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Worldwide fibre consumption and blend dyeing possibilities

Introduction

From the end of the second world war in 1945 onwards, wool had already become a relatively insignificant fibre and eventually has effectively become almost a ‘premium’ or ‘speciality’ fibre. The regenerated cellulosic fibres (viscose and the acetates) had become important as regards volume. However, in 1971, the synthetic fibres still did not account for 25% of worldwide fibre usage. There has been a steady decline in the percentage of cellulosic fibres used over a fifty year period but overall growth in fibre consumption over the same period has been phenomenal, due to population explosion and the increase in disposable income in developed countries. Polyester is perhaps the only synthetic fibre that has truly fulfilled the early aspirations of fibre research, in terms of volume, value and market share.

 Fibre statistics

The growth and use of fibres worldwide, especially synthetic fibres, over the period 1951 to 2014 is shown in Table 1. Such statistics are often difficult to acquire and analyse, often taking some time to appear after the year indicated.

The distribution of synthetic fibre use in 2005 is given in Table 2. Polyester and cellulosic fibres, either alone or in combination, accounted for 82% of world fibre usage in 2005, and this was still true in 2010. It is forecast that polyester consumption will continue to increase, having overtaken the previous historical dominance of cellulosic fibres by 2050. In 2012, synthetic fibres accounted for 65% of fibre usage whilst polyester accounted for 74 and 73% of this total of synthetic fibres in 2012 and 2013 respectively, the latter figure accounting for 46.7 megatonnes of polyester worldwide.

Table 1: Worldwide fibre statistics
Table 1: Worldwide fibre statistics

It was  estimated in 2012 that production of all synthetic fibres would reach 119.5 mega-tonnes by 2020 and 132 mega-tonnes by 2025. The garment and textile production industries utilising these fibres have 26 million employees worldwide.

 The green economy and sustainable technology

The total textile chain is under ever increasing pressure with an emphasis on occupational health, environmental health, safe working conditions, fair labour practices and social justice [1].

Table 2 - Synthetic-fibre distribution (2005)
Table 2 – Synthetic-fibre distribution (2005)

Concepts of quick response (QR), just in time (JIT) processing and right first time (RFT) processing make major contributions [2]. Major retail chains require the use of ‘sustainable technology’ which does not lead to the emission of greenhouse gases, use of non-renewable materials or the generation of waste.

The importance of cotton and polyester leads to problems in meeting these important objectives of sustainability.  Traditionally, during cultivation, cotton requires the use of chemicals as pesticides, fertilisers and harvesting aids. Some of these are toxic to farm workers and the environment in general but must be removed at the first stage in the wet-processing sequence, resulting in the production of effluent and inferior dyeing results if not completely removed, especially if hard water has been used during spraying. Whilst ‘organic’ cotton has been developed, which does not receive these spraying techniques, the supply of this premium fibre does not meet demand.

Conventional polyester dyeing requires a high energy input to apply disperse dyes at the high temperatures normally required. Only a few specialist polyester fibres can be dyed at lower temperatures and dye accelerants are ecologically unacceptable. However, a water-free dyeing process for polyester has been developed [3], and although this process is still in the early stages of bulk-production, a number of production-dyeing units have been installed throughout the world.

The benefits of blends

From statistics given in Table 1, it must be concluded that cellulosic and polyester must figure prominently in the production of blended-fibre fabrics, although it is difficult to obtain detailed information for the relative demand and importance of different fibres blends. Staple-fibre yarn blends have been long-established in woven fabrics and there is a wide variety of fabric constructions woven or knitted from two or more types of homogeneous yarns. Apparel and domestic textiles are important for such blended fabrics which may exhibit desirable two-way differences in physical appearance and provide scope for attractive multicoloured effects. The availability of wholly synthetic blend fabrics, such as polyester/acrylic dresswear, polyester/nylon outerwear or nylon/acrylic half-hose , as well as differential-dyeing variants, offered considerable scope for various coloured effects. Pile fabrics are important for upholstery and furnishings and often consist of a nylon or cellulosic backing fabric with a resilient pile of wool or acrylic staple yarns. Lightweight towelling, leisurewear and children’s clothing are possible using a cotton pile in a nylon support fabric. A considerable proportion of traditional woven floor-coverings were based on wool/nylon blends whilst the availability of differential-dyeing nylon allowed the production of multicoloured designs by the carpet tufting process. The development of microfibre variants of synthetic fibres have made an important contribution to the properties of blend fabrics, including handle, silk-like appearance, easy-care properties and comfort.

 A number of factors contribute to the justification to develop fibre blends including:

  • economy,  by using a cheaper fibre component  in the blend
  • durability, replacing a fragile fibre by a more robust component
  • improving physical properties, using the performance characteristics provided by each component
  • production of multicoloured effects
  • achieving an attractive appearance and tactile properties
  • achieving a balance of economy and physical properties
  • making a contribution to fabric engineering by selection of the blend components.

Colour effects achieved by blending

Four types of coloured effect can be achieved in blend dyeing:

  • solid effects in which the fibres are dyed as closely as possible to the same colour (hue)
  • reserve effects in which components are left undyed
  • shadow effects in which components are dyed to the same hue and brightness but the depth on one fibre is only a fraction of the others
  • contrast effects, usually the maximum contrast in hue on different components.

Due to difficulties in colour matching and dye selection, many blends are based on two-fibre combinations.With the exception of nylon/wool/viscose blends for carpets, ternary blends are seldom dyed in solid shades.

Table 3 - Classification of fibres by dyeing properties
Table 3 – Classification of fibres by dyeing properties

A number of shadow effects and multi-coloured designs can be obtained. Ternary blends on which disperse, basic and acid dyes can be used will give a limited range of three-way contrasts. The classification of fibre types as regards dyeability is given in Table 3 and the classification of binary blends is given in Table 4.

Table 4 - Classification of binary blends
Table 4 – Classification of binary blends

The colour effects which can be obtained with binary fibre blends are shown in Table 5.

Table 5  -  Colour effects attainable on binary blends
Table 5 – Colour effects attainable on binary blends

Processing techniques

As indicated by the statistics above, cellulosic and polyester fibres account for a large proportion of textile production, this being either as a 100% component or in blends or combinations with each other or with other fibre types. There are many physical and coloured effects which can be obtained from the large combination of fibres and their blends indicated in Tables 3 to 5. Where large lengths per colour are available for processing in fabric form, preparation and coloration can be carried out by continuous methods. Smaller quantities of fabric, fibre or yarn will normally be processed by batchwise techniques.

 Late-stage processing [4], such as package dyeing of yarn, fabric dyeing on modern jet machines and garment dyeing on rotary drum machines, offer a number of advantages, especially quick response in short time frames. Large weights of yarn, as required for carpet manufacture, are also dyed by package-dyeing techniques [5].

 Conclusion

There is much scope to develop wide ranges of fashionable textile fabrics based on various fibre combinations and their blends to produce desirable physical characteristics and colour effects, with the advantage of quick response, using late-stage processing techniques.

 References

[1] W.M. Boyd, J. Park and K. M. Park, Textile Today, 7. July 2014, 54

[2] J. Park, Textile Today, 4, March/April 2011

[3] J. Park, Textile Today, 7, August 2014, 22

[4] J. Park, Textile Today, 7, September 2014, 14

[5] J. Park, International Dyer, 158, 10, 48 (11/11/1977)

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