The goal of this study is to examine how the extrusion process affects the dispersion, length, and thermal degradation of cellulose fibers (CF) in polypropylene (PP) composites. Bleached sulfite CF are pelletized and then compounded (20 and 30wt%) in a co-rotating twin screw extruder. The pelletizing process of CF is found to cause extensive fiber breakage. The fiber length is decreased from an initial 1.7 to 0.8 mm. The results show that higher screw speed, higher fiber content, and two extrusions not only increase the shear energy, resulting in improved fiber dispersion but also cause fiber breakage and thermal degradation. The composite's mechanical properties are not improved with better fiber dispersion and the reason for this might be the extensive fiber breakage and thermal degradation. Moreover, it is found that the PP polymer is also slightly degraded during the compounding process.
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