Lyocell Fibers


Since 1998 the Lyocell process has been used in Austria and the special feature of this process is the solution of the pulp which is in an organic solvent (NMMO =  methylmorpholine- N-oxide), instead of CS2/NaOH, which has the effect of eliminating the odorous and noxious emission of sulphurous gases. The properties of the products from this Lyocell process are different to the standard viscose fibre, and therefore this process should not be regarded as an environmentally compatible alternative to the viscose process.

The core part of the Lyocell process is the direct dissolution of cellulose through NMMO (Nmethyl-morpholine-n-oxide). The solvent, which is 100 % biodegradable, is able to dissolve cellulose physically without any chemical pretreatment. Therefore, the chopped pulp is mixed with NMMO. Water is removed from the socalled ‘premix’ to form a solution, which is then filtrated and spun through spinnerets into an aqueous NMMO solution to make the filaments.

The wet filaments are cut and the staples run through several after-treatment sections. After washing out residual NMMO, spin finish is applied and the fibre is dried and packed.
Through a multistage cleaning process, more than 99.6 % of the solvent can be recovered. Also the water that is regained during the evaporation step is recycled back into the washing section of the fibre line. This leads to a low specific water demand and overall low environmental emission figures.
Generally, the process includes the following steps:
• dissolving
• spinning
• precipitating
• washing
• finishing
• drying

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Figure shows a simplified diagram of the Lyocell process.

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The Burn Test to Identify Textile Fibers


The burn test is a simple, somewhat subjective test based on the knowledge of how particular fibers burn. Be prepared to note the following when testing your fibers:
• Do the fibers melt and/or burn?
• Do the fibers shrink from the flame?
• What type of odor do the fumes have?
• What is the characteristic(s) of any smoke?
• What does the residue of the burned fibers look like?

The burn test is normally made on a small sample of yarns or thread which are twisted together. Since the fiber content of yarns used in one direction of a fabric are not always made up of the same fibers used in the other direction, warp and filling yarns should be burned separately to determine the entire fiber content of the fabric. This test is very helpful in determining whether a fabric is made from synthetic or natural fibers, but it is not foolproof and the characteristics observed during the burning test can be affected by several things. If the fabric /yarn contains blends of fibers, identification of individual fibers can be difficult. Two or three different kinds of fibers burned together in one yarn may also be difficult to distinguish. The odor and burning characteristics exhibited may be that of several fibers, thus making your results difficult to analyze. Finishes used on the fabric can also change the observed characteristics.

  • Pull a small sample of at least six to eight yarns from your fabric about 4 inches long, and twist them together into a bundle about 1/8 inch in diameter. You can also use a small snippet of the fabric if you only need to determine whether it is a synthetic or natural fiber fabric and you are not seeking to determine the specific fiber(s) that make up the fabric.
  • Hold one end of the bundle with tweezers over a sink or a sheet of aluminum foil (about 10 to 12 inches square) to protect your working area. If the sample ignites it can be dropped into the sink or on the foil without damage. Use either a candle or a match (automatic lighters work well) as your flame.

Potential Test Results

Natural, Organic & Manmade Fibers

In general, if the ash is soft and the odor is of burning hair or paper, the fabric is a natural fiber. Cellulosic fibers (cotton, linen and rayon) burn rapidly with a yellow flame. When the flame is removed, there is an afterglow, then soft gray ash.

Cotton: Ignites on contact with flames; burns quickly and leaves a yellowish to orange afterglow when put out. Does not melt. It has the odor of burning paper, leaves, or wood. The residue is a fine, feathery, gray ash.
• Hemp: Same as cotton
• Linen: Same as cotton
• Ramie : Same as cotton
• Rayon : Same as cotton, but burns slowly without flame with slight melting; leaves soft black ash.
• Silk: Burns slowly, but does not melt. It shrinks from the flame. It has the odor of charred meat (some say like burned hair). The residue is a black, hollow irregular bead that can be easily to a gritty, grayish-black ash powder. It is self-extinguishing, i.e., it burns itself out.
Tencel : Same as Rayon
• Wool, and other Protein Fibers: Burns with an orange sputtery color, but does not melt. It shrinks from the flame. It has a strong odor of burning hair or feathers. The residue is a black, hollow irregular bead that can be easily crushed into a gritty black powder. It is self-extinguishing, i.e., it burns itself out.

Synthetic Fibers

Most synthetic fibers both burn and melt, and also tend to shrink away from the flame. Synthetics burn with an acrid, chemical or vinegar-like odor and leave a plastic bead.
Other identifying characteristics include:
• Acetate: Flames and burns quickly; has an odor similar to burning paper and hot vinegar. Its residue is a hard, dark, solid bead. If you suspect a fabric is acetate, double-check by placing a scrap of it in a small amount of fingernail polish remover-if you’re correct, the fabric will dissolve
• Acrylic: Flames and burns rapidly with hot, sputtering flame and a black smoke. Has an acrid, fishy odor. The residue is a hard irregularly-shaped black bead.
• Nylon: It will shrink from the flame and burn slowly. Has an odor likened to celery. Its residue is initially a hard, cream-colored bead that becomes darker gray.
• Olefin/Polyolefin: Has a chemical type odor. The residue id a hard, tancolored bead. The flames creates black smoke.
• Polyester: It will shrink from the flame and burn slowly giving off black smoke. Has a somewhat sweet chemical odor. The residue is initially a hard cream-colored bead that becomes darker tan.
Spandex: It burns and melts, but does not shrink from the flame. It has a chemical type odor. Its residue is a soft, sticky black ash.

 

Textile Fibers


Fibers -units of matter characterized by flexibility, fineness and high ratio of length to thickness. Other necessary attribute for textiles are adequate strength and resistance to conditions encountered during wears, as well as absence of undesirable colour, and finally the property of dye ability.

In generally, the steps in the manufacture of fabrics from raw material to finished goods are as follows:
· Fibre, which is either spun (or twisted) into yarn or else directly compressed into fabric.
· Yarn, which is woven, knitted, or otherwise made into fabric.
· Fabric, which by various dyeing and finishing processed becomes consumers goods.

  • Classification of textile fibers 

According to the nature and origin different textile fibers can be classified as follows:

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Natural fibers include those produced by plants, animals, and geological processes. They are biodegradable over time. They can be classified according to their origin:

  • Vegetable fibers are generally based on arrangements of cellulose, often with lignin: examples include cotton, hemp, jute, flax, ramie, and sisal.
  • Animal fibers consist largely of particular proteins. Instances are spider silk, sinew, catgut, wool and hair such as cashmere, mohair and angora, fur such as sheepskin, rabbit, mink, fox, beaver, etc.
  • Mineral fibers comprise asbestos. Asbestos is the only naturally occurring long mineral fiber. Short, fiber-like minerals include wollastinite, attapulgite and halloysite
  • Manmade fibers
Manmade fibers include those produced by reacting chemicals. They are non biodegradable. They can be classified according to their origin there are two sorts of man-made fibers: Organic and Inorganic.(a). Organic fibersSyntheticor man-made fibers generally come from synthetic materials such as petrochemicals.

  1.  Polymer fibers

Polymer fibers are a subset of man-made fibers, which are based on synthetic chemicals (often from petrochemical sources) rather than arising from natural materials by a purely physical process. Such fibers are made from:
o polyamide nylon,

o PET or PBT polyester

o phenol-formaldehyde (PF)

o polyvinyl alcohol fiber (PVOH)

o polyvinyl chloride fiber (PVC)

o polyolefins (PP and PE)

o acrylic polymers, pure polyacrylonitrile PAN fibers are used to make carbon fiber by roasting them in a low oxygen environment. Traditional acrylic fiber is used more often as a synthetic replacement for wool. Carbon fibers and PF fibers are noted as two resin-based fibers that are not thermoplastic, most others can be melted.

o Aromatic polyamids (aramids) such as Twaron, Kevlar and Nomex thermally degrade at high temperatures and do not melt. These fibers have strong bonding between polymer chains

o polyethylene (PE), eventually with extremely long chains / HMPE (e.g. Dyneema or Spectra).

o Elastomers can even be used, e.g. spandex although urethane fibers are starting to replace spandex technology.

o polyurethane fiber

o Co-extruded fibers have two distinct polymers forming the fiber, usually as a core-sheath or side-by-side. Coated fibers exist such
as nickel-coated to provide static elimination, silver-coated to provide anti-bacterial properties and aluminum-coated to provide RF deflection for radar chaff. Radar chaff is actually a spool of continuous glass tow that has been aluminum coated. An aircraft-mounted high speed cutter chops it up as it spews from a moving aircraft to confuse radar signals.
2. Regunrated fibers

Regunrated fibers are the fibers produced from natural cellulose, including rayon, modal, and the more recently developed Lyocell. Cellulose-based fibers are of two types, regenerated or pure cellulose such as from the cupro-ammonium process and modified or derivitized cellulose such as the cellulose acetates.

(b). Inorganic fibers

  • Mineral fibers

o Glass fiber, made from specific glass, and optical fiber, made from purified natural quartz, are also man-made fibers that come from natural raw materials.

o Metallic fibers can be drawn from ductile metals such as copper, gold or silver and extruded or deposited from more brittle ones, such as nickel, aluminum or iron.

o Carbon fibers are often based on carbonised polymers, but the end product is pure carbon.

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