Temperature dependent wide angle X-ray diffraction studies on the crystalline transition in water saturated and dry polyamide 6/66 copolymer

The crystalline transition in water saturated and dry polyamide 6/66 copolymer (ratio 4:1 by mol) was investigated by means of temperature dependent wide angle X-ray diffraction (WAXD). The polyamide 6/66 copolymer (PA6/66) exhibits a poorly developed α-phase at room temperature after being cooled down from the melt. Uptake of water improves the crystalline structure by mobilizing the amorphous phase, thus facilitating chain relaxation in the crystalline phase. Upon heating, the effect of the glass transition on the change of the crystal lattice constants is seen. Further heating leads to a gradual crystalline transition from the α-phase to a pseudohexagonal phase. Different from the behavior in polyamide 6, this pseudohexagonal phase does not further transform to a high temperature α′-phase before melting. The delay of the crystalline transition in the water saturated PA6/66––as compared to the dry material can be understood as a result of the better ordered crystalline structure in it.