Engineering Technology of Denim Fabric

The final properties of fabrics depend on many various technical and technological parameters, which should already be adjusted during the design phase of a fabric. Only in this way, will production be efficient, and the desired final properties of the fabric attained, related to its type and end-use. It is impossible to precisely predict all physical properties of fabrics. Many factors influence, directly or indirectly. Therefore, we must understand the applications of the fabric which we intend to design. We must draw technical and technological parameters which must be associated with the design of fabric at the drawing board.

The versatility of Denim Fabrics

Abstract Considerable research work has been done on denim fabrics during recent years and their properties as well as sustainability well exploited. Nano titanium dioxide has been applied on denim fabrics for imparting multifunctional finishes for value addition adopting three routes – dry exhaust, microencapsulation, and nanoencapsulation. Efforts have been taken to develop comfortable denim clothing using regenerated cellulose derivatives, maintaining its rustic look for tropical regions.

The performance of the developed fabric has been assessed by using evaluation methods. To meet the stringent needs to withstand the global environment focus has been directed on the study of different techniques through which apparel industries are developing textiles with smart functioning, using new sustainable products to provide extra comfort and increased performance in an eco-friendly manner. Sustainability will be crucial for all the denim/jeans brands/Denim manufacturers to withstand in the global environment.

Desized indigo denim fabrics have been evaluated for breaking force, spectral characteristics, and a surface appearance by means of application of special finishes. The findings show that some of them are acceptable only as an effective segment on a garment. The resilience properties of stretch denim fabrics have been studied on the tensile properties and structural parameters by using the Kawabata evaluation system. The tensile properties are determined by the proportion or polyester and elastane in relation to cotton. The recent years have seen developments in denim. The major focus areas of innovation and development are comfort, performance, and environment-friendliness of different processes.

Basic cotton fibre properties

100% cotton yarns were used to develop new structural pattern denim fabrics. The cotton fibre properties were characterized by using Uster High Volume Instrument (HVI) systems. The cotton fibres were of a medium fineness (4.5 micronair) and averaged 29.5 mm in length. The fibres had a high tensile strength (29.6 g/tex) and elongation at break (8.2%). The yarn counts varied between 66 and 84 tex. The twist of the yarns was between 531 and 469 turns/m in the Z direction. The ring spinning system was used to produce carded cotton yarns.

Summary Statistics for ring-spun yarn properties

Twist factor/ multipliers used for Denim yarns

Higher twist multipliers are used

• To increase yarn tenacity and yarn elongation
• To produce lean yarns with low hairiness
• To improve spinning stability
• To obtain a clean-cut fabric appearance
• To improve the shifting resistance of the yarns.

The threshold between weaving and knitting yarns has been determined to be the following twist multiplayers.

• combed cotton yarn 3.7
• carded cotton yarn 3.9

Following yarns twist multiplayers have been classified as knitting yarns, standard adopted by Uster.

Yarns for fabric construction—Common Yarn Sizes for Denim Fabrics.

Yarn count Conversion tables

 

Warp yarns for bottom-weight jeans typically range in size from Ne 5.5 to Ne 12.5/1.  Finer yarns are used for lighter weight chambray shirting fabrics and lighter weight jeans, vests, dresses, and skirts.  These yarns may range in count from Ne 12.5 to Ne 30.0. Before the late 1970s, all denim yarns were ring spun.  Today, denim fabrics have different combinations of the ring and open-end yarns.

When you hear a term such as “ring/ring, open-end /open-end (OE/OE), and ring/OE,” it is referring to which yarn is in the warp and which yarn is in the weft, respectively.  For example, ring/OE indicates a ring-spun warp yarn and an open-end weft yarn.  Weaving a combination of ring-spun and open-end yarns can help to reduce fabric costs while still maintaining some favourable ring-spun fabric characteristics.

Elastic Denim Yarns

Core-spun yarns are produced conventionally on ring-spinning machines by introducing a spandex /Lycra/elasticron filament at the back of the front drafting roll of the machine.  The drafted cotton fibers twist around the spandex core to produce an elastic ring-spun type yarn.  There are also open-end and air-jet spinning machines that have been adapted to produce core-spun yarns.

The core filament yarn (normally spandex) is inserted through the rotor shaft on OE frame or the spindle of the air-jet frame, and the cotton fiber wraps around the spandex filament during the process of spinning.  The yarn is somewhat similar to the ring core-spun yarns in terms of yarn and fabric characteristics.  Open-end and air-jet core-spun yarns have fewer knots and splices as compared to ring core-spun yarns.

Denim fabrics of the following types are also manufactured

1. Indigo dyed cotton warp and viscose weft
2. Indigo dyed cotton warp and bamboo weft
3. Indigo dyed cotton warp and Tencel weft
4. Indigo dyed cotton warp and modal weft
5. Indigo dyed cotton warp and grey cotton weft

These fabrics showed fullness, bulkiness of fabrics which is highest with fabrics of the following types are

1. Indigo dyed cotton warp and viscose weft
2. Indigo dyed cotton warp and Tencel weft

Hence the following fabrics showed the largest value and contributing towards the comfort ability in summer suiting. a. Indigo dyed cotton warp and viscose filament

Dyes needed

Indigo is a type of blue dye and is generally used for coloring of cotton yarn which is used for production of denim cloth for blue jeans.

Fabric Geometry/Technology

Denim is manufactured in different weights ranging from 200-300 g/ m² which are categorized as light denim to 300-600 g/m², known as heavy denim. Traditional denim is a rather hard and high-density fabrics with high mass per unit area. Twill weaves such as three-up-one-down (3/1) and two-up one- down (2/1) are predominantly used for denim construction. The stretchable denim fabrics give the elasticity to fabric so that it closely fit to body without restricting the body movement, hence providing wear comfort. Lycra yarn is added to denim to increase its stretch and recovery properties.

Generally, adding 1-5% of Lycra with cotton will stretch the fabric over the body providing a more comfortable fit. The fabric containing Lycra are well known for their good stretchability and stretch recovery characteristics. The air permeability of a fabric is the ability of the fabric to allow the atmospheric air to flow thorough the fabric and reach the skin. The higher value of air permeability is observed in the fabric with lower value of Lycra content and it decreased as the Lycra content was increased.

For a more pronounced twill line in a denim fabric, the direction of twist in the warp yarn should be opposite to the twill direction in the fabric. For example, if “Z-twisted” yarn is woven into right hand twill, the twill line is less pronounced. If “S-twisted” yarn is woven into the same fabric, then the twill line is more pronounced. It must be remembered that only Z-twisted yarns are formed in open-end yarns, while ring-spun yarns have either “Z” or “S” twist. For this reason, open-end yarn can be used in left hand twills when a more pronounced twill line is desirable. Having the twist direction opposite from the direction of the twill line also tend to make the fabric handle a little softer.

Denim mills are searching for ways to produce denim fabrics of the highest quality at competitive prices. The engineering from raw fiber to finished fabric results in superior denim when modern fiber and manufacturing technologies are consistently applied throughout the processing chain.

However, the cost of these engineered products delivered to the market place demands, in addition to the prudence in tackling the volatility associated with the raw material, mainly cotton. Hence the engineering of denim fabrics begins with the selection of an appropriate combination of cotton fibre characteristics for different yarn types with the aid of modern HVI instruments.

Once fibre characteristics are known, yarn quality and processing performance can be predicted. index for various yarn types which can be used as a composite measure to arrive at variance with respect to actual yarn quality of various yarn types including individual characteristic yarns. The equation for calculating

Index=735 x [UHML x Str – 3 x Str -255 -6.6 x UHML]^0.22

Where UHML is Upper Half Mean Length in mm and Str is Strength in grams per tex as tested using HVI Mode

The above index which uses Fibre characteristics as tested using HVI Mode is deduced from the earlier ATIRA equation for predicting CSP of Open-end yarns using Fibre characteristics using ICC Mode.

CSP =720 x [2.5% SL x S – 300]^0.22 – [72.5 x Mc/2.5% SL + 16] x C

• Where 2.5% SL is 2.5% Span Length in mm
  S is Strength in grams per tex as tested using ICC mode
  Mc is Micronaire and
  C is Count in Ne

Cover Factor

To obtain better performance on the loom and fabric yield, a guideline for cover factor in developing new fabric constructions is classified under 3 categories for

1. i) Rings
   ii) Bulky Open-ends and
   iii) Shrinking Stretches.
2. Grey construction is used for calculations.
3. The formula used

Threads per inch
————————— ——– X 100
[28 X Square root of Count]

4. Changing Trend in Yarn Preferences

The beginning of the twenty-first century saw the explorations in different yarn options. The below list is arranged by their usage in volume, starting with warp followed by their use in the weft.

Crosshatch / Streak / Rain Denims

Recently, the usage of characteristic yarns, such as slubby and multi-count yarns, both in-ring spinning and open-end rotor spinning system in denim are on the rise. These yarns need additional monitoring of Slub parameters. Fancy yarn module of UT-5 serves this purpose with testing of Slub parameters -Slub frequency, Slub Length and Mass increase in addition to yarn diameter, yarn density and shape. Aggressive slub parameters tend to lower Yarn Strength and poor performance at subsequent processes.

Chinos

Two-ply chino denim in the indigo-dyed shade has a uniquely soft hand feel, Fabric cover and a luxurious appeal.

Tencel Denim

Woven century luxury cellulosic fibre made from specially grown woods and transformed in a non-chemical process that gives the feel of silk and comfort of cotton.

Stretch Denims

For stretch denim, Core-Spun Cotton Spandex, Poly-Spandex and Type -400 yarns are generally employed. Core-Spun Cotton Spandex yarns in denim range 10s to 16s Ne and uses generally 70 denier filaments; though 40, 55 and 120 denier filaments are also available. Spandex % of Core-spun cotton spandex yarn ranges from 3.5 to 5.5 %. The twist multiplier is 4.4.

Union Denim

Denims are differentiated with weft yarns to create Union Fabrics. The union denims produced in large volumes uses the following weft yarns in the same order – Polyester Texturized Filament, Stretch yarns of Poly Spandex and Type -400 yarns, and Pre-bleached Linen Yarns.

Poly Denim

Polyester Texturized Yarns in denim applications range 300 to 600 denier, with a tenacity of 4.0 g/tex and 20 to 27% extension. The bulk which is expressed in %HCC (Hot Crimp Contraction) is about 40 and nips per metre range from 70 to 90 for better performance.
Grey as well as dyed yarns are being used.

Poly Stretch Denim

Poly spandex yarns used in denim range 150 to 300 denier with 6 to 12 % spandex. Nips per metre for better weaving performance is 100 to 130. Type -400 yarns from Invista used in denim applications range 150 to 600 denier with a bulk of 50% HCC and nips per metre of 35 to 50.

Linen Vintages

Pre-bleached Linen yarns range 9s to 16s Ne [or 25 to 44 Lea]. Though these yarns have a very high strength of over 3000 CSP and 20 cN/tex, due to low elongation of 2% and the natural variation in yarn, the loom performance, as well as full-width defects, is poor in comparison with normal denim.

Value Engineering

In accordance with value engineering, quality fabrics can also be produced from Value mixings. However, the denim fabrics produced out of such yarns should not be meant for elaborate destructive garment washes.

Addition of 10% Recycled Waste

The full recycling of all opening and carding wastes, using a new line of machinery from Trutzschler and others, is attempted by few with a success. Its obvious importance in Denim manufacture lies in the overall weight on the final cost represented by the cost of cotton. Because of heavy yarns and fabrics, if one can save 3 or 4% on cotton costs, the impact on the bottom line can be remarkable.

This clean material has some residual trash in it not too different from the cotton used. Naturally, there are more short fibres. The yield will be approximately 50%, in other words from every 2 kgs of raw waste we get 1 kg of clean recycled cotton. This material is baled again and fed to the mix at the laydown. Normally 10% is used. A loss of some 0.5 to 1.0 cN/tex is then unavoidable, but with 10% it will be manageable.

Control of Yarn Realization

A one percent reduction in yarn realization has almost the same economic impact on the mill’s profit as an increase of one percent in the mixing cost. The control of yarn realization is thus as important to a mill as the control of cotton and mixing costs. One may find the detailed procedures for the control of yarn realization in Chapter 3, ATIRA Silver Jubilee Monograph “Process Control in Spinning”.

Mock Rings

Various attempts to duplicate superior denim made from ring yarns with rotor yarns of mock or slubby have always failed in fabric strength properties, fabric hand and appearance due to differences in yarn structure and yarn properties. Still, one wonders how much of the present so-called ring-spun Denim is such and how many are mock ring made in the open end.

Other Value Offerings

Cotton rich polyester denim is with superior hand feel, lustre and colour contrast for the fashion market. One may find a deep value in using dyed polyester texturised filament yarn in place of costly yarn-dyed cotton weft for high fashion denim. Poly Spandex yarns are replacing core spun lycra yarns in the value universe. Within Poly Denims, the denier is getting coarser day by day from 300 to 450 to 600. Though Linen Vintage denim is not in high volume, there are efforts to replace it with Jute in the value proposition.

Successful strategies in denim mean profit, often (now) even survival. Engineering the fabrics on a continual basis provides a way to achieve both quality and cost benefits of substantial proportions. At the same time, full manufacturing flexibility through modularization is being maintained, enabling the denim mill to meet new and changing trends in raw material and fashion.

The global desirability for ring-spun and slub yarns

In injected slub yarn, tensile and abrasion resistance are particularly very important parameters affecting its process performance and end-use. In single base injected slub yarn structure, slubs are developed by injecting fibres from outer side of the yarn with the sequence of untwisting base yarn followed by re-twisting after injecting the fibres. The tensile properties and abrasion resistance of injected slub yarns depend on the slub parameters.

The surface of the yarn, especially the slub part is very much susceptible to damage by abrasion during usage, due to lack of fibre migration between base yarn fibres and injected fibres. In this paper, an attempt has been made to see the impact of slub yarn configuration i.e. slub length, slub thickness and slub frequency on tensile and abrasion resistance of injected slub yarn. Empirical models have been developed to find the dependence of these properties on slub yarn configurations.

Configuration of slubs in particular slub length and slub frequency was found to be very significant on yarn tenacity, elongation and abrasion damage in terms of tenacity loss, elongation loss and hairiness rise of injected slub yarn. However, the impact of slub thickness is relatively less on the aforesaid parameters.

Conclusions

Denim wearing comport of a textile product is an essential property and a major concern when it comes to customer perceptions and preferences. The overall behaviour of fabric is mechanical parameters that can be measured by various objective test methods. The principal aim of the above study is to determine the comfort, astatic and durability of commercially available denim fabrics by subjective measurements.

This drawing board studies create a tactile score database for denim fabrics and investigate the relations between tactile comfort and shear behaviour. Sustainability is today a trend that is seen everywhere, with no exception for the textiles industry.  However, there is a rather significant downside regarding how the textile industry currently operates.

Acknowledgement: Technical and technological Facts in this write up has been selected from various reliable sources.