Question

a) Using the stress-strain graph below, explain which polymer (A or B) has the higher Youngs Modulus. What does this mean about the relative properties of polymers A and B? AX A' X stress strain b) The A and A' curves above are both true for the same polymer! How can this be true, and what does it tell you about polymer "A"? c) Polymer "B" can handle a lot of strain, but prior to the break point (X), the curve steepens sharply. What is happening on the molecular level with polymer B?

Answer 1

-EE where E is young modules. Shrey Strain Polymer A has higher young modules than B. The steepners of Cuire a indicates higher stress to strain ratio which is basically indication of higher slostic modules. Higher elastic modulus of a indicates it is a Brittle plastic Whereas the lower elastic modulusos B indicates it is an amorphous elastomer. This can be true as strain-stress behaviour of polymers odepend on the temperature. In first case the polymer is below its glass tramition temperature, hence shows under brittle failure. As temperature increcies the polymeragoes brittle to ductile transition and that results in a ductile failure. It indicates the polymer is a remi crystalline polymer having a weu defined glass transition temperature above which it behaves like being in rubbery state. Nore - Brinle-ductie transition temperature To is not always idential with Tg for many polymers. ? This happens because the polymer enderyoes Strain hardening with increase in stress, the polymer Chains are oriented in the direction of stress that results in stress induced Crystallizalion of amorphous polymers. As a result the strength and stiffness of plastic increases Which results in sharpening the curve before failure.