INTERACTION OF WATER AND HYDRATED CRYSTALLIZATION IN WATER-PLASTICIZED POLYACRYLONITRILE FILMS

It is known that pure water can be a solvent for polyacrylonitrile (PAN), but only at temperatures above its boiling point at atmospheric pressure. Thus, a PAN powder which had been blended with water could be compression moulded at 210-degrees-C like a thermoplastic material. The water-plasticized films were flexible and could be uniaxially drawn. X-ray diffraction studies on the dry (as-polymerized) powder and the plasticized film showed that there was a remarkable transformation in the diffraction pattern of the latter, which suggested the formation of a new hydrated polymorph. On drawing the plasticized film, the water was mostly expelled from the film and the d-spacings in the diffraction pattern reverted to those in the original, dry polymer. Infra-red dichroism studies led to the conclusion that the residual water molecules in the drawn film were preferentially oriented in a way which suggested hydrogen bonding to the nitriles. Raman spectroscopy showed that the nitrile vibration-band was shifted to higher frequency in the water-plasticized PAN compared with the dry polymer, and this was also indicative of hydrogen bonding of the water to the nitriles. Chain orientation factors were computed from the dichroism of the nitrile and water vibration-bands.