Optimizing Epoxy Vitrimer Composites With Sustainable Cellulose Nanofibril Reinforcements: Enhancing Thermal Dimensional Stability While Preserving Dynamic Covalent Behavior

Abstract

Vitrimers are networks with dynamic covalent bonds that are promising for recycling composite materials, which often suffer from significant creep. This study explores the integration of cellulose nanofibrils (CNFs), without any functionalization, into an epoxy vitrimer matrix to enhance mechanical performance and dimensional thermal stability, while preserving the dynamic covalent network properties. Using an optimized infiltration method of CNF template, CNF was effectively impregnated within the epoxy vitrimer matrix, as demonstrated by SEM and AFM morphological characterizations. A slight decrease in the composite's glass transition temperature is attributed to a reduced crosslinking density at the CNF-resin interface. A 10 wt% CNF resulted in a 77% increase in the composite's storage modulus compared to the neat resin. This CNF-interpenetrated network within the crosslinked vitrimers leads to a significant reduction in the composite's thermal expansion, which is crucial for applications requiring good dimensional thermal stability. Stress relaxation studies indicate a slight increase in the activation energy of topological rearrangement induced by the CNF, while maintaining complete relaxation, thus enabling the reshaping or recycling of composites.