Spandex Yarns

Spandex Yarns

Spandex, Lycra or elastane is a synthetic fiber known for its exceptional elasticity. It is stronger and more elastic than natural rubber. It is a polyester-polyurethane copolymer that was invented in 1958 by chemist Joseph Shivers at DuPont's Benger Laboratory in Waynesboro, Virginia. It was introduced in 1962 and it revolutionized the clothing industry in many ways.

The name "spandex" is an anagram of the word "expands". It is the preferred name in North America; in continental Europe it is referred to by variants of "elastane", i.e. elasthanne (France), elastan (Germany), elastano (Spain), elastam (Italy) and Elasthaan (Netherlands), and is known in the UK, Ireland, Portugal, Brazil, Argentina, Australia, New Zealand and Israel primarily as Lycra.

Spandex yarn is a classification of man-made fibers and is described in technical terms as segmented polyurethane and it is composed of 85% polyurethane polymer chain segments. The main raw materials of Spandex yarn are PTMEG and MDI.

Spandex yarn can be stretched four to seven times its initial length, yet springs back to its original length once tension is released. While spandex fiber appears to be a single, continuous thread, it is in reality a bundle of tiny filaments. It is a composed of “soft”, flexible, segments bonded together with “hard”, or   rigid, segments. This gives the fiber its built-in lasting elasticity.

Spandex fibers are produced in four different ways: melt extrusion, reaction spinning, solution dry spinning, and solution wet spinning. All of these methods include the initial step of reacting monomers to produce a prepolymer. Once the prepolymer is formed, it is reacted further in various ways and drawn out to make the fibers. The solution dry spinning method is used to produce over 94.5% of the world's spandex fibers.

Solution dry spinning

Step 1: The first step is to produce the prepolymer. This is done by mixing a macroglycol with a diisocyanate monomer. The two compounds are mixed in a reaction vessel to produce a prepolymer. A typical ratio of glycol to diisocyanate is 1:2.

Step 2: The prepolymer is further reacted with an equal amount of diamine. This reaction is known as chain extension reaction. The resulting solution is diluted with a solvent (DMAc) to produce the spinning solution. The solvent helps make the solution thinner and more easily handled, and then it can be pumped into the fibre production cell.

Step 3: The spinning solution is pumped into a cylindrical spinning cell where it is cured and converted into fibres. In this cell, the polymer solution is forced through a metal plate called a spinneret. This causes the solution to be aligned in strands of liquid polymer. As the strands pass through the cell, they are heated in the presence of a nitrogen and solvent gas. This process causes the liquid polymer to react chemically and form solid strands.

Step 4: As the fibres exit the cell, an amount of solid strands are bundled together to produce the desired thickness. Each fibre of spandex is made up of many smaller individual fibres that adhere to one another due to the natural stickiness of their surface.

Step 5: The resulting fibres are then treated with a finishing agent which can be magnesium stearate or another polymer. This treatment prevents the fibres' sticking together and aids in textile manufacture. The fibres are then transferred through a series of rollers onto a spool.

Spandex yarn is widely used in,

        •    Casual Wear

        •    Sportswear, Swim Wear, Body suits etc.,

        •    Innerwear, jump suits, lingerie accessories etc.,

        •    Socks, Hosiery, Glove, etc.

        •    Elastic Lace, Elastic Tapes.

        •    Medical products, Wrist support, Knee pad and Elastic bandages, etc.

        •    Elastic thin fabrics, Shirt, Skirts, Suits, Gauze, etc.

        •    Woolen Sweater, Denim Apparels.

        •    Medical & Hygiene Textiles.

        •    Automotive Interiors, Seat Belts, etc.

SPANDEX COVERED YARN

When spandex as the core in the percentage from 5% to 20%, is wrapped with various yarns and fibers such as nylon, polyester, etc for the end-product, what we get is a Spandex Covered Yarn. This is to increase the filament yarns with higher elasticity and construct textile fabrics for better draping property and keeping in shape for the end-products. It draws better properties than rubber yarn in intensity, stress, hard-wearing, ageing-resistant on the basis of chemical research. Elastic or Spandex covered yarn furnishes fabric with elasticity which is different from traditional fabric in the sense of touch and external factors.  Spandex Covered Yarn is widely used for woven and knitted fabrics ,textile - weaving, warp-weaving, knitting, underwear, pantyhose ,socks, garments, and  medical uses.

  
Spandex Covered Yarns are divided into two types - Conventional Covering Yarn [traditional covering] & Air-Jet Covered / Intermingled Yarn. 

Conventional Covered Yarn [CCY]

The conventional covering process can be defined as the traditional method of manufacturing covered yarns. Wrapping hard filament yarn around extend spandex fiber or rubber. In this process, the spandex fibre is drawn at a constant factor and is continuously fed through a hollow spindle and covered with a covering yarn from a flanged bobbin. The elongation, elasticity and look of the yarn depends on 3 factors, defined parameter of the draft, turns per metre and the covering yarn selected for the process.
Application  for these yarn are in the fashion sector for hosiery, bodies and seamless articles as they give the finished product a transparent look, outstanding  durability and a smooth appearance with a luxurious touch.

   A.    Single Covered Yarn [SCY] - When spandex is warped with one filament yarn it is called Single Covered Yarn. Hold Spandex fiber as center core, then warp one yarn in S twisted [ant –clockwise] way or Z twisted [clockwise] way around extend spandex fiber outer layer. Socks and underwear yarns use both S and Z according to the body structure of characters.

  B.   Double Covered Yarn [DCY] - When spandex is warped with two filament yarns in opposite directions we get Double Covered Yarn. Holding spandex fiber as the centre core, then wrapping two hard yarn on the lower and upper levels in mutually inverse way(S- twisted and Z-twisted) around extend spandex fiber outer layer gives DCY.

                                                                                                                                                

Air-Jet Covered/Intermingled Yarn [ACY]

The centre core spandex is covered by a multi-filament artificial yarn by air jets to manufacture Air Covered Yarns. In this process, the elastic yarn is intermingled with a filament yarn such as nylon or polyester using compressed air and wound straight onto the yarn spool. Therefore, the air-covered yarns have a powdery look and an exceptional softness. But the spandex protection is less in ACY when compared to CCY, however the productivity is high than compared to CCY.

For the warp in weaving, air-covered yarns undergo an additional working step on a two-for-one twisting machine which means that the sizing process can be omitted. Hard twisting result in improved strength and evenness, giving the final product a smoother surface.                    

Benlon India is producing a vast range of Air Covered Yarn ranging from 100 DN – 2500 DN .
Fine yarn of 100 DN is being used in sarees in Southern part of India like Bangalore, Salem and also in Varanasi and Mau (U.P). Rest from 300 - 2500 DN yarn is used in furnishing industry for curtains, bed covers, car seat covers and furnishing fabrics.

Spandex Covered Yarn Application

Spandex Covered Yarn	Applications	Pros on Fabrics	Cons on Fabrics
Single Covered Yarn(SCY)	Socks Pantyhose Circular knitted fabric Inner wear Sweater Denim Woven fabric Medical bands Shoes Ribbon Curtain Upholstery fabrics Elastic, etc.	Can get thinner fabric Better resilience Suit for filament & stable fibre	Exist torque
Double Covered Yarn(DCY)		The best protection for spandex Smooth & Soft	Much heavier Much expensive
Air Covered Yarn(ACY)		Cheaper than SCY High productivity	Only can use filament fibre Spandex will uncover easily Spandex’s draft ratio much uneasily control than SCY Worse sheen

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