Question

Using words and visuals, briefly describe the temperature dependence of stiffness for the following classes of polymers. Explain how the structure and bonding in these materials contributes to the observed temperature-dependent properties (structure-property connections).

Amorphous and semi-crystalline thermoplastics

Elastomers

Thermosets

Answer 1

A. Amorphous thermoplastics:-

Amorphous thermoplastic resins consist of statistical oriented macromolecules generally optically transparent and mostly Brittle. Exmple – Polycarbonate, polystyrene, polyvinylchloride and polymethyl-methacrylate. Amorphous thermoplastic resins is below the glass temperature Tg , molecular structure is frozen in a definite shape and the mechanical properties are barely flexible and brittle ie more stiffness. exceeding the glass temperature, the mechanical strength will decrease by increasing molecular mobility and the resin will become soft elastic ie stiffness decreases.

B. Semi-crystalline thermoplastics:-

Semicrystalline thermoplastic resins consist of statistical oriented macromolecule chains as amorphous phase with are usually opaque and tough elastic.Examples - Polypropylene and Polyamide. Below the glass temperatureTg the semicrystalline thermo-plastics is frozen and the material is brittle and above the glass temperature, the mechanical strength will decrease by increasing more molecular mobility and mechanical behavior of the material is tough elastic to hard.

2. Elastomers:-

Elastomers are plastics with wide crosslinking between the molecule chains. Examples - Polyurethane resin and Styrene butadiene resin.Below Tg they are hard elastic to brittle and Above the glass temperature Tg as elastomers are soft elastic. Raising temperature affects an increase of elasticity, caused by reducing the stiffness effects of the crosslinks and increasing the mobility of the molecule chains.

3. Thermosets:-

Thermosets are plastic resins with narrow crosslinked between molecule chains. Examples - Epoxy resin and Polyester resin. thermosets are hard and brittle. Due to strong resistance of molecular movement caused by the crosslinking, mechanical strength and elasticity are not temperature dependent ie no effect of temperature on stiffness.