Structure of nylon 6-iodine complexes and their drawability by solid-state coextrusion

Abstract

The structure and drawability of nylon 6-iodine complexes, prepared from selected concentrations of I2/KI aqueous solution, have been investigated. Four steps of complex formation have been deduced on systematically increasing the concentration of I2/KI solutions in contact with films of nylon 6. Inferences from the results of x-ray diffraction and thermal analyses are the following: (1) At the lowest concentration, the initial crystal phase of nylon 6 is maintained, with the chains merely being displaced by I− 3 ions, probably lying perpendicular to the nylon 6 chain axis. (2) At intermediate concentration, the crystal consists of two different phases; one is the crystal complex with the longer intermolecular distance caused by I − 3 the other is the original nylon 6 crystal. The complexed crystal phase develops into two subphases. These are surmised to be complexed with the I − 3 ions and I − 5 ions lying parallel to the chain axis. (3) At still higher KI3 concentration, the crystal may be complexed with the 1− 5 ions. The ultimate plasticized crystal is of only one structural phase, likely complexed with the I − 5 ions. The drawability of complexed nylon 6 is affected sensitively by its structure. The drawing was done by solid-state coextrusion with a high-density polyethylene billet at a temperature close to the highest melting point of the complex. Nylon 6 film which had contained the two subphases resulted in a structure with the highest drawability, providing an uniaxial draw ratio of 48.