Fabrication And Properties Of Resin Composite Reinforced By Laccase-modified Jute Fibers

Jute fiber reinforced composites have been widely used in many applications because of their low density, low cost, low toxicity, renewability, and excellent mechanical properties. However, jute fibers are hydrophilic and possess polar functional group, while most of the thermoplastic polymers are hydrophobic and have non-polar functional groups, resulting in weak interfaces and poor mechanical properties of the composites. In order to obtain high-performance composites, pretreatments of jute fibers aimed at improving the adhesion between fibers and matrix are necessary. The free radicals produced by laccase catalysis of the jute fibers can initiate hydrophobic alkyl gallate monomer free-radical chain reaction, and graft polymerization between lignin and alkyl gallate could occur. After the enzymatic graft modification, the hydrophobicity of the jute fabrics was improved, resulting in better interfacial compatibility between fibers and resin matrix. In addition, the hydrophobic polymer layer on the surface of jute fibers could be used as stress-transfer bridge between fiber and resin. Therefore, the mechanical properties of the composites were improved.In this paper, the grafting products were characterized by FTIR, elemental analysis and SEM. The saponification-reverse titration method was used to measure the grafting rate and the optimal reaction conditions for grafting alkyl gallate to the jute fibers were optimized. The results were as follows:laccase 2.5 U/mL, alkyl gallate 10 mM, pH 3.5, treating at 50℃ for 4 h. Contact angle and wetting time measurements showed that the surface hydrophobicity of the jute fabric was increased after the enzymatic graft modification. The longer the hydrocarbon chain of alkyl gallate grafted on jute was, the higher were the contact angle and wetting time.Based on analysis above, the jute was used as fiber reinforcement in the polypropylene (PP) composites. The results showed that alkyl gallate treated jute/PP composites showed lower water uptake and thickness sweling. The tensile and dynamic mechanical properties of the jute/PP composites were enhanced by the surface modification. Scanning electron microscopy images revealed stronger fiber-matrix adhesion in composites with modified fibers. The longer the hydrocarbon chain of alkyl gallate grafted on jute was, the better was the interface compatibility.The water absorption and thickness swelling of the DG-grafted jute fabric/epoxy composite were lower than those of the other composites. For the modified jute/epoxy composites, both the tensile strength and tensile modulus were increased. Dynamic mechanical properties and scanning electron microscopy images indicated that the adhesion between jute fibers and matrix was increased after graft modification of jute. Therefore, better interfacial compatibility were obtained, which satisfied the requirement for reinforcing the composites with better mechanical properties.