Modified pistachio shell waste: Structure, chemical interaction, and viscoelastic performance in biopolymer composites‐based starch

Abstract This work was focused on the changes in structural features of the pistachio shell (PS) waste upon alkaline and ultrasound treatment and their potential as sustainable reinforcement fillers in starch‐based films (SF). Scanning electron microscopy analysis revealed etching, thinning, and cavities on the surface of PS after alkaline/ultrasound treatment, which allowed the NaOH species to act internally on the microstructure of PS, promoting the alteration of the functional groups CO and CO of hemicellulose and lignin molecules, as well as an increment on their crystallinity index from 31.41% to 46.91%. X‐ray photoelectron spectroscopy analysis was used to identify the oxidation mechanism after modified PS was added to a starch matrix. The atomic ratio of the hydroxyl groups decreased, leading to an increase in stronger OCO (from 5.98–17.91%) and OC bonds (from 15% to 27.49%) interactions. Thermogravimetric analysis confirmed the interaction between starch and modified PS, which increased the storage modulus of the films from 198 MPa up to 721 MPa, thereby increasing the rigidity. The compatibility enhancement between modified PS waste and starch may interest the packaging industry and those looking to develop a scalable process. Highlights Alkali/ultrasound treatment determined the pistachio shell modification degree. The treatments disturbed the hydrogen bonds of lignocellulosic components. Pistache shells reduced COH interaction between starch and glycerol. The fibers interact strongly with starch by OCO and OC bonds. The modified pistachio shells improved the rigidity of starch films.