Preparation of a biobased core-shell flame retardant and its application in polylactic acid

Biobased flame retardant (FR) has attracted great interest owing to its green and degradable properties similar to polylactic acid (PLA). In this work, with ammonium polyphosphate (APP) as the core, chitosan (CS) and halloysite (HNT) as the shell, a biobased FR (APP@CS@HNT) with a core-shell structure was prepared through the self-assembly method. The flame retardancy of PLA composites has been improved with the addition of the FR (APP@CS@HNT). With the loading of 17 wt% APP@CS@HNT, the PLA composite shows a high limiting oxygen index value (29.4%) and achieves vertical burning (UL-94) test V0 rating. Compared with pure PLA, the cone calorimetry test indicates that the peak heat release rate (PHRR) and total heat release decrease from 299.88 to 152.29 kW/m(2) and from 102.0 to 71.2 MJ/m(2), respectively. The addition of APP@CS@HNT can also improve the smoke suppression performance of PLA composites. Such enhanced flame retardancy is mainly attributed to APP@CS@HNT prompting the PLA matrix to produce more continuous and denser carbon layers at a lower temperature to form physical barriers.