Tensile Property of iPP Based Composites Embedding “Plant Cell Wall”-Mimicked Frameworks of Ultratrace Amphiphilic Cellulose Nanofibrils Derived from Various Raw Materials

For the last decade, cellulose nanofibrils (CNFs) have attracted a considerable attention in utilization of a reinforcing filler for polymer materials because of their excellent physical properties. CNFs (= ACC-CNFs) prepared by aqueous counter collision (ACC) method own more hydrophobic nature on their surfaces than usual CNFs. Moreover, ACC-CNFs favorably adsorb to isotactic polypropylene (iPP) microspheres solely by their mixing in the aqueous dispersion. Recently, the iPP microspheres coated with ACC-CNFs (approximately 0.03 wt% as coverage) yielded an impact-resistant composite material embedding “plant cell wall”-mimicked frameworks via usual injection-molding. As impact-resistance exhibits a trade-off relationship against tensile strength usually in composite materials, the current study focuses on tensile properties of the above composite materials having the impact-resistant properties. The dependence of raw materials for preparation of ACC-CNFs on the properties of the molded products are also examined. As a result, ACC-CNF derived from bamboo bleached kraft pulp (= ACC-BBKP) /iPP microspheres yielded superior values in both elastic modulus and tensile strength without decreasing elongation at break when compared with other ACC-CNFs. Namely, the ACC-BBKP/iPP product has achieved to overcome a trade-off relationship between stiffness and toughness. Contrary to ACC-BBKP, ACC-CNF derived from microcrystalline cellulose allowed to improve stiffness of the product, while the improvement in toughness appeared in the molding product via ACC-CNFs derived from bacterial nanocellulose pellicles.