Micro- and Nano-crystalline Cellulose for Enhancing the Mechanical Properties of Epoxy

Abstract

Epoxy polymers have several important features, such as high bearing capacity and good chemical resistance. Thus, they are widely used in structural applications in various industries including aerospace, and automotive. Despite their broad usage, epoxy polymers are known for their high brittleness that hinders their application in high shock and fracture strength products. To overcome this shortcoming, fillers can be added to the polymer during the preparation. The physical and chemical properties of the final epoxy composite depend on the type of fillers and their interaction with the matrix. In this study, sustainable and biodegradable Nanocrystalline Cellulose (NCC) and Microcrystalline Cellulose (MCC), with good mechanical properties, high surface area, and abundant active surface groups, are used as fillers to reinforce epoxy polymer composites. The goal of this research work was to improve epoxy resin’s mechanical properties by using MCC and NCC fillers and compare their performance. The objectives were to optimize the fabrication recipe of the epoxy composites, investigate the effect of filler concentration on the mechanical properties of the composites, and study the effect of filler particle size. The physical-chemical properties of NCC and MCC-based epoxy composites were characterized using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Dynamic Light Scattering (DLS), Differential Scanning Calorimeter (DSC), Dynamic Mechanical Analysis (DMA), Thermogravimetric Analysis (TGA), Optical tensiometer, compact tension testing, and mechanical tensile testing.

The results showed that by the addition of the bio-based fillers (NCC or MCC) at concentrations below 5%, one can enhance the mechanical properties of the resulting epoxy composites without affecting epoxy’s surface and thermal properties. The maximum tensile strength of the filler-based epoxy composites was achieved at 2wt.% and 4wt.% for NCC and MCC, respectively. Overall, NCC was much more effective in enhancing the mechanical properties of the epoxy composites which was attributed to its morphology characteristics such as smaller particle size and better distribution in the epoxy matrix. The DSC, DMA, and TGA profiles of epoxy with or without any filler did not show any noticeable difference which was an indirect sign of no chemical bond between the filler and the epoxy matrix. The addition of fillers also did not change the surface properties of the epoxy composites which was evidenced by the contact angle measurements.