Biopolymer based nanocomposites: Comparing layered silicates and microcrystalline cellulose as nanoreinforcement

The goal of this work was to compare the mechanical, thermal and barrier properties of two different types of biopolymer based nanocomposites. The two nanoreinforcements chosen for this study were bentonite a layered silicate and microcrystalline cellulose (MCC). The polymer matrix used was poly(lactic acid), a commercially available biopolymer. The nanocomposites were prepared by incorporating 5 wt% of each nanoreinforcement into PLA using solution casting. The bentonite nanocomposite showed great improvements in both tensile modulus and yield strength, while the MCC nanocomposite only showed tendencies to improve the yield strength. The two materials had very different effects on the elongation to break. The MCC nanocomposite showed a more satisfactory behaviour compared to the bentonite which reduced the elongation to break greatly. The results from the dynamic mechanical thermal analysis (DMTA) showed an improvement in storage modulus over the entire temperature range for both nanoreinforcements together with shifts in the tan δ peaks for both nanoreinforcements to higher temperatures. Oxygen permeability testing and UV–Vis spectroscopy were also carried out to investigate how the addition of these two nanoreinforcements would affect PLA as a packaging material. The results showed a reduction in the oxygen permeability for the bentonite nanocomposite, but not for the MCC nanocomposite. The amount of light being transmitted through the nanocomposites was reduced compared to pure PLA indicating that both nanoreinforcements were not fully exfoliated.