MTRM798 Polymer Physics

Assessment Instructions

· Answers should be written legibly by hand or word-processed. All text, sketches and mathematics should be integrated into a single document, and submitted as a pdf.

· Include a first page detailing your student number, and the module code and name.

· If you have a DDS (Disability & Dyslexia Service) cover sheet, include a scanned copy of that as the second page of your submission During the assessment

· Your submission must be your own work, and you must not break any of the rules in the Academic Misconduct Policy. Do not collude with others. Do not ask anyone else to answer the questions for you. All such activities are expressively forbidden. You must answer questions entirely independently.

· Please be aware that:

1. All submissions will be subject to inspection for plagiarism and use of external tutoring support. Detection of such activity will constitute an assessment offence

2. We will viva a percentage of students after each assessment to discuss the answers they have provided as confirmation this is your own work

Question 1

Look around yourself and identify three polymer items: one made of an amorphous thermoplastic, one made of a semicrystalline thermoplastic and one made of an elastomer.

For each of the three items:

i) Very briefly describe the item (if possible, take a picture).

ii) Suggest which specific polymer has been used, including its chemical structure. What do you think are the main reasons (at least two) for such selection? State two reasons each.

iii) Suggest how the item has been manufactured. What do you think is the main reason for such manufacturing selection?

Question 2

a) Explain (max 3-5 sentences) why we cannot simply use Young’s modulus to design polymer products? Explain using diagrams how we can construct creep-isochrones that can be used for polymer design.

b) A freshly moulded poly(vinyl chloride) (PVC) test bar is cooled rapidly and tested. Upon testing it deforms homogeneously without the formation of a neck. A similar PVC bar from the same batch is tested after a year. Now it no longer deforms homogeneously but it fails by necking. Explain (max 3-5 sentences) what has happened.

c) A simple way to enhance the failure strain of polystyrene (PS) is by mixing in rubber particles. What is the main mechanism responsible for this increase in failure strain, and what role does the network density play in this? Explain in about 3-5 sentences.

d) Polyamide 6 (PA6) has a glass transition temperature (Tg) of 50 °C and polyvinylchloride (PVC) has a Tg of 70 °C. Which of these two polymers would you select for an application at 100 °C? Explain your answer (max 3-5 sentences). How would you modify that polymer for an application at 200 °C?

Question 3

a) Poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) are both thermoplastic polyesters. Explain (max 3-5 sentences) why PBT is often preferred over PET for injection moulding applications.

b) Explain (max 3-5 sentences) why polymers crystallise by chain folding rather than chain extension.

c) Sketch the stress-strain curve for an amorphous polymer and include the contribution of the inter-molecular component and the network component to the total stress.