1.5.1 SPE/QC/WF BIOCOMPOSITES

1.5.1.1 PROPERTIES OF CURED EPOXY RESINS

In order to optimize the curing condition of SPE and QC, the curing tem­perature and epoxy/hydroxy ratio were changed.24 Table 4.8 summarizes the tan 5 peak temperature measured by DMA and 5% weight loss temperature of SPE/QC cured at various conditions. When the curing temperature was changed from 150 °C to 190 °C for SPE/QC at a typical epoxy/hydroxy ratio of 1/1, the SPE/QC cured at 170 °C had the highest tan 5 peak temperature (78.4 °C) and 5% weigh loss temperature (335.4 °C). Because SPE is an aliphatic epoxy resin, it is presumed that some thermal degradation starts to occur at around 190 °C. Therefore, the curing temperature was fixed to 170 °C. When the epoxy/hydroxy ratio was changed from 1/0.8 to 1/1.2 at the curing temperature of 170 °C, the SPE/QC 1/1.2 had the highest tan 5 peak temperature (85.5 °C) and 5% weigh loss temperature (342.5 °C). This result suggests that four hydroxy groups of QC with five hydroxy groups per molecule actually reacted with SPE. Although it is not clear why SPE/ QC 1/0.8 had a higher tan 5 peak temperature than SPE/QC 1/0.9-1/1.1, it is supposed that cationic homopolymerization of SPE occurs by the action of acidic hydroxy proton at 5-position of carbonyl group of QC. Consequently, the epoxy/hydroxy ratio of 1/1.2 and curing temperature of 170 °C were selected as the optimized curing condition for SPE/QC. Table 4.8 also sum­marizes the thermal properties of the cured resins of SPE/PN, diglycidyl — ether of bisphenol A (DGEBA)/QC and DGEBA/PN. As a result of optimi­zation of the epoxy/hydroxy ratio for SPE/PN, SPE/PN(1/0.8) showed the highest tan 5 peak temperature (81.0 °C), which was still lower than that of SPE/QC(1/1.2) (85.5 °C). Although we did not fully optimize the epoxy/hy­droxy ratio for DGEBA/QC and DGEBA/PN, DGEBA/QC(1/1) and DGE — BA/QC(1/1.2) showed higher tan 5 peak temperature than DGEBA/PN(1/1). These results indicate that QC is a superior epoxy hardener to produce the cured resin with a high T