Homogeneous and toughened cellulose epoxy composites

Homogeneous and toughened cellulose-epoxy polymers were made by modifying an anhydridecured epoxy with two green modifiers, microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC). Without silane treatment, the MCC and CNC particles sedimented in the epoxy resin and formed either a gradient polymer or two distinct layers. This problem was resolved by the addition of (3glycidyloxypropyl)trimethoxysilane (GPTMS) during the three-roll mill process, which was able to act as a coupling agent between the MCC or CNC and the epoxy, to give a modified epoxy containing homogenously dispersed cellulose particles. The addition of MCC or CNC decreased the glass transition temperature of the epoxy, but doubled the fracture energy. By comparison, the addition of 10 wt% of nanosilica only gave a 57% increase in fracture energy. The toughening mechanisms of the MCC-epoxy and CNC-epoxy were identified to be crack deflection, pull-out and debonding of the cellulose particles, which was followed by plastic void growth. The modified Halpin-Tsai model was used to predict the increase in modulus and showed good agreement with the experimental modulus values. Analytical modelling of the fracture energies showed that particle debonding and particle pull-out contributed to the increased toughness, but the main toughening contributions were due to plastic void growth for CNC-epoxy and both plastic void growth and crack deflection for MCC-epoxy. In addition, plain-weave long glass fibre (GF) composite was manufactured with MCC using resin infusion under flexible tooling (RIFT). The interlaminar fracture energy of the composite was measured and it was found that the Xinying Deng, Anthony J. Kinloch, Soraia Pimenta, Gregory T. Schueneman, Stephan Sprenger, Ambrose C. Taylor and Wern Sze Teo 2 increase in toughness in the epoxy polymer was not translated to the composite. This was thought to be due to the silane that was used to treat the MCC-epoxy system migrating to the glass fibre surface and improved the fibre-matrix adhesion. This reduced the amount of fibre bridging and fibre pull-out, thus reducing the mode I interlaminar fracture energy of the MCC-epoxy glass fibre composite.