Composites, thermoplastic

One disadvantage of thermoplastics is that they soften appreciably as they are heated. As this happens, their modulus decreases and they begin to creep (slowly deform over time) 

Incorporation of fillers into thermoplastics alters all the properties of the material. Some of the changes will be beneficial and some will be detrimental. It should be noted that these are not absolutes and the determination of pros and cons is only meaningful to the proposed end-use of the material. Burditt listed 21 reasons why filler may be added to a polymer [4]. In addition to those intentional changes, there are a multitude of unintentional effects that must also be considered. In this chapter the main properties of composites and how they vary with filler type and level of addition will be discussed. 

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Polymers are characteri2ed as thermosetting and thermoplastic with respect to the methods by which they are joined. Thermosetting polymers are permanently hard and do not soften upon the apphcation of heat they are joined by mechanical fasteners and adhesives. Several methods have been devised to join thermoplastic polymers, as weU as thermoplastic composite materials, which soften upon heating. 

Composites. High molecular weight PPS can be combiaed with long (0.6 cm to continuous) fiber to produce advanced composite materials (131). Such materials having PPS as the polymer matrix have been developed by usiag a variety of reinforcements, including glass, carbon, and Kevlar fibers as mat, fabric, and unidirectional reinforcements. Thermoplastic composites based on PPS have found application ia the aircraft, aerospace, automotive, appliance, and recreation markets (see Composite materials, polymer-matrix). 

Fig. 5. Interlaminar fracture toughness, for a number of thermosetting and thermoplastic composites (36,37). Open white bars represent glass-fiber composites shaded bars are for carbon fibers. The materials are A, polyester (unidirectional) B, vinyl ester (CSM = chopped strand mat) C, epoxy (R/BR1424) D, epoxy (T300/914) E, PPS F, PES and G, PEEK. To convert J/m to fdbf/in. multiply by 2100.

Table 1. Mechanical Properties and Relative Costs of Thermosetting and Thermoplastic Composites...

Thermoplastic composites can be classified according to use, cost, performance, or processing methods. In the following discussion of the chemistry of the resin systems utilized in composites, three classes are considered ... 

Most of the resin systems used in commodity composites are slight modifications of the standard commercial mol ding grade material. Usually certain selected properties, such as purity or molecular weight range or distribution, are enhanced or carehiUy selected. In addition, special additives, such as flow controllers, thermal stabilizers, or antioxidants, are often added by the resin manufacturer prior to shipment. Many of the conventional or commodity-type resins used in thermoplastic composites are Hsted in Table 1 and the preparation of each of these is described. AH resins and blends described in the hterature are not Hsted, and the synthesis described is not the only procedure available, but is usually the most common commercial process. 

Poly(phenylene ether). The only commercially available thermoplastic poly(phenylene oxide) PPO is the polyether poly(2,6-dimethylphenol-l,4-phenylene ether) [24938-67-8]. PPO is prepared by the oxidative coupling of 2,6-dimethylphenol with a copper amine catalyst (25). Usually PPO is blended with other polymers such as polystyrene (see PoLYETPiERS, Aromatic). However, thermoplastic composites containing randomly oriented glass fibers are available. 

Dasch, C.J., Baxter, VV.J., and Tibbetts, G.G., Thermoplastic composites using nanometer-size vapor-grown carbon fibers. Extended Abstracts, 2Ist lliennial Conference on Carbon, 1993, pp. 82 83,... 

Wu, S.Y, Schuler, A.M. and Keane, D.V., Adhesive bonding of thermoplastic composites 1. The effect of surface treatment on adhesive bonding. 9th Int. SAMPE Symp., Oct. 13-15, 1987. 

Phillips, L.N. (ed.) Design with Advanced Composite Materials, Design Council, London (1989). Strong, B.A. High Performance Engineering Thermoplastic Composites, Technomic Lancaster, PA (1993). 

C. Charbon, S. Swaminarayan. Modeling the microstructural evolution of thermoplastic composites. Mater Sci Eng A 238A66, 1997. 

Potential advantages of both thermoplastics and cellu-losic materials combined with the economic and environmental viewpoint have lead to a promising utilization of both these materials in various forms of composites. Although various branches of cellulosic-thermoplastic composites industries are booming in recent years, their growth rate is very slow. In order to achieve the full potential of such valuable materials as various engineering materials and commodity products more incentives from academic, industrial, and governmental authorities are needed. 

Journal of Thermoplastic Composite Materials 13, No.2, March 2000, p.92-101 TERTIARY RECYCLING OF AUTOMOTIVE PLASTICS AND COMPOSITES... 

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