Mechanical and thermal characteristics of steam-exploded silane grafted Kigelia Pinnata fruit (KPF) fiber reinforced vinyl ester polymer composites

The cellulose-rich Kigelia pinnata aqueous fruit (KPF) fiber is a valuable natural biomass and has drawn attention as a renewable resource. Vinyl ester polymer matrix composites with better interfacial properties can have higher mechanical and energy dissipation properties. It can be obtained by the use of steam-exploded silane-grafted KP fibers with various fractions incorporated in the polymer matrix. KPF fiber grafting was maximized at 5% concentration after a steam explosion, removing hemicelluloses and lignin, thereby enriching a 23% crystallinity index (CI), leading to rich cellulose fiber. Steam explosion along with silane grafting increases the interfacial adhesion of the KPF fibers and the matrix through the interfacial bonding structure of Si–O–Si bonds, as confirmed by FTIR. A fiber with greater tensile strength was used to fabricate the vinyl ester composites. The highest tensile value of the steam-exploded silane surface-modified 30% KPF fiber-reinforced composite was 125 MPa compared to the unmodified one due to increased stress distribution and restricted polymer chain movements. Compared to the untreated 30% KPF fruit fiber composite, steam-exploded silane-treated fiber showed a 12% higher impact energy due to faster load transfer, causing more impact energy absorption. A relatively higher interlaminar shear strength was shown for 30% treated KPF composites than for 30% untreated KPF composites. The steam-exploded silane-treated fiber (30%) composite shows the greatest thermal decomposition temperature of 399 °C because silane-surface-treated fibers contact the organo-functional silane group in the polymer matrix. As a result, it obstructs polymer chain motions at higher temperatures, causing increased bonding strength.