YONGQI SHI, Chenyang Li, Lili Yu, Binqing Sun, Hui Li
Recycled polypropylene/bamboo fiber (rPP/BF) composites were fabricated using bamboo fiber (BF) as the reinforcing filler and recycled polypropylene (rPP) as the matrix resin, which offered an effective strategy for the recycling and resource utilization of waste petroleum-based plastics. The rPP/BF composites were subjected to interfacial modification: bamboo fibers were treated with 2 wt% KH792, and 2 wt% PP-g-MAH was applied as a compatibilizer for the rPP matrix. To further improve the mechanical, physical properties and thermal stability of the composites, ammonium polyphosphate (APP) and nano-SiO₂ aerogel were introduced as flame retardants. The effects of various flame retardants and modification routes on the performance of recycled rPP/BF composites were systematically investigated by oxygen index test, FTIR and TG analytical methods. Test results indicated that after different flame-retardant modifications, the elastic modulus and modulus of rupture of the rPP/BF composites decreased by 13.36%-47.63% and 16.76%-66.17%, respectively. The 72 h water absorption increased by 2.5%-42.5%. With the exception of group Z6, the thickness swelling rate after water absorption rose by 7.14%-114.29% for all other samples. The synergistic effect of APP and nano-SiO₂ aerogel significantly improved the flame retardancy of PP/BF composites, raising their flame-retardant grade to the flame-resistant level (≥ 32%), which was superior to that achieved by APP or nano-SiO₂ aerogel alone. FTIR confirmed that the flame retardants were successfully incorporated into the PP/BF composites. Furthermore, owing to the synergistic effect between APP and nano-SiO₂ aerogel, group Z6 displayed the lowest mass loss and the optimal thermal stability over the whole testing temperature range.