Urea‐activated 4,4'‐oxibis‐(benzenesulfonyl hydrazide) as foaming agent for low‐density unsaturated polyester resin manufacturing

The activation of foaming agent is critical to its application. In this study, 4,4′‐oxibis‐(benzenesulfonyl hydrazide) (OBSH) activated by urea was used in the manufacture of low‐density unsaturated polyester resin (LDUPR), and the results were compared with that of OBSH activated by zinc oxide and zinc stearate. The experiment results showed that the activation of OBSH by urea was better than by zinc oxide or by zinc stearate. A novel hydrogen bond activation mechanism of urea is presented in this research. Two stages, including the induction stage and the foaming stage, were proposed in the LDUPR manufacture according to the gas evolution curves of activated OBSH. The decomposition temperature and the decomposition time of OBSH activated by urea were determined to match the gelation time of UPR for the manufacture of LDUPR. The disadvantageous chemical behaviors of activated OBSH were eliminated in the induction treatment. The activated OBSH via induction treatment released gas maximally and distributed gas homogeneously in the resin glue, resulting in a better foaming effect than that of the previous foaming agents. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42824.