Evaluation of the acid hydrolysis as pre-treatment to enhance the integration and functionality of starch composites filled with rich-in-pectin agri-food waste orange peel

The poor management of citrus wastes as a result of their low compostability and value for animal feeding greatly hinders the disposal of this waste. Nowadays, the incorporation of vegetable biomass into a polymer matrix is widely considered as an emerging approach to reduce the environmental problem related to the accumulation and management of food wastes. However, the fibrillar morphology and chemical heterogeneity of biomass usually restrains the compatibility with polymer matrices. Despite that, starch composites containing up to 40 wt% of the neat/hydrolyzed orange peel with excellent mechanical, and moisture resistant features were successfully fabricated in this research. The compatibility between both components was improved by using a simple and scalable process based on the acid hydrolysis of the biomass. Indeed, it was demonstrated that the final properties of these biocomposites were tuned by modifying the acid conditions (type and concentration of acid). For example, composites treated with chlorohydric acid displayed superior Young’s modulus values (about 30% more) and slightly greater elongation than the composites composed by 40 wt% of neat orange peel. Moreover, the exposure of vegetable biomass to moderate acid conditions (0.1 and 1 M chlorohydric acid) resulted into the generation of highly-value products, such as organic acids or humic substances, able to form ester bonds with the starch matrix strengthening the water resistance and mechanical features of the composites. [Display omitted] •Orange peel showed a great compatibility with starch, showing remarkable properties with high content of filler (up to 40 wt%).•The acid hydrolysis provided a degree of tunability to the final properties of the starch composites.•Stronger hydrolysis conditions triggered the esterification between orange peel and starch, improving the functionality.•Acetic acid exhibited superior water and thermal resistance features with respect to HCl at the same concentrations.