Natural - Containing mainly two sub-groups of:

• Animal - Wool, Mohair, Silk, etc.
• Plant - Cotton, Linen, Hemp, Jute and less obvious fibres like Bamboo.

Both fibre groups have specific and often unique properties which lend themselves well to being either blended or used in a pure form for the end use intended. Primarily the majority of man-made fibres were developed as alternatives to natural fibres. Nylon for instance, developed in the 1930s by Dupont, was developed as a substitute to silk for parachutes and later women's stockings.

Acrylic fibre is derived from oil, as an alternative to such products as Wool and Cashmere. Ultimately in today's textiles we see the majority of products utilising the best of both natural and man-made fibres in blends. For schoolwear, Acrylic, Polyester and Cotton make up the majority of end products and we will cover these now in a little more detail.

Acrylic

The largest single producer of Acrylic fibre resides in Turkey, although Far East production continues to rise through increasing demand. China alone consumes over 1.3 million tonnes of acrylic fibre annually.

Acrylic fibre is produced from a Polymer containing Acrylonitrile - this is dissolved in solution looking rather like a syrup commonly known as ‘dope'. Pushed through a spinneret (rather like a watering can head) the resulting liquid is drawn off as continuous filaments of fibre. These are then washed, dried and crimped before being cut into a specified fibre length (known as a staple) suitable for blending and spinning into yarn.

The thickness of these filaments (determined by the hole size in the spinneret) will ultimately decide the denier of the fibre. Denier is defined as the mass of the filament in grams per 9,000 metres. Therefore the smaller the number, the finer the fibre, and the softer the fibre will feel. Most acrylic fibre is produced in a range between 0.5 and 15 denier, three to five denier is most commonly used in school knitwear. Dyeing can occur at fibre production stage or be applied in later processes of yarn or even garment production. (figure C summarises the process).

At this stage the acrylic fibre prior to cutting is known as ‘Tow' and consists of a continuous web of uncut filaments with no fibre length. The fibre is now ready for ‘converting' where it can be cut down into the required staple length to allow it to be blended and processed with other fibres. This is normally 20-30mm long for cotton production, 50- 60mm for wool spinning and in over 100mm for blending with Wool and other natural or manmade fibres for worsted spinning.

The blending process is commonly done by introducing the required fibres together to a blending box. This machine consists of a series of input rollers that introduce the various fibres in controlled proportions to the blending or gill head of the machine. Here a series of pinned bars termed as fallers begin to blend and comb the fibres so that they mix and lie in a uniform parallel direction to attain the best possible evenly spun yarn (rather like combing your hair). After several passages of blending, the mixed fibres are wound onto a package called a ‘roving' ready for spinning.

During spinning the fibres are closely controlled as they are drawn down to a required thickness of fibre where twist is inserted before winding at high speed onto a bobbin. The yarn can then be checked for irregularities as it is wound onto a cone for twisting. At the twisting stage generally two, three or four ends of the yarn are brought together and twist is inserted in the opposite direction to the spinning twist to bring the yarns together into a single twisted and finished yarn product.

If dyeing has not already taken place in fibre form it can be applied after the yarn production stage in large dye vats. Typically dyes known as disperse dyes are used, these are cheap and readily available in the marketplace. Acrylic yarns dye very easily and retain their colour properties well, even after repeated wash and wear cycles.

Once twisted the yarn can be knitted into fabric on what is commonly known as flat bed knitting machinery where panels of knitted fabric are constructed. These panels are then cut into required shapes of the garment - front, sleeves, back, etc. The resulting shapes are then joined and stitched together - a process known as cut and sew. (see figure D for process summary).

Acrylic fibre has been known to pill in fabric form although generally, in more recent times, fibre producers have developed what is now known as low pilling acrylic fibre. In such cases these producers will extrude acrylic fibre under low temperature conditions in the early stages of production, causing the resulting fibre to have a low tenacity (weak strength). As a result of this low tenacity, pills of fibre naturally form on the fabric, the strength of the fibre holding the pill to the fabric. This attraction is so weak that the pill formation simply breaks away from the fabric during normal wearing giving the appearance of a better performing and more presentable long life garment. Such technology has been successfully marketed by several producers. It should however be stressed that there are many factors both in yarn production and the after care of the garment that can also determine the overall pilling performance of a product.

Cotton

Cotton is generally a cheap and readily available product grown from a plant called the Gossypium. The plant is native to America, the Indian subcontinent and parts of Africa. The Arabic word for this product is ‘Al qutun' which is where the English name of cotton was derived from, as well as the Spanish name of ‘Algodon'.

After growth and harvesting, the cotton is passed through what is known as ginning or cotton gin process. Here, through effective automation, the cotton fibre is removed from the seed pod and all other impurities can also be removed. After this the product can be processed through the textile production cycle of carding which helps to remove further impurities before combing, blending and yarn production can begin. The latter of these stages are much like those of Acrylic described earlier. In school wear we often see blends with man-made fibres such as Polyester before yarn spinning. These are then knitted after spinning into fabrics for such end uses as sweat and polo shirts.

Cotton relies heavily on intense chemicals, fertilisers and pesticides for its growth and subsequent production and as such a number of growers are now moving to more organic forms of farming to address the needs and concerns of today's end users. It is believed that Cotton accounts for more than half of the world's demand for textile fibres today and is a hugely important traded product to the developing nations of the world. Cotton is renowned for its softness and natural strengths, particularly when wet, as well as very good absorption or wick ability of moisture. Dyeing is often more difficult than some man-made fibres. Traditionally direct dyes were used for cellulosic based fibres like Cotton but demands for better fastness of colour in washing have led to the development of reactive dyes; these are dyes that chemically bond with the cotton to give much stronger colour retention in fabrics and garments.

Polyester

The most commonly produced of all man-made fibres accounting for over 50% of all man-made fibre production in the world. Polyester is used in a whole variety of textile end uses from household drapery through to football shirts.

Polyester is produced by mixing and heating two chemicals together namely Ethylene glycol with Terephthalic acid. During this process temperatures can reach in excess of 200° C. After further processes under extreme temperatures and pressure a product called polyethylene terephthalate or ‘PET' is formed. As the PET cools it forms a liquid which can be extruded through a spinneret (showerhead like nozzle), much in the same way as Acrylic fibre, before being dried to a fibrous form ready for blending with other fibres and processing into yarn.

The product is also widely used in general plastics such as cartons and pop bottles where it is now effectively recycled. Items can be melted down and reformed into a fibre that can ultimately be reconstructed back into such textile items as fleece jackets and sweatshirts.

Blending with other fibres helps to give Polyester more appealing aesthetics to the end product than would be normal in its pure form. Dyeing is done using what are termed disperse dyestuffs and generally light fastness on Polyester is exceptional.

The product offers easy care, quick drying and good durability properties to the end garment and is often found blended with Cotton before yarn spinning (see acrylic process) and then knitted on a circular knitting machine. These machines, as their name indicates, exhibit a bed of circular arranged needles which form a tubular fabric. This fabric can then be easily dyed before cutting, drying and make-up into finished garments such as polo shirts.

Additional looped backs on the fabric can be created for later brushing of the fabric to give the brushed fleece effect you see on the inside of all sweatshirts. This adds comfort and warmth to the end product creating small pockets of air that are trapped between the garment and body.

Alternatively Polyester can be used in its purest form to create football shirts in filament form or fleece jackets that can have low pill and even shower / stain resistant treatments applied like Teflon fabric protector to offer additional benefits.

Ken Edgar is the Technical Director At Rowlinson. He has extensive knowledge of the industry on an international level. Prior to 2005 when he joined Rowlinson, he spent ten years at Acordis with responsibility for the Courtelle brand. In 2007 Rowlinson completed its purchase of Courtelle.

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