Processing, thermosets composites

The rigidi d thermoplastic sheet - Tiocess combines thermoplastic sheet vacuum forming with a spray-up or cold press molding process to add a thermoset composite stmctural backing to a decorative thermoplastic skin. Large parts such as bathtubs, hot tubs, recreation vehicle components, and camper tops have been produced by this process. 

Because most thermoset composites cure by a thermally activated reaction, a complicated heat transfer process occurs during solidification, the result of an exothermic cross linking reaction in the resin. The complications of thermoset resin curing are compounded by the competing mechanisms of... 

Processing requirements for thermoset composites, with specific examples of silicones, were recently reported.514 Composites based on the low molecular weight polysiloxanes for medical applications have been reviewed (in Russian).515 Silicone rubber/hydrogel composites have been evaluated for medical applications.516... 

The processing methods will be selected according to the importance of the series, part sizes and targeted properties. Table 6.1 suggests some processes, for thermoplastic and thermoset composites, according to the part sizes and production outputs. 

The other difference [21] is fhaf fhermosef composife shows higher balanced sfrength and toughness compared to thermoplastic composite, with a little brittleness. Thus, thermoset composite plates can be fabricated relatively thinner and have more applications. On the other hand, as mentioned before, a well developed injection molding process has been applied as the fabrication process of thermoplastic-based composite plates to assure high quality and low cost. 

The manufacture of polymeric materials, reinforced or unreinforced, is not a single process rather, it is a sequence of processes. For example, the making of a thermoset composite in an... 

Recendy, storm doors have been constmcted of advanced thermoplastic composites. Stampable, glass-mat reinforced polypropylene sheet is used to create a high strength outer skin. These compression molded skins are welded together using a friction or ultrasonic process then injection molded with a polyurethane foam core to produce an insulated structure. New technology for window frames incorporate the pultrusion of frame channels to produce a thermoset composite channel that can be filled with fiber glass for further insulation enhancement (12,31,33,34,48,49,54—56,60—67). 

Unlike thermoplastics, which are simply melted, thermoset resins chemically react from low-viscosity liquids to solid materials during processing, a process termed curing. Structurally, thermosets differ from thermoplastics because of the presence of cross-links in the former, which means that thermosets cannot be reshaped or recycled once the chemical reaction occurs. One advantage of thermosets vs. thermoplastics is that wetting the filler becomes much easier with a low-viscosity material. By far the most common thermoset composite is automobile tires, which consist of a polymer made from styrene and butadiene monomers and carbon-black filler. The actual recipe used is much more complicated, and can include other monomers or polymers, as well as other fillers. In the absence of filler, the cured resin is rubbery at room temperature, which makes tires a... 

Table 1 Typical molding processes in thermoset composites...

Parquharson S, Smith W, Rose J, Shaw M. Correlations between molecular (Raman) and macroscopic (Rheology) data for process monitoring of thermoset composites. J Process Anal Chem 2003 7(2), http //www.infoscience.com/JPAC/JPACUserPorm.html. 

Microwave processing has been used to process thermoset polymers and polymer composites, including polyesters, polyurethanes polyimides and epoxies, and in most studies it has been concluded that the curing speed is faster using microwave energy (Clark and Sutton, 1996). The effects of continuous and pulsed microwave irradiation on the polymerization rate and final properties also have been studied, and it was demonstrated that, for certain epoxies, a pulsed microwave cure resulted in improvements in mechanical properties, better temperature uniformity and a faster polymerization mte (Thuillier and Jullien, 1989). 

Boey. F.. and Lye, S. W., Void reduction in autoclave processing of thermoset composites. Part I High pressure effects on void reduction. Composites. 2J(4). 261 265 (1992). 

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