HYBRID GREEN COMPOSITES UTILIZING RENEWABLE LIGNOCELLULOSIC FIBERS TO REINFORCE SOY-BASED RESINS

Abstract

Plant-based green composites have recently emerged as sustainable alternatives to petroleum-based polymer matrix composites (PMC) in applications such as transportation and packaging.PMC techniques were employed to produce commercial-scale green composites made using one of the most wasted plant fibers, i.e., rice straw (RS). Thermoset resin sheets were prepared by denaturing soy protein isolate (SPI) and crosslinking it with glutaraldehyde. SPI resin was reinforced by hybrid RS/jute fabric (JFa) mats, to fabricate layered composites with high fiber content (up to 60%). Needle felting was used to interlace RS and JFa together and fabricate hybrid green PMC composites. The hybrid composites were characterized for their moisture absorption, tensile properties, flexural properties, interfacial shear strength (IFSS), dynamic mechanical properties, fracture surface analyses, and thermal stability. The obtained results reflect the geometric complexity of these systems, their hygroscopic nature, and enable further utilization of fiber waste in low-mechanical resistant composites. Mechanical properties of all composites were affected by moisture absorption, except their ductility. Triple-layered composites with the lowest fiber content (40%) resulted in enhanced Young’s modulus (Ey) and ultimate tensile strength (UTS), from 0.3 to 0.9 GPa and from 7.2 to 10.6 MPa, respectively, compared to pure resin. However, contrary to the logic, an inverse relationship was found between fiber content and each of the following: Ey and UTS; flexural modulus and ultimate flexural stress; and storage modulus. IFSS results as well as fracture analyses attributed this inverse relationship to the relatively weak fiber/resin interface, and to the deduction that fiber content has exceeded the resin’s capacity of fully wetting the fibers. Moisture absorption in addition to the weak interfacial strengths were the primary reasons to lowering the mechanical resistance of the hybrid green composites. These hybrid composites can be used in many applications, from furniture to housing and from transportation to packaging.