Thermoplastic liquid crystal polymer/plastic

Liquid crystal polymers (LCP) are a recent arrival on the plastics materials scene. They have outstanding dimensional stability, high strength, stiffness, toughness and chemical resistance all combined with ease of processing. LCPs are based on thermoplastic aromatic polyesters and they have a highly ordered structure even in the molten state. When these materials are subjected to stress the molecular chains slide over one another but the ordered structure is retained. It is the retention of the highly crystalline structure which imparts the exceptional properties to LCPs. 

Connectors, switches, electric distributors, fuse boxes and other electric fittings need a subtle balance of electrical and mechanical properties, durability, cost and aesthetics. This broad field creates fierce competition not only between engineering thermoplastics and SMC/BMC for the main applications but also with polypropylene and polyethylene or PVC for the lower performance parts and, at the opposite end of the scale, with high-tech plastics such as polyetherketone, polyetherimide, liquid crystal polymers. .. For example, without claiming to be exhaustive ... 

Some of the common types of plastics that are used are thermoplastics, such as poly(phenylene sulfide) (PPS) (see POLYMERS CONTAINING SULFUR), nylons, liquid crystal polymer (LCP), the polyesters (qv) such as polyesters that are 30% glass-fiber reinforced, and poly(ethylene terephthalate) (PET), and polyetherimide (PEI) and thermosets such as diallyl phthalate and phenolic resins (qv). Because of the wide variety of manufacturing processes and usage requirements, these materials are available in several variations which have a range of physical properties. 

RPs that combine two different materials (plastic matrix and reinforcement) are a separate major and important segment in the plastic industry. They are also called plastic composites and composites. There are also self-reinforcing plastics such as liquid crystal polymers (Chapter 1) and others.301 It is a fact that RPs have not come near to realizing their great potential in a multitude of applications usually due to cost limitations that particularly involves the use of expensive fiber reinforcements (carbon, graphite, silica, etc.).1 Information on thermoplastic and thermoset plastic RPs are reviewed in Chapter 15. 

Petra 140 (Allied Signal) is a 40 percent glass-reinforced polyethylene tereph-thalate from recycled soda bottles. It has a tensile strength of 26,000 psi and a heat-deflection temperature of 225°C at 264 psi. PC23MS-200 (MCR Polymers) contains at least 25 percent recyclate from personal computer compact disks and polyethylene terephthalate beverage bottles. DMDA-1343NT polyethylene (Union Carbide) contains 28 percent color-sorted recyclate and has physical properties similar to those of virgin stock. Encore resins (Hoechst Celanese) are a family of plastics based on 100 percent reclaimed thermoplastics such as acetal, polyester, polyphenylene sulfide, nylon 6/6, and liquid crystal polymer. 

Figure 1 Cost-related (specific) flexural strength of major thermoplastics, versus cost-related (specific) thermal tolerance. The unit cost is the market price in US cents (1992) of 1 cm plastics. The thermal tolerance is the temperature difference (AT) over room temperature (AT — T - room T), by which temperature (7 ) the flexural modulus is equal to 1 GPa. Designations, abbreviations WFRP-S, wood fiber reinforced PP (S type) of AECL, Canada (See Table 1) PMMA, polymethylmethacrylate PVC, pol)winyl chloride PS, polystyrene PP, polypropylene UP, unsaturated polyesters PA-GF, glass fiber (35%) reinforced polyamide PHR, phenolic resin EP, epoxy resin ABS, acrylonitrile/butadiene/styrene copolymer UF, urea/formaldehyde LDPE, low density polyethylene PC, polycarbonate POM, polyoxymethylene CAB, cellulose acetate butyrate LCP, liquid crystal polymers PEEK, polyether-etherketone PTFE, polytetrafluorethylene.

By blending these polymers, taking care to match melt viscosities and volnme fractions (see eq. 2 below), dual-phase continuity can be achieved (see Fig. 16) (59). In Figure 16a, droplets of material are dispersed in a continuous matrix, a morphology observed in rubber-toughened plastics. Figure 16b illustrates dispersed fibers, observed in liquid crystal polymers and some thermoplastic elastomers. If the fibers or cylinders are infinitely long, they exhibit one-dimensional phase continuity. 

Fig. 19.1 The plastics pyramid according to thermal literature data of common polymers preferred materials for HT-PEM applications are in the upper right region TPI thermoplastic polyimide, PES polyether sulfone, P P)SU poly(phenylene)sulfone, PE E)K polyether(ether) ketone, LCP liquid crystal polymer, e.g., Vectra, PPS polyphenylene sulfide, PTEE polytetrafluoroethylene.

Inoue T, Yamanka T, Makabe Y. Liquid crystal polymer. In Margolis J, editor. Engineering plastics handbook thermoplastics, properties, and applications. New York McGraw-Hill 2006. p. 239-56. Chapter 11. 

During the 1980s and 1990s, the pace of research and commercialisation of high-temperature plastics accelerated dramatically. The thermoplastic resin manufacturers introduced many new materials based on imide, sulfone, and ketone-based polymers. These include polyetherimide (1982) and polyphthalamide (1991). Polyketones and liquid crystal polymers were also commercialised in the 1990s. 

In the last two decades, numerous experimental and theoretical studies dealing with reaction-induced phase separation in multiphase polymer systems (mostly porous matrices, toughened plastics, melt processable thermoplastics [143], molecular composites, polymer dispersed liquid crystals, etc.) have been reported. A newcomer in this field should get acquainted with hundreds (possibly thousands) of papers and patents. The intention of this review was to provide a qualitative basis (quantitative occasionally) to rationalize the various factors that must be taken into account to obtain desired morphologies. 

These thermotropic liquid-crystalhne polymers have high melting points but can be melt-processed like other thermoplastics. The macroscopic orientation of the extended-chain crystals depends on the orientation imparted by flow during processing (molding, extrusion, etc.). Because of the fibrous nature of the extended-chain crystals, these plastics behave as self-reinforced composites, with excellent mechanical properties, at least in the chain direction. This is illustrated in Table 4.3 for molded specimens of a hquid-crystalline copolyester of ethylene glycol, terephthalic acid, and / -hydroxybenzoic acid [14]. In the direction parallel to the flow, the properties listed in Table 4.3 favorably compare with ordinary crystalline thermoplastics (nylons, polyesters) reinforced with up to 30% glass fibers. 

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