Renewable isosorbide-derived poly(phosphoester) for simultaneously enhanced flame-retardancy and mechanical property of polylactide

Incorporating flame retardant fillers is the most efficient way to improve the fire resistance of polylactide (PLA). However, most flame retardant fillers result in deterioration of the mechanical property of PLA so far. Therefore, to create high-performance PLA materials combining excellent flame retardancy with superior mechanical properties remains highly attractive and challenging. In this study, a novel isosorbide-derived poly(phosphoester) (PIDI) was synthesized and used as a bio-based flame-retardant for PLA. The addition of PIDI showed a marginal effect on the change of the glass transition temperature of the PLA composites, but the crystallinity degree of the PLA composites was improved by the inclusion of PIDI. Benefitting from the improved crystallinity, the tensile strength, flexural strength, and impact strength of PLA composite containing 15 ​wt% PIDI was enhanced by 19.4%, 14.1%, and 36.9%, respectively, compared to the virgin PLA. With the addition of 20 ​wt% PIDI, the PLA composite showed an LOI value of 25.5% and a UL-94 V-0 rating in the vertical burning test. The flame retardant effect of PIDI was also demonstrated by a notable reduction (−46%) in the peak heat release rate (PHRR) of PLA composite containing 20 ​wt% PIDI. Such a renewable isosorbide-derived poly(phosphoester) is one of the promising candidates for PLA bio-composites with an outstanding balance between flame retardancy and intrinsic physical properties.