Micro-crystalline Cellulose and Nano-crystalline Cellulose for Enhancing the Mechanical Properties of Epoxy - The Effect of Moisture Content

Abstract

Epoxy polymers have very good mechanical properties and chemical resistance; thus, they are utilized extensively in several fields including composites, adhesives, and surface coatings. We added Nano- and Micro-crystalline cellulose (NCC and MCC) to the epoxy matrix to enhance their mechanical properties and fracture toughness. NCC and MCC are extracted from renewable and biodegradable cellulosic sources (e.g., wood, cotton) and they have good mechanical properties, high surface area, and abundant active surface groups. The objectives of this study were to investigate the effects of (1) filler content, (2) particle size (NCC vs. MCC), and (3) filler moisture content (pristine vs. dried MCC/NCC) on the mechanical properties of epoxy composites. To assess the mechanical properties, a universal testing machine (UTM) was used to measure the tensile properties and calculate the fracture toughness. A scanning electron microscope (SEM) was used to examine the morphology of the crack in samples. The tensile strength of epoxy composites as a function of dried filler content showed a maximum at around 0.5 wt.%. The maximum tensile strengths of the filler-based epoxy composites were 56.2 MPa (53% improvement) and 49.5 MPa (35% improvement) for NCC and MCC-based epoxy composites, respectively. By pre-drying the fillers, higher tensile strengths were achieved for epoxy composites at relatively lower concentrations. NCC with lower particle size distribution was more efficient in reinforcing the epoxy composites perhaps due to its morphological characteristics and better distribution in the epoxy matrix. The maximum fracture toughness improvements of the epoxy composites were 11.217% (1.052 MN.m^0.5) and 1.977% (0.965 MN.m^0.5) for 2 wt.% NCC and 1wt.% MCC, respectively. The study showed the promising reinforcing properties of MCC and NCC in epoxy composites and the effect of their moisture content on the mechanical properties.