Fabrication of Green and Scalable N/P/S/Mn Containing Biobased Layered Double Hydroxide as a Novel Flame Retardant and Efficient Char Forming Agent for Polypropylene

To date, designing efficient bio-based flame retardants for polypropylene (PP) and exploring a green and scalable strategy have remained a hot topic of research. Here, we present a green and convenient preparation of a bio-based flame retardant (LDH-LS@CS@PAMn) for layer-by-layer assembly by utilizing water as an assembly medium. By electrostatic interactions, LDH-LS@CS@PAMn was prepared by the sequential assembly of sodium lignosulfonate-modified layered double hydroxide (LDH-LS) with positively charged chitosan (CS) followed by negatively charged sodium phytate (PAMn). With increasing LDH-LS@CS@PAMn loading in PP composites, the corresponding total heat release rate (THR) and peak heat release rate (PHRR) values were reduced remarkably. With loading 20 wt % LDH-LS@CS@PAMn, the THR and PHRR of PP/LDH-LS@CS@PAMn decreased by 37.6 and 59.1%, respectively, while the limiting oxygen index significantly improved to 31.6% and the V-0 rating was successfully passed by the UL-94. Especially for PP/LDH-LS@CS@PAMn composites, the total smoke production (TSP) was reduced by 47.4%. More importantly, the residual PP/LDH-LS@CS@PAMn char changed from gray to brown-black compared to PP/LDH, indicating a stronger residual char formation. The outstanding fire safety, smoke suppression, and char formation capabilities of PP composites were ascribed to the synergistic LDH-LS@CS@PAMn hybrid’s action. This work provided a feasible and reasonable modification idea to improve smoke suppression and flame retardancy for LDH.