Issue 78

N. Nayak et alii, Fracture and Structural Integrity, 78 (2026) 378-392; DOI: 10.3221/IGF-ESIS.78.22

SEM microstructural analysis SEM examination of representative fractured specimens confirmed the importance of fibre treatment and dispersion in determining composite performance. Alkali-treated composites showed better fibre embedding within the polypropylene matrix, fewer interfacial gaps and reduced fibre pull-out. These features indicate stronger fibre–matrix adhesion and more effective stress transfer during tensile, flexural and impact loading [15, 17, 20]. In contrast, untreated composites showed weaker interfacial contact, fibre pull-out, matrix cracking and localized voids, which explain their lower mechanical performance [7, 20]. The micrographs also indicated that the compression moulding route produced randomly oriented short-fibre composites with satisfactory fibre distribution. Random orientation is expected for compression-moulded short-fibre systems and contributes to more uniform behaviour than highly directional reinforcement. Powder or very short fibre forms improved dispersion, but their lower aspect ratio limited reinforcement efficiency compared with optimally sized short fibres. Overall, the SEM observations support the mechanical, dielectric and statistical results by confirming that improved interfacial adhesion, controlled fibre length and uniform dispersion are essential for obtaining reliable sisal fibre reinforced polypropylene composites. The SEM micrographs in Figs. 10–13 show the fracture morphology of treated and untreated composites and support the observed differences in fibre embedding, interfacial bonding, void formation and fibre pull-out.

Figure 10: SEM micrograph of alkali-treated sisal fibre reinforced polypropylene composite at 10 mm fibre length and 10 wt.% fibre loading.

Figure 11: SEM micrograph of alkali-treated sisal fibre reinforced polypropylene composite at 20 mm fibre length and 20 wt.% fibre loading.

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