MELTING BEHAVIOR OF NYLON 66

The effects of drawing condition and wet heat-treatment on the melting behavior of nylon 66 were studied. Double melting peaks are observed on the sample drawn at lower temperature than the glass transition temperature, while one broad peak which corresponds to lower one, is observed on the sample drawn at relatively higher temperature.When the sample is annealed, the lower melting peak also appears even in the sample drawn at higher temperature. The lower melting peak grows with annealing, and the melting temperature becomes higher with increased annealing temperature, whereas the higher one which appears in the as-drawn samples does not shift, but diminishes gradually with annealing. As the temperature shift of the lower melting peak is related to the change of the long spacing of the sample, the equilibrium melting temperature can be estimated according to the Hoffman-Weeks relation. Two cases are postulated for the relation between the long spacing and the thickness of crystals in the Hoffman plot. The equilibrium melting temperature is estimated as 294°C from the more reasonable one of the two cases. The double orientation of crystals can be also observed when drawing is performed at lower temperatures than the glass transition temperature, as we have already reported in the case of nylon 6.