Obtaining cellulosic nanofibrils from oat straw for biocomposite reinforcement: Mechanical and barrier properties

Abstract

The effect of oat straw nanofibrils addition on the mechanical and barrier properties of bionanocomposites based on cassava starch was evaluated. Nanofibrils were obtained after alkaline treatment of oat straw and consecutive passages in mechanical defibrillator. Five passages through the defibrillator promoted greater reduction in diameter of the nanofibrils and less agglomeration, with a yield of almost 100 %. For the preparation of bionanocomposites by casting method, different percentages of oat straw nanofibrils were used: 0%, 10 %, 20 %, 30 % and 50 %. The bionanocomposites were evaluated for their mechanical properties (tensile strength, elongation at break, Young's modulus and puncture force) and barrier properties (water vapor permeability, solubility and contact angle), in addition to opacity, color and morphology analyses. The addition of oat straw nanofibrils promoted an increase in stiffness and consequent decrease in the flexibility of bionanocomposites. In relation to barrier properties, there was a reduction in water vapor permeability and water solubility of the bionanocomposites with the increase of oat straw nanofibrils in the formulations. The materials presented hydrophilic character, but with low wettability. The morphological analysis indicated good interaction between the constituents of bionanocomposites. The effects observed in this study were generally pronounced when the addition of oat straw nanofibrils was higher than 30 %. Therefore, it is concluded that values of 30–50% of oat straw nanofibrils addition promote improvements in the mechanical properties and barrier of bionanocomposites based on cassava starch. The application of elaborate bionanocomposites should be investigated in order to confirm their viability as packaging or even as edible coating, as they may constitute sustainable alternatives to traditional polymers.