Phase transition behavior of Nylon-66, Nylon-48, and blends

Phase transitions, including alpha-beta phase transition and melting, of nylon-66, nylon-48 and blends were measured by simultaneous DSC-XRD and DSC-FT-IR. The molecular mechanism of alpha-beta transition and melting of nylon-66 and blends were estimated from DSC-XRD and DSC-FT-IR. On the broad endothermic peak between 100 and 200 degreesC, spacing of (010/110) of alpha-form expanded from 0.36 nm to 0.40 nm, and spacing of (100) of alpha-form changed from 0.44 nm to 0.41 nm, then (100) of beta-form appeared. The triclinic ab plane changed to the rhombohodral ab plane from 100 to 200 degreesC. The slide of hydrogen bonded sheet induced transition to the hexagonal beta-form. Double melting peaks on DSC heating curve were due to the melting of two types of beta-form consisted with weak and strong hydrogen bonded molecules. Composition dependence of alpha-beta transition temperatures obtained by DSC-XRD and DSC-FT-IR showed good agreement with that of the equilibrium melting temperature. Nylon-66 and nylon-48 are thus in a miscible state at the molecular level.