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The gel time during geopolymerization of blends of metakaolins having various compositions and at different temperatures was predicted owing to a kinetic analysis using oscillatory shear measurements and a reaction time-temperature superposition.

Starch and cellulose being both carbohydrate polymers, thermoplastic starch (TPS) is expected to be a suitable compatibilizer for materials made of cellulosic fillers and polyesters. This paper investigates the interactions between TPS and cellulose in Poly(butylene adipate-co-terephthalate) (PBAT), melt-blended composites. For this, microfibrillated cellulose (MFC) were dispersed in a commercially available polymer (Mater-Bi, MB), containing TPS already dispersed in PBAT. Microscopic observations were performed on composites based on either MB or neat PBAT reinforced with microfibrillated cellulose (MFC). Tensile tests and dynamic mechanical analysis in solid and in the molten state revealed a percolating network of fillers. Results indicated interaction between TPS and cellulose as the origin of the adhesion of the components but also of biphasic agglomerates.

Dispersion in the melt is a very serious issue that affects properties of composites based on cellulosic fillers as these materials tend to form agglomerates. The aim of this study is to test the efficiency of various methods to improve the dispersion of cellulosic fillers in PBAT polymer. First, periodate oxidation treatment was carried out on the fillers in an attempt to reduce the amount of hydroxyl groups responsible of the agglomeration of cellulosic fillers in composite materials. Secondly, as several studies have demonstrated the positive effect of using tert-butanol (TB) as a freeze-drying medium for preventing the aggregation of cellulosic particles, this method was tested to produce composites with reduced amount of agglomerates. Finally, the addition of a third component as a compatibilizer which has a similar chemical structure to cellulose such as starch was also tested. No significant improvement of mechanical properties was noticed in using TB as a freeze-drying medium or with periodate oxidation treatment on the cellulosic fillers at least in improving dispersion in PBAT composites. However, the addition of starch as a compatibilizer has proved its effectiveness through the creation of a percolating network and a better dispersion of the fillers in the polymer matrix.

L'article donne un panorama des connaissances sur le comportement viscoelastique non lineaire des polymeres fondus plus particulierement en cisaillement et en elongation uniaxiale. Les rheometres utilises pour caracteriser la viscoelasticite non lineaire sont presentes ainsi que les fonctions rheologiques les plus communement utilisees et leur lien avec la structure des polymeres. Des exemples d'applications au choix des materiaux pour les procedes de mise en oeuvre des matieres plastiques sont donnes. Enfin une introduction aux concepts, qui sont a l'origine des modeles et des equations constitutives utilisees pour la simulation numerique des ecoulements des polymeres fondus, est proposee.

To develop a new solventless and environment-friendly processing method for large-scale production of organic photovoltaic cells, the processability by extrusion of two photoactive polymers was studied. Poly(3-octylthiophene) was chosen as donor polymer and polystyrene grafted by fullerene C60 as acceptor polymer. In the molten state, poly(3-octylthiophene) exhibits a similar behavior to that of typical flexible polymers and then could be processed by extrusion at temperatures above 180 °C. An appropriate range of grafted C60 (from 4 to 12 vol%) has been determined in previous works from functional properties, thermal behavior and morphology observations displayed by a series of polystyrenes grafted by various fullerene C60 contents. The rheological properties (storage and loss moduli, melt viscosity) of the synthesized C60 grafted polystyrenes series are investigated. Two successive transitions in the viscosity are observed at 3–4 and 12–13 vol% of grafted C60, related to the percolation of C60 molecules and to the formation, growth and percolation of C60 aggregates, respectively. For extrusion compatibility with poly(3-octylthiophene), the optimal content of grafted C60 ranges from 7 to 12 vol% according to the rheological behavior. Thus, the processing of donor/acceptor heterojunctions by extrusion could now be considered to produce active layers of photovoltaic organic solar cells.

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The viscoelastic behaviour of cellulose acetate with a degree of substitution (DS) of 245 plasticized by triacetin was studied at short times by dynamic oscillatory measurements. Two distinct regimes and unexpected scaling behaviour according to plasticizer content were highlighted. The dynamics of chains and their structural organization are not modified up to 35 wt% of triacetin. The rheological behaviour is led by a constant correlation length corresponding to the distance between strong intermolecular interactions subsisting in the melt state at high temperature even in the presence of plasticizer. This particular structure involves the apparition of strain hardening effects during uniaxial extensional flow tests and an important elasticity corresponding to the apparition of a Weissenberg effect at really low shear rates during shear sweeps. Intramolecular hydrogen bonds are responsible of the high rigidity of cellulose acetate chains. Plasticized cellulose acetate in the melt state belongs to the class of associating polymers and its rheological behaviour is mainly led by stickers.

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International audience; This work analyzes the dispersion conditions of polar liquids with low viscosities into polymer melts. For this purpose, the curve of the critical capillary number in shear as a function of the viscosity ratio for low viscosity liquids dispersed into polymer melts was built. To obtain this curve, the disperse phase and matrix were chosen to have large polarity and viscosity differences (viscosity ratio between 10(-7) and 10(-2)). To this end, polyethylene glycols with various molecular weights, ethylene glycol, glycerol or water were mixed with olefinic copolymers in an internal mixer assumed to generate mostly shear. Concentrations of dispersed phase were low enough to prevent coalescence. In combination with viscosity data and measured interfacial tension, the critical capillary number was calculated from the droplet size in equilibrium conditions and the variation with viscosity ratio was compared with theoretical equations from the literature.

International audience; A series of branched poly(butylene succinate) (PBS) were synthesized with several branching agents namely trimethylol propane (TMP), malic acid, trimesic acid, citric acid and glycerol propoxylate. The structure of the branched polymers was analyzed by SEC and H-1-NMR. The effect of branching agent structure on crystallization was also investigated and played a significant role. Isothermal studies showed that glycerol propoxylate could act as a nucleating agent. By contrast high content of TMP disturbed the regularity of the chain and hindered the crystallization of PBS. From the non-isothermal kinetic study, it was found that glycerol propoxylate increased noticeably the crystallization rate due to the flexible structure of the branching agent. A secondary nucleation was observed with glycerol propoxylate attributed to the crystallization of amorphous fraction included between crystallites formed at the primary crystallization. Chain topology was obtained through rheological investigations and the synthesized polymers showed a typical behavior of a mixture of linear and randomly branched PBS. The incorporation of branches improved the processability of PBS for film blowing application and the modulus and the stress at break of the resulting film were significantly increased.

This paper focuses on the prediction of Young's modulus and impact strength of immiscible polyethylene/polypropylene blends, prepared in the melt, on the whole composition range, starting from the composition, interfacial tension, rheological properties and processing conditions. For this, the model proposed by Veenstra and a tentative model relating respectively the modulus and the impact strength to the composition were used. They were combined with a micro-rheological model developed previously to predict the limits of dispersed phase and co-continuous morphologies, and the characteristic sizes of the phase. The predictions were compared with experimental data for blends of isotactic and syndiotactic polypropylenes and low- and high-density polyethylenes originating from different polymerization process, especially regarding the catalyst systems. The effect of the catalyst systems and the type of morphology on the properties were analyzed, showing better properties for blends of metallocene polyolefins in comparison to those obtained using Ziegler-Natta catalysts.

This paper presents a micro-rheological model to predict the morphology of immiscible polymer blends, established during melt processing, on the whole composition range. This model based on elementary mechanisms of dispersion described in the literature, uses two different descriptions of the topology in the case of dispersed and co-continuous phases. By using a small number of material and process parameters (shear rate, viscosity of the phases and interfacial tension) and by analysing the stability of the droplets or threads of one phase in the matrix, it enables to calculate diagrams of continuity, sizes of phases and interfacial areas. The model was tested in comparison with experimental results on selected polyolefin blends, regarding the type of morphology, the interfacial area and the excess of elasticity at low frequency in oscillatory shear.

The effect of the melt viscosity and operating conditions on processing parameters in a co-kneader with a discharge die was experimentally investigated. Filling ratio, pressure, temperature, and residence time distribution were measured. Experiments were performed with polypropylene resins. The viscosity of the melt was varied either by changing the regulation temperature of the kneader or the molecular weight of the polymer. The filling pattern in the co-kneader shows the conveying capability of the various elements without any effect of the melt viscosity. Experimental residence time distributions remain the same at a given feed rate and screw speed, regardless of the viscosity of the material. The global degree of filling in a zone combining conveying elements, kneading elements, and restriction ring was found to be nearly constant in the conditions of this study and therefore a simple relation exists between the mean residence time and the feed rate. Beside expected variations of the die pressure and melt temperature when the viscosity, screw speed or feed rates change, a model based on heat equation and experimental data demonstrate the high capability of the co-kneader for heat exchange and for the control of self-heating during mixing. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

International audience; This paper investigates the decomposition kinetics of citric acid, sodium bicarbonate and their combinations in masterbatches with low density polyethylene in view of their use in injection molding with simultaneous polymer foaming. The thermal decomposition was studied by isothermal and non-isothermal calorimetry to separate the various chemical events. A multi-step autocatalytic model was used to determine the kinetic parameters. Results show that for sodium bicarbonate compounds, the kinetics can be modeled by first-order equations while for citric acid compounds it shows two steps of decomposition due to reaction intermediates. The parameters obtained for the mono-component masterbatches can be used to model the kinetics of compounds containing a mix of sodium bicarbonate and citric acid with the same multi-step coupled equations. Experiments and modelisation show that the reaction in the masterbatch proceeds in well separated steps corresponding to each species. In particular, at high heating rates such as those encountered during melting in the injection molding machine, the citric acid decomposition occurs in a single step making the analysis of the kinetics and the modelling of the overall foaming process more simple.

This paper investigates the viscoelastic behavior in the melt of biocomposites of Alfa fibers dispersed in a polyester-starch bioplastic of the Mater-Bi® type. Biocomposites with three kinds of short Alfa fibers (untreated or treated with alkali solutions at 1% or 5%) and at various filler contents were prepared by means of twin screw extrusion. The rheological properties of such biocomposites have been studied in oscillatory shear at 140, 160 and 180 °C at frequencies varying from 100 to 0.01 rad/s in the viscoelastic linear domain. The influence of fiber loading, alkali treatment of fibers, and temperature on the viscoelasticity of biocomposites was examined. Dynamic moduli increase with increasing fibers content. In addition, biocomposites exhibit a plateau of the storage moduli at low frequencies, indicating a percolated fibers network. This low frequency elastic behavior is enhanced by the treatment of the fibers. The ratio of storage modulus of biocomposites to that of the neat matrix at low and high frequency is used to characterize the influence of the fiber content and of the concentration of alkali treatment of Alfa fibers on both percolation and hydrodynamic effects. This made it possible to sense the effect of these parameters on the dispersion process of Alfa fibers in the biopolymer matrix.

The morphology development of blends of plasticized polyvinyl butyral (PVB) with plasticized polyvinyl chloride (PVC) is studied to obtain a droplet-in-matrix morphology. Such blends can be used for recycling wastes of plasticized PVB in PVC for flooring because migration of the plasticizer of PVB towards the surface is reduced. Model systems of PVC plasticized with diisodecyl phthalate (DIDP) and of PVB plasticized with dibutyl sebecate (DBS) are used as representatives of common compositions. The percolation threshold of the PVB phase occurs at 22 vol% of plasticized PVB. The morphology results of an equilibrium between break-up and coalescence. The dependence of the characteristic dimension upon the volume fraction is described by a power-law with exponent 1.5 slightly larger than the theoretical value.

International audience; Relationships for the prediction of various linear mechanical properties of polymeric sandwich foams obtained in injection processes were studied in comparison with shear, tensile, and flexural tests. The samples were obtained by a core-back foam injection molding process that enables one to obtain sandwich materials with dense skins and a foamed core as revealed by the morphological analysis. Tensile, shear, and flexural moduli were investigated for the skin, the core, and the overall foamed structure. In addition, the Poisson’s ratio of the skin was also determined. The core properties were specifically analyzed by machining the samples and removing the skins. Tensile and shear properties of the core can be well described by the Moore equation. The tensile modulus can be calculated by a linear mixing rule with the moduli of the skin and of the core in relation to the thickness of the layers. Shear and flexural moduli are described by a linear mixing rule on the rigidity in agreement with the mechanics of beams. Tensile modulus, out-of-plane shear modulus, and flexural modulus can finally be predicted by the knowledge of only very few data, namely the tensile modulus and Poisson’s ratio of the matrix, the void fraction, and thickness of the core. The equations were proved to be physically meaningful and consistent with each other.

International audience; The study of agglomerates of magnesiumhydroxide badly dispersed in an olefinic polymer by means of oscillatory shear flow in the melt indicates that the agglomerates behave as a distinct phase. Optical and rheo-optical measurements carried out on these agglomerates also show that they are wetted by the melt and that they can be easily deformed under shear. However, the relaxation of shape in oscillatory shear is also the trace of the existence of an effective interfacial tension between the agglomerates containing high amounts of filler and the polymer matrix. The analogy with the behavior of polymer blends and the modeling by the Palierne model enables the calculation of such an interfacial tension. The surface free energy of magnesiumhydroxide that can be calculated from this result by a simple mixing law is 95 mN m−1. This value is compared with data from the literature on brucite and similar minerals.

International audience; The dispersion of Mg(OH)2 agglomerates at low concentration in a polymer melt was investigated in a transparent counter-rotating shear cell. The influence of the viscosity of the matrix, the initial agglomerate size and the infiltration of the matrix was evaluated. Mg(OH)2 agglomerates have a low cohesion and a fractal structure. Two dispersive mechanisms already mentioned in the literature were identified: erosion and rupture. Critical conditions for rupture were measured and particle size analysis was performed in order to determine the kinetics of erosion. The infiltration of the matrix, which depends on the viscosity, was found to play a key role on dispersion mechanisms. In contrast to previous works, infiltration is more important with the high viscosity matrix. In infiltrated matrix, rupture was found to occur firstly through plastic deformation of the infiltrated agglomerate, and then the agglomerates split into small fragments. In the low viscosity matrix, fragments produced either by rupture or erosion are small aggregates

This paper considers an improvement of the emulsion models to take into account concentrated emulsions with no coalescence but with significant interaction between particles. For this purpose, a term proportional to the volume fraction of material in excess to the percolation threshold is added to the dynamic modulus. Its usefulness was tested to model the viscoelastic behavior in oscillatory shear flow of concentrated and diluted blends of a thermoplastic polystyrene with an epoxy-amine thermoset. These blends experience phase separation upon polymerization and the volume fraction of separated phase varies continuously with time. At low volume fraction of dispersed phase, the behavior could be described with a simple emulsion model that takes into account the plastisizing, dilution, and phase separation mechanisms. However, for concentration in excess to the percolation threshold, the modification can cope with a larger increase in the modulus related to the mechanical percolation of the dispersed particles.

The evolution of the viscoelastic properties of a molten thermoplastic/thermoset system during the course of the isothermal polymerization of the thermoset precursors has been investigated and modeled. Such systems are initially homogenous and phase separate upon polymerization of the monomers. In the present study, atactic polystyrene (85 and 60 wt%) is blended to a stoichiometric mixture diglycidyl ether of bisphenol A with 4,4′-methylenebis(2,6-diethylaniline). During the polymerization, polystyrene becomes the thermoplastic-rich matrix and an epoxy-rich dispersed phase appears. Both phases experience changes in their composition and viscoelastic properties. A rheokinetic model is proposed to take into account four contributions to the viscoelastic behavior: progressive deplastification of the polystyrene matrix involving a modification of the glass transition and thus of free volume, dilution of the network of entanglements of the matrix by the non yet converted low molar weight molecules, emulsion behavior after the separation of the epoxy-rich phase and finally interparticular interactions being assimilated to a mechanical percolation. Provided that the glass transition temperature of the matrix and the dynamic moduli of the neat components are known, the changes in the viscoelastic behavior of the system with time can be predicted with no ad hoc parameter and model calculations are in good agreement with the experimental data.

This paper deals with immiscible blends of poly(ethylene terephthalate) obtained by melt blending with polycarbonate. A large survey of the current knowledge in the field of these blends is presented. Resolved and unresolved issues concerning the effect of exchange reactions on the miscibility of the components are addressed. The experimental part of the paper focuses on the rheological behavior of PET/PC blends. Blends containing various polymer ratios were obtained by melt blending with and without transesterification catalysts. Oscillatory shear flow in the melt was used to characterize the rheology of the various samples. A plot of the oscillatory data, similar to the Van Gurp Palmen plot, is used to point out the broadening of the co-continuity window when in situ compatibilization takes place.

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International audience; This paper focuses on the analysis of thermal and mechanical properties of novel biocomposites of Alfa fibers dispersed in a bioplastic of the Mater-Bi (R) type in relation with their morphology. These biocomposites obtained by twin screw extrusion were injection molded. Mater-Bi (R) is a commercial biodegradable thermoplastic based on poly(butylene terephthalate-co-butylene adipate) and starch. Raw and alkali treated Alfa fibers were used as reinforcement. Thermal analysis showed significant increase of the crystallization rate with the incorporation of Alfa fibers and enhancement of thermal stability by alkali treatment. Modulus and tensile strength of biocomposites also increased whereas toughness and elongation at break decreased upon increasing the fibers fraction. Scanning electron microscopy (SEM) on fractured surfaces indicated good adhesion between the matrix and the treated or untreated Alfa fibers.

An experimental and theoretical analysis of the polypropylene foaming process using three different chemical blowing agents (CBA) was performed. A simple experiment was designed to analyze the foaming process of polypropylene (PP)/CO2 system under two different pressure conditions. The expansion ratio and final foam structure was measured both by direct observation and from optical measurements and image analysis, showing a good agreement. A single bubble simulation based on relevant differential scanning calorimetry and thermo-gravimetrical analysis experiments, assuming each CBA particles as a nucleation site and accounting for gas diffusion in the surrounding polymer matrix has been built. The sensitivity of the model to physical and processing parameters has been tested. The calculation results are compared to the experiments and open the route to a simplified method for evaluating the efficiency of CBA. POLYM. ENG. SCI., 55:2018–2029, 2015. © 2014 Society of Plastics Engineers

In this article, we have studied the residence time distributions (RTD) in a modular co-kneader. Several papers have already addressed the co-kneader modeling and operating mode but there is still a lack of experimental data on RTD. To investigate the RTD, we have used a colored tracer dispersed in polypropylene (PP) that was injected in the flow during the compounding of neat PP. The effect of operating parameters such as temperature, feed rate, and screw configuration was investigated, focusing on the influence of mixing and conveying elements in a zone where the polymer is molten. As can be expected, results on various screw configurations show that increasing the number of kneading elements makes the RTD longer. More interestingly, for a defined set of elements, their position does not change the experimental RTD. A chemical engineering approach was used to model the RTD, with an equation derived from a cascade of continuous stirred tank reactors. The model allows to retrieve an elementary RTD for each section of a defined type of elements and to propose a law for their combination in good agreement with experiments. POLYM. ENG. SCI., 55:1237–1245, 2015. © 2015 Society of Plastics Engineers

International audience; Alfa stems are rich in cellulose and they are an inexpensive, easily renewable source of natural fibers with the potential for polymer reinforcement. However, large amounts of non-cellulosic materials, surface impurities and low degradation temperature make natural fibers less attractive for reinforcement of polymeric materials, unless they can be modified in a proper way. In this paper, Alfa stems were treated with NaOH solution with two different concentrations (1 and 5 wt%). Raw and treated stems were crushed to obtain fibers. Stems and fibers were characterized by scanning electron microscopy (SEM) and optical microscopy, respectively. Their crystallinity index was determined by X-ray diffraction, thermal stability by thermogravimetry and structural change by FT-IR and C-13 NMR spectroscopy. Comparison and analysis of results confirmed some thermal, structural and morphological changes of the fibers after treatment due to removal of some non-crystalline constituents from the plant. SEM showed rougher surfaces after alkalization. FT-IR and 13C NMR showed a gradual improvement in cellulose level by alkali treatment with increasing NaOH concentration. The crystallinity index and thermal stability of treated Alfa fibers were also found to be improved.

The aim of this work is to validate the use of dynamic oscillatory measurements in the melt to characterize the dispersion of a filler in a matrix after melt blending. Polyethylene oxide (PEO) is used as a polymeric matrix. Active carbon is used as a filler at a constant filler volume content of 26.4%. The melt viscosity of the polymeric matrix is varied by melt blending of two miscible POE and polyethylene glycol (PEG) species having very different molecular weight distributions. This enables to obtain various matrix viscosities and in turn various states of dispersion of the filler that were characterized by optical microscopy and image analysis. Dynamic mechanical measurements in the melt in the terminal zone show a large increase of the moduli associated to the presence of the filler. Comparison with the results of optical microscopy shows that this increase is clearly related to the dispersion. The interparticle distance is likely to be the leading parameter rather than the number of particles. Characterization of the amount of bound polymer shows that the amount of bound polymer is nearly independent of the matrix composition. Futhermore, the composition of the bound layer reflects the matrix composition though PEO is slightly preferentially bound on the active carbon.

Composites of active carbon in a polymeric matrix composed of polyethylene oxide (PEO) and polyethylene glycol (PEG) having different molecular weight distributions were obtained by melt mixing. Characterization of the amount of bound polymer in the whole range of composition for the polymeric matrix has been performed after dissolution of the matrix in water. Size exclusion chromatography of the solution has been used to determine the composition of the polymeric bound layer. It has been shown that in these conditions of mixing, the amount of bound polymer slightly decreases from a pure PEG to a pure PEO matrix. Furthermore, PEO is preferentially bound to the active carbon. A simple model is used to show that bonding occurs preferentially by monomeric units rather than by chain ends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3490–3497, 2006

The article addresses the issue of recycling of poly(ethylene terephtalate) (PET) by melt blending with polycarbonate (PC). PET/PC blends containing various amounts of the immiscible polymers were prepared in a twin-screw extruder. Selected compositions were also prepared in the presence of an Sn-based catalyst to assess the influence of transesterification during melt mixing. The degree of miscibility in the blends was studied using differential scanning calorimetry, scanning electron microscopy, and mechanical testing. PET/PC blends exhibit enhanced tensile properties in comparison to neat components for compositions of PET higher than 50% and these properties are improved by the addition of a transesterification catalyst. The PET/PC blend containing 20 wt% of PC, prepared with stannous octoate, shows the smallest size of the dispersed phase because of transesterification reactions that generate copolymer molecules at the interface between the immiscible polymers. The melting temperature of PET is decreased with the increase of the PC content in blends extruded in the presence of the catalyst. Also, the temperatures of the cold crystallization of PET are higher than those of similar blends without added catalyst. Both features give rise to better molding properties because of a shortening of the cooling time in the range of 50–90 wt% of PET. POLYM. ENG. SCI. 46:1378–1386, 2006. © 2006 Society of Plastics Engineers

Rheological properties of poly(ethylene oxide)/poly(vinylidenefluoride)-(hexafluoropropylene) immiscible polymer blends were studied in the low frequency domain. According to the blend composition, two critical compositions were determined by rheology. These compositions exhibit a power law relaxation spectrum with a critical exponent Δ. This observation leads us to compare the evolution of the morphology in a binary blend with the process of gelation. The supermolecular structure at the limit of the cocontinuity zone is comparable to the chemical or physical incipient network obtained during the gelation. This point is discussed in term of self-similar superstructure and fractal dimension.

The work focuses on the detection of the co-continuity window in immiscible polymer blends. The purpose of the paper is to describe how rheological techniques can help to evaluate the composition range of the co-continuous morphology through the study of a particular system: PEO/PVDF-HFP. First, the blends were characterized by selective dissolution experiments and SEM observations. Then the ability of dynamic mechanical spectroscopy to detect the co-continuity was investigated in the melt and in the solid state. The evolution of the storage modulus of molten blends with their composition at a constant low frequency gives information about the co-continuity interval, especially as far as the onset of the continuity of the PEO phase is concerned. Then the immiscibility of the polymers and the continuity of PVDF-HFP as a function of blend composition have been highlighted by means of dynamic mechanical spectrometry below the melting point of PVDF-HFP. Comparison with results from classical methods shows fair agreement.

In this work, the linear viscoelastic behavior of some low-density polyethylene in the melt is used to obtain their architecture. In this way, the number of branches per molecule and long chain branching (LCB) content is determined. For this purpose, a method based on the molecular dynamics of simple star-shaped molecules is presented. It allows one to infer the topology of an average molecule through a set of 2N c parameters {C n i , the number concentration of a level i} and {M bi , the mass of a segment of level i} representing an irregular Cayley tree with N c levels. The inverse problem uses the complex shear modulus as a function of the frequency data along with a minimization algorithm. Results from the present method are compared with NMR and SEC measurements of the level of branching. It appears that SEC and rheology leads to similar results on the determination of LCB while NMR overestimate the number of branch points per molecule. Moreover, rheology allows one to go further than the basic evaluation of LCB content and shows a picture of the structure of the molecules that is in agreement with the kinetics of free radical polymerization of polyethylene.

Poly(n-butyl methacrylate) (PBMA) composites with calcium carbonate (CaCO3) were prepared by in situ radical copolymerization of butyl methacrylate (BMA) and methacrylic acid (MA) with precipitated calcium carbonate. To compare the different rheological behaviors of the monomer mixtures with CaCO3 and the composites, the steady and dynamic viscosities of BMA/MA/CaCO3 and poly(BMA/MA/CaCO3) were measured by means of steady and oscillatory shear flows. The viscosity of the mixture BMA/MA/CaCO3 was found to increase evidently with the increasing of CaCO3%. The influence of MA% on viscosity of BMA/MA/CaCO3 was slight. During the in situ polymerization, the viscosity of the reacting system was measured to be enhanced by a factor of about 104 from the monomer/CaCO3 mixture to composites. The dependency of zero-shear viscosity on molar mass of PBMA was also investigated. The relation between the zero-shear viscosity and molar mass is η0 = 10−15Mw3.5. The evolution of the viscosity with the temperature for both PBMA and its composites was obtained and time–temperature superposition was used to build master curves for the dynamic moduli. The flow activation energies were found to be 115.0, 148.6, and 178.7 kJ/mol for PBMA, composite PBMA/CaCO3 (90/10), and PBMA/MA/CaCO3 (89/1/10), respectively. The viscosity of the composites containing less than 10% CaCO3 was lower than that of pure PBMA with the same molar mass. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1376–1383, 2003

The structural evolution of a maize flour was followed by means of oscillatory shear measurements during heating at a rate of 10 °C/min in presence of water. These measurements were performed in a special plate and plate vessel designed to prevent moisture loss. The phenomena of gelatinization and gelation were clearly identified and their connection with the moisture content also demonstrated. Moreover, the complex mechanisms involved in gelatinization and gelation in native starch were separated. Softening of the amylose zones, exchange of water and amylose within the starch granules followed by amylopectin melting leads to the gelation of starch.

International audience; Tuning the chain-end functionality of a short-chain cationic homopolymer, owing to the nature of the initiator used in the atom transfer radical polymerization (ATRP) polymerization step, can be used to mediate the formation of a gel of this poly(electrolyte) in water. While a neutral end group gives a solution of low viscosity, a highly homogeneous gel is obtained with a phosphonate anionic moiety, as characterized by rheometry and diffusion nuclear magnetic resonance (NMR). This novel type of supramolecular control over poly(electrolytic) gel formation could find potential use in a variety of applications in the field of electro-active materials.

The relationship between copolymer composition, molecular weight distribution, and rheological properties of random styrene acrylonitrile copolymers synthesized by radical polymerization in bulk was investigated. From differential scanning calorimetry analysis, glass transition temperature was obtained and increases with the acrylonitrile content. The knowledge of the glass transition is a key factor to compare the different copolymers in an iso-free volume condition for melt rheology. Owing to time temperature superposition, a large frequencies window ranging from the terminal zone until the glassy plateau can be obtained. Thus, the mechanical spectroscopy was used to estimate the rubbery plateau modulus and the Newtonian viscosity.

A series of ethylene vinyl acetate (EVA) copolymers was studied by dynamic mechanical spectroscopy to understand the relative influence of composition, structure, and molecular weight distribution on their rheological behavior in the melt. The examination of their viscoelastic properties in a large temperature range showed that the glass transition temperature is nearly independent on their composition because of the statistical nature of the copolymers, though some long sequence of polyethylene homopolymer may exist at low vinyl acetate (VA) content. The successful use of the time temperature superposition for oscillatory experiments in the melt confirmed the previous remarks, because the application of the Williams Landel Ferry (WLF) equation leads to a unique set of WLF coefficient, whatever the composition of the EVA. This enables the comparison of the rheological behavior in the melt at the same temperature, in the same free volume condition, and at last it was shown that in the terminal zone, the molecular weight distribution is more influent on the behavior of EVA copolymers than their composition. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2625–2630, 1999

The rheological behaviour of a linear low density polyethylene melt is studied using a wide range of techniques: shear and elongational stress growth at constant strain rate, steady shear flow, extrudate swell and isothermal melt spinning. The analysis of the behaviour is based on the Wagner constitutive equation which appears to be suitable. Moreover, the extrudate swell and the isothermal spinning are simulated by taking into account the past shear and elongation deformation in the reservoir, the contraction and the die of a capillary rheometer. For this purpose, the Finger deformation tensor is evaluated using a Protean coordinate system. This approach is shown to be very useful to test the validity of the constitutive equation and to determine its characteristic parameters.

In this work, blends of three different vinylidene fluoride (VdF) based homopolymers and copolymers with poly(ethylene oxide) were investigated. We focused on the continuity domain and, more particularly, on the cocontinuous morphology of these systems. The melt-mixed blends were characterized by different techniques. The morphology was identified through a selective extraction technique and was confirmed by scanning electron microscopy. Dynamic oscillatory shear measurements were performed with a constant stress rheometer in the linear viscoelastic domain in the whole composition range. Because of the high viscosities and long relaxation times of the VdF-based polymers, the interfacial effects were hidden by the intrinsic behavior of the neat components. Nevertheless, the combination of the different techniques highlighted the similarity of the systems toward morphological development, whatever the VdF monomers. The experiments and theoretical analysis indicated that the rheological behavior dominated the interfacial effects in such systems with a large viscosity ratio and that it also dictated the boundaries of the continuity domain. The originality of this study came from the use of three different VdF-based polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The behavior of two polymers, namely, low-density and linear low-density polyethylenes, was studied in transient and steady-state shear and elongational flows. The predictions of Wagner's model with a damping function using a generalized invariant were calculated. The model appears to be suitable for predictions of the shear and elongational transient flows on the range of strains experimentally tested. The shear flow curves can also be recovered by the model on a very broad range of shear rates. The model is then used to assess extensional data obtained with the convergent flow analysis proposed by Cogswell.

The linear viscoelastic behavior of polydisperse polypropylenes in the melt is predicted using the molecular weight distribution (MWD) as determined from gel permeation chromatography, on the basis of simplified molecular dynamics: single exponential form of the relaxation modulus of narrow fractions, double reptation, tube renewal, and constraint release. Owing to a few approximations, the calculation only requires a few parameters, namely the scaling law for the zero shear viscosity of narrow fractions η0 = f(M), the plateau modulus G, and the value of the molecular weight between entanglements Me. Using this method a relaxation spectrum of Maxwellian contributions with a large number of modes is obtained. This spectrum well predicts the rheological behavior in the terminal zone of samples obtained by controlled peroxydic degradation of polypropylene with polydispersity ranging from 4 to 10. Attention is focused on the zero shear rate viscosity, frequency, and modulus of the crossover of the storage and loss moduli from experiments and calculations, because these parameters are generally thought to be sensitive to both average molecular weight and polydispersity and are relatively easy to get from dynamic experiments. How the initial spectrum can be conveniently reduced to a more simple spectrum with only a few modes, without significant loss of information, is shown. This spectrum may be useful and time saving in calculations, for example, to describe the memory function in nonlinear constitutive equations while keeping its physical meaning in relation to the MWD. © 1996 John Wiley & Sons, Inc.

A discrete relaxation spectrum using a small number of modes is derived to describe the relaxation behaviour of monodisperse polystyrene melts. Attention is focused on keeping the physical meaning of the relaxation times. Therefore, molecular dynamics theories are used in the terminal, plateau and transition zones and in the case of entangled melts. The spectrum is divided into three parts corresponding to three assumed different relaxation mechanisms: Rouse mechanism at short times, modified Rouse for tube equilibration and reptation with tube fluctuation in the long time range. This description only requires the knowledge of a limited number of parameters, namely the molecular weight of the polymer under investigation, the scaling law for Newtonian viscosity, the plateau modulus and the molecular weight between entanglements. The method is successfully applied to entangled monodisperse polystyrene melts and enables the recovery of final spectra containing only a few relaxation modes.

Polarized light microscopy shows that polypropylene crystallizes from the melt into a well-distinguished spherulitic structure. Therefore, it provides a useful model for molten-filled polymers, where the growing spherulites are considered to be filler particles dispersed in a matrix fluid. Although spherulites are randomly dispersed in the space, two dispersion models (simple cubic and centered cubic) are discussed to correlate the transformed fraction α(t) with the volume fraction of filler ϕ(t). The combination of these results with those of differential scanning calorimetry (DSC) shows that the transformed fraction α(t) is a direct indication of the volume fraction of filler ϕ(t). The rheological study, using oscillatory experiments coupled with DSC results, shows the relative sensitivity of the rheological functions to structural changes of the liquid during crystallization. Furthermore, they reveal the existence of a yield effect above a certain criticl value of the filler content (ϕc = 0.4). In the absence of this yield effect, a model is proposed to predict the variation of the rheological functions with the filler content. This model shows not only a variation of the plateau modulus, but also the modification of the characteristic times of relaxation of the polymer matrix, whereas the shape of the relaxation spectrum remains unchanged. © 1996 John Wiley & Sons, Inc.

The Pade-Laplace method using the Laplace transform and the Pade approximants has been used to recover a discrete relaxation spectrum from dynamic oscillatory data in the molten state for polymers. The method detects by its own stability the number of modes of the spectrum and has been shown to be able to provide spectra with a low number of modes. These spectra are found to be sufficient to obtain an accurate description of the linear viscoelastic behavior in a large frequency range from the terminal zone to the plateau zone. Some intrinsic parameters of the numerical technique have been extensively studied in order to refine it. Its applicability is shown in the case of polystyrene having monomolecular, bimodal or broad molecular weight distributions. It can easily be implemented on a personal computer and the computing time is of the order of a few seconds.