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Extrusion of Oriented LCP Film and Tubing
Published in Robert R. Luise, of High Temperature Polymers, 1997
Multiaxially oriented film and tubing can be processed from LCPs, compounds and blends using shear flow to orient the LCP molecular domains. Melt flow must be controlled to achieve desired directions of orientation and subsequent properties such as tensile strength and modulus, coefficient of thermal expansion, gas barrier properties, and electrical properties. When processed in thin-oriented layers or at low concentrations in LCP-thermoplastic blends, LCPs show performance and cost benefits over other types of film and tubing. Oriented film and tubing made from LCP can provide cost savings for the following reasons: LCPs have higher performance than their proportional increase in cost;-thus they can reduce the total amount of polymeric material needed, which results in a direct cost reduction plus savings on surcharges that may be placed on the weight of material in a specific part.LCPs combine high temperature and chemical resistance with very good mechanical, electrical, and barrier properties; and can replace several different types of polymers with one LCP layer.Biaxially oriented LCP film and tubing are made by a single-step extrusion process which is inherently less costly than composite processing, so that LCPs can replace fiber-reinforced composites in certain price-sensitive applications.
Molding Processes
Published in Richard L. Shell, Ernest L. Hall, Handbook of Industrial Automation, 2000
For convenience of sizing and handling, preforms are typically used. The fibrous preforms are initially shaped to approximate the shape of the parts. The most widely used preforms are based on SMC, and bulk molding compound (BMC) [21]. The SMC contains resin, fibers, and other ingredients are prepared into a sheet form for easy loading into the mold. The BMC includes resin, fibers, catalyst, and other ingredients mixed into a puttylike mass which can be extruded into a ropelike form for easy handling and placement into the mold. Most recently, the high-performance thermoplastic and thermosetting polymers containing 60–70% by volume of continuous carbon fiber reinforcement are compression molded into structural composite parts for high-performance aerospace and industrial applications [17–19,22–24]. Matrix polymers for these composites are polyetheretherketone (PEEK), polyetherimide (PEI), polyarylene sulfide (PAS), polyphenylene sulfide (PPS), polyamideimide (PAI), polyethersulfone (PES), and thermoplastic or thermosetting polyimides (TPI). Preimpregnated prepregs, where the reinforcing carbon fibers are already embedded in the resin matrix, and postimpregnated prepregs, where resin and reinforcing carbon fibers are hybridized or cowoven, are utilized. The prepregs are laid up and compression molded into the laminates. In addition, a new technology for making self-reinforced or in-situ prepregs based on thermotropic liquid crystalline polymers (LCP)/thermoplastic (TP) has been recently proposed [25]. The LCP/TP prepregs are first made by extrusion followed by extension to achieve large aspect-ratio LCP fibrils in TP. Then, the prepregs are compression molded into laminates with the required packing sequence. Unidirectional or quasi-isotropic laminates can be obtained in a way very similar to conventional fiber-reinforced laminates.
Polymer Heat Exchangers
Published in Sadık Kakaç, Hongtan Liu, Anchasa Pramuanjaroenkij, Heat Exchangers, 2020
Sadık Kakaç, Hongtan Liu, Anchasa Pramuanjaroenkij
Liquid crystal polymers (LCP) have the properties of both polymer and liquid crystals. They can be used in applications that exceed 300°C. Also, they show a chemical resistance to basic and acidic solvents. They have low thermal expansion coefficients and high tensile strengths. Because of these properties, they are advantageous in heat exchanger designs.
Exploring photo-deformation of polydomain liquid crystal polymers by homogenization
Published in Soft Materials, 2020
Liquid crystal polymers (LCPs) possess anisotropic elasticity due to their average molecular orientation, called the director .[1–11] Photochromic LCPs are doped with photochromic moieties such as azo-dyes. Under polarized ultraviolet (PUV) light with a suitable wavelength, a monodomain LCP material, namely with a uniform director throughout the sample, contracts along caused by reduction in the degree of orientation through a polarization-dependent trans-cis photo-isomerization process.[4] Due to light absorption, such contraction in the monodomain LCP becomes differential in absorption depth, leading to a bend toward light.[5] However, in practice, monodomains are not always as readily available as polydomains, since to prepare the former usually requires uniaxial stress to align the LC orientation uniformly whereas the latter can be spontaneously formed by cooling down a high symmetry isotropic LCP. A polydomain LCP is formed by domains each of which has a uniform director, where the directors are aligned uniformly in their own domain but heterogeneously in different domains. Polydomain LCPs have been showing such interesting applications as being actuated to make self-excited waves[12], designed into a flytrap[13] and a robot caterpillar[14] by prepatterning their LC orientation, and preprogrammed their shapes by domain topological defects.[15]