Surface modification of abaca fiber via radiation-induced graft polymerization for reinforcement of polymer composites

• Main Author: Barba, Bin Jeremiah D.
• Format: text
• Language: English
• Published: Animo Repository 2020
• Subjects: Abaca (Fiber); Radiation chemistry; Polymerization; Chemistry
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/5945; https://animorepository.dlsu.edu.ph/context/etd_masteral/article/12988/viewcontent/Barba_BinJeremiah_11797576_Thesis_Partial.pdf
• Institution: De La Salle University

Abaca fibers are known for being one of the strongest fibers in the world and are widely utilized in polymer composites because of their excellent mechanical properties, low density, renewability and low cost. Factors limiting their maximum potential are their inherent hydrophilicity and poor compatibility with polymeric matrices, both of which affects fiber-matrix interaction. Fiber-matrix interaction at the interphase is one very important property in the area of polymer composites that facilitates stress transfer between resin and filler. Here, we present an approach to address this problem through radiation-induced graft polymerization (RIGP). RIGP is a simple, environment-friendly method of surface modification for natural fibers which can introduce compatible groups on the fiber surface without damaging its bulk properties. Glycidyl methacrylate was successfully grafted on the surface of abaca woven fabric by RAFT-mediated RIGP in emulsion. The degree of grafting and molecular weights were varied using different absorbed doses, monomer concentrations and RAFTto-monomer ratios. Grafting was verified by FTIR, SEM, XPS and TGA. Molecular weight analysis using GPC and NMR showed linear increase in the molecular weights with the monomer conversion. There is a good agreement of the measured molecular weights and the theoretical values, while also achieving narrow polydispersity in the grafted polymers. PGMA-grafted abaca fibers showed increased tensile strength, thermal stability and moisture resistance over unmodified fibers. Using the grafted abaca as composite reinforcement material showed improvement in tensile and flexural strength of at least 23 and 59% compared to untreated fibers. The highest improvement was noted for fabrics grafted using RAFT mechanism owing to its uniform coverage which elicits a better compatibilization effect. Shorter grafts were also observed to produce the greatest improvement in mechanical strength, thermal stability and moisture resistance owing to higher graft density which translated to better interfacial adhesion. Further functionalization of the PGMA-grafted abaca fibers in order to introduce covalent linkages between the fiber and the resin was successfully carried out using 1- vinylimidazole. However, the derivatization process ended up making the fiber brittle and resulted in lower tensile strength and thermal stability than its grafted counterpart. This decrease in fiber integrity also affected resulting composites. The results of composite testing showcase the potential of the technique as a surface modification tool for the enhanced utilization of natural fibers in the composite industry.