Polymeric composites consisting of a matrix resin (including fluoropolymers) and a reinforcing fiber are well known in the art. By adding the fiber to the matrix resin certain properties of the resin alone are often improved. These properties can include creep resistance, tensile strength and modulus, and flexural strength and modulus. Generally speaking, the reinforcing fiber chosen has a higher tensile modulus and strength than the polymer alone. When a fluoropolymer is used as the matrix resin, as described herein, the resulting composite often has many of the attributes of fluoropolymers such as high temperature resistance and chemical resistance, which make such composites useful as parts, for example, for the chemical processing industry. It is the object of this invention to provide a method for the production of such fluoropolymer composites that exhibit improved properties.
U.S. Pat. Nos. 4,414,356 and 4,163,742 issued to Michel and Mansure, respectively, describe a process for making tetrafluoroethylene copolymer-graphite fiber composite by mixing the polymer and fiber together in a slurry and then removing the water to obtain an intimate mixture of fiber and polymer. It is also known that fluoropolymers have very low surface energy and are difficult to wet, especially as fine particulates, in aqueous media. Accordingly, the current art depends on the extensive use of organic solvents and emulsifying agents (as in the case of fluoropolymer dispersions) to overcome this obstacle. The amount of "wetting and dispersing" agents in such a slurry according to the art can be comparable to the weight of fluoropolymer resin. These organic dispersion aides must be recovered or disposed as waste. It is highly desirable to find a method for intimately co-dispersing finely divided fluorocarbon and other thermoplastic resins in aqueous media, essentially without the need for solvents and dispersing agents.