Heliyon (Jan 2024)
Green3: A green extraction of green additives for green plastics
Abstract
PLA/PBAT bioplastic is a commercial biodegradable plastic employed for packaging and several food and agriculture applications. In this regard, properties such as the antioxidant ability to extend food shelf life and light resistance, are of great interest in the production of packaging and mulching films, respectively. These features are obtained by developing blends with pure chemicals and/or natural products as additives. In the present work blend formulations of PLA/PBAT with a walnut shell extract rich in antioxidants were developed and evaluated for their properties in comparison with classic PLA/PBAT. Specifically, natural additives, and most importantly the production process were purposely selected to i) be green and cost-effective; ii) confer antioxidant properties; and iii) improve material performance.To this aim, a walnut shell extract (EWS) with high antioxidant activity was obtained thanks to a novel green and cost-effective microwave-assisted extraction (MAE) procedure. A response surface methodology was utilized to explore how the total phenolic content (TPC) and antioxidant activity are influenced by varying aqueous ethanol concentration, extraction time, and microwave power. The highest predicted TPC and antioxidant activity were achieved when employing the ideal conditions for Microwave-Assisted Extraction (MAE): using a mixture of 30 % ethanol in water, an irradiation time of 120 s, and a microwave power of 670 W. The optimized EWS was characterized by HPLC-MS determining qualitative and quantitative data with the identification of flavonoids, fatty acids, and anacardic acids among the main components, responsible for antioxidant activity. The resulting EWS powder was melt-mixed at 140C° and 20 RPM with the bio-based PLA/PBAT bioplastic at two different concentrations (0.5 and 1.5 w/w) by forming film specimens. All EWS-based bioplastic films showed increased antioxidant features determined by the DPPH bleaching test, TEAC, and ORAC assays. The films keep the antioxidant capacity even after 7 days of UV-accelerated aging. Remarkably, adding 1.5 % EWS boosted the bioplastic UV light resistance, reducing the abatement of molecular masses by more than 60 % without affecting mechanical properties.
