The transformation behaviors of nylon 12 were investigated using wide-angle X-ray diffraction (WAXD), X-ray fiber patterns and differential scanning calorimetry. The γ' form could be distinguished from the γ form in spite of their very similar WAXD patterns, because the γ form cannot be transformed into the α form, while the γ form can be so transformed under high pressure. The γ' to γ transformation occurs on annealing above 110°C at atmospheric pressure. The γ to γ' and α to γ' transformations occur on drawing at atmospheric pressure above 50°C and above 70°C, respectively. The transformation behaviors presented in this paper and in a previous paper [N. Hiramatsu, S. Hashida and S. Hirakawa: Jpn. J. Appl. Phys. 21 (1982) 651] are summarized.

ABSTRACT:Thermal behavior under high pressure of the y form nylon 6 obtained by iodine treatment was investigated by means of a high pressure differential thermal analysis. The crystalline structures which resulted in the endo-and exo-thermic peaks in the thermogram were examined with the wide angle X-ray diffraction measurement. Under relatively low pressure kg em-2 ), two endothermic peaks were found. With increasing pressure, the lower temperature side endotherm due to the melting of the y form crystal became small, while the higher one due to the melting of the converted rx form crystal became large. Under high pressure (above 2000 kg em -z) an endotherm due to the melting of the converted rx form crystal and an exotherm were observed. This exotherm is attributed to they to rx form transformation. In this case, the transformation occurred without melting the y form crystal, in contrast to the situation at atmospheric pressure. The pressure dependences of the melting peak temperatures of the rx form and they form were almost the same and equal to !Soc per 1000 kg em-2 •

For poly(ethylene terephthalate) crystallized and/or annealed under elevated pressure, the melting behavior was studied, using a differential scanning calorimetry technique at atmospheric pressure. The melting point of the sample crystallized from the melt by slow cooling under elevated pressure is lower than that of the sample crystallized at atmospheric pressure, although the former sample has a slightly thicker lamella than the latter one. This implies that the fold surface energy is much larger in the elevated pressure crystallized sample. The atmospheric pressure melting point increases greatly by annealing under elevated pressure. In particular, a remarkable increase in melting point is observed at the early stage of the annealing for the elevated pressure crystallized sample, which may be due mainly to the decrease in fold surface energy in addition to lamella thickenning. An electron micrograph of the sample annealed for a long period after the melt crystallization under elevated pressure shows a morphology of a band structure composed of extended-chain-like crystal.

Behavior of transitions and the nature of high-pressure phase in polytetrafluoro ethylene are studied using methods of ultrasonic waves, thermal expansion, differential thermal analysis and X-ray diffraction. A phase diagram is obtained in pressure range from 1 atm. to 6,500 kg/cm2 and in temperature range from room temperature to 165°C. Three phases are found; phase I above 30°C, phase II below 20°C, both at 1 atm. and phase III above 5,000 kg/cm2. The triple point is located at 75°C and 5,000 kg/cm2. Pressure dependence of transition temperatures is obtained as 15 and 9 degrees per 1,000 kg/cm2 for the 20°C and 30°C transitions at low pressure, 9 degrees per 1,000 kg/cm2 for both transitions at intermediate pressure range from about 3,000 to 5,000 kg/cm2, -13 and 50 degrees per 1,000 kg/cm2 for the II–III and the III–I transitions, respectively. It is suggested that the high-pressure phase (phase III) may be a closely packed but disordered phase.

The formation conditions of α form Nylon 12 under high pressure from the melt and from the quenched state were investigated by means of high-pressure differential thermal analysis and wide-angle X-ray diffraction. The α form was formed by crystallization from the melt above 200 MPa, and the γ form disappeared in the sample obtained above 500 MPa. The quenched state was transformed into the α form at lower temperature than the melting point of the α form under high pressure, whereas the γ form was hardly transformed at all. The thermal behavior of the α form at atmospheric pressure was also studied. Two endotherms due to the meltings of the α and γ forms and one exotherm due to the α to γ form transformation were observed. This transformation occurred without melting of the α form at a slow heating rate and was regarded as a monotropic transition.