Chemical modifications of acid-treated pine needle fillers reinforced epoxy nanocomposites for enhanced thermomechanical properties using a response surface methodology approach: fabrication and optimization

This study explores the design and development of chemically modified epoxy nanocomposites reinforced with acid-treated pine needle (PN) fillers, aiming to enhance the mechanical and thermal properties of sustainable materials. The research examines the effects of nitric acid treatment on PN fillers, focusing on improvements in filler adhesion, surface roughness, and contaminant removal. Characterization techniques such as Fourier-transform infrared spectroscopy (FTIR) and Thermogravimetric Analysis (TGA) confirm the chemical modifications and enhanced thermal stability of the treated fillers. FTIR analysis confirmed chemical modifications through enhanced C–O–C and reduced –OH absorption bands. The acid-treated fillers exhibited a density of 1,120 ± 43.42 kg/m 3 , confirming their suitability for lightweight applications. TGA results indicated improved thermal stability of the acid-treated fillers, with the onset of major degradation delayed from approximately 265 °C in untreated fillers to around 288 °C in treated fillers, and a higher residual weight observed at 600 °C. Epoxy nanocomposites were fabricated using precise filler-epoxy mixing, degassing, and curing processes. Tensile and impact tests, conducted according to ASTM standards, revealed significant improvements in mechanical properties, particularly tensile strength (TS) and impact strength (IS), influenced by filler weight, ultra-sonication time, and degassing time. Response surface methodology (RSM) and analysis of variance (ANOVA) were employed to optimize the composite synthesis process, yielding an optimized composite with a TS of 60.85 MPa and an IS of 14.67 kJ/m 2 . The optimized composite exhibited a 25 % increase in TS and a 30 % increase in IS compared to neat epoxy. These findings highlight the potential of acid-treated PN fillers in producing high-performance, eco-friendly composites for automotive, aerospace, and construction applications. Future work will explore further optimization and real-world performance testing of these composites.