Crop Nitrogen Fertilization Schedule in Bread Wheat Affects the Mechanical Performances of Thermoplastic Films Obtained by Plasticization of Flours

Recent research has investigated the plasticization of wheat flour as a non-food alternative application. In this work, we analyzed the performances of thermoplastic films obtained using flours of two bread wheat cultivars (Bologna and Bora) grown in fall-spring under four nitrogen (N) fertilization treatments: (1) continuously well-N-fed (N300 = 300 kg N ha(-1), split throughout the growth cycle); (2) N-fed only very early (N60-0 = 60 kg N ha(-1), just one month after sowing); (3) N-fed only extremely late (N0-120 = 120 kg N ha(-1) at pollination); (4) unfertilized control (N0). Flours were characterized for glutenin and gliadin fractions, Chopin's alveograph parameters, Field Emission Scanning Electron Microscopy (FESEM) images, and thermogravimetric analysis (TGA), while films were evaluated for mechanical properties (tensile strength at break, sigma(b); elongation at break, epsilon(b); Young's modulus, E) and FESEM images. Differences among treatments for absolute and relative abundances of gluten fractions and alveographic parameters were extremely marked and gave rise to differences in tensile properties of thermoplastic films. Within each cultivar, the ranking of treatments for epsilon(b) values was N0 > N60-0 > N0-120 > N300. Thus, epsilon(b) was inversely correlated with crop N availability and total gluten content of the flour. The sigma(b) was less variable among N treatments; however, in both cultivars, it was high in N0 and N300 and appreciably lower in N0-120. Overall, the best mechanical performances were obtained with flours from crops not subjected to imbalances in N nutrition (N0, N300). Our work demonstrates that bioplastic engineering needs to take into consideration the variability of biological source material like that caused by different crop N availability.