Question

1. What are the 4 molecular structure of polymers? Write down the relationship between materials's strength and different molecular structure?

2. What are the three phases that a composite has, and what are their roles in the composite?

3. Give 3 examples for the materials that can be used as matrix phase and reinforcement phase.

4. What is the reason of using plies in different directions for some of the laminate composites?

Answer 1

1: Based on molecular structure, polymers are divided into the following 4 types

(a): Elastomers: These are rubber like polymers having elastic property. The polymer chains are held together by the weakest intermolecular force, that allows the polymer to stretch. e.g. neoprene, Buna-S et.

(b): Fibers: Fibers possess high tensile strength and high modulus of elasticity due to strong intermolecular forces like H - bonding among polymer chains. e.g. Nylon-6,6, terylene etc.

(c): Thermoplastic polymers: These polymers are capable of contineous softening on heating and hardening on cooling. The extent of intermolecular force is intermediate between elastiomers and fibers. PVC, polythene etc.

(d): Thermosetting polymers: These are cross linked and heavly branched molecules, which on heating undergo extensive cross linking. Hence these polymers cannot be reused.

2: Three phases of a composite are

(a) Contineous phase: It acts as the matrix and can be a bulk material with particles or fibers dispersedthrough it. It provides protection to the dispersed phase from mechanical and chemical damage.

(b) Reinforcement (a type of dispersed phase): It is the dispersed phase that is used in matrix to increase strength.

(c) Filler (a type of dispersed phase): It is used to fill up the matrix at a reduced cost and for other purpose.