Abstract
The present paper is concerned with deducing the heat setting conditions (temperature and stress) of an elongated P. P. filament, its thermal stress which works on the filament preventing its thermal shrinkage. The thermal stress shows maximum values (fmax•) at a temperature (Tmax•) which varies with its thermal shrinkage (%), and satisfies the experimental formula;- fmax•=K(T0-Tmax•), K, T0: constant. Using this formula, the heat setting conditions of an elongated P. P. filament may be estimated.
1) When only the shrinkage (%) of the P. P. fiber elongated at T°C, which arises due to the relaxation at room temperature, is known the conditions of heat setting may be estimated from the cross point between the straight line connecting the maximum points above expressed and the thermal stress curve of the sample elongated to the known shrinkage (%).
2) When temperature of the heat setting condition of an elongated sample is only known, the conditions may be estimated from the cross point between the straight line and the striaght line which is perpendicular to the setting temperature.
3) When conditions of heat setting on an elongated sample are unknown, first, the thermal relaxation curves which are dependent upon the sum of the thermal relaxation curves of the elongated P. P. fiber (normal stress relaxation curves obtained by heating) and thermal stress curves caused by the secondary bonds unbroken by elongation (especially in low elongation), must be measured.
Increasing its elongation, a curve which is made only by the normal thermal stress relaxation curve, may easily be found and its heat setting conditions may be obtained.
