Polypropylene (PP)[#3] is used as a matrix in numerous composite products. It's appeal is both
low density and low cost. Because polypropylene is semi-crystalline, its heat distortion
temperature increases significantly from 55° C to 130°C with the addition of 20 wt% glass fiber
reinforcement (Matweb). Since polypropylene is non-polar, it absorbs very little water. Due to
its glass transition temperature below room temperature, it exhibits good impact strength.
Because of these properties polypropylene is used 90% of the time in glass mat thermoplastic
(GMT) sheet material for compression molding. Short and long fiber-reinforced polypropylene
made by melt impregnation is available from many sources for injection molding applications.
Continuous fiber reinforced polypropylene containing >50 vol % fiber is usually made by
powder coating (Applied Fiber Systems, 2000) or commingling polypropylene with reinforcing
fibers (Vetrotex, 2000).