer formation had to be taken into account to explain the improved mechanical properties. [ABSTRACT FROM AUTHOR]

The mutual diffusion process and interphase developmenttaking place at an asymmetrical polymer–polymer interface betweentwo compatible model polymers, poly(methyl methacrylate) (PMMA) withvarying molecular weights and poly(vinylidene fluoride) (PVDF) inthe molten state, were investigated by small-amplitude oscillatoryshear measurements. The rheology method, Lodge–McLeish model,and test of the time–temperature superpositon (tTS) principlewere employed to probe the thermorheological complexity of this polymercouple. The monomeric friction coefficient of each species in theblend has been examined to vary with composition and temperature andto be close in the present experimental conditions, and the failureof the tTS principle was demonstrated to be subtle. These were attributedto the presence of strong enthalpic interaction between PMMA and PVDFchains that couples the component dynamics. Hence, a quantitativerheological model modified from a primitive Qiu–Bousmina’smodel that connected the mobility in the mixed state to the propertiesof the matrix was proposed to determine the mutual diffusion coefficient(Dm). The modified model takes into accountthe rheological behavior of the interphase for the first time. Inturn, viscoelastic properties and thicknesss of the interphase havebeen able to be quantified on the basis of the modified model. Effectsof the annealing factors like welding time, angular frequency, temperature,and the structural properties as well molecular weight and Flory–Hugginsparameter (χ) on the kinetics of diffusion and the interphasethickness and its viscoelastic properties were investigated. On onehand, Dmwas observed to decrease withfrequency until leveling off at the terimnal zone, to depend on temperatureobeying the Arrhenius law, and to be nearly independent of PMMA molarmass, corroborating the prediction of the fast-mode theory. On theother hand, the generated interphase which reached dozens of micrometerswas revealed to own a rheological property approaching its equivalentblend. Scanning electron microscopy coupled with energy dispersiveX-ray analysis (SEM-EDX) and transmission electron microscopy(TEM)were also carried out and confronted to the rheological results. Comparisonsbetween mathematical modeling of concentration profile based on the Dmobtained from rheology and the experimentalones of SEM-EDX and TEM were conducted. Thus, a better correlationbetween theory and experimental results in terms of mutual diffusionand the interphase properties was nicely attained. The obtained dataare in good agreement with literatures using other spectroscopicalmethods. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study has been to gain a fundamental understanding of the mechanisms and conditions governing thermal degradation of poly (lactic acid) (PLA), poly (butylene-adipate-co-terephtalate) (PBAT) and their blends upon processing conditions. Thermal degradation of biodegradable PLA and PBAT was investigated firstly by thermal analysis and size-exclusion chromatography (SEC). It is shown that neat polymers degrade upon processing hence the decrease of the molecular weight, rheological and mechanical properties. Secondly, the reactive extrusion of polymers was performed with various amounts of chain extension/branching agent, containing nine Glycidyl methacrylate (GMA) functions, named Joncryl. The incorporation of this multi-functional oligomer showed an improvement of their thermal stability. SEC and intrinsic viscosity measurements of these modified PLA and PBAT confirmed the increase of viscosity and molecular weight probably related to the formation of extended and branched chains. Rheological investigation of extended/branched PLA and PBAT as well as their modified PLA/PBAT (80/20) (wt/wt) blends with various concentrations of GMA reactive functions exhibited higher viscosity and storage modulus compared to the unmodified samples. This increase becomes more pronounced as the concentration of Joncryl increases. Viscoelastic properties were assessed and related to the molecular structure of modified polymers. Hence, the mechanisms of degradation, chain extending with GMA functions and their competition have been proposed. The effect of reactive compatibilization on the PLA/PBAT blends has been confirmed using transmission electron microscopy (TEM), scanning electron microscopy (SEM) observations and tensile tests by the improvement of phase dispersion and the increase of both Young''s modulus and strain at break. [Copyright &y& Elsevier]

The diffusion process in the molten state at a polymer/polymer interface of symmetrical and model bilayers has been investigated using a small-amplitude oscillatory shear measurement. The polymers employed in this study were poly (vinylidene fluoride) (PVDF) and poly (methyl methacrylate) (PMMA) of varying molecular weights and polydispersities. The measurements were conducted in the linear viscoelastic regime (small deformations) so as to decouple the effect of flow from the diffusion. The focus of this paper has been to investigate the effects of healing time, angular frequency ( ω), temperature, and molecular weight on the inter-diffusion and the triggered interphase between the neighboring layers. The kinetics of diffusion, based on the evolution of the apparent diffusion coefficient ( D) versus the healing time, was experimentally obtained. The transition from the non-Fickian to the normal Fickian region for the inter-diffusion at the interface was clearly observed, qualitatively consistent with the reptation model, but it occurred at a critical time greater than the reptation time ( τ). In non-Fickian region, effects of frequency and temperature were studied with regard to the ratio of the apparent diffusion coefficient to the self-diffusion coefficient ( D/ D). The D determined in the Fickian region was found to be consistent with Graessley's model as well as with the literatures. And the dependence of the D on the frequency agreed well with the Doi-Edwards theory, in particular, scaling as $D_{\rm s} \sim \omega^{1/2}$ at ω > 1/ τ and $D_{\rm s} \sim \omega^{0}$ at ω < 1/ τ. Our experimental results also confirmed that the dependence of the D on the temperature for PMMA and PVDF can be well described by the Arrhenius law. Moreover, blends of PMMAs have been proposed in order to be able to change the $\overline M_\emph{w} $. The rheological investigations of these corresponding bilayers rendered it possible to monitor the effect of $\overline M_\emph{w} $ on the diffusion process. The obtained results gave $D_{\rm s} \sim \overline M_\emph{w}^{-1}$, thus corroborating some earlier studies and some experimental results recently reported by Time-Resolved Neutron Reflectivity Measurements. Lastly, the thickness of the interphase and its corresponding viscoelastic properties could be theoretically determined as a function of the healing time. [ABSTRACT FROM AUTHOR]

The aim of the present work is to examine the effect of the rheological behaviour and surface properties on the sintering of various polymers. Model polymers, liquid at room temperature and commercials materials with different viscosities and structures are used. Zero-shear viscosities and relaxation times are extracted from rheological curves. The surface tension of the materials is measured by the sessile drop method when possible. The sintering of two particles put in close vicinity is recorded using a CCD camera at regular intervals time. Two substrates with different surface tension are employed. The effects of viscosity, surface tension and relaxation time on the sintering kinetics are discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the experimental investigation of the interdiffusion/reaction mechanisms of asymmetric polymer–polymer interfaces. The study deals with the assessment of the chemical reactions occurring at the interface between two reactive polymers. A focal point of the investigation was to study these interfacial reactions by an array of techniques at very different space scales: from macroscopic viscoelastic investigations to IR and NMR spectroscopies at the molecular scale. The studied material pairs include PE-GMA/PA6 as the reactive system (RS) and PE/PA6 as the non-reactive one (NRS) – of coextruded multilayer polymers, i.e., after processing. The linear viscoelastic properties of the reactive multilayer systems were determined and the mechanisms were analyzed by NMR and FTIR measurements. Substantial reactions occurred during the rheological measurements and the results indicated the preferential formation of a copolymer at the interface, triggered by the neighboring layers. Moreover, the contribution of an interface/interphase effect was investigated along with the increase in the number of layers. The results showed that the variation in dynamic modulus of the multilayer system was a result of both diffusion and chemical reaction. Specific experiments were carried out to follow-up on the physicochemical phenomena, and the results were rationalized by comparing the obtained data with theoretical models. The effect of this interphase was quantified at a specific welding time and oscillation frequency thanks to rheological modeling. Because of the coupling between rheology and spectroscopical tools, potential reactions between the GMA functions and the amine/carboxylic polyamide chain ends were explored. The results highlighted that the main reaction mechanism was constituted by the crosslinking reaction between the GMA and carboxylic acid units, and not by that between GMA and amine end functions. [Copyright &y& Elsevier]

To increase the lifetime of metallic molds and protect their surface from wear, a fluorinated ethylene propylene (FEP) polymer was coated onto a stainless-steel (SS304) substrate, using an air spray process followed by a heat treatment. The microstructural properties of the coating were studied using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) as well as X-ray diffraction. The mechanical properties and adhesion behavior were analyzed via a nanoindentation test and progressive scratching. According to the results, the FEP coating had a smooth and dense microstructure. The mechanical properties of the coatings, i.e., the hardness and Young's modulus, were 57 ± 2.35 and 1.56 ± 0.07 GPa, respectively. During scratching, successive delamination stages (initiation, expansion, and propagation) were noticed, and the measured critical loads LC1 (3.36 N), LC2 (6.2 N), and LC3 (7.6 N) indicated a high adhesion of the FEP coating to SS304. The detailed wear behavior and related damage mechanisms of the FEP coating were investigated employing a multi-pass scratch test and SEM in various sliding conditions. It was found that the wear volume increased with an increase in applied load and sliding velocity. Moreover, the FEP coating revealed a low friction coefficient (around 0.13) and a low wear coefficient (3.1 × 10−4 mm3 N m−1). The investigation of the damage mechanisms of the FEP coating showed a viscoelastic plastic deformation related to FEP ductility. Finally, the coating's resistance to corrosion was examined using electrochemical measurements in a 3.5 wt% NaCl solution. The coating was found to provide satisfactory corrosion protection to the SS304 substrate, as no corrosion was observed after 60 days of immersion. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of the coefficient of thermal expansion (CTE) of a thermosetting polymer during cure reaction is an important parameter for industrial applications such as composite processing since it influences the development of internal stresses in the material. The CTE being almost impossible to measure on a reacting thermoset, we propose to use an indirect method based on the modelling of ionic conductivity by a modified WLF equation, allowing to calculate the evolution of CTE from dielectric spectroscopy measurements. This method is applied to a dicyanate ester thermosetting polymer, leading to encouraging results both qualitatively and quantitatively. [Copyright &y& Elsevier]

In a previous paper, the kinetic behavior of a cyanate ester trimerization was studied. In this paper, the thermophysical properties (heat capacity, thermal conductivity) are measured and modeled (as a function of temperature and conversion) for the neat resin and for a glass fibers composite. These models (thermophysical and kinetics) are used to simulate the thermal transfers in an instrumented heated mold. The calculated local temperatures and surface heat fluxes appear to be in very good agreement with measurements, for both the neat resin and the composite. [Copyright &y& Elsevier]

The multilayer coextrusion process is known to be a reliable technique for the continuous fabrication of high-performance micro-/nanolayered polymeric products. Using laminar flow conditions to combine polymer pairs, one can produce multilayer films and composites with a large number of interfaces at the polymer-polymer boundary. Interfacial phenomena, including interlayer diffusion, interlayer reaction, interfacial instabilities, and interfacial geometrical confinement, are always present during multilayer coextrusion depending on the processed polymers. They are critical in defining the microstructural development and resulting macroscopic properties of multilayered products. This paper, therefore, presents a comprehensive review of these interfacial phenomena and illustrates systematically how these phenomena develop and influence the resulting physicochemical properties. This review will promote the understanding of interfacial evolution in the micro-/nanolayer coextrusion process while enabling the better control of the microstructure and end use properties. [ABSTRACT FROM AUTHOR]

This paper is dealing with the polyisobutylene (PIB) migration phenomenon through the post-consumer agricultural waste multilayer films based on four linear low-density polyethylene (LLDPE) matrices. Through this work, a bridge between shear, elongational rheology, and tack surface properties was revealed on both model and recycled blends. Hereto, effects of aging time and temperature were investigated and rationalized depending on the short- and long-chain branching in LLDPE matrices as well their polyethylene (PE) crystallization. The linear viscoelastic properties were influenced despite the small PIB amounts. This migration influenced also the slippage in steady flow regime. It was also demonstrated that transient uniaxial extensional properties are very sensitive in the presence of PIB, which seems to hold back the PE strain hardening properties. Therefore, the axial force and the surface friction coefficient were determined and discussed in correlation with bulk rheological findings. Hence, the obtained results contributed to unveiling new insights on the physical mechanisms governing the PIB migration with or without fillers to inhibit its migration in their recycled films. [ABSTRACT FROM AUTHOR]

Multilayered polymer films are increasingly used in the daily life, but their macroscopic properties are always limited by the layer–layer interfacial compatibility. In this work, the influence of interface modification through in situ layer–layer interfacial reaction during a multilayered assembly is revealed from micro‐ to nanolayer films, based on maleated poly(vinylidene fluoride) and polyamide‐6. In the presence of interfacial reaction and confinement, layer architecture and microstructure are highly dependent on the number of layers. Specifically, for nanolayer films having smaller layer thicknesses and higher reaction extent, layer integrity is reduced with the occurrence of interfacial instabilities. Depending on the microstructural evolution from multilayer assembly, those films exhibit quantitatively different extensional rheological and dielectric properties from micro‐ to nanolayers. More importantly, dielectric spectroscopy reveals the contribution of copolymer‐rich interphases to the dielectric performance of micro/nanolayered films. Additionally, charge transport dynamics in nanolayered films also differ significantly from their microlayered counterparts. They are attributed to the strong dependence of interfacial reaction extent and resulting microstructure on the number of layers and layer thicknesses. This work clearly illustrates how the control of layer–layer interfacial reaction in micro/nanolayer assembly can tune the interfacial, microstructure, and macroscopic properties of multilayered products. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flexible polymer PENGs were prepared with interface-engineered PVDF/CNTs nanofibers. • PVDF- g -MA stabilized electrospinning flow to yield defect-free composite nanofibers. • Interfacial anchoring of PVDF- g -MA promoted electroactive β -phase in PVDF matrix. • A small amount of PVDF- g -MA boosted piezoelectric outputs (10.6 V, 3.15 µW/cm2) • Our strategy enhanced PENG with preserved flexibility avoiding excessive filler use. Polymeric piezoelectric nanogenerators (PENGs) hold great promise for flexible energy harvesters and self-powered sensors. However, achieving high piezoelectricity in inherently piezoelectric polymers while maintaining their flexibility remains a challenge. Herein, we propose a simple yet effective approach to fabricate flexible and cost-effective PENGs based on interface-engineered composite nanofibers of poly(vinylidene fluoride) (PVDF)/carbon nanotubes (CNTs) using electrospinning. Our strategy involves the incorporation of a tailor-made interfacial coupling agent, maleic anhydride grafted PVDF (PVDF- g -MA), onto PVDF/CNTs interfaces. This mild interface-engineering strategy not only promotes interfacial interactions within composites but also stabilizes electrospinning flow jets, yielding defect-free nanofibers. More importantly, the interfacial anchoring of PVDF- g -MA molecules promotes the preferential crystallization of electroactive β -phase within PVDF matrix. By incorporating a small quantity of PVDF- g -MA (up to 1.0 wt%), our approach significantly enhances piezoelectric outputs while preserving flexibility. This eliminates the need for excessive nanofiller usage that can sacrifice the flexibility associated with conventional methods. Remarkably, the resulting composite nanofiber-based PENGs exhibit excellent piezoelectric performance, generating high output voltages (10.6 V) and remarkable power density (3.15 µW/cm2) under tiny force stimuli. Our findings open new avenues for efficient and scalable fabrication of polymeric piezoelectric nanogenerators for flexible and wearable energy harvesting and self-powered sensing applications. [ABSTRACT FROM AUTHOR]

A new valorization strategy for Olive Solid Waste (OSW) has been carried out consisting in incorporating this biomass as filler in a biopolymer matrix. In this study, biocomposites based on poly( d, l‐lactide) (PLA) and OSW fillers were prepared with various filler contents. It was highlighted that the inclusion of OSW under high temperatures resulted in the degradation of the matrix leading to a reduction of the viscoelastic properties and molar masses. Nevertheless, it was shown that this degradation of PLA matrix could be attenuated through two approaches. The first was chemical and consisted in using a chain extender agent named Joncryl, containing glycidyl methacrylate (GMA) functions. The second route was physical and involved coating the OSW with the hydrophobic biopolymer poly(ε‐caprolactone) followed by mixing with PLA. Meanwhile, the effect of the OSW with and without Joncryl on the thermal stability, the melt and crystallization properties was assessed. Furthermore, the rheological properties of the controlled systems PLA/OSW/Joncryl and/or PLA/(OSW) coated with PCL were investigated in the molten state. The improvement of the shear viscoelastic properties corroborated the measured molar masses. The physicochemical matrix/filler interactions had to be taken into account to explain the improved rheological, morphological and tensile mechanical properties. POLYM. COMPOS., 39:E152–E163, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract: The TEMPO-mediated oxidation of date palm lignocellulosic fibers (DPLF) from Phoenix dactylifera – i.e. cellulosic fibers still containing their initial lignin and hemicellulose components – was performed under conditions leading to a high degree of oxidation. The resulting carboxylated fibers were shown to still contain high residual contents of lignin (12%, w/w) and hemicelluloses (34%, w/w). The ultrastructure of the oxidized DPLF was revealed by scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy. These techniques not only confirmed the surface carboxylation of the DPLF, but also gave some insight on the oxidation heterogeneity when going from the surface to the core of the fibers. Finally, in relation with the chemical data and the morphology of the substrate, it has been possible to propose a heterogeneous oxidation kinetic model, which was applied with success not only to DPLF but also to the cellulose whiskers extracted from the rachis of the palm from P. dactylifera. [Copyright &y& Elsevier]

Poly (lactic acid) is an industrially mature, bio-sourced and biodegradable polymer. However, current applications of this eco-friendly material are limited as a result of its brittleness and its poorly melt properties. One of the keys to extend its processing window is to melt strengthen the native material. This paper considers the chain extension as a valuable solution for reaching such an objective. An additive based on epoxy-functionalized PLA was employed during reactive extrusion. The reaction times as a function of chain extender ratios were determined by monitoring the melt pressure during recirculating micro-extrusions. Once residence times were optimized, reactive extrusion experiments were performed on a twin screw extruder. Size exclusion chromatography provided information about the molecular weight distributions (MWD) of the modified PLAs and revealed the creation of a high molecular weight shoulder. The rheological experiments highlighted the enhancement of the melt properties brought about by the chain extension. Shear rheology revealed some enlarged and bimodal relaxation time spectra for the extended materials which are in accordance with the MWD analysis. Such a modification directly amplified the shear sensitivity of modified PLAs. Regarding the rheological temperature sensitivity, it was found to be decreased when the chain extender content is raised as shown from the Arrhenius viscosity fit. The reduction of the polar interactions from neat to highly chain-extended PLAs is here proposed to explain this surprising result. Chain extension was also found to impact on the elongational melt properties where strain hardening occurred for modified PLAs. Investigation of the chain extension architecture was made from the rheological data and revealed a long-chain branched topology for the modified PLAs. [ABSTRACT FROM AUTHOR]

At the present time, the rheology of sheet moulding compounds (SMC) during forming is not well known. In order to provide better experimental data, an experimental program was carried out as a result of the development of a new rheometer especially dedicated to this kind of material. Homogeneous simple compression and simple shear tests are presented. They allow the evaluation of the influence of the main parameters on the SMC behaviour: strain rate, temperature and fibre fraction. It is shown that the SMC can be considered as a strongly anisotropic non-linear viscous medium. [Copyright &y& Elsevier]