Simultaneously improving the toughness and flame retardancy of Poly(lactic acid) by incorporating a novel bifunctional macromolecular ionomer

Abstract

Improving the toughness or flame retardancy of poly(lactic acid) (PLA) has been widely concerned. However, due to the bad interfacial compatibilization and low efficiency of anti-flammability for these traditional additions, seldom researches can simultaneously and efficiently improve the toughness and flame retardancy of PLA. In order to make up the bland of study on bifunctional macromolecular additive for simultaneously improving the toughness and flame retardancy of PLA, the ionomer additive PBAUI was synthesized. This well-designed structure of PBAUI played a very important role in the modification of PLA. The hard segment of PBAUI not only improved interfacial compatibilization with PLA through hydrogen bonding interactions and ionic aggregation but also improved the flame-retardant efficiency through the phosphorus-containing ionic group. Based on the good interfacial compatibilization between PLA and PBAUI, the soft segment of PBAUI could further provide high quality toughening effect. Therefore, PLA/PBAUI blends achieved excellent toughness-strength balance, even the content of PBAUI was only 5 wt%, the tensile strength of blends still preserved as 86.6% of PLA, which was accompanied by the high tensile elongation at break (≥250%). At the same time, the fire safety of PLA was significantly improved by adding a very low content of PBAUI. Only 5 wt% PBAUI was added into PLA, the blend passed UL-94 V-0 rating and had a low peak heat release rate of 366 kW/m2, and the LOI value increased from 19.5 vol% for the neat PLA to 28.0 vol% for the blend. It is worth mentioning that the incorporation of PBAUI had tiny impact on the transparency of PLA. The transmittances of PLA/PBAUI blends still kept 48% at 800 nm when the content of PBAUI increased to 5 wt%. PLA/PBAUI blends possessing toughness, flame retardancy and transparency will benefit their application in the fields of plastic packaging, automotive industry, instruments shell, thin films and coatings.