Mechanisms contributing to mechanical property changes in composites of polypropylene reinforced with spray-dried cellulose nanofibrils

This study revealed the effects of spray-dried cellulose nanofibril (SDCNF) addition (3,10 and 30 wt%) and maleic anhydride polypropylene (MAPP) coupling agent (2 wt%) on the mechanical properties of polypropylene (PP). Results indicated that the elastic moduli of the PP composites increased as the SDCNF content increased above 10 wt%. The addition of MAPP into the SDCNF/PP composites did not improve the elastic moduli. Flexural strength of PP was improved when the SDCNF content increased above 10 wt%, while the tensile strength of PP decreased as the SDCNF content increased. The addition of MAPP into the SDCNF/PP composites increased the strength of the composites when the SDCNF content was above 10 wt%. Without the addition of MAPP, the composite's impact strength did not exhibit a significant increase among the pure PP and SDCNF/PP composites. No significant differences in crystallinity or crystal forms were found in the pure PP and PP/MAPP/SDCNF composites. The spherulitic size of PP was reduced after adding SDCNF into the PP.