On the dissolution behaviour of extended chain polyethylene fibres

The influence of stress on the dissolution behaviour of extended-chain high molecular weight polyethylene fibres in p-xylene was investigated. Freely suspended in the solvent, the fibres dissolved at 119.5°, a temperature close to the equilibrium solubility temperature of 118.6° for perfect polyethylene crystals. However, when a stress of 0.4 GPa was exerted by straining the fibre 0.7%, it could withstand a temperature as high as 130° for at least three days. At still higher temperatures the induced stress relaxed completely, and dissolution immediately followed. These phenomena indicate that the fibre has a network structure. The cross-links are of a physical nature. Molecules are connected by topological defects such as entanglements, intertwinings and twist disclinations. These defects are trapped in crystallites; therefore the theory of Gee and Flory is applicable predicting that in such a system dissolution temperature of extended chain crystallites increases with stress. The required stress is transduced by tie molecules bridging the amorphous regions between crystallites. A study of dissolution under stress seems to be a direct method for the detection of topological defects such as entanglements