Effect of catalysts on cure time of polyester SMC processing

Abstract

In this research, three types of catalysts: t-butyl perbenzoate (TBPB), 1,1-di-(t-butyl peroxy) cyclohexane (DTBC), and benzoyl peroxide (BPO), and the effect of added parabenzoquinone (PBQ) were studied. The effect of types and concentration of catalysts on storage life of the SMC, mechanical properties, and curing characteristics in the mold of the SMC at 1 and 2 minutes were investigated. When the TBPB catalyst was used, the storage time of SMC could be as long as 45 days. Between 17-30 days the hardness of SMC was suitable for molding at 150°C and 2 minutes curing time. The shorter curing time (1 minute) gave lower strength to the composite but with an addition of PBQ of 0.025 phr, the strength was enhanced. So did the SMC with the DTBC catalyst and the storage life of SMC was about 30 days. The dual catalysts system of the DTBC catalyst in conjunction with the TBPB catalyst provided a faster cure than did the TBPB catalyst alone. By using the BPO catalyst, it was found that the molding temperature was reduced to 120°C but the viscosity of paste was increased rapidly and the sheet could be stored for only 10 days. After a 1 minute of cure, the strength of composite became somewhat lower than that of a 2 minutes curing time, and was also lower than those by TBPB and DTBC catalysts by 10%. Therefore, the most suitable catalysts for the SMC in this research were TBPB and DTBC, in the presence of 0.025 phr of PBQ in the SMC component, the BPO cannot be used as the sole catalyst in the SMC.