Getting the best results from cotton-rich fabrics

Polyester used to be regarded as a cheap, inferior alternative to cotton but as cotton prices rose sharply, so manufacturers started to find different ways of combining cotton and polyester fibres.
Cotton-rich mixtures started to appear and became increasingly popular. They are now widely used by textile rental operators, with most opting for a 70:30 cotton-polyester blend while others prefer an 80:20 ratio.
This inclusion of a small amount of polyester is believed to prolong textile life as polyester does not weaken with high levels of bleaching and this small proportion improves both the fabric's tensile strength and its tear strength.
However, the transition from
100% cotton to cotton-rich has brought some problems that manufacturers and rental launderers have had to learn to solve.
To get the best results from cotton-rich fabrics, rental laundries need to take great care with the specification and to check the delivered textiles against it. They also need to understand the fine detail of what is required both in the textile mill and in the laundry.

Construction for 70:30 blends
The benefits of polyester lie in its superior strength to cotton and in its ability make the fabric more stable thus reducing the amount of shrinkage that a cotton-rich textile will suffer over multiple launderings when compared to 100% cotton.
However, to achieve this reduction in shrinkage, the fabric needs to have polyester in both the warp and weft.
Cheaper fabrics, where the polyester fibres only run in one direction, will generally not last as long before tearing or going into holes as those made from yarns with an intimate blend of polyester and cotton in both warp and weft.
Weaving is an expensive process as mills have to invest heavily to acquire a modern loom and the production process is very slow.
This means that fabrics that have a minimum of weft threads per cm are cheaper to produce.
The best option for rental laundries is a "square" fabric, one that has almost as many picks (weft threads) as ends (warp threads). This makes it very stable in washing, ironing and in use on a hotel bed. So it might have 30 ends and 26 picks.
Renters might be offered a cloth which has the same weight per unit but is constructed with 40 ends and 16 picks.
While this would be less expensive, it would be less stable and therefore a poor choice as stability should never be sacrificed on grounds of cost.
The inclusion of polyester may make fabrics lighter.

The sizing effect
Sizings are applied to textiles at two critical points in manufacture. First the warp ends are sized to lower the coefficient of friction between yarns and shuttle so allowing higher shuttle speeds and lowering weaving costs proportionally.
Then, a final sizing is applied as part of the cloth finishing process. This makes the cloth easier to handle in cut, make and trim (CMT) as it allows the automatic cutting and sewing machinery to be used at high speed.
When the finished bedlinen is delivered to the rental operator it will usually still have the final sizing and in many cases still retain some or all of the warp sizing as well.
This does not matter if the sizing is formulated so that it comes off in the first wash. Some textile suppliers control sizing very well and ensure that it is non-durable and comes away easily but it is important that the rental operator remembers to specify that sizings must be non-durable.
Even when non-durable sizing has been specified and used, the initial wash before the item goes into circulation is very important both to remove the sizing and to prevent staining on the unwashed sheet as this can be very difficult to remove.
Failure to specify non-durable, easily removable sizing can result in work suffering cracked-ice creasing and this can remain for the first 20 cycles, however good the ironer.
The wrong sizing spec can cause even greater problems if the manufacturer then uses a sizing that lowers the permeability of the sheet during washing as this can lead to the sheets causing blockages in the tunnel washer and to membrane press bursts.

Pilling in use
Unfairly, polyester has a reputation for being prone to pilling, producing tiny balls of fibre when it is rubbed.
Manufacturers of modern cotton-rich products control any tendency to pilling simply by getting the fibre staple lengths and the yarn twist correct, so that all the fibres are held firmly in the yarn structure and cannot be rubbed out.
Sometimes a guest's nightwear will shed fibres that can stick together to form pills. These pills are then held onto the sheet's surface by a single polyester fibre. However, even this type of pill problem rarely occurs when the hotel uses cotton-rich sheets.

Strength and shrinkage potential
The British Standards Institution has produced a draft standard for healthcare textiles (DD ENV 14237:2002). This is also helpful for laundries serving the hospitality sector.
It sets out minimum purchase standards and thus defines an affordable set of criteria that can be readily achieved and will ensure that the textile performs well in rental use.
The BSI document calls for tensile strength in both the warp and weft of 400 Newton (400N). This has proved invaluable in organisations trying to increase textile life from 100 - 120 wash-and-use cycles to around 200 cycles.
The use of cotton-rich textiles with their polyester content makes this strength target much easier to achieve and should eventually translate into longer lasting textiles.
This BSI document also specifies a maximum shrinkage of 7% in the warp and 7% in the weft, measured after three washes at 92C followed by finishing (ironing) under zero tension.
The actual shrinkage in rental use is different because the rental operator uses a multi-roll ironer.
As a result, the roll-to-roll stretch, coupled with the drag against the stationary bed, creates a slight elongation in the direction of ironing.
The shrewdest high-volume rental operators make allowances for this in the specification, with the amount allowed depending on the direction of travel through the ironer.
For example, if a duvet cover will be ironed bag end first, then the spec might allow for 4% wash shrinkage in the length but 10% in the width. These are the percentages by which the size of the covers ordered exceeds the size of the duvets that they are designed to fit.

Shrinkage and distortion
The multi-roll ironer can not only reduce the length of cotton-rich items it can also cause distortion. Polyester is a thermoplastic polymer, which is heat sensitive and therefore it softens at high temperatures (typically above 165C).
This characteristic does not matter too much when the textile passes through the first two rolls of a three-roll ironer but as the piece dries out in the third bed the polyester can soften and lose its strength. So the force that stretches the item can cause distortion and the piece will gradually lengthen with every wash and iron process.
A tendency to "neck-in" means that as the length distorts, the piece becomes narrower. So a sheet can progressively "shrink" in width in the direction of travel though the ironer.
Over 20 - 30 wash and use cycles, the width can reduce by over 15%. The sheet will still cover the same area as it did after the first few washes (that is after to normal wash shrinkage) but the distorted shape makes it unusable.
Wash shrinkage is a property of the fabric and is the responsibility of the cloth maker, assuming that it has been washed correctly.
Distortion caused by the ironer bed being too hot for the polyester fibres is usually the launderer's responsibility and this fault can be avoided by using lower bed temperatures for cotton-rich work.
It is important to note that reducing the temperature for these blends does not result in lower productivity.
Cotton-rich fabrics retain less moisture than 100% cotton and the polyester content allows the moisture to evaporate more quickly.
Cotton-rich fabrics do not need the high bed temperatures that can be achieved with high-pressure steam and gas-fired thermal oil ironers. These fabrics can be ironed successfully on setting of 8 bar steam or a thermostat setting of 165C for a thermal-oil heated ironer.
If an ironer is processing both cotton and cotton-rich fabrics, it is important to have a set-up that allows the operator to change the settings rapidly.
Some ironer manufacturers provide this option on the original equipment. On a thermal oil ironer, changing the thermostat setting is easy. On a steam-heated ironer the ideal solution is to have a pressure reducing set and a three-way valve.

Whiteness and brightness
A 100% cotton can be kept white simply by using a detergent with good suspending power (to prevent
re-deposition) and by low level bleaching.
However, if the fabric contains polyester, the laundry needs to take great care to avoid redeposition and the fabric must also be protected from protected from alkaline hydrolysis and from oxidation caused by excessive bleaching.
Once polyester fibres have turned grey, it is very difficult to restore the whiteness.
Cotton-rich fabrics will also need a detergent system that can break the strong attraction that the polyester content has for oily soiling.
Many detergent suppliers can supply a product that is suitable for both cotton and cotton-rich fabrics but the laundry needs to check this.
Cotton-rich products also need a detergent with good quality OBAs (optical brightening agents).
The detergent supplier should be able to provide a product with brighteners that will bond both to cotton and to polyester, giving a real "wow" factor.
Cotton-rich products combine the luxurious handle and breathability of cotton with the cost advantages and high productivity that can be obtained with polyester.
Given the increasing importance of energy efficiency and productivity, cotton-rich could be the fabric of the future, provided that the way this fabric reacts to certain conditions is understood.