A zinc-embedded multicomponent copolymer customized for polypropylene and its synergistic flame-retardant effect and outstanding mechanical properties

Abstract

The poor compatibility between the common polar intumescent flame-retardant system (IFR) and the nonpolar polypropylene (PP), as well as the high additive amount, seriously impacts the mechanical properties of the composites. This study introduced collaborative flame-retardant technology to construct block copolymer flame retardants and prepared a zinc-embedded multicomponent copolymer (PM-Zn2+) customized for PP composites. In the PM-Zn2+ system, zinc oxide was embedded into the copolymer composed of piperazine phosphate oligomer and melamine phosphate. PM-Zn2+ exhibited an amorphous structure with extremely low crystallinity and demonstrated specific morphological adaptability. The PM-Zn2+ were well dispersed in the PP matrix and changed their morphology during processing. When applied to PP, excellent flame retardancy and mechanical properties were obtained by using a minimal amount of flame retardants (20 %). PM-2 %Zn2+ gave PP an LOI value of 31.5 %, and achieved a UL94 V-0 rating (1.6 mm thick), exhibiting a lower heat release rate and smoke release. The flame-retardant mechanisms of PM-Zn2+ mainly involved the synergistic and aggregative effects. Transition metal zinc synergistically interacted with polyphosphate groups to create a charring barrier effect and enhance synergistic smoke suppression, leading to a significant reduction in combustion intensity. In comparison to the Mix-Zn/PP composites, the mechanical properties of PM-Zn2+/PP were significantly enhanced due to the specific morphological adaptability and improved compatibility. The elongation at break increased significantly from 15.6 % to 627.9 %, marking a remarkable improvement of 40-fold improvement, while the impact strength rose from 23.7 kJ/m2 to 54.3 kJ/m2, representing a 129 % enhancement. Finally, the zinc-embedded multicomponent block copolymer offers a promising approach to developing high-performance flame-retardant polypropylene materials.