Live chat with material and textile scientist Tony Pierlot

Wool before and after scouring (Imagine credit: CSIRO)

Figure 1. Wool before and after scouring (Imagine credit: CSIRO)

Hello and welcome to our 11th live chat with an expert. This week we spoke to Tony, a chemist/material scientist by trade, who is now a team leader at CSIRO Materials Science and Engineering (Australia) and a world leading expert in wool and its properties. Working for the textile industry, he develops new products or ads functionality to existing textiles (quickdry, water proof etc) and has done a lot of research into testing their washing properties.

Q: People often say that wool keeps your baby warm in winter and cool in summer. How does that work?
Tony: Wool is traditionally viewed as a winter fibre because it can be made bulky and warm and is a good insulator. Lightweight fabrics however can also be made from fine wool, and these can be as cool and breathable as other fabrics, such as cotton. Breathability, so important in summer, comes from the ability of wool to absorb moisture.

Q: So does that mean that one garment (one pair of wool over-pants) would be ideal to use all year round?
Tony: Yes, but nowadays with air conditioning in cars, houses and transport it is probably not as important as in the past.

Q: So how come wool works as a semi-waterproof cover, when cotton wouldn’t? We use wool covers over our night nappies, and they work really well, but what’s the science behind it?
Tony: Wool has a thin layer that is bonded onto the outside of the fibre that makes it somewhat waterproof, whereas cotton does not, so it readily absorbs water. Generally, woven fabrics are tighter than knits so they are more water resistant.

Q: What are the washing guidelines for wool covers? The instructions say to hand-wash, which I do, but they still felt and shrink anyway. What would your top tips be for preventing that?
Tony: Be gentle with hand-washing as the more agitation the more likely it is to shrink. Wool can be treated to be shrink resistant, but I am not sure if this is available for covers. A gentle wool cycle in a washing machine can be as gentle as hand washing – these cycles tend to have more soak time than agitation all the time.

Q: Is there any solution to the shrinking/washing problem? For example by blending wool with other fibres, to make it more washable but still keep its wondrous properties?
Tony: Yes, blends of wool with around 50% of another fibre will be less prone to shrinkage. Woven fabrics are typically less prone to shrinking than knitted fabrics are. One thing to be aware of is that sometimes when wool is washed in a normal cycle and it does not shrink in the first, or maybe even the second cycle, an assumption is made that it won’t shrink at all. But on the next cycle, all of a sudden, it can shrink a lot. Shrinkage has what we call an induction period, where nothing appears to happen at first, but then it all goes quickly after that.

Q: That’s interesting about the induction period, what causes that?
Tony: It’s the nature of wool with its scale structure, the fibres start to move and then become entangled. The scale structure acts like a ratchet so fibres tend to move in one direction.

Q: How necessary is it to lanolise our wool nappy covers? I understand that all manufactured wool products are stripped of their lanolin but my wool marching band jacket is pretty effective in the rain (it’s a serge/twill). It seems to me like the fibre itself has water resistance, not just the waxy lanolin.
Tony: I assume the cover is a knit, so it’s an open structure and less water resistant. Woven fabrics are tight and therefore more resistant particularly due to the water resistant (technical term hydrophobic) coating on the fibre surface. Fabrics like wool can both be water resistant (repel liquid water) but at the same time absorb water vapour in the internal structure of the fibre.

Q: So would we be better off making wool covers out of woven or felted wool?
Tony: Knitted structures have the advantage that they are extensible and stretch, whereas woven and felted wool can be quite inextensible. So designs that do up rather than pull over would be better suited for the latter.

Q: Could you explain more about the structure of the fibre? Does it have a sort of hydrophobic shell? And we heard about tiny tubes which allow breathability, do those run through the fibre like trains through a tunnel, or across the width of it?
Tony: Yes the fibre has a hydrophobic shell, it has a layer of scales that overlap like tiles on a roof on the outside. On the inside it has protein structures called intermediate filaments that are glued together by another type of protein, a bit like fibreglass products. It’s the glue that absorbs the moisture. Wool typically has one layer of scales hair has many

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Figure 2. The structure of merino wool (Image credit: CSIRO)

Q: So what is it about wool that gives it anti-bacterial properties?
Tony: We had a fact sheet on our website that I will see if I can find and send a link, it’s quite complicated to explain on here!

Q: I just found a diagram of wool online (see figure 2). The structure is so complicated! Why so?
Tony: It is indeed, you see now why I’m struggling to explain it! The complicated structure is just nature: using proteins to build a fibre that is anchored well in the skin and that can also shed dirt from the tip due to the scale structure.
Q: Why is merino soft to the touch compared to other less expensive ones? I have eczema and ordinary wool feels like a million small cacti but merino is OK.
Tony: Merino wool is very fine, typically 20 micrometres in diameter. Other types can be 30 micrometres or more. It is the larger diameter wools that not only feel harsh on the skin, but also cause that scratchy feeling. So fine wool products are softer and should not prickle.

Q: What factors affect the longevity of fabrics? Nappies get washed a lot more than most items of clothing, so what can we do as users to prolong their lives? Or what materials should we choose to have the longest life?
Tony: No fibre, natural or synthetic, has the full spectrum of properties that one would like in a garment. So some limitations on all, overcome to some extent through blends of fibres. Tumble drying is harsh on natural fibres so avoid that if possible!

 

A massive thank you to Tony for speaking to us and answering all our questions, all the way from the other side of the globe!

 

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