Biocomposites Composed of Bio-Based Epoxy Resins, Bio-Based Polyphenols and Lignocellulosic Fibers
In recent years, renewable resources-derived polymers (bio-based polymers) and composites (biocomposites) are attracting a great deal of attention because of the advantages of these polymers such as conservation of limited petroleum resources, possible biodegradability, the control of carbon dioxide emissions that lead to global warming. This chapter deals with the preparation, thermal and mechanical properties of the bio-based network polymers prepared by bio-based epoxy resins and bio-based polyphenols, and their biocomposites with lignocellulosic fibers. As biobased epoxy resins, glycerol polyglycidyl ether (GPE), polyglycerol polyglycidyl ether (PGPE), sorbitol polyglycidyl ether (SPE) and epoxidized soybean oil (ESO) were used. As bio-based polyphenols, tannic acid (TA) which is a hydrolysable tannin and quercetin (QC) which is a flavonoid were used. Also, the polyphenols (TPG) prepared by the reaction of tung oil (TO) and pyrogallol (PG) and guaiacyl pyrogallolarene (PGVNC) prepared by the reaction of PG and vanillin (VN) were also used. As lignocellulosic fibers, wood flour (WF) made from Sanbu cedar crushed into powders through 3 mm screen mesh and microfibrillated cellulose fiber (MFC) were used. The thermal and mechanical properties of the bio-based polymer networks and their biocomposites were investigated in detail by means of dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA) and tensile test. The morphology of the fractured surface of the biocomposites was observed by field emission-scanning electron microscopy (FE-SEM). Consequently, the SPE cured with PGVNC showed the highest tan δ peak temperature (148 °C). The PGPE/TA/ WF and GPE/TA/WF biocomposites with WF content 50-60 wt.% showed the highest Young’s modulus (4-5 GPa). The SPE/TA/MFC biocomposites with MFC content 10 wt.% showed the highest tensile strength (80 MPa).