A Si-containing polyphosphoramide via green chemistry for fire-retardant polylactide with well-preserved mechanical and transparent properties

Abstract

A solvent-free green approach has been developed to synthesize a Si-containing polyphosphoramide (DM-Si) for creating transparent and fire-retardant PLA materials. • A green strategy for a Si-containing polyphosphoramide (DM-Si) was developed. • 1 wt% DM-Si significantly improves the fire safety of PLA. • The toughness of PLA increases to 4.7 MJ/m 2 but maintaining its tensile strength. • The transparency of PLA fire-retardant composites is well-preserved. Renewable polylactide (PLA) features good biodegradability, high optical transparency and mechanical strength. However, inherent flammability severely restricts its practical applications in packaging, fabric and electronics. Polyphosphoramides have recently demonstrated high fire-retardant effectiveness in PLA, but their synthesis usually involves the use of a large volume of toxic organic solvents, in addition to their negative impacts on the transparency of PLA. Herein, we report a one-pot green solvent-free approach for massively synthesizing a silicon (Si)-containing polyphosphoramide (DM-Si). The results show that with only 1.0 wt% of DM-Si, the resultant PLA material exhibits desirable fire retardancy, e.g., a UL-94 V-0 rating and a limiting oxygen index of 27.9%, and a 68% increase in toughness relative to virgin PLA. Moreover, both the tensile strength and transparency of PLA are well-preserved. This work provides an eco-benign yet facile strategy for the synthesis of efficient flame retardants for bioplastics with balanced mechanical strength and transparency, which hold great promise as sustainable materials for many industrial applications.