Mechanical properties improvement and fire hazard reduction of expandable graphite microencapsulated in rigid polyurethane foams

Nowadays, reducing the fire hazard and improving the mechanical strength of rigid polyurethane foams (RPUFs) at the same time are important research direction in the fields of safety materials. Expandable graphite (EG) is an effective flame retardant for RPUF, but would destroy the compatibility of the matrix. In this article, EG is capsuled by melamine cyanurate (MCA) and then microencapsulated expandable graphite (MCEG) is obtained, which is added into RPUF. The mechanical properties of composites were evaluated by compressive strength test, torsion strength test and shear stress test. The fire characteristics including smoke and heat production of RPUF composites were studied using cone calorimeter test. And the thermal decomposition and flammable properties were further evaluated using thermogravimetric analysis and limiting oxygen index. The results show that the mechanical properties of RPUF containing MCEG are similar with RPUF and better than RPUF containing EG. Furthermore, MCA cover would impede expanding of EG, which weakens the protective and insulation effects of expanding layer. Therefore, the composites containing MCEG decompose faster and produce more smoke than the composites containing EG. However, MCA and EG have the synergistic enhancing effect on the flame retardant property of composite. POLYM. COMPOS., 40:E1006–E1014, 2019. © 2018 Society of Plastics Engineers