Tencel Process Optimization in Conventional Cotton Processing Machineries and a Quality Comparison with Similar Cotton Yarn Count

Lyocell is a manmade fiber derived from cellulose [1], better known in the United States under the brand name Tencel. Tencel fiber, though related to rayon, is a kind of regenerated cellulose fiber produced in a way called “solvent spinning method”, the production mainly uses coniferous wood pulp as raw materials. Tencel fiber has the advantages of both naturalfiber and synthetic fiber. Such as cellulose fiber, tencel fiber has good hygroscopic, permeability and performance, its wearing comfort is much better than polyester, and its feel, gloss, drape are all good. The strength of tencel fiber is higher than that of cotton fiber and viscose fiber; it also has advantages such as warm and soft and comfortable; in addition, tencel has good performance and dimensional stability; it can be blended with othernatural fiber and synthetic fiber [2]. The source ingredients of tencel fiber mainly come from green cellulose fiber in nature, chemical solvent used in production can be recycled, so it won’t cause any damage to human andthe environment. After using, tencel fiber can be decomposed completely in soil, which can greatly reduce the environmental destruction, therefore, tencel fiber is also known as “green fiber and eco-friendly fiber”. Tencel fiber, as a kind of biodegradable fiber, will become the mainstream in the future [3]. Because, throughout the world modern civilization’s greater inclination and attention towards environmental protection, social development towards the direction of environmental protection and sustainability, processing and manufacturing green textiles. It is an extremely strong fabric with industrial uses such as in automotive filters, ropes, abrasive materials, bandages and protective suiting material. It is primarily found in the garment industry, particularly in women’s clothing (Table 1).


Introduction
Lyocell is a manmade fiber derived from cellulose [1], better known in the United States under the brand name Tencel. Tencel fiber, though related to rayon, is a kind of regenerated cellulose fiber produced in a way called "solvent spinning method", the production mainly uses coniferous wood pulp as raw materials. Tencel fiber has the advantages of both naturalfiber and synthetic fiber. Such as cellulose fiber, tencel fiber has good hygroscopic, permeability and performance, its wearing comfort is much better than polyester, and its feel, gloss, drape are all good. The strength of tencel fiber is higher than that of cotton fiber and viscose fiber; it also has advantages such as warm and soft and comfortable; in addition, tencel has good performance and dimensional stability; it can be blended with othernatural fiber and synthetic fiber [2]. The source ingredients of tencel fiber mainly come from green cellulose fiber in nature, chemical solvent used in production can be recycled, so it won't cause any damage to human andthe environment. After using, tencel fiber can be decomposed completely in soil, which can greatly reduce the environmental destruction, therefore, tencel fiber is also known as "green fiber and eco-friendly fiber". Tencel fiber, as a kind of biodegradable fiber, will become the mainstream in the future [3]. Because, throughout the world modern civilization's greater inclination and attention towards environmental protection, social development towards the direction of environmental protection and sustainability, processing and manufacturing green textiles. It is an extremely strong fabric with industrial uses such as in automotive filters, ropes, abrasive materials, bandages and protective suiting material. It is primarily found in the garment industry, particularly in women's clothing (Table 1).

Historical background and production
Whatever it's called, Tencel or Lyocell is a sustainable fibre, regenerated from wood cellulose. It is similar in hand to rayon and bamboo, both regenerated fibres. However, Tencel is one of the most environmentally friendly regenerated fibre for several reasons. Tencel fibres are grown sustainably. Tencel has earned Forest Stewardship Council (FSC) certification that the products come from environmentally responsible forests. Tencel eliminates the negative environmental impacts of traditional fibre processing, using new Abstract Tencel a regenerated fiber manufactured from cellulose derivatives, is getting popularity nowadays due to its biodegradability and environment amenity depending on the less land and water consumption relative to organic and conventional cotton. Spinning process optimization of tencel is performed and reviewed in this article in comparison with conventional cotton process. Wider setting with low production speed is observed for tencel processing with superior yarn quality. Quality parameter of different yarn count evaluated and compared. Mass uniformity and its cv is significantly higher in tencel yarn; breaking strength is 50% greater in tencel along with breaking elongation; tencel yarn possess more twist (>15%) while twist cv is slightly lower; yarn cuts in autoconer machine is lower in tencel yarn.
sustainable technologies. As a new kind of cellulose fiber, tencel fiber has been published for many years. It's now popular in UnitedStates, Japan and other countries mainly for the production of high fashion. 1939 Patent appears describing the dissolution of cellulose in amine oxide. Kaoerzi Company had started researching cellulose fiber production with NM-MO solvent method since 1978. 1969-1979 American Enka/Akzona Inc. work on spinning fiber from a solution of cellulose in amine oxide but did not scale up. In 1981, the company used amine oxide as a new solvent to spin; the experiment showed that the spinning method is feasible. In 1983, the company set up experimental factory; in 1987, the continuity of large scale plant was established. In 1989, it's named tencel fiber after recognized by the International Bureau of Artificial and Synthetic Fiber Standards, then American factories began commercial production of tencel and its production capacity had reached 55 million kilograms. Tencel has some distinct advantages over traditional fibres in terms of chemical processing, which can often be extensive and toxic. For example, Rayon manufacturing generates highly polluting air and water emissions, uses catalytic agents containing cobalt or manganese, and creates a strong unpleasant odor. Tencel products can be decomposed, solvent of which is non-toxic, the celllose used for Tencel is treated in what is known as a closed loop process in which the solvents are recycled with a recovery rate of 99.55%. The tiny amount of remaining emissions is decomposed in biological purification plants. Because of the natures of the material, the processing never requires bleach. This methos of manufacturing of fibre was awarded the "European Award for the Environment" by the European Union. So it is regarded as the third generation of regenerated cellulose fiber. Because of its unique properties, it had been applied into a variety of goods in many fields. The whole Asia has also appeared upsurge of tencel development [4]. Japan is currently the largest developers of tencel textiles, lots of men products in department stores were tencel goods. It can be said that tencel fiber goods in Japan entered a new stage. Textile software and hardware for tencel, especially the commercialization of tencel commodity, were also under development in Japan. This had helped Japan to maintain a leading position in the manufacturing of tencel fiber. In 2000, the British tencel fiber output reached 6,140,000 tons. Tencel fiber with its incomparable superiority is in rapid development in international and domestic market. Tencel is used in a variety of applications, including men's wear, sheets, and blankets. Since it's absorbent and dries quickly, it is also suitable for towels. Clothes made from this material are often recommended for traveling because they are light and keep their shape well. Tencel® is also available as fabric for sewing, as yarn for knitting or crocheting, and as fiber for spinning. Besides it use as a cloth, it is also used in making bandages, baby wipes, oil filters and carpeting for cars, as well as conveyor belts and plastic parts. In powder or fiber form, this material is used in making specialized papers, as an additive for building materials, and in making foam mattresses [5].
The purpose of this study is to analyze the suitability of conventional cotton processing machineries in tencel processing and establish a successful benchmark and provide necessary guidelines for yarn manufacturers.

Tencel in comparison with organic and conventional cotton fibers
Bearing in mind that the figures below include wide room for variation that makes any strict head-to-head comparison impossible, we can distill the discussion down to some basics (Table 1).

Lyocell fiber spinning process
This section provides a description of the process steps required for making lyocell [6]. A diagram of the process is shown in Figure 1. The principles are simple. Firstly, the pulp is wetted out with dilute aqueous amine oxide to fully penetrate the pulp fibers. The subsequent removal of the excess water under heat and vacuum is a very effective way of making a homogenous solution with a minimum of undissolved pulp particles and air bubbles. The solution is highly viscous at its operating temperature (90 to 120°C) and must be processed in similar high pressure equipment to that used in melt polymer systems. The fibres are formed by spinning into an air gap and then coagulating in a water/ amine oxide bath. They are then washed and dried and cut. The wash liquors are recovered, purified, concentrated then recycled. The process description below applies to the two commercial-scale operations of Tencel® and Lenzing. Variations in detail have been cited in patent applications and the literature but these are at a much smaller scale of operation ( Figure 1).

Methodology Fiber selection
Before start of the production following fiber characteristics were measured and bale laydown was done according to the quality parameters ( Table 2).

Yarn Spinning Process
Spinning is the twisting together of drawn out strands of fibers to form yarn, and is a major part of the textile industry ( Figure 2).

Testing of machine gauge and yarn characteristics
Following tests were carried out on the Square Texcom ltd. Situated at kathali, valuka, Mymenshing (Table 3).

Results and Discussion
Process optimization and benchmarking for Tencel and Cotton fiber:

Opening and cleaning
Fiber length uniformity is the main reason for closer setting in Mixing Bale Opener (MBO). In addition to the length uniformity tencel fiber is free from foreign matter. Which lead to narrower setting of grid bar angle as 2 to 3. Another important aspect of tencel processing is the bypass of two saw tooth beater and it is advised to use only one pin beater. More beater exploits fiber to pass through more beating action and which was highly responsible for curling of fibers and finally generation of fiber to fiber entanglement neps. Some of the fabrics are    observed to be white specks on the surface. It is advised to set larger beater grid angle and more beating sections for cotton than that of tencel processing due to less length uniformity and large number of foreign matter (Table 4).

Carding
As tencel fiber processing was performed in the carding, usually designed for cotton processing, with higher point density more than 960 points per square inch does not allow higher speed of production. Higher jamming of cylinder-flat region and cylinder-doffer region was highly noticeable and less nep generation was observed in carding machine. Ultimately numerous complaints of nappy yarn and white specks ( Figure 3) on fabric surface were done by the buyers of the yarn. Finally, in optimization of carding setting at a speed of 45-50 kg per hour at a delivery speed of 250 m/min was maintained successfully in comparison to cotton processing speed, which was significantly higher 65-70 kg per hour in the same machine. In order to improve web quality; licker-in speed, cylinder and flat speed was reduced as well as gauge of those elements were amplified. On the other hand for cotton setting optimized narrower with higher processing speed. Tencel fiber is with larger fiber volume quality is smooth and fluffy, its moisture regain rate is higher but its cohesion is not good, so the carding should choose with less number of card clothing 800-850 points per square inch clothing similar to polyester or polyester blend in order to reduce yarn neps and improve cotton web quality [7,8] (Table 5).

Drawing (Breaker and finishing)
Higher staple length and length uniformity are the primary reason for wider setting in tencel processing compare to the cotton processing in drawing frame machine. Hygroscopicity, higher moisture regain rate, is highly responsible for generation of roller lapping and jamming       of the drawing frame machines. It is optimized as 47/49 roller setting for front to back zone whereas in cotton 37/42. Higher top roller weighting 380-380-320 (front top roller to back roller) along with larger amount of break draft 1.6-1.9 was optimized for tencel and on the other hand for cotton those were 320-320-320 and 1.15, respectively [9]. Second drawing is mainly in order to make the fiber straight and to make the weight unevenness reduced to a certain extent. Draft configuration may be the most important aspect for tencel processing as well as lower production speed to improve straightening of back hook and enhancement of web quality ( Table 6).

Simplex
Number of twist per unit length of tencel roving was carefully observed and was substantially lower than that of cotton; twist value was appropriately increased which allows lower appearance of spinning head. Beside this precise measurement of spinning tension and its optimization was done at 1.033 both for cotton and tencel. Optimization of the above mentioned due to less roller lapping and unevenness of yarn. may be slipping tendency due to lack of fiber cohesion and spin finish on the tencel fiber creates layer on the roller surface and roller slip occurred thus higher break draft was advised to intensify desired total draft [10,11] (Table 7).

Ring frame
Roller gauge both for tencel and cotton processing was 60/42.5 (back to front roller) maintained and yarn count variation was noticeable for tencel. Suitable drafting force in optimizes the yarn quality; exact roller pressure on pneumatic drafting with apron guidance and proper spacing with 70/42.5 (back to front roller) for tencel fiber. Higher break draft 1.72 facilitates achieving tencel yarn of less thick, thin places and minimum end breakage. Lighter traveller with flat cross-sectional shape optimizes the yarn quality profile for tencel yarn ( Table 8).

Analysis of yarn quality parameters
Comparison of yarn properties of Tencel and Cotton yarn, greater cohesion between the fibers and length uniformity may be the significant contributor on higher tensile strength of tencel yarn. Fiber migration, the displacement of fibers along the yarn axis during spinning, is dependent on the amount of twist inserted on the yarn. Higher amount of twist per unit length higher the packing density thus cotton yarn is firm than compare to tencel yarn and exhibited lower elongation percentage than compare to that of tencel yarn (Tables 9  and 10).
By lubricating the fiber surfaces, the fibers move smoothly against each other and machine parts like the yarn guide, trumpets and aprons. This prevents friction and potential fiber breakage and protects the fibers from the static electricity charges that are generated due to interfiber friction, friction between the fibers and machines parts, and the low electrical conductivity of the fiber. A spin finish can also prevent fibers from splitting from each other, thus leading to less hairiness and less fiber lapping in the final yarn. By promoting greater adherence between fibers, a spin finish can improve the efficiency of bale opening. The spin finish increases cohesion between the fibers and the machine parts, reducing fly which otherwise introduces defects into the yarn [12].
Uniform draft distribution after several trial and errors allows much uniformity of tencel yarn along with less thick, thin and neps which finally exploits less yarn cut in autoconer machine than compare to that of the cotton yarn. This is because of less thick, thin, and abnormal neps in the tencel yarn (Tables 11-14).

Conclusion
Tencel yarn, comprise of high strength fibers, exhibits higher breaking strength over conventional 100% cotton yarn. Other yarn parameters like breaking elongation, mass uniformity, and hairiness of tencel yarn are significantly better in comparison with that of cotton yarn. Another important aspect of tencel yarn is Eco friendliness which overweighed lower production speed. Ultimate quality profile of tencel yarn facilitates its uprising popularity. Eco friendliness will enhance the use of tencel on basic garments manufacturing as well as          intensify use of tencel as blend with cotton, jute etc. which will solve the problem of dependency on synthetic fiber to a large extent and sustain environment [13].