Mechanical properties of mechanically-defibrated cellulose nanofiber reinforced epoxy resin matrix composites

Abstract

Cellulose nanofibers (CNF) have recently attracted attention as one of the reinforcements for composite materials. However, the same as other nanofibers, CNFs can be easily agglomerated and the nano-level defibration is necessary to obtain their outstanding properties in polymer matrices. To overcome this issue, two major defibration methods, chemical and mechanical defibration have been considered. The chemically-defibrated CNF is expensive and so prevents the practical realization of CNF as general-purpose products. Therefore, the mechanical defibration method by a clean low-cost water jet was focused on. Mechanically-defibrated CNF reinforced epoxy resin matrix (Epoxy-CNF) composite was fabricated via mechanical mixing and the variation of their tensile and flexural properties with different CNF volume fractions was evaluated. The tensile and flexural moduli of the epoxy resin were increased by CNF addition, while the fracture elongation was decreased. The calculated ultimate tensile strength (UTS) and ultimate flexural strength (UFS) of the Epoxy-CNF composites, using the aspect ratio of the agglomerated CNF clusters, indicated the validity of the random dispersion model considering the agglomerated CNF as one whole fiber. It seems that epoxy resin is enhanced by the mechanical interaction when the CNF volume fraction is higher than 0.37 vol.%.