Aproveitamento de partículas da casca de café na produção de painéis compósitos fabricados com resina poliéster

Abstract

Coffee production generates large amounts of husk residues, accounting for approximately 45 55% of the fresh fruit weight. In Brazil, one of the world's largest coffee producers, improper disposal of these residues has become a significant environmental issue. This study aimed to investigate the potential of coffee husk as a reinforcing material in polymer biocomposites, seeking to provide a sustainable solution for the utilization of these agro-industrial residues. To achieve this, a detailed characterization of coffee husk particles (CHP) was performed, including physicochemical, thermogravimetric, X-ray diffraction, and scanning electron microscopy analyses. The results showed that CHP have a composition rich in lignin (37.26%), cellulose (30.96%), and hemicellulose (20.39%), with an apparent density of 430 kg/m³ and a relative density of 1490 kg/m³. Thermogravimetric analysis indicated that the material exhibits thermal stability up to 210°C, with major degradation occurring at 325°C. Additionally, the cellulose crystallinity index was 33.62%, and microscopy images revealed a rough surface, which may enhance interfacial adhesion in polymer matrices. Based on these characteristics, composite panels were produced using CHP in a polyester matrix, with volume fractions of 30%, 40%, and 50%. The panels were fabricated by cold pressing and evaluated in terms of their mechanical, physical, and thermal properties. The results demonstrated that increasing the CHP content led to an improvement in flexural modulus (reaching 3.59 GPa) and Shore D hardness (86.4), but also caused a 36.5% reduction in flexural strength due to void formation and lower interfacial adhesion. Impact toughness increased by 11.6%, indicating that the particles act as barriers to crack propagation. Water absorption increased proportionally to the CHP content, stabilizing after 24 days of immersion, while the thermogravimetric analysis of the composites revealed thermal stability up to approximately 300°C. In summary, coffee husk proved to be a viable material for the production of sustainable biocomposites, with suitable properties for applications requiring stiffness and impact resistance. This study highlights the potential of CHP as an eco-friendly alternative to reduce the use of conventional materials, contributing to the circular economy and the development of more sustainable products.