A study of order in polymers by X-ray diffraction

• Main Author: Preedy, J. E.
• Published: University of Surrey 1973
• Subjects: 548
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.469417

X-ray diffraction methods have been employed to determine order parameters in polymeric materials (mainly polyethylene). Two types of order have been defined; structural order, (i.e. crystallinity, unit cell dimensions, crystallite size and perfection) and alignment order (preferred orientation). Existing methods of analysis have been examined, modified and compared for a range of polymer types. The effect of molecular weight, molecular weight distribution, branching and conditions of crystallisation have been shown to alter the order parameters. The parameters of structural order have been examined over a range of temperatures up to the melting point of the polymers. These reveal changes in order due to recrystallisation above about 110°C, and a further change a few degrees below the melting point. Computer data processing techniques have been developed to produce pole figure plots and to determine orientation functions. These enable both qualitative and quantitative characterisation of preferred orientation in deformed and processed material. (310) twinning has been identified in both cold drawn and rolled polyethylene. (110) twinning is observed in polyethylene sheet after rolling, annealing and then further drawing. The operative twinning mode has been explained in terms of the fold geometry of the crystalline regions. Cold rolled polyoxymethylene has been shown to undergo a phase transformation from the hexagonal to orthorhombic phase. Films of polyethylene produced by the commercial process of extrusion blow moulding have been examined. The orientation results from a stress crystallisation procedure and the actual orientation may be related to the machine variable. The molecular chain axis distribution is defined by means of the orientation functions. These enable a quantitative correlation of the orientation with film properties to be made.