March 18, 2013 Flax Fiber Terms and Definitions
Flax Fiber Terms and Definitions
Bast Fibers – These refer to commercially valuable plant fibers which are found in the stems of plants as opposed to commercially valuable fibers which are found in the leaves (e.g., sisal, abaca) or in the seed pods (e.g., cotton, coir). Bast fibers are composed mainly of cellulose and hence form a subset of fibers within the whole set of cellulosic fibers, which include such fibers as those from wood, and from cotton. The most commonly used bast fibers are jute, flax, kenaf, hemp and ramie.
Breaking – Traditionally after the seeds were removed from dry, retted flax straw, the flax was “broken” by passing it through a crimping device, by hitting it at right angles with a smooth board or by pounding it with a large wooden mallet. The purpose of this “breaking” was to break the brittle non-fiber part of the stem called shives into small pieces without doing damage to the flexible fibers that surround the stem. The smaller the shives, the easier they are to remove from the fibers. In modern flax mills, flax straw is broken by passing the straw between rapidly rotating fluted rollers that mesh together with neighboring rollers.
Carding – In general, fibers less than eight inches (20 cm) in length are cleaned, roughly aligned and formed into a thin continuous strand of fibers (called a sliver) by a carding machine (commonly called a “card”). Such fibers include cotton, wool, non-continuous filament synthetic fibers and flax and hemp tow. The main parts of a carding machine consist of a fiber inlet system, a very large diameter cylinder with a number of smaller cylinders arranged next to the circumference of the large cylinder. The cylinders are covered with fine saw teeth or pins and rotate at different speeds. Different diameters of cylinders, different types of teeth and different ratios of speed are needed to optimize the carding action on different types of fibers. All other things being equal, yarns from carded fiber will be coarser than yarn that is combed. However, if fibers are to be combed, they must always be carded first because a card is need to produce a sliver and a combing machine always needs raw fibers in the form of a sliver. Thus combed fibers should, in theory, always be more expensive than carded fibers.
Combing – Higher quality scutched flax tow or hackled flax tow destined for higher end yarns are often put through a combing machine. This will clean the remaining shives out of the fiber, straighten the fibers and remove the short fibers (called “combing noils”). A flax combing machine is, in principle, similar to a wool or cotton combing machine. A horizontally held uncombed “sliver” (i.e., a wide continuous band) of fiber is passed through a roller and comb system to produce combed sliver, combing noils and combing waste. (see Hackling)
Cottonized Flax – Over 90% of the world’s spinning equipment are designed to quickly and effectively spin fibers that have the length and diameter of cotton fibers. This is referred to as the “cotton” system. No other spinning system is as productive or cost-effective as the cotton system. By coincidence, the ultimate fibers of flax have approximately the same length and diameter of cotton, however, the ultimate fibers of flax are normally glued with pectins and lignins into long line or tow fibers. Several processes have been developed to break the tow or long line into ultimate fibers so that the ultimate flax fibers can be spun and/or blended easily using the cotton system. The process of breaking down long line or two fibers into ultimate fibers is called cottonization and the product is called cottonized flax. Flax has traditionally been cottonized using mechanical systems (i.e., mechanical cottonization) but it can also be done using enzymes, steam explosion and ultra-sound.
Decorticating – Sometimes bast fibers are only partly retted or not retted at all before the stems are put through a series of rollers, hammers and/or shakers to extract the fibers. This process is called decorticating and it is used to replace the processes of breaking, scutching and hackling but it generally produces a very coarse fiber that is not used in textiles but is rather used for industrial purposes like paper making and geotextiles. Decorticating is generally much cheaper than breaking, scutching and hackling but the quality and value of the resultant fibers is not as high.
Geotextiles – Textile products that are deliberately placed in contact with the ground are often referred to as geotextiles. Such geotextiles are often in the form of mats of natural or synthetic fibers and/or sheets of synthetic material. They are often used to prevent soil erosion on the sides of newly constructed road embankments, building sites, reservoirs, tailings ponds, etc. They are also used in agricultural applications such as mulch material for horticultural and tree crops and may be impregnated with seeds for products like “roll-out” lawns and playgrounds. Natural fibers are preferred in geotextile applications where it is desired to have the geotextile decompose after several years (e.g., after the grass is established on the road embankment) whereas synthetic fibers are preferred where it is desired to have the geotextile last for many years (e.g., as a lining for a tailings pond).
Hackling – After the flax fibers are scutched, the long line fibers are eventually put through a hackling machine which straightens the fibers, cleans any remaining shives out of the fibers and removes fibers, which are weak or short (called hackled tow). This process is called hackling and it is done by pulling vertically hanging long line fibers past a series of finer and finer combs. Once the bottom half of the long line fibers are hackled, the machine turns the fiber over so that the top half of the long line fibers can be hackled. The hackling process produces hackled long line (ready to be turned into hackled sliver) and hackled tow. In general, only flax and hemp fibers longer than 0.5 meters are hackled. Shorter flax and hemp fibers are combed as are short fibers like cotton and wool. (see Combing)
Long Line – In general, these are the most expensive flax or hemp fibers and are used to spin the finest (i.e., smallest diameter) yarns. Traditionally they were used to produce 100% pure woven linen and 100% pure woven hemp fabrics but they are also now used very extensively to produce higher end linen and hemp knitwear. Most long line fiber processing lines can only handle long line fibers that are longer than 0.5 meter in length and shorter than 1.0 meter. Long line fibers are composed of bundles of “ultimate” fibers which are glued by pectins side by side and end to end to make a fiber “bundle” which looks like a very thing yarn to the naked eye.
Retting – “Retting” is from a Dutch word meaning to “rot” or break down. The bast fibers of plants form part of what the layman might call the “inner bark” of plant stems. These fibers are tightly held within the plant by glue-like substances called pectins and lignins. Before clean bast fibers can be easily removed from the stems, the pectins and lignins must be softened and/or removed. The most common and cheapest method of doing this is to allow microorganisms to grow on the surface of the stems. As they grow, these organisms dissolve the pectins and lignins and hence make it easier to remove the fibers from the stems. However, if the straw is allowed to ret for too long a period, the organisms will also start to dissolve the fibers and hence the fibers will get weaker. Retting can be done in several ways. These include placing the straw in cold water (cold water or river or bog retting), placing it in warm water (warm water retting or tank retting) or by placing it in a thin layer next to the ground (dew or field retting). Straw can also be placed in mixtures of chemicals and water (chemical retting). In recent decades, people have searched for alternative ways to remove the pectins and lignins without retting. The most common of these methods include treating the straw with enzymes (sometimes called enzymatic retting), steam explosion (sometimes called flash hydrolysis) and ultra-sound.
Scutching – After flax straw is broken and the straw has been shaken to remove the loose shives, there are generally some shives still stuck to or tangled within fibers. The scutching process attempts to scrape loose and/or disentangle this remaining shives from the fiber by stroking the fibers in a manner similar to combing fibers with a comb that has no teeth. In modern flax straw mills this is done by having straw which has already been broken and shaken, pass between rotating beaters or turbines which have paddles or arms that beat and scrape the remaining shives from the fibers.
Shives – The shives are the non-fiber parts of the stems of flax plants.
Sliver – After bast fibers are hackled or carded, they are arranged in a continuous ribbon-like band of fibers called a sliver. This sliver can then be further combed, blended and made narrower and more consistent in size in preparation for spinning.
Tow – In bast fiber processing, there are only two main types of fiber; the long straight strong fibers called long line and the short, bent and/or weak fibers called tow. During processing, tow fibers are produced at each stage of fiber preparation. Hence there is breaker tow (usually coarse short fibers with lots of shives), scutching tow (medium coarse to medium fine short fibers with some shives) and hackled tow (short fine strong fibers with few or no shives). There is a wide range of prices paid for tow because tow can have a wide range of properties. In general breaker tow is the cheapest and hackled tow is the most expensive.
Ultimate Fiber – The ultimate fiber is the smallest easily separated “bast” fiber in flax or hemp. The ultimate fibers of flax are roughly the length and width of a cotton fiber; the ultimate fibers of hemp are slightly thicker and longer than those of flax. To the naked eye, an ultimate fiber would look like the split end of a human hair.