CMGD

The mechanical properties of reinforced thermoplastics depend on such characteristics of the filler as granulometry, orientation and dispersion. These d@erent microtextural parameters were determined by using a single tool: image analysis, which was coupled with optical and electron microscopies. The dtflerent materials tested were based on polypropylene obtained by extrusion and injection steps. For the deferent samples analysed, the processing conditions and the filler concentration were constant, and variability was due to the dtflerent average lengths of the$ller incorporated in the matrix. The dtrerent filler parameters were determined with particular emphasis on the techniques of dispersion characterisation. The techniques developed in this study were based on image analysis. They enabled us to estimate filler-size distribution and development of the three-dimensional orientation inside the material and between direrent samples. The development of the filler dispersion was also made apparent. In addition, the relationships obtained between the direrent microtextural parameters were investigated. The general conclusion is that image analysis is very suitable for characterisation of this kind of material. 0 1998 Elsevier Science Ltd. All rights reserved

Biocomposite ; fibres de cellulose ; PLA ; extrusion ; efficacité énergétique Résumé -Afin de mettre en place une méthode de détermination de l'efficacité énergétique du procédé de mélangeage d'un bio 3 composite PLA renforcé de fibres courtes de cellulose, nous avons d'abord dressé le bilan énergétique de ce procédé dans le cas du polymère pur. Le processus se déroule en deux phases : la fusion et le mélange. Dans la phase de fusion, le polymère doit fondre et atteindre la température de consigne ; une fois cette température atteinte, la phase de mélange démarre. L'efficacité dans la phase de fusion est définie par le rapport entre l'énergie théorique nécessaire pour atteindre la température de consigne et l'énergie réellement consommée au moment où cette température est atteinte. Il a été montré que l'efficacité de la phase de fusion augmente avec la température de consigne et diminue avec la vitesse de rotation. Dans le cas présenté ici, l'efficacité de la phase de mélange est nulle puisqu'il n'y a qu'un constituant. Quelques essais sur des composites ont également été réalisés. Il a été montré que la consommation énergétique augmente fortement avec le taux de fibres dans le cas de suspensions concentrées et qu'elle varie peu avec le facteur de forme dans le cas de suspensions diluées et semi-diluées. Il a également été montré que l'influence de la vitesse de rotation est similaire dans le cas du polymère pur et dans le cas des composites.

The sharkskin defect in linear low density polyethylene has been studied using both flow birefringence and roughness measurements. Roughness measurements allow us to detect accurately the onset of the defect and to quantify its amplitude. With increasing flowrate, the sharkskin defect appears at a critical value of the flowrate and then grows. This critical value and the maximum amplitude of the defect increase with temperature. Birefringence patterns give information on the stress distribution at the die entrance. At the appearance of the sharkskin defect, all birefringence patterns are identical and independent of the flowrate and the temperature. The influence of die geometry and the addition of lubricant to the polymer were investigated.

This paper presents a method for determining the sputtering yield of a material bombarded by an ion beam, using a 3D stylus surface mapping system. Data obtained of copper are discussed. The influences on the sputtering yield of progressive addition of zinc is observed. The results are in good agreement with previous theoretical results.

New environmentally-friendly ways to think and to design call for the introduction of new polymers and composites with an enhanced sustainability based on (1) renewable raw materials, (2) environmentally-friendly end-of-life treatment and (3) low impact manufacturing processes. Poly(lactic-acid) is bio-based and biodegradable and then fulfil the two first criteria. In our case, compounding of PLA with cellulose fibres was studied using a batch mixer and the influence of the material formulation and the compounding process parameters on melt viscosity and energy balance was observed. Inside a batch mixer, the rotors bring mechanical energy which is function of torque, screw speed and time . The mixing chamber is regulated and the heat transfer between its wall and the polymer is assumed to be convective . The energy input is the addition of specific mechanical energy (SME) and specific thermal energy (STE). During the melting phase, a torque peak is observed as well as a strong increase of the material temperature and of the pressure inside the mixing chamber. Once the melting phase is over, the torque and temperature reach a plateau and the pressure drops off. At this steady state, the heat transfer from the polymer to the walls is compensated by viscous dissipation. The heat transfer coefficient can be determined by estimating this viscous dissipation using the double-Couette approximation proposed by Bousmina et al. . Using torque and temperature data for different process parameters, viscosity was fitted with a power law taking into account the effects of temperature and SME . Energy consumption decreases with the chamber temperature and increases with the rotor speed. The energy required for the melting phase decreases with the rotor speed but does not significantly vary with the chamber temperature. Temperature only has an influence on the mixing phase; the higher the temperature, the lower the viscosity and then the lower the mechanical energy requirements. For pure PLA, energy consumption has been converted into energy efficiency considering the theoretical energy required for the melting is a function of heat capacity and melting enthalpy. This energy efficiency was plotted as a function of viscosity. A given rotor speed implies a given range of viscosity and the more energy is brought to the system, the more the viscosity decreases. An increasing temperature will shift toward lower viscosity the range of viscosity corresponding to a given rotor speed at the reference temperature. It will also decrease the rate at which viscosity is decreased by the energy input. From these considerations, it was possible to determine shift factors to obtain master-curves of energy efficiency. For composites, it was shown that energy consumption strongly increases with the fibre content in the case of concentrated suspensions and that the aspect ratio of the fibres has no significant influence for diluted and semi-diluted suspensions. The influence of the process parameters is similar for composites and pure polymers.

The aim of this paper is to investigate the optical properties of the recycled polymer during numerous internal reprocess using experimental design. The process conditions (material temperature, mold temperature, injection rate) and recycling on the gloss and colorimetric properties of polypropylene containing 2 wt% of pigment was studied. Several injection parameters and cycles numbers must be tested. One most limit for this kind of study is the large number of experiments that requires longtime and significant investments. The idea is to vary three injection parameters (Temperature of material, Temperature of the mold, injection rate) for five injection cycles using statistical approach. The three variables (materiel temperature, mold temperature and injection flow) were investigated at three industrial used levels. The number of recycling varies from cycle 0 to cycle 4 at five levels. The complete matrix for screening was designed using D-optimal quadratic design. The experimental design was generated with the statistical software MODDE 10.1-Umetrics. A set of 45 experiments was carried out to determine the influence of injection parameters and recycling on the appearance properties of samples. The statistical software package Nemrodw ® version 2007, LPRAI (Marseille, France) was used to analyze the experimental design.