Fabrication of highly efficient biodegradable oligomeric lactate flame-retardant plasticizers for ultra-flexible flame-retardant poly (lactic acid) composites

Biobased multifunctional plastic additives not only overcome the toxicity and non-degradability of phthalates but also provide multiple functions to polymers. In this study, novel biodegradable oligomeric lactate flame-retardant plasticizers (PBCL) integrated from l-lactic acid and crotonic acid with excellent fire-retardant and plasticizing functions were synthesized to overcome the inflammability and fragileness of poly(lactic acid) (PLA). The results revealed that PBCL-plasticized PLA composites achieved a good balance between flexibility and fire retardancy. Even with a ratio of 0.2:1 of 9,10-dihydro-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to 2-(2-n-butoxyethoxy) ethanol of crotonic acid lactate ester (BCL), the plasticized PLA blends showed the highest elongation at break (433.72 %), accompanied by a high limiting oxygen index (27.1 %). Remarkably, the vertical burning tests (UL-94) indicated that all blends passed UL-94 V-0 grade, signifying their superior fire resistance. Interestingly, the addition of PBCL had minimal impact on the transparency of PLA, with the transmittances of all composites still remained at above 87 % at 800 nm. Furthermore, the PBCL-plasticized PLA composites exhibited better migration resistance and volatility resistance than commercial plasticizer acetyl tributyl citrate (ATBC). Additionally, the biodegradability of PBCL was studied through the degradation experiments using active soil and tenebrio molitors, with characterization of the degradation products. The results of the biodegradation experiments showed that PBCL decomposed into non-toxic and harmless small molecules. This study presents an eco-benign method for developing biodegradable additives with flame-retardant and plasticizing functions, holding excellent prospects for industrial applications.