K. Bosnick, A. Benhalima, N. Chapleau, M. Champagne
National Research Council Canada,
Keywords: cellulose nancrystal, polylactide, polyethylene, packaging film, barrier material
Summary:To support the sustainability of the food packaging industry, a move from petroleum-derived packaging products to renewable-derived ones is needed. In addition, a complete compostability of the packing is desirable for reducing waste at the end of the product’s life-cycle. Polylactide (PLA) is a compostable thermoplastic that is derived from renewable resources (e.g. corn starch) and has many desirable properties for food-packaging applications. However, PLA suffers from some deficiencies compared with petroleum-derived materials that limit its immediate adoption for this application, including poor oxygen barrier and mechanical characteristics. An improvement in these properties through compounding with a renewable-derived, compostable filler may lead to a competitive composite product that could replace petroleum-derived, non-degradable ones. Cellulose nanocrystals (CNC) represent a potential filler material that satisfies these key requirements. However, CNCs are highly hydrophilic and not easily blended with hydrophobic polymers, requiring a modification of the CNC particle`s surface. In this work, compatibilized CNC particles are blended with PLA and cast into packaging films to assess the potential for improving food-packaging related properties. As a control, the compatibilized CNC particles are also cast in polyethylene (PE) and the composite films characterized. A number of strategies are explored for compatibilization, including the use of maleic anhydride grafted oligomers, quaternary ammonium surfactants, and an acetylation reaction. The compatibilized CNCs are characterized physico-chemically and the nanocomposite films are characterized for their dispersion, mechanical, and oxygen barrier properties. The use of maleic anhydride grafted oligomers for the compatibilization is found to be inadequate, producing a poor dispersion of the CNCs and a low quality packaging film. The modification of the CNC by acetylation is found to be more effective than the maleic anhydride grafted oligomers but does not lead to an improvement in the mechanical properties of the PLA matrix and the modulus remains constant for the PE matrix at 2 wt % loadings. However, compatibilization by the use of surfactants is found to be very effective, especially using dimethyl dodecylethyl ammonium bromide (DDAB) surfactant. Significant increases in the modulus (7-16%) are observed for both PLA and PE matrices with DDAB modified CNCs. The oxygen transmission rates are found to be comparable for the neat PE films and the modified CNC nanocomposite films. Further optimization of the processing conditions is needed to get acceptable barrier properties in the PLA matrix and is currently underway.