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Polymers contain ordered crystalline regions; chains fold to produce lamellae. When lamellae are nucleated from a small area, round agglomerates known as spherulites are formed. In a fully crystalline material they impinge on each other and appear polygonal under the microscope. In this TLP, polymer crystallisation and spherulite formation have been discussed. Micrographs of spherulites showing the distinctive Maltese cross were presented and their appearance was explained in terms of birefringence.

From the section of the TLP dealing with mechanical testing, you should have gained an understanding of the mechanism of necking and cold drawing by which a semicrystalline polymer deforms under a uniaxial tensile stress above its glass transition temperature. Furthermore, Considère's construction, which is a simple way of determining whether a polymer sample will neck and cold draw, was derived. The stress-strain curves produced by such experiments should now be familiar, for varying strain rates and relative temperatures.


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