Evaluating the effects of thermal pretreatment of bamboo fibers on characteristics of bamboo–polypropylene thermoplastic composites

This study investigates the influence of thermal pre-treatment on the properties of bamboo fiber-reinforced polypropylene composites (BPCs). Reinforcement with bamboo fibers (BFs) is known to enhance mechanical performance but typically leads to hydrophilicity, restricting the use of bamboo–polypropylene composites (BPCs) for indoor applications. To overcome this, Dendrocalamus stocksii (Munro) BFs were subjected to vacuum-assisted thermal pre-treatment at 160°C, 180°C, and 200°C before incorporation into a thermoplastic polypropylene (PP) matrix. The primary objective was to augment hydrophobicity and chemical compatibility by diminishing the presence of free hydroxyl groups. Additionally, the impact of a coupling agent, maleic anhydride-polypropylene (MAPP), on the composites was also assessed. The BPCs were fabricated using a twin-screw extruder, maintaining a 40% BFs to 60% PP ratio. This study comprehensively evaluated the physical, mechanical, and morphological characteristics of the BFs pre-heat treatment, including density, water absorption, flexural and tensile properties, and Scanning Electron Microscopy analysis (SEM), to investigate their synergistic effects on composite performance. The results indicated that thermal treatment temperature positively correlated with improvements in the density and water absorption of the BPCs. Notably, after 2000 h of water absorption, improvements ranged from 0.67% to 38.30% through the various temperature treatments. The incorporation of MAPP into composites with thermally modified fibers (BPCT) collectively enhanced the flexural and tensile strength. Specifically, the BPCTs' flexural strength at 180°C demonstrated a 21.9% increment compared to untreated BFs, while tensile strength at the same temperature increased by 31.92%. Although most mechanical parameters improved with thermally modified bamboo, elevating the temperature beyond 180°C adversely impacted the strength properties. SEM micrographs revealed improved compatibility between the thermally modified BFs and the PP matrix, further enhanced by MAPP addition, as evidenced by void-free mechanical interlocking. With desirable improvements in quality parameters, thermally treated bamboo-reinforced polypropylene thermoplastic composites exhibit a strong potential as substitutes for chemical pre-treatments.