Advances in the Dyeing and Finishing of Technical Textiles

M. L. Gulrajani

• Publisher: Woodhead Publishing
• Year: 2013
• Print ISBN:
  9780857094339
• eBook ISBN:
  9780857097613
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

The use of distinctive colourants and finishes has a significant impact on the aesthetic appeal and functionality of technical textiles. Advances in the textile chemical industry facilitate production of diverse desirable properties, and are therefore of great interest in the production of textile products with enhanced performance characteristics. Drawing on key research, Advances in the dyeing and finishing of technical textiles details important advances in this field and outlines their development for a range of applications.Part one reviews advances in dyes and colourants, including chromic materials, optical effect pigments and microencapsulated colourants for technical textile applications. Other types of functional dyes considered include UV- absorbent, anti-microbial and water-repellent dyes. Regulations relating to the use of textile dyes are discussed before part two goes on to investigate such advances in finishing techniques as mechanical finishing, softening treatments and the use of enzymes. Surfactants, Inkjet printing of technical textiles and functional finishes to improve the comfort and protection of apparel are also explored. The use of nanotechnology in producing hydrophobic, super-hydrophobic and antimicrobial finishes is dealt with alongside coating and lamination techniques, before the book concludes with a discussion of speciality polymers for the finishing of technical textiles.With its distinguished editor and international team of expert contributors, Advances in the dyeing and finishing of technical textiles is a comprehensive guide for all those involved in the development, production and application of technical textiles, including textile chemists, colour technologists, colour quality inspectors, product developers and textile finishers. - Discusses important advances in the textile chemical industry - Considers developments in various dyes and colourants used in the industry, including water repellent, functional and anti-microbial dyes - Chapters also examine advances in finishing techniques, the use of nanotechnology and speciality polymers in technical textiles

Part I

Advances in dyes and colourants

1

Chromic materials for technical textile applications

R.M. Christie, Heriot-Watt University, UK

Abstract:

This chapter discusses the principles of chromic materials as applied to textiles. The most important chromic phenomena – thermochromism, photochromism, ionochromism and electrochromism – are dealt with in individual sections, each providing a description of the physicochemical principles underlying the colour changes and a discussion of the molecular structures of the most important colorant classes. An overview of the main non-textile applications of chromic materials sets the scene for more detailed discussion of progress through ongoing research towards technical and smart textile applications. The chapter concludes with informed speculation on likely future trends in the development of products based on chromic textiles.

Key words

chromic

photochromism

thermochromism

ionochromism

electrochromism

chameleonic

1.1 Introduction

Chromic materials may be defined as dyes and pigments that exhibit a distinct colour change when exposed to an external stimulus, especially when the change is reversible and controllable. A wide range of materials that exhibit colour change effects have been investigated in recent decades and numerous products have been introduced commercially. Currently, chromic materials are most commonly used in high-technology non-textile applications which exploit the chromic effect produced by the stimulus, for example in ophthalmics, thermometry, electronics and biomedicine. Although these colorants have not been developed specifically for textiles, there is growing interest in their potential for applications in technical and smart textile products. This chapter provides an overview of the chemical types and properties of the most important classes of chromic materials, a discussion of the underlying scientific principles and a review of their commercial applications, with particular emphasis on developments that have taken place towards textile applications. Following the overview of the general principles of chromic materials covered in Section 1.1.1, Sections 1.2–1.5 deal individually with the four chromic phenomena which have been most extensively studied for textile applications – thermochromism (colour change due to a change in temperature), photochromism (UV-light induced colour change), ionochromism (especially halochromism where the colour change is related to pH variation) and electrochromism (colour change due to electric current flow). Section 1.6 deals with miscellaneous chromic materials, and the chapter concludes in Section 1.7 with speculation on future trends in the development of products based on chromic textiles.

1.1.1 An overview of chromic materials

Over the last 150 years, a comprehensive range of synthetic dyes have been introduced industrially for the purpose of dyeing the different textile fibre types with the complete gamut of colours. Traditional textile dyes are required to provide a constant, predictable and reproducible colour and, as far as is technically feasible, a permanent colour in terms of exposure to external effects such as light and washing. Any variation in the colour of a coloured fabric, for example when exposed to a change in temperature or to light, would normally be regarded as highly undesirable, i.e. a defect. However, it has been recognised in recent decades that there are potential important commercial niche applications for dyes and pigments that exhibit a distinct colour change when exposed to an external stimulus, especially when that change is controllable and reversible. Such colorants are collectively referred to as chromic materials (Talvenmaa, 2006; Bamfield, 2001; Bamfield and Hutchings, 2010; Christie, 2001; Dawson, 2010; Somani, 2010). A wide range of chromic phenomena are now well known and the underlying physical and chemical principles have been established. An extensive range of materials that exhibit the colour change effects have been investigated and, where appropriate, introduced commercially. The industrial applications which have emerged are generally in ‘high technology’ areas, for example in thermometry, ophthalmics, electronics and biomedicine, where the particular colour change (chromic) effect produced by the stimulus is specifically exploited. It is significant in the context of this chapter, however, that these stimuli-sensitive colorants have not been developed specifically for textiles, although there is evidence for growing interest in their potential, especially for technical and smart textiles applications.

Chromic phenomena are named using the suffix chromism preceded by a prefix which is used to describe the stimulus giving rise to the colour change. Table 1.1 provides a list of chromic phenomena and the stimuli involved. Thermochromism, photochromism, ionochromism and electro-chromism are the most extensively studied phenomena. The others listed are generally rather less well established and either have limited commercial exploitation currently or are essentially academic curiosities. Indeed, the list in the table is probably not exhaustive.

Table 1.1

Chromic phenomena with the associated stimulus

Chromic phenomenon	Stimulus
Thermochromism	Heat
Photochromism	Light
Ionochromism	Ions
Electrochromism	Electric current flow
Solvatochromism	Solvents
Vapochromism	Vapours
Mechanochromism	Mechanical action
Chronochromism	Time
Radiochromism	Ionising radiation
Magnetochromism	Magnetic field
Biochromism	Biological sources

Chromic materials offer considerable potential to provide specific functions in intelligent or smart fabrics and clothing, which are designed to sense and react to environmental conditions (Talvenmaa, 2006; Tao, 2001). Smart textiles may be categorised as either active or passive. A passive smart fabric reacts to an environmental stimulus, such as heat, light or humidity, by a change of state that is useful for a particular application, for example by providing a warning signal. Most active smart fabrics react to an external stimulus by means of a sensor which generates an electrical current, and this in turn provides an additional response that is a useful reaction in the context of the particular application. In this respect, chromic materials may be considered as passive smart materials. An example of the potential for applications on textiles is as chromic sensors which provide a response to a change in environment by means of a visible colour change. Such textile-based chromic sensors provide the advantage of a self-contained response that does not require electrical circuitry. The main commercial applications of chromic materials on textiles have been focused until now on creative design and novelty products. The commentaries by designers who have experimented with the creative use of chromic technologies commonly contain recurring themes which explain the relatively limited exploitation to date. The materials currently available are limited in scope and availability, are relatively expensive and have been designed for non-textile applications so that they cannot be used in exactly the same way as traditional textile dyes. They may also show limited stability in certain environments, leading to questionable longevity of products based on chromic textiles.

An ambitio...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Woodhead Publishing Series in Textiles
• Part I: Advances in dyes and colourants
• Part II: Advances in finishing techniques
• Index