That shrinking feeling

The linen processed in a textile rental laundry is central to the company’s business. Linen must be kept clean and in good condition to avoid a series of problems and customer complaints.

Poor rinsing or poor washing processes will create pressure on the laundry line leading to bottle-necks, slowing production and damaging both machinery and the company’s profits.

Sometimes a new batch of linen will have faults that are not immediately visible but that will become apparent during the laundry processes, leading to problems for the textile rental business.

Recently the Laundry Technology Centre (LTC) has also seen an alarming increase in the number of enquiries and complaints about unusually high levels of dimensional changes, usually shrinkage, after the linen has been processed.

Traditionally LTC would expect to see shrinkage of around 5 – 7% for sheets and similar products. The highest levels of shrinkage will occur with 100% cotton.

Cotton-rich products will have a lower level while polycotton and 100% polyester will have the least shrinkage.

The shrinkage on sheeting has two causes – relaxation shrinkage and wash shrinkage.

For cotton, wash shrinkage is the main factor and for polyester it is relaxation shrinkage – the release of the slight stretch set in by the cloth finisher when the cloth was set under tension.

Problems escalate when standard sheeting starts to shrink by up to 24%, which is upsetting, especially for the housekeeper who tries to dress a bed with a fitted sheet and finds that the mattress ends up looking like a cowboy’s saddle.

The mathematical term for this shape is a hyperbolic paraboloid, which may be of use when making a written complaint.

This surge in excessively high levels of shrinkage has several causes. The dramatic worldwide increase in the price of cotton and the tendency for the price of polyester to follow the oil price have meant that both laundries and textile manufacturers are trying to reduce operational costs.

After the fabric has been woven a whole variety of different treatments may be applied.

These can include de-sizing to remove the dressing that was placed on the yarns to assist the weaving process or the application of special fabric finishes designed to give special performance characteristics.

All woven fabrics used for rental textiles will undergo a bleaching process to turn the creamy yellow loom-state fabric (known as “grey cloth”) to a pure white.

The same processing line is also used to chemically pre-shrink cloth intended for rental use to avoid unexpected changes in dimensions, which would make the end-product unfit for purpose.

This “shrinking” process will often require up to an hour of immersion in a hot, strong solution of sodium hydroxide (caustic soda).

The time taken will vary from manufacturer to manufacturer, depending on the rental company’s specification and the exact processing conditions.

Costs of pre-shrinking

The cost of this process depends on the time taken to produce a fully pre-shrunk material. A long process will also increase the cost of the finished fabric per square metre as pre-shrinking reduces the amount of material for sale.

Pre-shrinking is energy-intensive and because the caustic must be rinsed completely from the fabric it also uses a considerable amount of water and incurs effluent charges.

After the shrinking process has been completed, the roll of cloth will ultimately be passed through a stenter where it is placed under tension and heat-set into shape.

The cloth might also be “singed” at this point, to burn any loose fibres off the fabric surface.

Heat-setting produces a much more stable cloth but it also sets a slight stretch into the cloth.

This stretch is normally removed during the first three wash cycles in the laundry, with most of the stretch being released in the first wash. This release of tension is often referred to as relaxation shrinkage and it affects every type of fabric.

It must be included in textile specifications, which may allow up to 5% total shrinkage in both the warp and weft during test washing.

This allowance is supposed to cover both relaxation shrinkage and normal wash shrinkage.

For rental purposes the relevant international standard specification is that given in BS/EN/ISO 14237. The standard relates to healthcare textiles as no standard specifically covers rental textiles.

Test wash

The test wash process referred to in this standard is carried out at 95C and this is followed by ironing under zero tension and 24 hours conditioning at 60% relative humidity at room temperature.

This procedure brings out most of the wash shrinkage and the relaxation shrinkage in a single wash. The factory turning the fabric into bedlinen must take account of the total shrinkage allowed. Failure to do so will result in sheets that do not quite fit the beds and pillows and duvets that poke out of the end of their covers.

If the textile manufacturer does not fully pre-shrink the fabric it will affect the shrinkage potential during laundering. The loom-state fabric’s shrinkage potential could be as much as 24 – 25%, depending on the quality of the raw cotton used to produce it.

If the textile mill cuts the pre-shrink time by half, then at the end of this process the fabric might only have been shrunk by 12% rather than the full 24%.

Some laundries might think that this does not matter as they only wash linen at 71C for 5 – 8 minutes and don’t use caustic soda, so there shouldn’t be a problem. However, such thinking is not correct.

Raised temperatures

The cotton shrinkage process requires exposure to strong alkali at raised temperatures.

Boiling in caustic soda merely achieves this shrinking process in the shortest time possible.

Washing at 71C in sodium metasilicate will continue the shrinking process – but at a slower rate. So if a sheet that has only been partially pre-shrunk goes into the rental laundry’s system, the results may be adequate for the first 10 – 15 cycles as the sheets may only shrink a few millimetres during each wash.

But after a total of 20 – 25 wash cycles, each of 8 minutes, the sheet will have been exposed to a strong alkali for over 3 hours.

Within six months of the laundry introducing the fabric, it will have completed the pre-shrinking process and the customers will start to complain that the sheets no longer fit the beds.

As the shrinkage is gradual, taking place over 25 wash cycles, the partially pre-shrunk fabric may pass the test process 1A for BS6330 in the early stages of its laundry life as it will only shrink by the permitted 5% in the warp and weft. Technically it meets the standard and is deemed “fit for purpose”. However, if the shrinkage continues for the next

25 washes, the sheet will then be 12 – 15% smaller than it was when first purchased.

As a result, the stock will have to be replaced after six months rather than the 24 months in the laundry’s budget calculations. With these figures the laundry could eventually risk bankruptcy.

Lateral thinking

One innovative launderer managed to persuade a customer that had to deal with bedlinen that no longer fitted to down-rate their textiles. The king-sized sheets now fitted a double bed and the double sheets became a “generously-sized single”. The hotelier agreed and the laundry only had to replace the king-sized sheets. This is a good example of lateral thinking on the part of the rental launderer.

As this strategy will not always work, laundries need to take steps to avoid complaints from irate customers and the unwanted cost of having to replace stock six months after its introduction.

When a laundry receives a consignment of stock, it should take one sheet and lay it out flat then carefully measure it in both the length and the width.

The results could be surprising as LTC has often found that the new sheet does not match the dimensions on the delivery note or on the specification.

Make a note of the dimensions and then wash the sheet in a strong alkali for 60 minutes at 90C. Ideally use caustic soda but straight sodium metasilicate will give a similar result.

The alkali should be added at a rate of 15g of dry alkali per kg of work – or sufficient alkali to achieve a 1% solution.

After 60 minutes, rinse and extract the sheet then finish it on a hot-head press, taking care to smooth out any wrinkles and creases without placing any tension on the fabric.

If the laundry does not have a hot-head press, it should lay the sheet out flat and let it dry naturally.

When doing this, take care to smooth out as many wrinkles and creases as possible without placing the sheet under tension.

When the sheet has been dried and conditioned, measure it and record the results then calculate the amount of shrinkage.

This simple process will show the laundry what the consignment will look like in six months time.

The table at the foot of this page shows how to calculate the percentage shrinkage based on a sheet that measures 210 x 150cm (length x width) when new but after the test process described now measures 180 x 130cm width.

As will be seen that sample sheet would have suffered a total area shrinkage of 25.7%.

It is therefore essential that laundries specify that the fabric must be fully shrunk before delivery and that after 25 wash cycles, the shrinkage in both the warp and weft should be no more than 5%.

It is likely that the initial purchase price for fully pre-shrunk fabric will be slightly higher than that for fabric that has not been pre-shrunk but the extra cost is only a tiny fraction of the cost or replacing a whole consignment aftersix months.

Ensuring that textiles are good quality and that they do not fail in laundering before the end of their budgeted life is central to any textile rental business.

They must be well specified and well cared for otherwise the rental business risks serious problems and even failure.