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Calendering is mainly applied to PVC for manufacturing sheets or films. After describing the basics of the process, PVC formulations are presented as well as the different stages of their gelation and the calendering process itself. The different devices controlling the thickness and its uniformity are described. Models of increasing complexity predict calendering forces, polymer heating and sheet thickness as a function of the rheology of the material and the processing parameters. These models make it possible to understand the occurrence of defects and to optimize operating conditions to avoid them. The specific case of post extrusion calendering is finally presented.
Plastics pose significant environmental challenges, slowing down the transition towards a circular economy. This article explore the different routes of valorization of plastics and highlights the barriers limiting the performances of the recycled materials. The potential of plastics in many applications evidences their innovating character. However, the dissemination of microplastics has become a major concern which can be partially solved by the development of plastics showing lower environmental footprints, ecodesign and artificial intelligence for more efficacy of waste sorting.
In order to improve the mechanical properties of thermoplastics while maintaining ease of shaping, discontinuous micrometric fibers are often used as reinforcement. The forming process will orient fibers in directions which are not necessarily favorable to reinforcement. It is therefore necessary to fully understand and control the orientation of these fibers to deduce the induced properties. This article presents models for predicting the flow behavior of these composites and the issues related to fiber orientation, with applications in injection molding and extrusion-based 3D printing.
High density polyethylene is a widely used material in France and throughout the world. This article describes the different polymerization processes allowing the production of high density polyethylene grades thanks to different catalysts (Ziegler-Natta, Chromium, Metallocene) and different reactors (gaz phase, solution, slurry…). The so produced grades offer a wide range of properties (mechanical, thermal, chemical…) that will also be detailed in this article along with the corresponding commercial applications and the end-articles production processes.
The concept of circular economy (CE) encompasses the limits to growth in a finite world and proposes a restorative and regenerative vision. It opposes a linear vision of economy leading to a pervasive production of waste and deterioration of the environment. However, there is no accurate and unique definition of circular economy and this entails various criticisms. Among circular economy strategies, the recycling of materials, despite its limits, play a major role and is prone to contribute to loosen the constraints of supply concerning the strategic materials. Ecodesign of products coupled with relevant indicators is also an essential tool in order to preserve resources.
The concept of residence time distribution (RTD) is crucial in many extrusion applications, particularly when dealing with reactive systems, degradation problems or scale-up issues. In this article, after introducing the basic notions concerning RTD, the different measurement methods will be detailed, followed by the presentation of experimental results on the influence of the main extrusion process parameters (screw speed, flow rate, temperature, screw profile, etc.). Finally, the different theoretical approaches for describing and/or predicting RTD will be reviewed.
The behavior of polymers in the solid state results from two forms of organization adopted by the macromolecular chains of glass and crystal. In a glass, the macromolecular chains are by essence at the amorphous state and produce entanglements which participate in the visco-elasticity of the mass material. Reversely, the chains characterized by a regular and symmetrical conformational structure or bearing groups capable of strong molecular interactions of polymers are likely to produce crystalline zones. After presenting the various types of oriented polymers, this article also deals with the incompatibility of polymers between themselves and the difficulty mixing them.
A wide range of hollow bodies composed of thermoplastic polymers can be found in the pharmaceutical, cosmetic and food industry. One of their manufacturing techniques, the biaxially oriented blow moulding process has evolved considerably over the last few years. This process applied to polyethylene terephthalate has allowed the creation of attractive, light and resistant containers. Technological breakthroughs in the biaxially-oriented industry have contributed to this improvement. Blow-moulding machines can be easily integrated in a bottling production line and are even sometimes itegrated into the filling-machine. Also, the intermediary printing steps of these vials and bottles are effected either on or off-line.
Thermoforming is a thermoplastic polymer forming process that converts a semi-finished product − a film or an extruded sheet − into a formed part. The article clarifies the concept of stretching and thermoformability, and investigates how the triangular pattern of relationships between the polymer properties,the semi-finished quality level and the thermoforming process may impact the overall process performance and the formed part quality. The article reviews the various thermoforming operating types, and details the successive stages configuring a thermoforming machine. Finally, the article proposes several geometric and numerical thermoforming simulation models of increasing complexity.
The development of new polymeric materials often requires mixing various polymers or mixing a polymer with inorganic fillers or fibers. These mixing operations differ from those encountered in other areas of chemical engineering because the very high viscosity of molten polymers prevents turbulence, the main mixing mechanism for low viscosity systems. This article introduces some basic concepts that govern the operations of mixing and allow their effectiveness to be quantified. These help explain how various mixing processes work.
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