STUDENT : 23857498 Section A (9 marks) Question 1 (2) Discuss how the chain alignment for linear and crosslinked polymers affect crystallisation. For linear polymers, crystallisation is easily accomplished because there are few restrictions to prevent chain alignment whereas in crosslinked polymers the crosslinks prevent the polymer chain from aligning into a crystalline structure thus making the polymer amorphous. Question 2 (3) Given two polymers of molecular weight 280g/mol and 28000g/mol. Explain which polymer has the highest melting point and what can you conclude about the relationship between the molecular weight and the melting temperature. 28000g/mol polymers has the highest melting point. Melting point is determined by the amount of van der waals forces in the polymer. The polymer with the molecular weight 28000g/mol has more van der waals forces which need to be overcome to melt. We can conclude that as the molecular weight increases the melting temperature increases. Question 3 (2) Two polymers of the same material, one is crystalline and the other is amorphous. Explain how the density is affected by the differences of these two polymers. The density of a crystalline polymer will be greater than the amorphous polymer because the chains are closely packed together for the crystalline polymer. Question 4 (2) List 2 things that increases the rate of diffusion in polymers - Molecules are diffused must be small. Molecules must be chemically inert (must not react with the polymer). Section B (11 marks) Question 1 (2) How does increasing the temperature affects the mechanical properties of polymers? - It decreases the tensile modulus Reduces tensile strength Enhance ductility Question 2 (2) Explain how the relaxation modulus curve behave for a viscoelastic polymer. - The magnitude of relaxation modulus decreases with time As the temperature increase the relaxation modulus decrease Question 3 (1) How is the creep and relaxation modulus common? - The are both temperature sensitive They both decrease with increasing temperature. Question 4 (2) How does elastic deformation occur in semicrystalline polymers? - Amorphous regions: chain molecules elongate in the direction of the applied tensile stress. Crystalline regions: the lamellar crystalline thickness increase. Question 5 (2) Name and explain the factors that influence the mechanical properties of semicrystalline polymer. - Molecular weight. As the molecular weight increases the tensile strength increases Degree of crystallinity. The strength of the material and tensile modulus increases with degree of crystallinity. Heat treatment. Heat treating semicrystalline polymers increases crystallinity thus increasing the strength of the material. Question 6 (2) Which type of rubber would you use for your shoe sole, vulcanized or unvulcanised rubber and why? Vulcanised rubber sole - Vulcanised sole protects your shoes from being worn out - Resistant to abrasion - Provides a long life for your shoes.
