Development of long fibre heat cure phenolic dough moulding compounds

Traditionally, dough moulding compounds (DMCs) have been based on unsaturated polyester resins (UPR), fillers and glass fibre reinforcements. Such systems however are inflammable and will emit dense, toxic smoke on combustion. Phenolic resins, on the other hand, have excellent flame retardant properties, but slightly inferior mechanical properties. Phenolic DMCs are based on mineral fillers and glass fibre reinforcements, compounded into a phenolic resol (heat cure) resin. Compounding these systems using a co-rotating twin screw extruder, instead of the traditional method using a Z-blade mixer, results in long fibre DMCs which have better mechanical properties than short fibre DMCs. In this study, a wide range of inorganic materials, their pH being one of the selection factors, have been investigated as potential phenolic DMC fillers. Viscosity measurements were carried out on resin/filler mixtures, while on the cured samples flexural and impact properties were investigated. Producing DMCs using a twin screw compounder, the effects of filler loading, types of glass fibre, glass fibre loading and machine output on flexural and impact properties were investigated. Phenolic dough moulding compounds containing 20 wt % high integrity glass fibres and small amounts of aminosilane treated china clays (40 phr filler) had superior mechanical properties. These systems have a flexural strength of more than 120 MPa, which would allow them to compete with traditional UPR-based DMCs.