Addition of wheat straw nanofibrils to improve the mechanical and barrier properties of cassava starch-based bionanocomposites

Cellulose nanofibrils (CNFs) were obtained from wheat straw, and different concentrations (0 %, 10 %, 20 %, 30 % and 50 %) of the CNFs were incorporated into cassava starch-based films. Thirty passages through a microfibrillator allowed us to obtain well-dispersed CNFs with reduced thickness (34.26 nm). The addition of CNFs promoted an average increase in tensile strength values on the order of 126.69 %. The treatments with higher CNF addition percentages (30 % and 50 %) presented higher Young's modulus values (566.68 and 585.72 MPa, respectively), which indicates an increase in stiffness. The elongation and puncture force decreased with the addition of CNFs, presenting average reductions of 83.72 % and 56.66 %, respectively. A significant decrease in water vapour permeability was observed for the treatments with higher percentages of CNFs added, with a drop from 2.15 x 10(6) in the control film to 1.39 x 10(6) g mm/KPa-1 day(-1) m(2) in the film with the maximum addition percentage. The contact angle values increased from 43.45 degrees in the control film to 68.66 degrees in the sample with the maximum CNF concentration. The lower hydrophilicity of the treatments with 30 % and 50 % CNF additions is evidenced by the lower values presented for the Cobb test (99.84 and 99.31 g m(2)), polar surface free energy (0.41 and 0.19 mN m(-1)) and polarity (0.01 and 0.007). In these treatments, there were stronger interactions between the CNF and starch molecules. Thus, the addition of 30-50 % wheat straw CNFs is recommended to strengthen the structure and improve the barrier properties of cassava starch-based films.