Synergistic flame retardancy in polylactic acid composites using microwave-exfoliated nanosheets and zeolite with an intumescent flame retardant

Abstract

Polylactic acid (PLA) is flammable and tends to produce melt dripping during combustion. The addition of intumescent flame retardant (IFR) significantly enhances its flame retardancy, while synergistic flame retardancy enables control over both the IFR loading and the resulting flame-retardant effect. This study employed a two-stage microwave exfoliation method to simultaneously prepare molybdenum disulfide nanosheets (MDNs), montmorillonite nanosheets (MMTNs), and zeolite powder (ZP). These were used as synergistic agents in combination with an IFR to prepare MDNs/MMTNs/ZP/IFR/PLA composites via melt blending and injection molding, and the flame retardancy of the composites was subsequently tested. The results demonstrate that the composite PLA-9 exhibits the best flame retardancy, with a total flame retardant loading of 20 phr (i.e., 20 wt%), of which the nano-synergist (MDNs/MMTNs/ZP = 1:1:1) accounts for 2 phr and IFR accounts for 18 phr. The limiting oxygen index reaches 44.6 %, and it achieves a V-0 rating in the UL-94 test. Compared to pure PLA, the peak heat release rate and total heat release are reduced by 72.4 % and 36.6 %, respectively. Total smoke production, as well as CO and CO ₂ emissions, decrease by 84.3 %, 48.1 %, and 77.2 %, respectively. This study provides a novel approach for developing high-efficiency, environmentally friendly flame-retardant PLA-based composites.