Richard Neale of the Laundry Technology Centre Worldwide replies to a Danish reader's query about ironing temperatures for polycotton fabrics. He uses the term "shrinkage" where there is a loss in dimension in one direction with no increase in the other direction. The term "distortion" is used where the dimensions change but the total area stays the same.
The origin of my comment regarding the maximum ironing temperature for polycotton is that in the UK, textile suppliers widely regard 150C as the maximum safe temperature - this figure may originate from the two-dot iron care symbol used on retail products.
In practice UK commercial launderers have few problems up to 167C, judging from our team's observations at laundries throughout the UK.
However, launderers operating above 167C report distortion problems with both polycotton and cotton-rich fabrics. The higher the temperature of the ironer bed surface, the greater the problem.
The problem can be minimised by reducing the drag between textile and bed (by increasing the frequency of waxing).
It can also be reduced by lowering the roll-to-roll stretch in the ironer (to 0.1% from the more typical 0.2% per roll).
Some UK rental operators, using ironers powered by 12bar steam, buy textiles that are over-sized in one direction to compensate.
The typical levels of distortion, which LTC has measured on several sites, is 14 - 26% reduction in the warp direction over around 25 washes and ironings, when the textile is fed selvedge first (that is with the weft in the machine direction through the ironer).
This has been a significant problem during 2013 - 2014 because of the change from 100% cotton to 70:30 cotton-rich, which launderers have been treating as cotton, rather than treating it as they would for 50:50 polycotton.
The full letter and Richard Neale's reply appears in the March edition of LCNi.
