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This article provides an overview of additive manufacturing technologies applied to polymers, highlighting advantages such as cost-effectiveness, lightweight design, recyclability, and design freedom. It presents the fundamental principles and classifications, as well as the advantages and limitations compared with conventional techniques. The main technologies, including extrusion, photopolymerization, powder bed fusion, material jetting, and direct ink writing, are analyzed in terms of mechanisms, materials, and applications. The article also addresses current challenges and future perspectives, notably 4D printing.
This article describes the preparation of nanocomposites based on polypropylene and lamellar clay by twin-screw extrusion. After presenting the potential utility of these materials, the experimental techniques for preparing and characterizing them are described. The influence of the processing parameters (screw speed, feed rate or mixing time, barrel temperature) on the microstructure is then evaluated, first in an internal mixer, then in a twin-screw extruder. Finally, the article shows how a modeling approach based on continuum mechanics can help solve optimization and scale-up problems.
The extrusion process involves the continuous manufacture of finished or semi-finished products, or the transformation of materials, within a screw/sleeve system. Single-screw extrusion refers to a single screw rotating inside a cylindrical barrel (see in Techniques de l'Ingénieur), while double-screw extrusion refers to two screws, generally parallel, rotating inside a barrel with a figure-of-eight cross-section. However, under the very general term of bivis extrusion, we find machines of very different designs and with a variety of specific applications. While counter-rotating machines, derived from internal mixers for the rubber industry or dough kneading, appeared around 1880, corotating extruders were born around 1935 in Italy.
Among the various extrusion techniques, counter-rotating twin-screw extrusion is probably the least known and least widely used at the industrial level, although it is unavoidable in some application areas, such as the production of PVC profiles. The purpose of this article is to present the various configurations encountered in practice, to describe their geometries, to explain their mode of operation and their main applications, and finally to describe the modeling approaches that have been developed to understand and optimize these processes.
The first part of this article "Single-screw extrusion was essentially devoted to the mechanisms involved in extrusion. In this second part, we will deal with the technical aspects of manufacturing and operation, as well as reviewing the main practical problems encountered in extrusion, and giving some simple recipes for solving them.
Extrusion is by far the most important polymer shaping process. The basic principle of single-screw extrusion is the use of a screw that rotates inside a cylindrical barrel. A continuous process, extrusion is used to manufacture finished products or semi-finished products of constant cross-section (films, sheets, tubes, profiles, etc.) by passing them through a tool called a die. In this case, the main functions of the process are to melt the solid polymer, then pressurize and mix the molten polymer, in order to feed the die under the right conditions, which will give the manufactured product its shape. In addition to shaping, extrusion is also used for granulation, compounding and polymerization.
Additive Manufacturing (AM) has grown considerably in recent years. The gradual transition from prototyping activities to direct manufacturing of functional parts undermines traditional methods of design and manufacturing based on conventional methods. This article focuses on the different AM technologies and fields of use throughout product life cycles. Various industrial applications are described through examples from the advanced technology sector.
The article presents the different key-steps in the life cycle of biobased and/or biodegradable polyesters. It describes the elaboration processes of each of these polyesters, going back to the raw materials used, especially when these are of plant-based. These production processes can be biotechnological approaches as well as fairly conventional chemical methodologies. For each of these polyesters, the main functional properties and current or future applications are detailed and criticized with regard to the issues of today. Their strengths but also the drawbacks limiting their development are explained.
The knife-over-roll coating process is dedicated to viscous fluids. This article illustrates this process for the deposition of plastisol formulations for flooring applications. The coexistence of smooth spherical PVC particles and rough calcium carbonate aggregates in a Newtonian plasticizer imparts to this suspension a highly non-monotonous behavior. A specific numerical model is proposed to account for this complex rheology. The lubrication approximations allow predicting the deposited thickness on the substrate and the stress exerted on the knife as a function of the plastisol rheology and the coating parameters.
This paper is reviewing the different elements available along cable extrusion lines from the preparation of the polymer granules and conductor to the winding on a bobin. The goal of the payoffs is to allow a continuous feeding of the line with a conductor, a wire, or a cable. Two types of lines are used: those producing single wires by insulating a single conducting wire, and those producing cables by depositing a sheath on assembled wires. As an important component of the cable line, the extruder is conveying, melting and homogeneizing the insulation or sheathing material. Once cooled down, the wire or cable is wound on a bobin for its storage and transport.
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