Surface grafting of acrylonitrile butadiene rubber onto cellulose nanocrystals for nanocomposite applications

Grafting of carboxyl-terminated butadiene-acrylonitrile rubber (CTBN) to cellulose nanocrystals (CNCs) surfaces was investigated to tailor the properties of CNCs for polymer composite applications. Toluene and dimethyl sulfoxide (DMSO) and their combinations at varying volume ratios were examined as the reaction media with a goal of achieving efficient coupling of the CTBN while maintaining the high crystallinity of CNCs. Fourier transform infrared spectroscopy and nuclear magnetic resonance (+H NMR) confirmed the grafting of CTBN to the CNCs. Transmission electron microscopic (TEM) analysis revealed that the modified CNCs (mCNCs) was coated with CTBN. Likewise, the dispersion of mCNCs in toluene was observed to be better than in water as observed from TEM. mCNCs with 11.74% coupling efficiency was added to polylactic acid (PLA) via a solvent casting process at 1 and 5 wt%. For the composites containing 1 and 5 wt% of mCNCs, an increase in the tensile strengths of 25% were observed in both cases. Whereas, those containing CNCs exhibited changes of 7 and -12% for concentrations of 1 and 5 wt%, respectively. Interestingly, the modulus remained mostly the same when comparing the mCNCs and CNCs despite the presence of rubber chains on the mCNC. However, increases of ca. 40 and 58% were observed for composites containing 1 and 5 wt% of either CNCs or mCNCs. Results from this study show that CNCs properties can be tailored to improve their dispersion and enhance mechanical properties of polymers.