Thermoplastic Polymeric Composites

An example of such a catalyst system is racemic isopropylene bis(l-indenyl) zirconium dichloride in combination with an alumi-noxane (21). The reaction is carried out in hydrocarbon solvents, e.g., toluene. A solution of norbornene in toluene with the catalyst is degassed and then pressurized with ethene. The polymerization is carried out while stirring at 70°C under constant ethylene pressure at 18 bar. After completion, the polymer is precipitated in acetone and filtered (21). The cycloolefin copolymers obtained in this way have a high thermal shape stability and it is possible to use the polymers as thermoplastic molding compositions. 

Organic matrices are divided into thermosets and thermoplastics. The main thermoset matrices are polyesters, epoxies, phenolics, and polyimides, polyesters being the most widely used in commercial applications (3,4). Epoxy and polyimide resins are applied in advanced composites for structural aerospace applications (1,5). Thermoplastics Uke polyolefins, nylons, and polyesters are reinforced with short fibers (3). They are known as traditional polymeric matrices. Advanced thermoplastic polymeric matrices like poly(ether ketones) and polysulfones have a higher service temperature than the traditional ones (1,6). They have service properties similar to those of thermoset matrices and are reinforced with continuous fibers. Of course, composites reinforced with discontinuous fibers have weaker mechanical properties than those with continuous fibers. Elastomers are generally reinforced by the addition of carbon black or silica. Although they are reinforced polymers, traditionally they are studied separately due to their singular properties (see Chap. 3). 

Transition of adhesives in thermoset wood composites to thermoplastic polymeric materials and realization that a key point would be a uniform mixing of cellulose fiber with the plastic. 

U.S. Pat No. 6,827,995 [53] discloses a single coextrusion process of making a WPG as a hollow profile comprising a weatherable outer layer made of a first polymeric material, a core layer made of a thermoplastic polymeric foamed composition including a wood component, and an inner layer made of a third thermoplastic material. The first and second polymeric materials are PVC or acrylonitrile-styrene-acrylic polymer or a combination thereof. The third polymeric material is PVC. 

U.S. Pat, Nos. 6,122,877 [107] and 6,682,814 [108] (both by Andersen Corporation) disclose a cellulosic fiber-polymeric composite comprising 45-70% of thermoplastic polymers such as PVC, polyethylene and its copolymers, polystyrene, polyacrylate, polyester and their mixtures, and 30-65% of wood fiber, such as sawdust. 

M. K. Bisaria, P. Andrin, M. Abdou, and Y. Cai. Injection moldable conductive aromatic thermoplastic liquid crystalline polymeric compositions. US Patent 6 379 795, assigned to E. 1. du Pont de Nemours and Company (Wilmington, DE), April 30, 2002. 

The family of polymeric composites splits into those which use thermosetting resins and those which use thermoplastic resins. The EUROCOMP programme is only concerned with the thermosets. 

Even PE, PP and polyvinyl chloride resins, still the most commonly used thermoplastic polymeric materials with wood, have low thermal stability above 200 °C. However, their inherently undesirable mechanical properties, such as the creep-resistant properties of the polyolefin matrix, have impeded further applications of the wood plastic composites (WPG) as structural composite materials. In attempts to overcome these drawbacks, attention has been given to the silane-crosslinking of wood/PE composites [38], the use of high-performance engineering thermoplastics such as Nylon 6 [39] as a single polymeric matrix, the modification of the matrix by incorporation of organoclay [40], and stretching wood/PP composites [41]. 

Bastioli C, BeUottiV, Montino A.Tredici GD, Lombi R, Ponti R. Biodegradable polymeric compositions based on starch and thermoplastic polymers. US 5,412,005. Novamont 1991. 

At the moment, fiber reinforced polymeric composites are exclusively joined by gluing, by screws or by rivets. But these techniques do not exploit the potential given by fiber reinforced polymers. The outcome is below the expectations, and thus fiber reinforced thermoplastics do not penetrate new applications. 

Mallon, P.J., O Bradaigh, C.M. and Pipes, R.B. (1989) Polymeric diaphragm forming of continuous fibre reinforced thermoplastic matrix composites. Composites, 20, 48-56. 

Essentially, physical methods are employed on natural fiber during processing in order to separate natural fiber bundles into individual filaments and also to modify the surface structure of the fibers so as to improve the use of natural fibers in composites. Physical methods can be divided into two categories viz (1) steam explosion and thermomechanical processes and (2) plasma, dielectric barrier techniques, radiation modification, ultrasonic treatment, and corona discharge. In an effort to impart and improve reactivity, these physical treatments have been used to modify thermoplastic polymeric films like polyethylene and polypropylene and thermosets, such as epoxy. 

Thermal properties of thermoplastic starch composites reinforced with pehuen husk showed the potential of this bioliber as an excellent reinforcement for composite materials. TPS composites showed a good interaction between the fibers and the plasticized starch matrix due to the natural affinity between husk and starch in the pehuen seed. TPS/PLA/PV A blend showed partial miscibility or co-continuous phase and TPS/PLA/PV A composites presented also discontinuities at the biofiber-polymeric matrix interface. The incorporation of biofiber improved the thermal stability of the composites, increasing the initial decomposition temperature. The biofiber hinders the out-dififusion of the volatile molecules (e.g., glycerol), retarding the decomposition process of starch composites. On the other hand, the degree of crystallinity of composites decreases when pehuen husk content increases (Castano et al. 2012). 

Bernardo, C. A., Cunha, A. M., and Oliveira, M. J. (1993) The effect of recycling on the properties of thermoplastics composites, in G. Akovali (ed). The Interfacial Interactions in Polymeric Composites, Kluwer Academic Publishers, Dordrecht, pp. 443-448. 

Ramie fiber-reinforced thermoplastic biodegradable composites were manufactured using the in situ polymerization method. Ramie fibers were treated with coupling agents to improve their compatibility and to strengthen the interface. 

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