Enhanced thermal stability, flame retardancy, and mechanical properties of casein-modified rigid polyurethane foams
Xu Zhang, Qihong Guan, Shuai Ding, Zhi Wang, Hua Xie
Abstract
Rigid polyurethane foam (RPUF) is now widely used in various industries, and there is an increasing interest in preparing green RPUF with high flame retardancy and mechanical properties. In the present work, a casein-modified rigid polyurethane foam was prepared using a one-step foaming method. The thermal, flame retardant, smoke suppressant and mechanical properties of modified RPUFs were examined using thermogravimetric analysis, limiting oxygen index (LOI) testing, cone calorimetry (CONE) testing, smoke density testing and compression studies. The results showed that the foam with 6 wt% casein (RPUF-C3) had the highest initial decomposition temperature and the highest carbon residue. The initial decomposition temperatures were 204.28 °C, 227.18 °C, 213.96 °C and 207.93 °C for the four heating rates and the residual carbon was 18.66 %, 21.12 %, 18.82 % and 22.96 %, respectively. The highest average activation energy (E) calculated by the four methods, indicating the best thermal stability. In addition, RPUF-C3 exhibited the best flame retardant and smoke suppressant properties, with an improved limiting oxygen index (LOI) of 22.1 % and the peak heat release rate (PHRR) and total heat release (THR) of RPUF-C3 were the lowest. RPUF-C3 also showed significant improvements in smoke suppression, mechanical and thermal insulation properties, outperforming non-modified foams. The findings suggested that casein actively contributed in RPUF and provided an effective reference for the development of new green and efficient RPUF.