Stabilization of Polylactic Acid and Polyethylene with Nutshell Extract: Efficiency Assessment and Economic Evaluation

Recovery of functional molecules from byproducts of agro-food industries is an appealing approach to waste reduction and to obtain safe and value-added phytochemicals with antioxidant and antimicrobial properties. However, more information about the operational costs is needed for successful industrial scale-up. In this study, the potential of pecan (Carya illinoinensis) nutshell (NS) as a source of antioxidants was investigated. To this aim, a hydroalcholic NS extract (NSE) was thoroughly characterized, and its effect was investigated on thermo- and photo-oxidative stability of two polymers widely used in food packaging, polylactic acid (PLA) and polyethylene (PE). Twenty-six phenolic constituents, including proanthocyanidins, were identified in NSE, and its effective radical scavenging capacity was assessed. NSE acted as a thermal stabilizer for PLA and PE films, both in an oxygen-depleted environment (i.e., during melt processing) and in the presence of oxygen during polymer service life. NSE showed great potential as a PLA stabilizer, due to the compatibility with the polyester matrix. Under UV-light irradiation, NSE was more effective in protecting PE than PLA, due to combination of peroxy radical scavenging and inhibition of Norrish-type photolytic cleavage. Finally, from the experimental data, an economic evaluation of batch and continuous mode NSE manufacturing was performed, demonstrating that the process is technically and economically viable. Overall, these results emphasize the potential of NSE as a low-cost, safe, and sustainable additive for the stabilization of polymer films in packaging and other applications.