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Date November 2020 Marks available 1 Reference code 20N.3.hl.TZ0.3
Level HL Paper 3 Time zone TZ0
Command term Suggest Question number 3 Adapted from N/A

Question

Carbon fibre reinforced plastic (CFRP) is a useful composite. Epoxy is a thermoset polymer that is used as a binding polymer when making CFRP.

 

Outline the two distinct phases of this composite.

 

[2]
a.

Thermoplastic composites are increasingly replacing thermosets.

Suggest one advantage of thermoplastic polymers over thermosets.

[1]
b(i).

Explain how thermoplastics, such as polyvinylchloride, PVC, can be made more flexible by the addition of phthalate ester plasticizers.

[3]
b(ii).

Explain why phthalates are replaced by other plasticizers in the production of plastics.

[2]
b(iii).

Classify PVC and polyethene terephthalate, PET, as addition or condensation polymers and deduce the structural formulas.

[3]
c.

Markscheme

carbon fibre reinforcing phase ✔

«in a» matrix phase of epoxy ✔


Award [1 max] for “reinforcing phase «embedded» in a matrix”.

a.

can be recycled
OR
can be reformed when hot
OR
high impact/chemical/abrasion resistance ✔

b(i).

Any three of:

plasticizers embed/fit between «polymer» chains ✔

keep polymer strands/chains/molecules separated/apart ✔

weaken intermolecular/London/dispersion/attractive/forces/instantaneous induced dipole-induced dipole/forces «between chains» ✔

prevent chains from packing closely/forming regular packing/structure ✔


Accept “van der Waals/vdW” for “London”.

b(ii).

Any two of:
readily released into environment
OR
have weak intermolecular forces «rather than covalent bonds between chains» ✔

get into biological systems by ingestion/inhalation ✔

interrupt endocrine systems
OR
affect release of hormones
OR
effect development of male reproductive system ✔

considered carcinogenic
OR
can cause cellular damage ✔

can cause early puberty in females ✔

can cause thyroid effects ✔

can cause asthma ✔


Do not accept just “are a health concern”.

b(iii).

PVC: addition AND PET: condensation ✔

structure of PVC monomer ✔

structure of PET monomers ✔


Accept full OR condensed structural formulas.

c.

Examiners report

Most had some idea of a composite and tended to gain at least one mark for stating "reinforcing phase embedded in a matrix".

a.

This was well answered and most stated that one advantage of thermoplastic polymers over thermosets is that they can be recycled.

b(i).

This also was well done and some managed to score all three marks.

b(ii).

This question required an explanation of why phthalates are replaced by other plasticizers in the production of plastics. This question was found to be very challenging and even the better candidates failed to score both marks. The weaker candidates typically stated that they are just a health concern, which was deemed insufficient to warrant even a salvage mark.

b(iii).

This question on PVC and PET was very well answered. All three marks for their correct classification and the corresponding structures of their monomers was frequently scored.

c.

Syllabus sections

Options » A: Materials » A.5 Polymers
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