抄録
Investigation was made on the relation between the temperatures (Tmax) at which the maximum thermal stress was observed and the equilibrium thermal shrinkage in free state.
The results obtained are as follows:
1. A fiber contains frozen strains when the polymer molecules take the nonequilibrium configuration in the production process.
The thermal shrinkage of a fiber may be caused by disorienting effect due to breakdown of either crystallites or secondary bonds among the oriented molecular chains in the amorphous region.
According to Boltzmann, the probability that a restrictive energy Ei is released, is proportional to exp {-Ei/(kT)}. So, assuming that the equilibrium thermal shrinkage (%) in free state is owing to breakdown of these secondary bonds and crystallites, the following formula may be obtained; where, lT is the equilibrium thermal shrinkage (%) in free state at T°K.
The first term on the right hand side of the above equation represents the frozen energy released at T<Tmax, and the second term is the frozen energy released at T<Tmax (°K). Assuming that the latter is larger than the former, the following results are obtained.
Thus, plotting In lT vs. 1/T shows two straight lines having one transition temperature point which satisfies the experimental results on P. P. monofilament (draw ratio: 7)
Applying the above relation, the apparent activation energy of these two remperature ranges are calculated as 9 and 18kcal/mol respectively.
2. The equilibrium thermal stress F of a filament (draw ratio: 7) at the constant temperature below Tmax agrees with the stress in cooling from Tmax at the same temperature. Using the relaxation time τ=texp{(F-f/a)}, the apparent activation energy obtained from the slope of a straight line is 7kcal/mol which is about, the same as that obtained from lT (where f: the thermal stress of a filament at time t, a: constant).
3. Linear relationship, fmax=K(T0-Tmax) (K, T0: constants) is retained in the lower range of temperature than that at which the discontinuous point of lnlT_??_1/T curve is observed.
