Pultrusion of Thermoset/Fiber Composites

Abstract

Pultrusion of thermoset/fiber composites generally consists of pulling continuous rovings and/or continuous glass mats through a resin bath or impregnator and then into preforming fixtures, where the section is partially shaped and excess resin and/or air are removed. Finally, the preformed profiles are pulled through heated dies, where the section is cured continuously (Batch 1989; Meyer 1985; Price 1979; Richard 1986). The pultrusion process is one of the most cost-effective continuous processing techniques for producing thermoset composite materials. The laminating resin may be an unsaturated polyester resin, a vinyl ester resin, or an epoxy resin, but the majority of pultruded thermoset products currently use unsaturated polyester resins. The reason for this is that epoxy resins require high heat inputs and have relatively slow gelation, although some effort has been spent on development of new epoxy resin systems that can be pultruded at speeds comparable with unsaturated polyester resin systems (e.g., 0.6–0.9 m/min). Han and coworkers (Han et al. 1986, Han and Chin 1988) formulated and then solved numerically, via the finite difference method, a system of equations describing the cure kinetics of a thermoset resin and the heat transfer between the resin and the die wall, in order to model the pultrusion process for thermoset/fiber composites. Subsequently, other investigators (Batch and Macosko 1993; Chachad et al. 1995; Gorthala et al. 1994a, 1994b; Ma et al. 1986) reported similar studies. Experimental studies (Batch and Macosko 1993; Chachad et al. 1995; Ma et al. 1986; Price 1979; Price and Cupschalk 1984; Roux et al. 1998) on the pultrusion process for thermoset/fiber composites have also been reported. Some research groups (Aström and Pipes 1993; Larock et al. 1989; Ma and Chen 1991; Ruan and Liu 1994) have investigated the pultrusion process of fiber-reinforced thermoplastic polymers. While there are some similarities between the pultrusion of thermoset/fiber composites and fiber-reinforced thermoplastic polymers, the most important difference between the two lies in that the former involves chemical reactions during processing, whereas the latter does not.