Preparation and properties of benzoxazine blends with intumescent flame retardancy

A benzoxazine containing both alkynyl and aldehyde groups (PHB-apa) was used to modify typical diamine type benzoxazine (PH-ddm) with different ratios to get good flame retardancy. The effects of PHB-apa on curing reaction behavior, heat resistance and thermal stability of the copolymers of PHB-apa and PH-ddm, poly(PH/PHB)s, were analyzed by DSC, DMA and TGA, respectively. The flame retardancy of poly(PH/PHB)s was investigated by vertical combustion test, limiting oxygen index (101) and cone calorimeter. The results suggested that the flame retardancy of PH-ddm was greatly improved by adding a small amount of PHB-apa. When the addition amount of PHB-apa was only 1:12 (the molar ratio of PHB-apa to PH-ddm), the 101 value of poly(PH/PHB-12) was as high as 33.8 and UL-94 test was improved from V-1 to V-0 rating. Moreover, the structures and morphologies of the residual carbons of poly(PH-ddm) and poly(PH/PHB) after combustion were studied by SEM. It was found that the pores in carbon layer of poly(PH/PHB) were dense and homogeneous. Furthermore, the pyrolytic volatile products of poly(PH-ddm) and poly(PH/PHB) were analyzed by TGA-IR and Py-GC/MS to discuss the degradation and flame retardant mechanism. (C) 2019 Elsevier Ltd. All rights reserved.