Comparative Analysis of the Coffee and Cocoa Industry By-Products on the Performance of Polyethylene-Based Composites

Abstract

The application of plant-based by-products from the food industry as minimally processed functional fillers for polymeric composites is an increasingly popular trend among researchers and manufacturers. While minimizing the preprocessing of lignocellulosic fillers leads to an increase in the sustainability of the overall composite and a decrease of the carbon footprint, filler modification is usually indispensable to obtaining sufficient mechanical and thermomechanical properties of a composite. The goal of the presented study was a comprehensive analysis of the structure, mechanical and thermal performance of polyethylene-based (PE) composites with spent coffee grounds (FK) and cocoa husks (KK). Differential scanning calorimetry (DSC) measurements showed the antioxidant activity of both fillers, extending the oxidation induction time by 100% (54 min) compared to pure PE (20 min). Composites with up to 5 wt% of the filler were characterized by low porosity (0.5%) and revealed tensile strength of about 20 MPa, which is comparable with the results of unmodified PE. However, the materials' ductility was affected, reducing elongation at break and tensile toughness by two orders of magnitude. In order to quantify changes in adhesion at the interface, a comprehensive analysis of thermomechanical parameters based on dynamic mechanical analysis (DMA) was carried out, including the assessment of interactions on the interface of the composite caused by the increase in free volume inside composites' structure.Graphical