油変性フェノール樹脂の粘弾性

抄録

The chemorheological study of rubbers was developed by A.V. Tobolsky by means of chemical stress relaxation measurement. We should also propose a different method by means of dynamic-mechanical measurement on chemorheological study for the same purpose as he has conceived, i.e., investigate both the cross linking and the scission reactions of thermosetting type of polymers.
For the investigation of the cross linking and the scission reactions two types of coating films were used here as shown in Table I, Chinese tung oil-modified phenolic resin and epoxy resin ester for comparison with it.
Dynamic modulus E₁ of the samples used here has been exhibited rubbery plateau at the higher temperature ranges, where the values of dynamic modulus E₁ are indepedent on the frequencies of measurement, as shown in Figs. 1 and 2. Time dependency of dynamic modulus E₁ at the higher temperature region is shown in Fig. 3 in straight lines within shorter time ranges.
Dynamic modulus E₁ obtained at the plateau region is expressed by Eq. (1) according to rubber elasticity.
E₁=3_ρRT/M_c (1)
Density of cross links ν (mol/g) in polymer is expressed by Eq. (2) from Eq. (1).
ν=E₁/(3_ρRT) (2)
The slopes of the straight lines of dynamic modulus E₁ at each temperature shown in Fig. 3, therefore, may correspond to the reaction-rate constant k of cross linking for the sample, respectively. As such dependence of the reaction-rate constant k on temperatures is known to be expressed by the Arrhenius Eq. (3).
k=Aexp(ΔH/RT) (3)
In this way the apparent activation energy ΔH of the cross linking reaction for the four samples can be calculated as shown in Table III, from replot in the form of log k vs. 1/T as shown in Fig. 4. From the break of slopes of the straight lines in Fig. 4 we can obtain two different values of ΔH for a sample. This phenomenon will be accounted for by the fact that there are two types of cross linking reactions for a sample over the temperature range used herein.
In order to ascertain what kinds of cross linking reactions had taken place during the baking process we continued the chemical experiments as shown in Figs. 5, 6, 7 and 8, respectively. It is clear that there are two heat generations due to chemical reactions from the results of Differential Thermal Analysis (DTA) of the samples as shown in Fig. 5, i.e., the heat generation located in lower temperature region takes place both in air and N₂ flow, whereas the higher temperature in air only. From the results shown in Figs. 6, 7 and 8, the heat generation located in lower temperature region seems to be caused by the cross linking reaction after degradation of hydroperoxide formed in the drying oil of the sample, the higher temperature may be due to another type of cross linking reaction accompanied with the degradation of drying oil.
Those results of chemical experiments approximately agree with the results obtained dynamic-mechanical measurements mentioned above.