Fabrication of long bamboo fiber-reinforced thermoplastic composite by extrusion and improvement of its properties

As a natural and renewable resource, bamboo is attractive to reinforce thermoplastic due to its excellent mechanical performance. However, it is difficult for long bamboo fiber bundles (LBF) to premix with thermoplastic pellets and could not fluently feed into screw extruder because of its tendency to entangle. To address this challenge, a new method for premixing and feeding LBF and thermoplastic matrix was initially proposed. The polypropylene (PP) film was used as a carrier to wrap long bamboo fibers (about 120mm long), and the PP roll that enclosed the bamboo fibers was fed into and compounded by a twin rotor. The extruded mixture was finally hot-pressed into plates. The compounding process was monitored and analyzed. The fiber size measurements showed that the rotor with a smooth arris and less arris number reduced the damage to LBF. The optimal LBF distribution and orientation in the PP matrix was obtained when the LBF content was arranged at 40 %. The LBF/ PP composite achieved the improved tensile strength and modulus, increasing by 54.44 % and 39.67 %, respectively, compared to the composite reinforced with the traditional bamboo powder. Also, LBF reduced the thermal expansion of the composite by 39.25 %. In terms of water absorption deformation and thermal degradation, no significant difference was found between the two composites at the same fiber contents. Dynamic mechanical tests and dynamic oscillatory rheological tests indicated that the LBF restricted PP movement more than short fibers and showed higher modulus, loss coefficient and complex viscosity. The results indicated that wrapping fibers with thermoplastic film is a promising approach for extruding long fiber reinforced thermoplastic composites, which provides potential applications of LBF in the fields of thermoplastic prepreg.