Achieving simultaneously toughening and flame-retardant modification of poly(lactic acid) by in-situ formed cross-linked polyurethane and reactive blending with ammonium polyphosphate

Preparing poly(lactic acid) (PLA) composites with toughness and flame retardancy simultaneously is a challenge that many researchers faced. In this paper, flame-retardant and toughened PLA composites were prepared by reactive blending with in-situ formed polyurethane as the toughening phase and ammonium polyphosphate (APP) as the flame retardant. By adding glycerin as a cross-linking agent, the dropping behavior of the composites during combustion is reduced, and the toughness is greatly improved. Compared with the blended composites without the cross-linking agent, the tensile strengths of the composites with the cross-linking degree of 10% are increased by 16%, and the impact strength is increased by 11 times. The composites with 5% APP and 10% cross-linking degree had balanced performance, the vertical combustion can reach V-2 level, and the elongation at break is about 200%. The research provides a simple method to fabricate flame retardant and degradable PLA-based composites with simultaneously enhanced mechanical properties. Graphical abstract Compared with linear polyurethane, the PLA composite material toughened by cross-linked polyurethane not only had a higher elongation at break but also decreased the droplet during the combustion process.