Unit 2 - Lecture 12 Topic 3

Question 1

Aramid:

Answer 1

A long chain of synthetic aromatic polyamides in which at least 85% by mass of the amide linkages are attached directly to two aromatic rings and in which imide groups may be substituted for up to 50% of the amide groups. While nylon is a polyamide fibre, aramid’s are aromatic polyamide fibres.

Question 2

Para-aramid example:

Answer 2

Kevlar

Question 3

Meta-aramid example:

Answer 3

Nomex

Question 4

How do aromatic rings affect fibres?

Answer 4

They provide stiffness and more energy is required to break or decompose them. It makes the molecular make-up highly crystalline and highly oriented with the fibre axis.

Question 5

Cross-sections of meta-aramids vs para-aramids:

Answer 5

Meta-aramids are peanut shaped while para-aramids are rounder.

Question 6

What is the heat and flame resistance of aramid fibres?

Answer 6

Exceptionally high.

Question 7

What is the strength of aramid fibres?

Answer 7

Very high. Para-aramid’s are higher in strength though than meta-aramids.

Question 8

What is the UV resistance of aramid fibres?

Answer 8

Poor, aramids are vulnerable to UV degradation.

Question 9

What is the stretch resistance and tenacity of aramid fibres?

Answer 9

Aramids have high tenacity and resistance to stretch.

Question 10

What is the abrasion resistance and chemical resistance of aramid fibres?

Answer 10

Aramids have excellent impact and abrasion resistance. They are also resistant to most chemicals.

Question 11

What is the moisture regain of aramid fibres? Are the fibres stiff?

Answer 11

Aramid moisture regain is about the same as nylon at around 4.5%. Aramids are stiff fibres: Para-aramids are not suitable for apparel, while meta-aramids are used in protective clothing applications.

Question 12

Why are aramids difficult to dye?

Answer 12

Due to high crystallinity, meta-aramids (i.e., Nomex®) can not be coloured more brightly or in a wider range of colours.