The aim of this investigation was the optimization of preparing gluten film containing cellulose nanofibrils (CNF). An optimization procedure using central composite design (CCD) with three factors (CNF, glycerol, and sodium dodecyl sulfate (SDS) concentrations) was used in order to investigate the effect of these parameters on the mechanical (tensile strength—TS, elongation at break—εb) and thermal properties of gluten films and to establish a formulation to depict the relationship between the mentioned factors and mechanical properties. Through regression analysis, it was found that TS and εb well fitted by quadratic polynomial equations (R2 = 0.99 and 0.98, respectively) and the glycerol concentration was the most significant factor influencing them. The optimization was based on maximizing TS and εb. The optimum conditions determined using response surface methodology (RSM) were defined as: CNF concentration, 11.129 g/100 g, glycerol concentration, 35.440 g/100 g and SDS concentration, 6.259 g/100 g. The predicted responses for these film preparation conditions were a TS of 3.630 MPa and εb of 86.033%. The verification experiments were conducted under optimal conditions to compare predicted and actual values of dependent variables. This experiment indicated that both predicted and actual values (TS of 3.721 MPa and εb of 88.935%) almost coincide each other and therefore the estimated models were reasonable and of high accuracy to predict dependent variables values. The scanning electron microscopy (SEM) images showed non-agglomerated and well dispersed CNF in the gluten matrix. Differential scanning calorimetry (DSC) results indicated that there is not any significant difference (P > 0.05) between the glass transition temperature (Tg) of optimum nanocomposite (−29.12 °C) and control film (−29.64 °C) and their thermogravimetric analysis (TGA) thermograms showed similar degradation behavior.
Several thousand tons of plastic goods are landfilled every year, increasing the problem of municipal waste disposal. This study investigates the optimum conditions for preparation of eco-friendly gluten-based composite reinforced with CNF, as a replacement of plastic packaging materials with the aim of reducing environmental pollution.