If flax fibre can be produced with properties enabling it to be spun on a cotton system, it can open up the potentially high value markets for flax growers, processors and spinners, state Dr Prabal Majumdar and Achintya Samantaa, who provide the results of a project in spinning 100% flax yarn using ring frame.

Flax fibre is extremely variable in length and difficult to control in its conversion into yarns. Many costly processes and much skill are involved in yarn-production^[1]. Carefully-produced, good quality yarn is essential to produce a good quality fabric and to increase the efficiency of the loom. Certain improvements in fields of mechanisation and productivity have been made during 1950 - 1960 in the existing flax spinning system ^[2].

At present there is a demand for finer flax yarns, which is very difficult to produce with reasonable quality in the existing flax spinning system. New developments in the field of machining technology cannot be expected in the near future, due to high investment costs. Probably the most fundamental recent change in spinning techniques has been the application of ring spinning in the production of linen yarns. Still the fact remains that all the machinery use in flax spinning is far behind in productivity than the other textile industries like cotton and synthetic. The hurrying of flax yarn-production in the existing system can be dearly paid for at the later stage of weaving.

In the processing of flax as a natural product, from a straw-like, agricultural product to a high value raw material for modern industrial sectors, development of processing technology is required, which facilitates a design of the fibres, corresponding to processing possibilities (cotton spinning), and the desired end-product (yarn) ^[3]. The requirement is that the profile of flax fibres should strongly resemble that of cotton, to avoid any extensive modifications of cotton machines ^[4].

Fibre length and fibre fineness are the two most important factors in the production of yarn on ring spinning machines. The similarity of cotton and flax filaments stimulated the idea of converting the flax fibre into a cottonised "cotton-like" fibre. The methods of adapting flax fibre to cotton processing methods consisted of obtaining a mass of thin filaments similar to cotton after destroying the adhesive complex of the middle layers for processing them with the cotton spinning system ^[5]. It is observed that good amount of splitting takes place after bleaching of the flax fibre, which is normally done in roving form. Considering this, it is expected that drafting in the ring frame would be easier and by proper control of the break draft the regularity of the yarn could be improved upon.

The traditional processing system for bast fibres is outdated and economically unable to produce competitive products except in few isolated causes^[6]. New techniques for processing bast fibres on conventional staple spinning system are to be developed with a view to utilise existing spinning equipment without the need for huge capital investment for specialised wet spinning machinery.

In the present work efforts have been made to process the flax fibre on cotton ring frame and to select the proper spinning parameter for better spinning performance. Five different counts have been spun and their tensile and evenness characteristics have been studied in comparison with the yarn spun in the existing system.

Experimental

Materials and methods

For this experiment 100% flax fibres have been used, which are imported from Belgium and France. Fibres are coming as a bale form. The bales are then opened and sorted as a bunch of approximately 80 gm. Sorted bunch are feed into the Hackling machine for removing sort fibre, other impurities and to parallelise the fibre. It produces a continuous sliver with a spreader. Length wise mixing of different grades of flax fibres is done in the first gill box passage. Six different grades of flax fibres mixed to prepare the sample material. Specifications of individual fibre are given in detail in Table 1.

As there is no auto leveler in the conventional preparatory system, six passage of gill box has been used. Number of total doubling was 73728 (6 * 6 * 8 * 8 * 8 * 4). This high amount of doubling has been given to produce more even sliver for roving frame.

Degumming of the prepared roving has been achieved by immersion of roving bobbin in a hot alkali (NaOH) solution with the aid of other auxiliaries such as sodium metasilicate, sodium sulphite and caustic solution. These auxiliaries help as a chelator for metal ions and also convey scouring properties. Further bleaching is achieved by application of hydrogen peroxide. It is also possible to discover changes with respect to the basic material.

• Hurds removed more easily.
• Fibres are purified.
• Unwanted fibre ingredients are largely removed.
• Whiteness of the fibre is increased.

Another main objective of chemical treatment of the fibre at the roving stage is to achieve a degree of separation and breakdown of fibre bundles, which is sufficient to permit the wet-spinning process, whilst maintaining structural integrity of the roving under tension.

This bleached roving is used as a feed material in ring frame. The details process parameters of the ring frame used for this test are given below:

Name of the ring frame: TRYTEX miniature laboratory ring frame

• Drafting angle: 55⁰

• Spinning angle: 10.82⁰


• Back ratch setting: 62 mm


• Front ratch setting: 60 mm


• Lappet hook clearance: 3 mm


• Back bottom roller diameter: 28 mm


• Front bottom roller diameter: 28 mm


• Back, middle and front cots rollers diameter: 28.6 mm


• Ring diameter: 46 mm


• Traveler use: C type traveler


• Top arm type: SKF pk2025 c1


• Front top Roller presser: 25 kg/cm²


• Middle top Roller presser: 15 kg/cm²


• Back top Roller presser: 25 kg/cm²

Wet flax fibre strand has a high tendency to lapping. In 45^o drafting angle the length of spinning triangle is larger, which increases the chance of bottom roller lapping. Reducing spinning triangle by increasing the drafting angle to 55^o has reduced the chance of bottom roller lapping as well as reduced the end breakage rate as it helps to propagate twist to the front roller nip. But increasing the drafting angle also increases the spinning angle, which influences the yarn hairiness.

The other necessary changes made in the existing cotton ring frame are:

• Creel holder has been changed to suit for double flanged flax roving.
• Top apron from the main drafting zone has been removed and used only cots roller over bottom apron.
• A lap catcher has been incorporated over the front top roller to prevent the top roller lapping as wet flax strand has a high tendency to lap over the relatively smaller size top roller.

From the bleached wet roving bobbins, five set of counts have been produced, which are generally run in the industries. In linen count system (lea) those are 25 lea, 50 lea, 60 lea, 80 lea and 85 lea.

The different ring frame parameters used for different counts are given in Table 2.

At the time of experiment it was found that break draft of 1.3 gave satisfactory spinning performance. Break draft below this has shown frequently occurrence of slabs, which increases the yarn faults and ends-down rate. For courser count range twist multiplier of 2.5 gave good running performances, whereas in case of medium count range it was minimum 2.8 and for finer count it was minimum 3.0, which gave satisfactory spinning performance.

Testing

As a single material sows different properties in different atmospheric condition so it is important that all the samples, prior to testing, are conditioned in a standard atmospheric condition. All yarn bobbins were dried in drying chamber at 90⁰C temperature for 1 hour and 30 min and subsequently conditioned at 20⁰C and 65% RH for 4 hr.

Condition samples were tested on USTER^® TENSORAPID 4 for determining:

• Tenacity (Rkm)
• Elongation (%)
• Breaking force (lbf)

In all the cases gauge length has been kept at 500 mm and elongation rate at 500 mm/min.

As finer yarns are giving more unevenness and more imperfection so, only 60 lea, 80 lea, and 85 lea yarns are tested for evenness testing.

USTER TESTER 3 has been used for determining yarn evenness characteristic. Testing speed was set in 400 m/min and testing time set for 1 min. Properties measured are:

• U%
• Thin place/km
• Thick place/km
• Neps/km
• Hairiness index

To compare the prepared sample with the conventionally spun yarn, equivalent count of conventionally spun yarn has been tested for the same parameters.

Result and discussion

The tensile testing results of the cotton system spun samples and conventionally spun yarns are given in Tables 3 and 4.

In this experiment yarn tensile properties are represented by their breaking strength and Rkm values. Table 3 and Figure 1 (a, b, c) show that Yarn strength and elongation properties are not that much affected by changing the processing system. In coarser count range cotton system spun yarn shows relatively higher strength whereas in finer count ranges conventional system spun yarn shows a little greater strength. In case of elongation% almost in all count, spun in cotton system ring frame shows a little higher value. The low twist level compared to the conventional system, in finer yarn though gives sufficient strength to achieve good spinning performance in cotton system ring frame, it shows lower strength and higher elongation% than the conventionally spun yarn. High storing time of wet roving samples may be the other cause of decrease in the strength of individual fibres. As individual fibre strength ultimately affects the yarn strength so yarn strength also decreases. Fibre alignment in the yarn strand also plays a role in determining the yarn elongation. If fibres are more parallel to the yarn axis then it shows higher elongation as effect yarn elongation is also more. In the cotton system ring frame, the provision of applying break draft increases the parallelisation and better alignment of individual fibre in the yarn strand, which ultimately increases the yarn elongation and strength.

From Table 5 it can be observed that in case of 60 lea (22.38 Ne) U% value, thin place (-50%), neps (+200% & +400%) has been less than the other finer count but the hairiness increases more than the other finer count. So finer the yarn count, higher is the unevenness and imperfections level but lower the hairiness index, which matches with the common behaviour of ring frame spun yarn. Occurrence of thick place (+50%) has not shown any trend in variation within the count.

From Figures 2, 3 (a, b, c, d), and 4 it observed that occurrence of U%, thick place (+50%), thin place (-50%), and hairiness is high in cotton ring frame spun yarn than in conventionally spun yarn. But occurrences of neps both in +200% levels and +400% levels have been reduced.

In the drafting zone when the flax cells are separated from each other there is no positive control over it. Proper wetting system helps in good splitting of the individual cell.

With the absence of proper wetting system for the roving strand in the laboratory ring frame, the fibres are not separated from each other uniformly along the drafted strand and so occurrence of unevenness and thick-thin faults is more.

As the number of fibre in the yarn cross section is less in the case of finer yarn so amplitude of fault is more in case of finer yarn.

Uncontrolled atmospheric condition is also responsible for increasing yarn faults in the experimental procedure. As drafting angle increases, spinning angle also increases. So edge fibres in the strand are not trapped into the yarn structure and create hairiness. Using of light weight traveler in the experiment increases the hairiness of the yarn as it increase the balloon dimension.

Frictions of yarn with the balloon control ring and lappet guide increase the hairiness.

In conventional system there is no balloon control ring and lappet design is also different; so it reduces the yarn abrasion and also the chance of yarn hairiness.

As in cotton system ring frame break draft is applied first and then the fibre enter the comparatively high draft zone, so in break draft zone curled and criss-crossly arranged fibre tries to align themselves on the strand axis. This aligned fibre drafted easily in the main drafting zone reduces the chance of fibre breakage and formation of neps.

Conclusion

It can be now concluded that:

1. It is possible to spin the flax yarn successfully in cotton system ring frame. One can easily get the benefit of versatility and auto motion developed in cotton system ring frame in the production of flax yarn, and produce quality yarn with high productivity.
2. Spindle speed can be increased up to 7,000 rpm without affecting the spinning performance. Whereas in conventional spinning the spindle speed can be increased up to 6,300 rpm keeping the good spinning performance.
3. Twist multiplier (in Ne system) of 2.5 for courser count, 2.8 for medium count and 3.0 for fine count gives satisfactory spinning performance. It can be set to higher side for improving the yarn strength. But it will reduce the yarn elongation.
4. Break draft of 1.3 is found suitable for all the count range.
5. In case of coarser yarn, tenacity is better than the finer count.
6. Elongation% is better in cotton system spun yarn than in the conventionally spun yarn for all counts of yarn.
7. U%, thick place, thin place and hairiness increase in cotton system ring frame spun yarn.
8. Occurrence of neps of +200% & +400% is reduced in cotton ring frame spun yarn compared to the conventionally spun yarn.
9. Generation of fly – flap is reduced in cotton system ring frame, which is a major problem in conventional ring frame.

Acknowledgement

The authors of this paper would like to thank Mr D J Barman Roy, General Manager, Jaya Shree Textile, Rishra, for providing all the facilities related to this research work and valuable suggestions for a successful research.

References

1. Waldemar Cierpucha, Ryszard Kozlowski, Jerzy Mankowski, Józef Wasko, Tomasz Mankowski: Applicability of Flax and Hemp as Raw Materials for Production of Cotton-like Fibres and Blended Yarns in Poland, Fibres & Textiles in Eastern Europe July/October 2004, Vol 12, No 3 (47).
2. Natalia Sedelnik, Stanislaw Zareba, Jerzy Szporek: Preparation of Enzymatically Modified Flax Fibre for Producing of Rotor-Spun Yarn for Apparel, Fibres & Textiles in Eastern Europe January/March 2006, Vol 14, No 1 (55).
3. Dr J E G Van Dam: Optimisation Of Methods Of Fibre Preparation From Agricultural Raw Materials, Dept of Fibres and Cellulose, Agrotechnological Research Institute (ATO-DLO).
4. Matthew Horne, Ray Harwood, Paul McCormick and Jane Harwood (2008): The Commercial Production of Short-Fibre Flax for Cottonisation, International Conference on Flax and Other Bast Plants.
5. A P Moryganov, V N Galashina, N S Dymnikova, V G Stokozenko, and A R Danilov: Modification Of Flax Fibres: From Research To Realisation, Fibre Chemistry, Vol 40, No 3, 2008.
6. Ray Harwood, Vyvyan Nusenbaum, and Jane Harwood (2008): Cottonisation of Flax, International

Note: For detailed version of this article please refer the print version of The Indian Textile Journal May 2012 issue.

Dr Prabal Majumdar
Government College of Engineering and Textile Technology,
12, William Carey Road,
Serampore, Hooghly,
West Bengal 712 201.

Achintya Samantaa
Wool Research Association,
Kolshet Road, Thane (W) 400 607.
Email: aksamanta@wraindia.com.