Novel bio-based lignosulfonate and Ni(OH)2 nanosheets dual modified layered double hydroxide as an eco-friendly flame retardant for polypropylene

In this paper, a functionalized layered double hydroxide (LDH-LS@Ni(OH)2) flame retardant was designed and fabricated based on a multi-modifier system consisting of lignosulfonate (LS) and Ni(OH)2 and used as a novel flame retardant for polypropylene (PP). In this multi-modifier system, LS as a compatibilizer and charring agent to improve compatibility and char yield, and Ni(OH)2 was utilized to improve the graphitization of char residual, resulting in a PP/LDH-LS@Ni(OH)2 composite with higher thermal stability. With the addition of LDH-LS@Ni(OH)2 was only 15 wt%, the PP/LDH-LS@Ni(OH)2 composite achieved a limiting oxygen index (LOI) of 30.8% and passed the UL-94 V-0 rating. At the same time, the peak heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) were significantly reduced by 62.7%, 29.5%, and 46.2%, respectively. The flame retardant properties of LDH-LS@Ni(OH)2 were mainly due to the catalytic charring effect of the transition metal elements and the physical barrier effect of the hydrotalcite. More specifically, as a highly efficient flame retardant, LDH-LS@Ni(OH)2 has promising potential in reducing the fire hazards of PP composites.