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Epoxy nanocomposites reinforced with acetyl, hexanoyl, and dodecanoyl surface modified Cellulose Nanocrystals (CNC) were fabricated. Surface modified CNCs were dispersed in epoxy resin with a co-solvent. After complete removal of the co-solvent, a typical two component epoxy system was achieved where hardener was then added to cure the resin. Acetyl grafted CNC (CNC_a) and hexanoyl grafted CNC (CNC_h) both had good dispersion in cured epoxy as observed visually and through electron microscopy. Tensile modulus, tensile strength, and work of fracture of epoxy were improved with the addition of CNC_a and CNC_h. CNC_a reinforced epoxy had the highest increases in mechanical properties. Dodecanoyl grafted CNC (CNC_d) led to aggregation in the epoxy which led to insignificant changes in mechanical properties. The addition of CNC_a increased glass transition temperature (T g) of epoxy while CNC_h and CNC_d led to T g depression.

Cellulose nanocrystals (CNCs) are renewable, sustainable, and abundant nanomaterial widely used as reinforcing fillers in the field of polymer nanocomposites. In this study, two-part epoxy systems with CNC-enhanced hardeners were fabricated. Three types of hardeners, Jeffamine D400 (JD400), diethylenetriamine (DETA), and (±)-trans-1,2-diaminocyclohexane (DACH), were evaluated for their compatibility with CNC. The roles of CNC additions and hardener types in epoxy properties were analyzed with tensile testing and dynamic mechanical analysis. The CNC-reinforcing effects on epoxy depended on the structure of hardeners. For example, with less than 2 wt% CNC, Young's modulus was increased by 16% in JD400-cured epoxy and by 19% in DETA-cured epoxy, but had minimal effect for the DACHcured epoxy. In general, the DETA-cured specimens had the highest increases in mechanical properties among the three hardeners evaluated. These results indicate that CNC additions to pre-formulated hardeners could be an alternative approach for dispersing CNCs within epoxy matrices and for improving the mechanical properties of epoxy. However, residual acetone and water during the curing reaction plasticized the epoxy matrices and must be limited for further property improvements.

Polyamide 11 (PA11) nanocomposites reinforced with Cellulose Nanocrystals (CNC), dodecanoic acid surface modified CNC (CNC_d), and CNC with methyl laurate (CNC+ML) as plasticizer were fabricated. With the addition of CNC alone, tensile modulus and strength of the PA11 were improved, but the toughness decreased at high CNC concentration. Using CNCs that were surface modified, the tensile modulus and strength both increased while the toughness of PA11 was preserved. CNC_d also led to the formation of shear band like structures during uniaxial tensile testing. When PA11 and nanocomposites were annealed near their melting point, a higher T m peak indicated that smaller crystals were melted and recrystallized. The addition of CNC inhibited this transformation, while CNC_d promoted it at early stages of annealing. Overall, the combination of shear banding and crystal transformation inducing properties of surface modified CNC provides an intriguing option for future improvement of CNC polyamide nanocomposites.