Evolution of polymer blend morphologies during extrusion in a flat die

The control of blend morphologies during process is of prime importance in order to predict the final properties of polymer blends. A coextrusion technique combined with static mixers was developed in order to smartly blend polymeric melts and to optimize the blend morphologies during the flow in static mixers [1]. The aim of this paper is to study the evolution of those blend morphologies during extrusion in a flat die. The effect of the viscosity ratio and the interfacial tension are also investigated. The experimental observations are confronted with numerical simulation results

Crystallization behavior of poly(lactide)/poly(β-hydroxybutyrate)/talc composites.

The authors thank Dr. Patrice Lefrançois (CNAM) for SEM observations. They are also grateful to Pr. Jack R. Plimmer USDA, Agricultural Research Service, USA for his discussions during this work.The morphology and miscibility of commercial poly(lactide) (PLA)/poly(b-hydroxybutyrate) (PHB, from 5 to 20 wt %) blends prepared by melt extrusion method, were investigated using differential scanning calorimetry (DSC) and Fourier transform infra-red spectroscopy (FTIR) observations. The results show that for all the studied blend contents, PLA/PHB blends are immiscible. The effects of PHB and talc on the nonisothermal cold crystallization kinetics of PLA were examined using a differential scanning calorimetry (DSC) at different heating rates. PHB acted as a nucleating agent on PLA and the addition of talc to the blend yielded further improve-ment, since significant increase in the enthalpy peak was observed for samples containing 10 wt % PHB and talc (from 0.5 to 5 phr). The crystallization kinetics were then examined using the Avrami–Jeziorny and Liu–Mo approach. The simultaneous presence of PHB and talc induced a decrease of the crystallization half time. The evolution of activation energies determined with Kissinger’s equation suggests that blending with PHB and incorporating talc promote nonisothermal cold crystallization of PLA. The synergistic nucleating effect of PHB and talc was also observed on isothermal crystallization of PLA from the melt

Dispersion of carbon nanotubes in polypropylene via multilayer coextrusion: Influence on the mechanical properties

The authors would like to thank PSA for funding this research and providing some of the materials used in this study. We also would like to thank R. Glénat, P. Soria, E. Dandeu, A. Grand- montagne and A. Dubruc for their help in the preparation and the optical and mechanical characterizations of the samples presented in this study.Multilayer coextrusion was used to disperse Carbon Nanotubes (CNT) in polypropylene (PP). The dilution of commercially available masterbatches using a twin-screw extruder was first applied to produce several formulations, which were then mixed with PP using a multilayer coextrusion device to obtain films or pellets with CNT concentrations between 0.1 and 1%wt. The influence of the specific mechanical energy (SME) during the dilution step, of the addition of a compatibilizer, and of the multilayer tool on the CNT dispersion within the matrix was highlighted. The effect of the dispersion on the thermomechanical properties of the resulting materials was studied. We showed notably that films containing 0.2%wt CNT, 1%wt of PPgAm, prepared at high SME presented a Young’s modulus increase of 25e30% without significant decrease in the elongation at break. These results, using low amounts of CNT and industrially available devices, may show a new path for producing nanocomposites

Ion exchange membranes based upon crosslinked sulfonated polyethersulfone for electrochemical applications

Synthesis and characterization of new ion exchange membranes made from chlorosulfonated polyethersul- fone (SO2Cl-PES) crosslinked by polyaminated crosslinking reagents have been performed. Two examples are described: one crosslinked by hexane diamine, the other by amino-polyethersulfone (NH2-PES). Sulfonated polyether sulfone (S-PES) and NH2-PES have similar chemical structures that allow compatibility. Surpris- ingly enough, better results were obtained using amino-polyethersulfone. The best results have been obtained using SO2Cl-PES with 1.3 SO2Cl group per monomer unit crosslinked by 0.2 equivalent of NH2-PES. The membranes, less brittle than pristine SPES and insoluble in solvents such as DMAc, were characterized by TGA, DMA, DSC, ionic conductivity, transport numbers, and water swelling. The results showed that these membranes presented very promising performances for use in Proton Exchange Membrane Fuel Cells

Technological solutions to reduce the geometrical defects during the cast film process

International audienceThe polymer cast film process induces some geometrical defects : the width reduction (neck-in defect) and the inhomogeneous decrease of the thickness distribution (edge bead defect). These defects prevent from predicting the film final dimensions and thus from a high industrial productivity. In this paper, a numerical model developed by the authors is used to test and optimize two technological solutions, aimed at reducing the geometrical defects : a localized air cooling on the edges of the film at the die exit and an "encapsulation die" which enables the extrusion of a high melt strength polymer along the outer edge of a core polymer. Numerical results are confronted with experimental investigation

Oxidative degradation of polylactide (PLA) and its effects on physical and mechanical properties

The thermo-oxidative degradation of polylactide (PLA) films was studied between 70 and 150 C. It was shown that the oxidative degradation of PLA leads to a random chain cission responsible for a reduction of the molar mass. These molar mass changes affect Tg and the degree of crystallinity, and it was found that Tg decreases according to the Fox–Flory theory whereas the degree of crystallinity increases due to a chemicrystallization process. A correlation between molar mass and strain at break during oxidation has been established: PLA displays a brittle behavior when Mn falls below 40 kg mol 1 in agreement with relationships linking the critical value for embrittlement with the molar mass between entanglements

Relationship between fiber chemical treatment and properties of recycled pp/bamboo fiber composites

This article reports the preparation of recycled polypropylene (RPP)/bamboo fiber (BF) composite via direct melt blends using a twin screw extruder. The effects of the chemical treatment of BF surface (alkaline and acetylation) on fiber structure and composite mechanical, thermal, rheological properties have been investigated. We showed that alkali treatment increases the contact surface of BF within composites, resulting in a more homogenous dispersion of fibers in the polymer matrix. Alkali treatment improves mechanical properties such as tensile strength as well as the Charpy impact strength. Reinforced composites obtained with acetylated BF show better mechanical properties due to grafting of acetyl groups onto the cellulose fiber surface and thus improve compatibility between BF and matrix. The rheological properties of RPP/BF composites depending on the BF content and treatment methods are also analyzed. Predominant factors that influence the properties of relevant materials are identified. Maleic anhydride grafted polypropylene is used as a compatibilizer to improve the adhesion between the cellulosic phase and the RPP matrix

Forced assembly by multilayer coextrusion to create oriented graphene reinforced polymer nanocomposites

A potential advantage of platelet-like nanofillers as nanocomposite reinforcements is the possibility of achieving two-dimensional stiffening through planar orientation of the platelets. The ability to achieve improved properties through in-plane orientation of the platelets is a challenge and, here, we present the first results of using forced assembly to orient graphene nanoplatelets in poly(methyl methacrylate)/ polystyrene (PMMA/PS) and PMMA/PMMA multilayer films produced through multilayer coextrusion. The films exhibited a multilayer structure made of alternating layers of polymer and polymer containing graphene as evidenced by electron microscopy. Significant single layer reinforcement of 118% at a concentration of 2 wt % graphene was achieveddhigher than previously reported reinforcement for randomly dispersed graphene. The large reinforcement is attributed to the planar orientation of the graphene in the individual polymer layers. Anisotropy of the stiffening was also observed and attributed to imperfect planar orientation of the graphene lateral to the extrusion flow