Comparative study of physical, mechanical, thermal, and morphological properties of raw, alkali, and 3-aminopropyltriethoxysilane (APTES)-treated Agave angustifolia Haw fibers for green-composite reinforcement

Agave angustifolia Haw fiber has high potential as reinforcement for green composites. However, its hydrophilic nature limits compatibility with polymer matrices. A novel cellulosic fiber from Agave angustifolia Haw was investigated by systematically comparing the effects of alkali and silane treatments. This work presents an integrated evaluation of structural, thermal, mechanical, and interfacial property changes resulting from the combined NaOH–(3-aminopropyl) triethoxysilane (APTES) treatment. FT-IR confirmed successful silanization through the Si-O-Si band at 1080 cm⁻¹ and a degree of substitution of 1.32. The combined NaOH-APTES treatment resulted in the most significant improvement in fiber performance, with a 21.03% increase in the crystallinity index from 51.20% to 72.23%. This structural enhancement led to a marked increase in tensile strength from 212.116 ± 40 MPa to 391.542 ± 58 MPa and an increase in tensile modulus from 7.768 ± 1.2 GPa to 21.634 ± 1.3 GPa. Thermal stability was also enhanced, with the onset of degradation temperature reaching 334.10 °C. Surface modification increased fiber hydrophobicity, as indicated by a rise in the water contact angle from 37.32° to 82.65°. The NaOH–APTES-treated fiber also exhibited the highest interfacial shear strength (10.694 ± 0.8 MPa), indicating improved fiber–matrix adhesion. SEM–EDX analysis confirmed a cleaner silane-coated surface with silicon detected at 1.09 ± 0.15 wt%. These results highlight the potential application of NaOH–APTES-treated Agave angustifolia Haw fibers as reinforcement for high-performance green polymer composites with improved interfacial bonding, mechanical strength, and thermal stability.