Constructing lignin based nanoparticles towards flame retardant thermoplastic polyurethane composites with improved mechanical and oxidation resistant properties.

A multifunctional lignin derivative nanoparticle (C-P-Lignin) was synthesized by grafting phenyl dichloro sphosphineoxid and 1, 4-dimethoxyacetylene stepwise on the lignin, then it was applied to prepare the thermoplastic polyurethane (TPU) composite with improved mechanical properties, oxidation resistance, and flame retardancy. The tensile strength, the elongation at break, and the toughness of the TPU/2C-P-Lignin sample reached 28.3 MPa, 941 %, and 139.0 MJ/m respectively, which were increased by 39.0 %, 3.4 %, and 33.9 % respectively compared with that of the control TPU sample. The anti-fatigue property was also improved. More importantly, the mechanism of the improved mechanical properties was also calculated and simulated by FTIR and Materials Studio software. The TPU/2C-P-Lignin sample exhibited superior oxidation resistance during the process of photoaging and thermal oxidative aging. Furthermore, the peak heat release rate and the smoke production rate for theTPU/2C-P-Lignin sample was reduced by 50.0 % and 53.8 % compared with that of the control TPU. The reason was that the C-P-Lignin is conducive to the formation of uniformly distributed carbon layers. It is expected that this work can provide a new method for expanding the utilization of waste wood as a multifunctional lignin-based filler to improve fire safety and extend the service life of TPU polymers.