Synthesis of new cellulose-ester derivative to improve fiber/matrix interface in hemp fiber reinforced polymer composites: Investigation of composite properties

Natural fiber reinforced composites attract great attention due to their environmentally friendly, biodegradable and recyclable materials. Hemp fiber is used in many sectors due to its superior mechanical properties. Like other natural fibers, hemp fibers also require some chemical modifications to improve their interfacial bonds with polymer matrices and to reduce their hydrophilic character. In this thesis, acetyl and caproyl cellulose esters were synthesized under microwave reaction conditions in order to improve the weak fiber/matrix interface in hemp fiber reinforced composites. In acetyl chloride modifications (AC), tensile strength increased by up to 38.5% and flexural strength increased by up to 44.3% compared to the untreated sample (H-AC-15). In the CC group samples, the highest tensile strength was obtained in H-CC-15 with a 39% increase, while flexural strength increased by 53.4% compared to UT. Contact angle measurements showed that the modifications made the surface of the fiber hydrophobic. Bending tests performed after water uptake revealed that surface modification has a direct effect on environmental strength. While the bending strength decreased by 35% after water uptake in the UT sample, especially the H-CC-15 sample showed the lowest strength loss with 18.5%. SEM analyses also supported these findings, and visible improvements were observed at the interface.