Fabric Barriness in 100% viscose is one of the biggest problems confronting textile technicians worldwide. The problem is most severely noted in knitted fabrics. This study deals with the root cause of the barriness issue in 100% viscose knit fabrics. It was found that barriness in 100% viscose knit fabric occurred mainly due to the mix up of viscose yarn lots, count and TPI variation in the same viscose yarn lot. Keywords: 100% Viscose knit fabric, Barriness, Yarn lot, Count, TPI
1. Introduction
In textile production, one of the most common and often perplexing qualitycontrol problems is barriness – repetitive yarn-direction streaks. The Textile Institute (1,2) defines barriness as:
1. Unwanted stripes in woven fabrics, in the direction of the weft
2. A fault in a weft knitted fabric (usually knitted on a MultiFinder machine) appearing as light or dark course wise stripe(s) and arising from differences in lustre, dye affinity (or unlevel dyeing) in the yarn, yarn spacing or loop length, yarn linear density or defective plating.
In simple terms, barriness is a fabric defect characterised by textural bands or colour bands in the course or filling direction. Barriness is basically a visual phenomenon and any property of yarn which makes it 'look' different from the adjacent yarn in a fabric would result in this defect. In the broadest sense, all 'barriness' is the consequence of subtle differences in yarn reflectance between individual knits in the yarn structure (3). These differences, when associated with one or more complete knit courses, cause relatively light or dark bands and streaks and can result in barriness (4,5). Any mechanism that can change the reflectance of a yarn in a knit structure is a potential barriness source.
From a spinner's point of view, the last mentioned is of prime concern. He should ensure that the yarn which he produces and delivers to the knitting sector is free of differences which can lead to barriness (6,7).
The factors that can cause or contribute to barriness are varied and diverse. For this reason, when a barriness problem is detected, the skills of a sleuth may be required to track down and eliminate its cause (8,9). Fabric barriness in 100% viscose is one of the biggest problems confronting textile technicians worldwide. The problem is most severely noted in knitted fabrics.
Inability to adequately define this defect initially affected the understanding of its probable causes. Subsequently, it was recognised that barriness may result from a variety of factors, which may have originated from the yarn or in the knitting machine (10,11,12). Such a wide range of causes has made it extremely difficult to completely eliminate the incidence of barriness. It has been widely accepted that, rather than an inadequacy with respect to any raw-material property or process optimisation, it is the 'inconsistency' or the variation aspect which is the primary cause.
The yarn-quality characteristics that are responsible for barriness in knitted fabrics are mainly the concern of the spinner. Of the various quality characteristics tested, variation in viscose yarn, ie. different yarn lot, count and twist, are considered to be important properties that need proper control to avoid barriness. The varied and diverse causes of barriness can be generally summed up in one word as: Inconsistency.
An inconsistency that leads to barriness can originate in one or more of the following categories (3,8):
a. Mixed yarn
b. Yarn formation/supply
c. Fabric formation
Within these three categories the first, mixed yarn, is by far the most prevalent cause of barriness. Considering all above the factors, systematic research was carried out in order to discuss the general idea about factors responsible for the creation of barriness. This paper attempts to study these – ie. mixing of different yarn lots, mixing of different counts and mixing of different TPT in same lot – as influences on the knit fabric quality in terms of barriness.
2. Experimental Methods
The problem of barriness is seen most severely seen in knitted goods. Therefore, studies were made of the influence of different yarn lots of viscose, different counts of the same viscose and different TPI of the same viscose
2.1 Preparation of basic yarn samples
2.1.1 Preparation of samples with different spun time (Different Yarn lot) levels
The extent of influence of different spinning times for preparation of yarn with the same viscose fibre was studied. For this study, viscose fibre was taken of 1.2d x 38 mm cut length with fibre tenacity of 2.65 gpd, keeping all the spinning parameters same. Half the quantity of fibre was spun at a time and another half quantity of viscose fibre was spun after 30 days. The samples are designated as in Table 1.
2.1.2 Preparation of samples with different count levels
The extent of influence of yarn count was studied by first preparing samples of different levels of count. For this study 30s viscose yarn, which is normally used in hosiery, was used, and another 28s viscose yarn of same lot, keeping all the remaining parameters the same. The samples are designated as in Table 2
2.1.3 Preparation of samples with different TPI levels
The influence of twist on the tendency to form barriness was studied by taking into consideration two levels of twists per inch. To avoid very abnormal conditions of spinning, one of the levels was maintained at the normal level used by the mill for regular production. The other sample was obtained by maintaining TPI levels at a higher level from the nominal. The samples are designated as in Table 3.
2.2 Fabric preparation
For the different yarn lot, count and TPI samples, to detect the presence or otherwise of the barré effect, different combinations of two levels were selected and the respective yarn samples were knitted into single-jersey fabrics on a circular knitting machine with 2.7mm stitch length, having 24 inch m/c gauge and 21 inch diameter, such that the two different levels of the combination formed alternate portions of the fabric. The fabrics were knitted with 96 cones of each of the two levels feeding the machine.
2.3 Dyeing
The fabrics for all the combinations were dyed using Procion Blue HE dye of 2% concentration. The same batch of dye bath was used to dye all the fabrics pertaining to a particular property, in order to eliminate the introduction of any possible errors in the process of dyeing. Systematic presentation of dyeing process is shown in Figure 1 and process details are given in Table 4. Figure 1
2.4 Colour Measurements
The colour-difference values for the levels in all combinations were estimated by testing the fabrics using a GretagMacbath Colour Eye A Model spectrometer. Since the pattern width was too low to be tested directly on a spectrophotometer, separate fabrics were knitted for this purpose, with only one level throughout the length of the fabric.
3. Results and Discussion
3.1 Influence of different yarn lot
The colour-difference values obtained for the different yarn-lot sample combinations are given in Table 5.
It can be seen from the table that the colour-difference values show significant relationships with different yarn lots. The fact was confirmed by separate visual observation of the fabrics, which showed up significant incidences of barriness.
3.2 Influence of count
The influence of count on the fabric appearance is represented in Table 6, where again the differences in colour for the different combinations are shown.
From the table it can be seen that the colour-difference values show a significant relationship with differences in count. The fact was confirmed by separate visual observation of the fabrics, which showed up significant incidences of barriness, even with a difference of just 2 counts.
3.3 Influence of TPI
The influence of TPI and subsequent the colour-value difference obtained on the fabric is represented in Table 7.
It can be seen from the table that the colour-difference values show a significant relationship with difference in TPI. The fact was confirmed by separate visual observation of the fabrics, which showed up significant incidences of barriness, even with a difference of just 2 TPI.
The above observations are graphically shown in Figure 2.
Figure 2
The graphs show that mixing of yarn lots has a significant impact on barriness tendency, and count and TPI mixing have a moderate impact on Barriness tendency. 4. Conclusions
Differences in spinning time yarn characteristics are one of the prime causes for the incidence of barre in 100% Viscose knitted fabrics. Of the two yarn properties considered for analysis in this paper, twist and count of the yarn seems to exert a relatively influence on the generation of barre in 100% Viscose knitted fabric.
5. References
1. Herbert T. Pratt, 'Some Causes of Barre', Knitting Times, June 13, 1977, p18 -22
2. Textile Terms and Definitions (Tenth Edition), A Textile Institute Publication, p 20
3. J.W. Coryell and B.R. Phillips, 'Identification of Barre Sources in Circular Knits',
4. Textile Research Journal, February 1979, p 105 - 117
5. Joseph M. Yankey, 'The Solutions for Controlling Fabric Barre', Proceedings of the Beltwide Cotton Conferences p 738
6. E.R. Kearns, H.A. Davis and S.W. Coryell, 'Predicting barre performance in textured polyester double knits', Knitting Times, October 9, 1978, p 16 - 21.
7. M. Makansi, 'Preparation and Control of Fabric Streaks' Part I - Theory', Textile Research Journal, August 1987, p 463 - 472
8. M. Makansi, 'Perception and Control of Fabric Streaks' Part II : Experimental, Textile Research Journal, September 1987, p 495 - 502
9. K.P. Chellamani and K.P. Janakiraman, 'Influence of Fibre Properties on Shade Variation in Dyed Fabrics', Resume of papers, 39th Technological Conference, 1998, p 153
10. H.S. Shah and R.S. Gandhi, Instrumental Colour measurements and Computer Aided Colour Matching for Textiles, 1990.
11. W.D. Wright and L.W. Hager, 'A Tool for Assessing Barre', Textile Chemist and Colorist, Jan 1995, Vol. 7, No. 1
12. Herbert T. Pratt. 'A Descriptive Terminology for Barre', Textile Chemist and Colorist, March 1984.
13. D.A. Zaukelies, 'An Instrument for the Measurement of Barre in Knitted Fabrics', Textile Research Journal, January 1981.