Polyester Microfibres offer higher levels of value addition in the Textile Supply Chain. However, the large internal surface area, much larger than with conventional polyester fibres, poses particular problems to the processor. This applies especially to the chemical preparation and dyeing stages.
The dyeing of microfibres is an extensive subject. There is insufficient space in this column to cover the question fully. It is hoped that the basic principles are outlined here, sufficiently to tempt interested readers to further their research by reference to the book about to be published entitled Polyester World.
2. Full Article
2.1 The Emerging World of Textiles
It is assumed here that the world of textiles has divided into three sectors (Fig 1).
Fig 1. The World of Textiles
Synthetic Microfibres should certainly be regarded as a higher value added sector driven by Niche Performance.
- The subject of Microfibres covers both Polyester and Nylon.
- This study focuses on Polyester.
- Important issues covered here include :
- This memorandum does not cover garment confection.
2.2. The Development of Microfibres
- The development of Microfibres has provided opportunities to produce new generations of fibres and blends of potentially novel characteristics which have not previously been possible from conventional fibres.
- As an example, consider the recent development of towels made from polyester Microfibres which are claimed to be more absorbent than cotton towels, despite the fact that conventional polyester is hydrophobic.
- This novel characteristic is due to the increased internal surface area of Microfibres, which in turn presents processing issues / difficulties including dye selection and choice of dyeing method.
- Fabrics have been produced with a very wide range of high density materials which demand specialized processing.
- Fabric constructions based on microfilament synthetic yarns are commonly referred to as :
o MICROFIBRES (Europe & USA)
o SHIN GOSEN (Japan).
- Fabrics from these sources use a combination of :
- conventional, fine and / or superfine filaments.
- filaments of widely differing shrinkage characteristics.
- very high and low twist yarns.
- textured, air textured and flat filament yarns.
- variations in cross-sectional shape.
- Effect fabrics available include :
- imitation silks
- peach skins
- suedes (light to heavy)
- air and moisture permeable waterproofs
- staple blends and yarn mixtures with viscose rayon, cotton and wool.
- Outlets include :
- lens wipes
- and (more recently) a new generation of towels.
2.3. Definition of a Microfibre
- We include here :
- an outline description of the term Microfibre.
- a comparison of Microfibres with natural fibre counts.
- typical decitex per filament ranges of :
- conventional polyesters
- weight reduced polyesters
- polyester microfibre
- polyester supermicrofibre.
- Precisely how fine a synthetic yarn is can be described in terms of decitex or denier.
Decitex - the weight in grammes of 10,000 metres of yarn
Denier - the weight in grammes of 9,000 metres of yarn
Hence, a 176 decitex yarn can also be described as a 150 denier yarn
- A useful term to remember is the Decitex per filament (dtexpf).
- The dtexpf denotes the decitex of a yarn divided by the number of filaments within the yarn; as shown in the following example.
- There may be several definitions of a microfibre , but the most commonly used is :
Table 1. A perspective on filament fineness
2.4. Microfibre Processing Flow Algorithms
- We consider here:
- In considering the critical success factors for processing micro fibre fabrics it must be realized that :
- higher value addition results from successful processing
- the cost of failure is correspondingly high.
- Complex processing requires :
- due consideration to dye selection and high quality auxiliaries
- a complete awareness and understanding of the complexities involved.
- The issues apply to each processing stage :
- In developing areas where environmental impact of chemicals used in wet processing is of increasing importance specialized advice should be sought before embarking on any new project.
- The recommendations will necessarily vary depending on:
- fabric construction
- end use requirements.
RIGHT FIRST TIME PRODUCTION IS VITAL
Microfibre Processing Flow Algorithm (1)
Microfibre Processing Flow Algorithm (2).
- We consider here :
- Important Factors in the De-size Scour/Relax Process include :
- Fabrics woven from polyester microfibres will probably contain very high twist, high shrinkage yarns. Microfibre based fabrics have a high bulk density and a particularly large surface area.
- The very large surface area of microfibres means that 2-5 times more fibre processing aids will have been used relative to conventional polyester based fabrics.
- Higher concentrations of processing aids are also needed to protect the delicate polyester micro fibrilles.
- Inefficient, or non-uniform removal of fibre processing aids may lead to spotting problems with disperse dyes and poor coverage and levelling.
- To minimize creasing it is important to :
- allow the necessary controlled shrinkage of the microfibre filaments to take place during the scouring stage.
- conduct relaxation under conditions of minimum tension.
- take care when planning the preparation operation; the shrinkage / relaxation of polyester microfibres takes place at lower wet processing temperatures than with conventional polyesters.
- Insufficient care at the preparation stage can lead to crease and crows feet marks after dyeing.
- The main requirements (and therefore objectives) are to :
- optimize removal of fibre processing aids
- whilst minimizing creasing and maintaining the desired
A GENTLE BUT EFFICIENT PREPARATION IS VITAL.
2.6 Identification of sizes
- As already mentioned (several times), polyester microfibre based fabrics contain large quantities of fibre processing aids.
- Before establishing a procedure to optimize the removal of size it is important to firstly identify whether the size is polyester or polyacrylate based (techniques for removal differ).
- Details of size identification and removal are provided in our book Polyester World.
2.7. Preparation: Machinery and Methods
- There are many options possible for preparing woven fabrics based on microfibres.
- Three options are listed in order of decreasing efficiency in both
- the removal of sizes, oils and waxes.
- and tensionless relaxation in preventing creasing and achieving the desired aesthetics.
- These options are discussed fully in the book Polyester World.
2.8. Dyeing Microfibres
- In the publication Polyester World we consider :
About the Author:
David Parkes is currently the Managing Director of Dyehouse Solutions International. He has over 40 years international experience of the dyeing and finishing industries of all cellulosic fibres. He has had over 60 papers published at International Conferences and Symposia. He has spent the last two years building up work experience in India and Pakistan.