High-Temperature X-ray Diffraction Studies on the Crystalline Transitions in the α- and γ-Forms of Nylon-6

The crystallization of nylon-6 from the melt was monitored in situ by X-ray diffraction. The nylon-6 was found to crystallize into a high-temperature α‘-phase as indicated by the two-peak nature of the diffractogram. On cooling from the crystallization temperature to room temperature, nylon-6 retained the two-peak nature. However, data analysis indicates a change from high-temperature (HT) α‘-phase to low-temperature α-phase at ∼180 °C. On heating, the α-phase transformed into the α‘-phase at about 190 °C and melted in the α‘-phase. The transition took place over a temperature range where both phases coexisted. However, samples crystallized from the melt at temperatures 140 and 180 °C showed the α-phase at room temperature, but on heating the α-phase first transformed into a pseudohexagonal phase and before melting the pseudohexagonal phase further transformed into the α‘-phase. The α-phase was transformed into the γ-phase, by potassium iodide−iodine treatment, and the behavior of the γ-phase with temperature had been studied for the first time. The γ-phase was very stable and did not show any crystalline transition below the melting point.