Cocoa waste recovery for starch-based biocomposites: Outdoor exposure assessment approach

The aim of this study is to evaluate the development and outdoor performance of bio-based composite laminates incorporating cocoa bean husk as lignocellulosic reinforcement, achira starch, and an acrylic polymer matrix. To achieve this objective, eight formulations were evaluated, varying reinforcement content (15 % and 30 %) and compression temperature (75°C and 100°C), with two matrix types: acrylic-only (AP) and starch–acrylic hybrid (AS:AP). Samples were subjected to 720 hours of environmental exposure under natural conditions, and their evolution was assessed using mechanical testing, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), microbiological inspection, stereomicroscopy, and scanning electron microscopy (SEM). The results showed that mechanical properties exhibited time-dependent changes, with all formulations initially increasing in modulus and tensile strength, likely due to UV-induced densification and plasticizer loss followed by degradation. Among the evaluated formulations, the M4 biocomposite showed the best mechanical performance. FTIR analysis at 720 h, reveled new bands associated with the material degradation. TGA analyses revealed trends in water loss, glycerol migration, and acrylic polymer degradation. Moreover, SEM confirmed degradation after outdoor exposure. Microbiological staining demonstrated the presence of Aspergillus spp., Penicillium spp., and potentially Cladosporium spp. In brief, AS:AP matrices displayed superior thermal stability and microbial resistance, particularly at higher processing temperatures, attributed to enhanced starch–resin interactions and tighter polymer networks. This study demonstrates that the integration of starch, particularly at 100°C, enhances structural integrity, weathering resistance, and resistance to biodegradation, supporting its potential use in sustainable materials engineering for outdoor applications.