Investigation of heat insulation and mechanical effects of neem (Azadirachta indica) leaf filler on waste cotton denim reinforced epoxy composites for sustainable applications

The rapid increase in textile waste, particularly denim, poses a significant global environmental challenge, necessitating sustainable recycling strategies. This study explores the development of eco-friendly polymer matrix composites using post-consumer cotton denim fabric (CDF) as reinforcement in an epoxy matrix and neem ( Azadirachta indica ) leaf powder as a natural filler. Alkali-treated CDFs were incorporated through the hand lay-up method, and composites were fabricated with varying neem filler (NF) contents. Results revealed that NF incorporation effectively reduced thermal conductivity, enhancing insulation properties up to an optimal content of approximately 10 wt%. At this level, tensile, flexural, impact, and hardness properties improved by 60 %, 78 %, 48 %, and 88 %, respectively, compared with untreated CDF-composites (UT). Excessive NF loading, however, induced brittleness and reduced mechanical strength due to filler agglomeration and weak interfacial bonding. Thermogravimetric analysis (TGA) confirmed an increase in char residue and a slightly delayed decomposition onset in NF composites, indicating improved thermal resistance. Moreover, SEM micrographs showed better fiber–matrix adhesion and filler dispersion at moderate NF levels. Overall, CDF–NF hybrid composites offer a sustainable, low-cost alternative with balanced thermal insulation and mechanical performance, suitable for structural and thermal-management applications.