YOUR AIMS
On completion of this lesson you should be able to:
• understand the various nomenclature and classification systems used for polymeric materials of commercial and engineering importance
• understand the processes of polymerisation
• recognise the wide range of molecular and solid state structures shown by polymers
• appreciate the properties of polymers which are of engineering significance.
SELF-ASSESSMENT QUESTIONS
1. What type of polymers do the following letters represent: PC, MF, SBR?
2. What are the raw material costs of the following: ABS, PU, CR?
3. Why are most polymers amorphous or semi-crystalline at room temperature?
4. Calculate the volume % crystallinity of a sample of UPVC with a density of 1390 kg m-3. The density of completely amorphous UPVC is 1385 kg m-3 and the fully crystalline polymer is 1422 kg m-3.
5. Using the structure classification system how would you classify PA 66 and NR?
6. Why are polymer densities low compared with other materials?
7. Why are polymers good thermal and electrical insulators? Use a materials data source to give the thermal conductivity and resistivity of polystyrene.
8. A tensile test on a specimen of polyacetal, 25 mm long, 6 mm wide and 2 mm thick, at 20°C, showed an initial strain of 0.005 when the load was 210 N, and the break load was 960 N when the extension was 2 mm.
Determine the stress and strain at the break and estimate the modulus of elasticity from the initial loading conditions.