In situ Fourier transform IR spectroscopy and variable-temperature wide-angle X-ray diffraction studies on the crystalline transformation of melt-crystallized nylon 12 12

The crystalline transformation in nylon 12 12 was monitored by variable-temperature wide-angle X-ray diffraction during heating, isothermal and cooling processes. It could be found that the a phase of the sample transforms into a,, phase at about 130 degreesC if the sample is heated from room temperature to a high temperature, which is the so-called Brill transition temperature. In addition, nylon 12 12 was found to crystallize into the gamma phase when isothermally crystallized at high temperature from the melt. Upon further cooling from the crystallization temperature to room temperature, the reverse transition from the gamma phase to the alpha phase can be detected. Furthermore, in situ Fourier transform IR spectroscopy was also used to study the Brill transition of nylon 12 12 samples on both heating and cooling. It is interesting that the hydrogen-bond strength in nylons decreases dramatically and that some Brill bands of nylon 12 12 disappear abruptly during the Brill transition on heating.