Experimental investigation on surface morphology of Palmyra palm leaf stalk – sisal fiber reinforced polymer hybrid composite

Abstract

Natural fiber–reinforced polymer composites have gained increasing attention as sustainable alternatives to synthetic materials; however, their broader application is constrained by weak fiber–matrix interfacial bonding and inconsistent surface characteristics. This study addresses this limitation by examining the influence of alkaline treatment and fiber configuration on the surface morphology of Palmyra palm leaf stalk–sisal hybrid composites. Fibers were extracted manually and treated using a 5% NaOH solution for 24 h to enhance interfacial compatibility by removing hemicellulose, lignin, and surface impurities. Hybrid composites with a fixed Palmyra–sisal ratio (50:50) were fabricated via hand lay-up at varying fiber-to-matrix volume fractions (10/90, 15/85, and 20/80) in both unidirectional and chopped orientations. Surface morphology was characterized using optical profiling and scanning electron microscopy to evaluate fiber–matrix adhesion, void distribution, and surface roughness. The results reveal that alkali-treated composites exhibit significantly improved surface integrity, characterized by reduced voids, enhanced fiber embedding, and more uniform roughness compared to untreated counterparts. Among all configurations, the treated unidirectional composite with 20/80 fiber-to-matrix ratio demonstrated the most favorable morphology, indicating superior interfacial bonding. The findings confirm that controlled alkaline treatment and optimized fiber architecture play a critical role in improving surface characteristics. These improvements suggest strong potential for the developed hybrid composites in lightweight structural and automotive interior applications, while also highlighting the need for future quantitative and mechanical performance validation.