Cellulose nanocrystals (CNCs) are an ideal reinforcing agent for polymer nanocomposites because they are lightweight, nano-sized, and have a high elastic modulus. To date, using cellulose nanocrystals in common matrices has been generally unsuccessful due to their hydrophilicity and incompatibility with hydrophobic polymers. To overcome the poor compatibility, we have grafted poly(methyl methacrylate) (PMMA) onto the surface of the nanocrystals for the first time using a one-pot, aqueous in-situ “grafting from” polymerization reaction with ceric ammonium nitrate initiator to produce poly(methyl methacrylate)-grafted-cellulose nanocrystals (PMMA-g-CNCs). We compared the compounding of CNCs and modified CNCs with PMMA using two processing methods; melt mixing and wet ball milling. We examined the morphological, mechanical and rheological behaviour of the nanocomposites and found that ball milled composites had lower mechanical and rheological performance compared to melt mixed composites for both CNCs and modified CNCs. Additionally, we found that high (>1 wt. %) loadings of CNCs had a positive effect on the performance of nanocomposites, while low loadings of CNCs and all loadings of PMMA-g-CNCs had no net effect on the performance of the nanocomposites compared to the control. The morphology of nanocomposites showed some agglomeration in the samples with CNCs, but more pronounced agglomeration in samples with PMMA-g-CNCs. This is consistent with the decreased rheological and mechanical behaviour of composites with PMMA-g-CNCs compared with CNCs. / Thesis / Master of Applied Science (MASc)