Composite development and characterization: Cocoa Bean shell and Propylene – Ethylene – 1 - Butene Terpolymer for potential fused granular fabrication applications

Abstract

Approximately 5.5 billion tons of agroindustrial waste are generated annually worldwide[1]. A substantial portion of this waste remains untreated, leading to soil disposal and the production of greenhouse gases[2]. Specifically, the cocoa industry generates an estimated 700 thousand tons of waste annually[3]. The growing interest in sustainability has driven industries to adopt Circular Economy principles with a focus on utilizing residues from various industries to manufacture cost-competitive and eco-friendlier goods. This study presents a composite based on cocoa bean shells (CBS) and propylene-ethylene-1-butene terpolymer (PP-T), with a focus on its physical, thermal, and mechanical characteristics and its potential application in Fused Granular Fabrication (FGF). The raw materials, and the composite (10wt.% CBS), were thermally characterized, including thermogravimetric analysis (ASTME1121) and differential scanning calorimetry (ASTM D3418). Physical properties were assessed through water absorption (ASTMD570) and density (ASTM D792) analysis, while chemical characterization was achieved using FTIR. Tensile (ASTM D638) and flexural (ASTM D790) properties, were determined by testing molded compressed specimens. The developed material's potential application in FGF was explored. The study was focused on the determination of 3D printing temperature and provides a comprehensive tensile (ASTM D3039) and flexural characterization of 3D-printed specimens. It is essential to ensure that the processing temperature is above the polymer melting temperature (~130°C) while remaining below the thermal degradation temperature of CBS (~230°C). Water absorption shows the importance of well-dried materials before processing to avoid the presence of voids in the composite. Density does not show significant variations. Tensile properties proved to be comparable between the neat PP-T and the composite. Furthermore, the flexural strength showed improvement in the composite, increasing by 43%. The application of the developed composite pellets in FGF was explored. A temperature tower was 3D-printed to assess the impact of nine extrusion temperatures on the finishing quality of the piece. This process facilitated the selection of the 3D printing temperature. The tensile strength in the composite was reduced by 27% compared to the neat PP-T. This decrease can be attributed to the CBS acting as fillers. In this case, the flexural strain was comparable for both materials (7.8% - neat PP-T / 7.6% - composite). The composite's potential as a sustainable and functional alternative in additive manufacturing is notable. Characterization demonstrates a direct influence of the natural fiber from CBS on thermo-physical-mechanical properties. The feasibility of manufacturing the composite through 3D printing via FGF was demonstrated, presenting a practical and viable opportunity for producing parts with diverse requirements.