Water-based processing strategy for cellulose nanocrystal/polymer nanocomposites
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The objective of this research is to develop a water-based processing method for incorporating large filler loadings into nanocomposite systems. Specifically, cellulose nanocrystal/poly(vinyl alcohol) (CNC/PVA) nanocomposite aqueous suspensions and films were processed and characterized at CNC loadings up to 67 wt.% with respect to polymer concentration. Both aqueous suspended and freeze-dried CNCs were studied with this method. Two methods for incorporating the CNCs were investigated: solution processing and batch mixing of aqueous suspensions. The materials produced by these methods were characterized using rheology of aqueous suspensions and a method for understanding the morphology of these aqueous suspension through rheological characterization was developed. The CNC/PVA suspensions were dried and the structure of the film studied using x-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry. With regard to characterization of polymer structure by these methods, PVA crystallinity was seen to increase with increasing CNC loading. Finally, dynamic mechanical analysis and micro-tensile testing were conducted on consolidated films and CNCs were seen to increase modulus, yield stress but decrease strain at failure. Biodegradation studies were also conducted and CNCs were seen to increase the biodegradation characteristics of PVA. While the general trends in experimental data were the same, differences in properties between systems made with solution processing and batch mixing were observed, attributed to differences in the CNC dispersion. Overall, results indicated that this methodology is feasible for the industrially scalable production of highly loaded nanocomposites.