Sustainable Pinecone—Cottonseed Hybrid Composites: Mechanical, Physical, Thermal, and Morphological Performance

The increasing generation of agricultural and industrial waste has created a growing need for sustainable materials that can reduce environmental burdens while maintaining desirable performance. This study explores the development of hybrid composites using pinecone waste and cottonseed waste generated during spinning operations as reinforcement materials in epoxy and PCL (polycaprolactone) matrices. Four composite formulations were produced and evaluated in terms of their physical, mechanical, thermal, morphological, and crystallographic characteristics. Density, water absorption, tensile, compressive, flexural, and thermal conductivity properties were measured using standard testing procedures. Surface morphology and fiber–matrix interactions were examined through scanning electron microscopy (SEM), while X-ray diffraction (XRD) was used to investigate the crystalline structure of the composites. The epoxy-based formulations exhibited superior tensile and flexural performance, reduced moisture uptake, and lower thermal conductivity, indicating their suitability for interior and semi-structural applications. In comparison, the PCL-based composites demonstrated higher compressive load resistance and greater deformation capability, suggesting potential use in biodegradable packaging and cushioning materials. SEM analysis revealed noticeable differences in filler distribution and interfacial characteristics among the formulations, whereas XRD confirmed the crystalline features associated with both the polymer matrices and lignocellulosic reinforcements. Overall, the results demonstrate a practical route for converting forestry residues and spinning-industry waste into functional composite materials, supporting waste valorization and resource-efficient material development.