Dr Stuart Gordon (CSIRO Textile and Fibre Technology/ Cotton CRC) explains new technology being developed to measure fibre fineness and maturity the parameters desired by spinners. CSIRO Plant Breeder Greg Constable talks about the factors that influence fineness and maturity and how they are being improved through plant breeding.

Stuart you have been doing some work on fineness and maturity. Can you tell me how those parameters are measured now and what’s wrong with that?

We use micronaire to get an idea of fibre fineness but micronaire is a product of both maturity and fineness because micronaire actually measures specific surface area so it measures the airflow or measures out the pressure difference between, the pressure difference over a plug of fibres of a specific weight and those fibres can be course and immature or they can be find and mature. So which is it?

You are developing systems that measure those two things independently, starting with fineness, what is it and how are you proposing to measure it?

Cotton fibre fineness is defined in terms of mass per unit a length or gravimetric fineness we call it or linear density and so we describe it in terms of milligrams per kilometre and the term we use is militex or desitex which is tens of grams per kilometre or desigrams per kilometre but millitex is milligrams per kilometre and that’s how we define fibre fineness. So for upland cottons we are looking at millitex values between say 150 and 200 millitex normally for Australian cotton. With 150 millitex being preferred if you are looking to spin fine count yarns.

And maturity. What’s it and how do you measure it?

Maturity is a little bit more difficult to measure. Its usually measured, currently its measured relative to airflow or some other fibre parameter but if we are to divide it in sort of first principles it’s the degree of thickening in the fibre wall. So cotton fibre is a single cell and the thickness of that cell wall will define its maturity and the way we measure in the first principles is we actually section the cotton fibre and measure the cross sectional area and express that as a ratio to the area of the circle the same parameter as that cross section. So that’s the definition of fibre maturity.

So sometime in the future growers will be able to have through standard classing houses have access to fineness and maturity rather than just a single micronaire value?

Ideally, I think the spinning industry for a number of years has been looking for that segregation and if you look back in the literature and industry forums over the last ten to twenty years there has been that call for that differentiation of micronaire into its two components and we hope at CSIRO that we have two new instruments that will enable at least the Australian cotton industry to start doing that and particularly at the breeding stage where we are looking to have definition of new varieties based on the new varieties that are fine and mature and I understand that the environment plays a big hand in the cell wall development so its environment still has a big factor there but if we can have varieties that lean toward the finer end and that we are able to grow to maturity then we will have a premium fibre.

From a spinners prospective, the person that’s using the product. What’s going to be their preferences in terms of fineness and maturity?

They are going to want a fibre really around the sort of well, around the 150 to 160 millitex mark and with a maturity ratio of about .8 or an average maturity ratio .8. Now, I am using maturity ratio there which is another scale again but I guess there also needs to be some education about what scale of maturity we use so in saying that we are just talking about a fibre. If a use a maturity ratio we are talking about a fibre that has maturity ratio or 1 and if I talk about the degree of thickening, which I defined before, then we are talking about a value of about .8 or 7.8.

But in short they want a fibre that’s fine but mature?

In short, they just want a fibre that’s fine and mature and long and strong.

CSIRO Plant Breeder Greg Constable

Greg, we have just heard from Stuart Gordon talking about how they have got instruments to measure fineness and maturity and he has mentioned that the spinners are really interested in a fine but mature fibre. Can you just tell me starting with fineness, what are the main determinants of fibre fineness?

There are different varieties that are finer than others Dave and the very extreme is Pima. So the Pima has this very fine fibre and within out upland varieties there is a range there from varieties that are nice and fine to varieties that are relatively course. Siokra V-16 was an example of a nice fine fibre.

So in terms of say agronomic or climatic conditions what could influence fineness?

Fineness will be initially influenced by the conditions in that first 20 days of fibre development because it can actually expand in diameter at that time. But mainly the fineness will also be affected by conditions during boll filling. So good warm sunny conditions will increase the diameter of the fibre slightly and obviously they will more thick.

Moving on to maturity, what can influence maturity?

That is mainly from the conditions during bolls, boll filing and fibre thickening. That last 40 days of boll filing again sunny, warm conditions, good water and nutrition will give a more mature fibre and if it’s a courser fibre it will end up with a higher mic.

Is there varietal differences between maturity?

Absolutely, there is probably a little bit more variation in our upland varieties for maturity than there is for fineness. So some varieties have more mature fibres than others.

Is that because they fill those fibres for a longer period of time or do they fill more per day?

Probably both and in the case of most of the varieties we have got I imagine it is both but the narrower sort of germplasm that we have these days is probably more to do with per day rather than longer boll periods.

How are you using this fineness and maturity information in the breeding program?

We have instruments here. We have the older fineness maturity testers that are measured both fineness and maturity and we use that in parallel with our HVI line for measuring the fibre properties of breeding lines and we are putting heavy selection pressure on for fine mature fibres. The complexity is a) the fineness maturity testing is slower but the most frustrating aspect is that fine fibres are correlated with lower yield so we are always sort of struggling to make advances with one while not changing another one.

Why do you think there is that negative correlation between fineness and yield?

It’s a good question and I think its to do with the fact that there are a limited number of fibres on the seed and if those fibres are finer or other words smaller diameter there is not enough sync for actually filing fibres and for setting cellulose which is our lint yield.

Further Information:
Robert Eveleigh, John Marshall,  Craig McDonald, David Kelly or James Quinn