Question

PRE-LABORATORY - QUESTIONS ....... The following preparatory questions should be answered before coming to lab. They are intended to introduce you to several ideas that are important to aspects of the experiment. You must turn in your work to your instructor before you will be allowed to begin the experiment. 1. What do we mean by thermoplastic polymer? 2. What is the definition of thermosetting polymer? 3. What is glass transition temperature (as it relates to polymers)?

Answer 1

Thermoplastic polymer : Thermoplastics or thermosoftenting plastics are polymers that becomes moldable and pliable at enhanced temperatures. Thermoplastics usually have high molecular weights and the chemical bonds are associated by intermolecular forces that are weak upon increase of temperature yeilding a viscous liquid. This vicious liquid can be formed into various shapes by different molding techniques.

Thermosetting polymer : Thermosetting plastics or the thermosets are those polymers that are irreversibly hardened by adding a curing agent to a prepolymer solution forming extensive cross-links between the polymer chains. Thermosets are insoluble and infusible. Thermosets are formed during manufacturing procedure of the plastic and reshaping the plastic is not possible due to presence of irreversible chemical bonds.

Glass transition temperature (T_{​​​​​​g}​​​) : Glass transition temperature is a temperature above which the Gibbs free energy is such that it favours segmental mobility (polymer segments slips along each other upon application of force) of a polymer chain and the polymer displays plasticity. Below T_{​​​​g}​​​​​ the polymer behaves like a rigid glassy substance where segmental mobility is almost negligible and hence the polymer is brittle.