Thermal stability and flame retardancy of cellulose nanocrystals reinforced epoxy nanocomposites

Abstract

Epoxy is a type of thermosetting resin that has been widely used in different applications, such as for adhesives, sealants, coatings, paneling, and electronics boards, due to its excellent mechanical strength and chemical resistance. Despite its advantages in mechanical performance, epoxy has drawbacks related to flammability and compromised thermal stability. This drawback has a profound impact on the final processing and applications of epoxy resin. In this study, a bio-based additive, cellulose nanocrystal (CNC), was successfully developed and added to the epoxy resin to enhance the flame retardancy and thermal performance of the resulting epoxy composite. CNC was extracted from cotton linters and used directly as an additive to the epoxy matrix, with varying concentrations (0.5 wt% and 1.0 wt%). The fabricated epoxy composites were evaluated for flammability using a cone calorimetry test and for thermal stability by thermogravimetric analysis. The thermal stability results obtained were significant; 0.5 wt% and 1.0 wt% CNC-added epoxy composites demonstrated a significant improvement in the onset of thermal degradation. The cone calorimetry test revealed a 17% reduction in peak heat release rate (pHRR) and total heat release rate (HRR), indicating substantial improvements in flame resistance. The CNC promoted the char formation in the epoxy matrix due to the absence of oxygen in the char layer, thus preventing further flame penetration into the inner layer. The CNC-reinforced epoxy has the potential to be used as a flame-retardant additive in polymer composite applications as well as in coating parts where heat and thermal resistance are important.