When PGVNC is used as an epoxy hardener, it is supposed that all the phenolic hydroxy groups are hard to react with epoxy groups because of the steric hindrance. So, the epoxy/hydroxy ratio (1/1.14, 1/1.76, 1/2.65, 1/3.97) and curing temperature (150, 170, 190 °C) were optimized for the curing system of SPE and PGVNC. Table 4.9 summarizes the tan 5 peak temperature measured by DMA and 5% weight loss temperature of SPE/PGVNC cured at various conditions. When the epoxy/hydroxy ratio was changed at the fixed curing temperature of 170 °C which is a standard curing temperature of epoxy resin, SPE/PGVNC(1/2.65) had the highest tan d peak temperature, although 5% weight loss temperature decreased a little with decreas­ing epoxy/hydroxy ratio. When the curing temperature was changed between 150 and 190 °C at the fixed epoxy/hydroxy ratio of 1/2.65, the cured resin at 190 °C showed the highest tan 5 peak temperature (148.1 °C) and 5% weight loss tempera­ture (319.2 °C). This result suggests that 6.0 of 16 hydroxy groups of PGVNC are reacted with epoxy groups of SPE. For example, this number corresponds to the sum of two hydroxyl groups of four guaiacyl groups and four sets of one hydroxyl group per one pyrogallol unit in the guaiacyl pyrogallol[4]arene. Also, when the curing temperature is 190 °C, the tan d peak temperature of SPE/PGVNC 1/2.65 was high­er than that of SPE/PGVNC(1/1.76). We did not investigate the curing temperature higher than 190 °C, considering the stability of wood flour which is subsequently added. When SPE was cured with PN at 190 °C, SPE/PN(1/1) had a higher tan 5 peak temperature and 5% weight loss temperature than that of SPE/PN 1/2.65. This result is reasonable, considering that all the hydroxy groups of PN can react with the epoxy groups of SPE in contrast to the case of SPE/PGVNC.

Figure 4.39 shows the temperature dependency of E and tan 8 for SPE/ PGVNC(1/2.65) and SPE/PN(1/1) cured at 190 °C. The tan 8 peak temperature of SPE/PGVNC(1/2.65) (148. 1 °C) was much higher than that of SPE/PN(1/1) (78.1 °C). Also, the E of SPE/PGVNC(1/2.65) was higher than that of SPE/PNQ/1) over the temperature range from 0 to 200 °C. The fact that SPE/PGVNC has high glass transition temperature and rigidity should be attributed to the pyrogallol[4] arene structure. Figure 4.40 shows the comparison of tensile properties of SPE/ PGVNC(1/2.65) and SPE/PN(1/1). The SPE/PGVNC showed a higher tensile modulus than SPE/PN(1/1) in agreement with the result of DMA. However, tensile strength and elongation at break for SPE/PGVNC(1/2.65) were lower than those of SPE/PN(1/1), indicating a more brittle character due to the rigid calixarene struc­ture.

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Temperature (°С)