Characteristic impact resistance model analysis of cellulose nanofibril-filled polypropylene composites

Notched and unnotched Izod impact strength of cellulose nanofibers (CNFs) and microfibrillated cellulose (MFC)-filled impact modified polypropylene (PP) composites were measured and compared with microcrystalline cellulose (MCC)-filled composites. An Izod impact fracture initiation resistance theory was formulated and a characteristic impact resistance model was developed to evaluate the unique impact characteristics of cellulose nanofibril-filled PP composites. As filler loading increased CNF and MFC-filled composites showed higher characteristic impact resistance than MCC-filled ones. Among the cellulose fillers used in this study, CNF were found to be the most resistant of the three materials tested in terms of characteristic impact resistance. Even though impact resistance in not the only evaluation tool, characteristic impact resistance is an evaluation tool used to determine the material’s unique and hidden impact characteristics. The characteristic impact resistance model is useful for analysis of the impact behavior of any polymer composite material. It was also found that impact modified PP used in this study is more fracture resistant, but more crack sensitive, than conventional PP.