The thermal behaviour of nylon 66, associated with the morphologies identified previously, has been examined. The thermograms for the crystallization temperatures (T~), between 247°C and 265°C, were distinctly different from those at low T? and from those given by samples crystallized non-isothermally on cooling. The endothermic peak could be identified with the melting of negative and zero birefringent spherulites (the latter of both kinds). On cooling, samples crystallized in the T? range of 247-265°C, display certain characteristic exotherms indicating further crystallization. In view of the fact that 'morphologically' the preceding crystallization had been complete, such crystallization must take place within the appropriate morphological entities themselves, conforming to the particular morphology present already, or alternatively the effect may correspond to a solid-solid transformation. In addition to the above, a new high melting crystal form with Tm in the range of 280-285°C has become apparent forming under conditions corresponding to zero birefringent spherulites (high To) but distinct from the latter, not conforming to any morphology seen in our previous study. Finally, the new information and issues arising therefrom are summarized and placed in perspective
Посилання на статтю:
Studies on the crystallization and melting of nylon 66: 3. Melting behaviour of negative spherulites by calorimetry / C. Ramesh* and A. Keller // Polymer. – 1994. – Vol 35. – P. 5300-5308.