The Global Textile and Clothing Industry || Recent advances in textile manufacturing technology

© Woodhead Publishing Limited, 2012

113

7Recent advances in textile manufacturing technology

T. STEGMAIER, Institute of Textile Research and Process Engineering (ITV) Denkendorf, Germany

Abstract: In the textile industry progress in technology and products is enormous. This chapter gives an overview of the new materials and technologies available, such as attractive polymers in combination with new spinning methods, three-dimensional (3D) textile formation, environmentally friendly fi nishing and computerized patterning. In addition, the chapter discusses sustainability and the environment, bionics, the use of nanotechnology in textiles and numerical simulation resulting in innovations.

Key words: sustainability, 3D textiles, nanotechnology, bionics, numerical simulation, innovation.

7.1 Introduction

The textile industry is considered to be a traditional industry; however, prog-ress in technology and products in recent years has been enormous. This is especially true in the diverse fi eld of industrial applications. For example, highly specialized fi bres and polymers are being developed which are con-tinuously extending the areas of application of textile products in industry.

New polymers and additives with special fi bre properties such as fl ame retardancy, high chemical resistance and high tenacity are now available that can withstand high-temperature application. A broad range of fi bres have been developed based on petrochemical polymers. In the last few years poly-mers processed from renewable biomass have been developed to replace tra-ditional fi bres, as well as to create new properties such as biodegradation.

The form of a single fi bre can vary from traditional round to special forms like rectangle, trilobal, hollow and even more complicated cross-sections. The fi neness of fi bres is especially important for soft textiles and for fi ltra-tion aspects; this can be decreased from micrometre down to the nanometre scale. By processing two polymers in one nozzle, a huge range of astonishing fi bre properties can be generated.

The traditional textile and clothing industry has been inspired by other industrial technologies which can extend the possibilities of treatment of

114 The global textile and clothing industry


natural and man-made fi bres. In this way the borders of design and pro-duction have been moved to a higher level. Progress in the fi eld of chem-istry also offers expanding challenges in fi nishing, coating and laminating of textile material in order to extend and adapt its functionality. Because of these developments, new application technologies are available to cre-ate water-based, solvent-based and solvent-free formulations as coatings for fi bres. One-side and two-side application technologies have been developed for fl exible fabrics, as well as for stiff fabrics. For very thin coating layers, nanotechnology gives the opportunity to improve functionality in nearly all specialized properties of traditional and technical textiles.

In the area of textile machinery, there has been substantial progress in the fabrication of three-dimensional (3D) textiles. Weaving, knitting, warp knitting and nonwoven technologies are continuously improving to extend the height of a textile and to structure the material with regard to forces and demands from the application. As textile production is highly intensive in terms of nat-ural resources, such as water and energy, sustainable evaluation is becoming an increasingly important issue for risk management and marketing.

7.1.1 Advances in polymers and fi bres

Biopolymers for fi bres and coatings

An alternative to natural fi bres and man-made fi bres based on petrol chemis-try are fi bres made of biopolymers. These are regrowing materials, harvested from fi elds or forest, chemically treated and – in the case of textiles – formed into fi bres using extrusion processes or used as coating polymers. One such polymer, which has been available for decades, is known as viscose. In recent years, more efforts have been put into replacing other high-functional fi bres, like polyester or polyamide, which are made with fi bres of regrowing poly-mers. New man-made fi bres based on natural regrowing resources are now available, which make use of polymers like cellulose (bamboo), polylactides, proteins (soy beans) and polyamides. Mono- and multifi laments can be pro-duced, as well as staple yarns in different counts.

Bi-component spinning technology

Bi-component fi bre spinning technology offers exciting new properties for fi bres by combining two polymers in one fi lament. In the bi-component spinning process two polymers are extruded from the same spinneret, form-ing different fi bre parts in one fi lament, depending on the nozzle. Another term for bi-component fi bres, which is particularly prevalent in Asia, is ‘con-jugate fi bres’. By this technique, it is possible to produce fi bres of any cross-sectional shape or geometry that can be imagined. Bi-component fi bres are

Recent advances in textile manufacturing technology 115


commonly classifi ed by their fi bre cross-section structures as side-by-side, sheath-core, islands-in-the-sea and citrus fi bres or segmented-pie cross-sec-tion types. 1

Bi-component fi bres made of PP/PE are in demand in the nonwoven market. Their main applications include:

nonwoven fabrics for nappies, feminine care and adult incontinence • products (as top sheet, back sheet, leg cuffs, elastic waistband, transfer layers) air-laid nonwoven structures are used as absorbent cores in wet wipes • spun-laced nonwoven products like medical disposable textiles and • fi ltration products.

Phase change materials for extended comfort

Phase change systems are smart materials which use latent thermal energy to keep the human skin at a constant temperature. They store thermal energy by melting, and then give this thermal energy to the surrounding environ-ment if it gets colder. In textile fi bres, micro encapsulation is normally nec-essary to integrate phase change materials when using spinning technology. Polyacrylic fi bres are already on the market and, since 2011, a bi-component fi bre made of polyester has also been developed ( Fig. 7.1 ).

Staple fi bres were launched in the textile market fi rst, followed by fi la-ment fi bres. Fibres with temperature management are particularly appli-cable to underwear and other products worn next to skin, such as socks, T-shirts, shirts and trousers. Polyester fi bres offer the added value of

7.1 PCM in hollow fi bres.



balancing temperature coupled with the physiological characteristics of a conventional polyester fi bre (e.g., low moisture absorption, ability to trans-port moisture, improved wrinkle resistance, superior light, water and wind resistance and an above-average durability). The result is increased com-fort; chilling and sweating is reduced due to optimum climate regulation. 2 Of course, the reduced mechanical strength also needs to be considered in textile construction.

7.1.2 Sustainability in materials

Sustainability is a growing business factor which needs to be considered in textile production, especially with regard to marketing. A comprehensive analysis is necessary which includes all resources, such as water, electricity, chemicals and machines in production of raw materials, during processing and distribution, throughout the product’s life-time as well as when recy-cling. By focusing on sustainability a company generates business value, and has the potential to attract new customers and reduce risks for the future.

In such analyses, natural fi bres are often defi cient in environmental aspects when compared with man-made fi bres. Cotton, in particular, requires inten-sive care when growing and harvesting, with the support of pesticides, fungi-cides and irrigation water. During processing in textile production, chemical auxiliaries are necessary for scouring, bleaching, dyeing and fi nishing, as well as large amounts of water and energy. These environmental aspects will have to be improved substantially towards sustainable methods in order to continue supplying the growing demand for clothes from the increasing population on Earth if we are to protect the environment comprehensibly for future generations.

7.1.3 Advanced 3D and 2D fabric manufacturing technologies

Spacer textiles

In the past few years there have been exciting developments in the area of spacer textiles. Two separated textile fabric layers can be connected by a spacer, which mostly consists of a monofi lament yarn. Due to this specifi c method of construction, an air space is created which provides a high degree of heat insulation and can also improve air conditioning and mechanical damping. This technology is used in knitting and warp knitting, as well as in weaving. The distance between under- and over-layer can vary from 1 mm up to 65 mm and more ( Fig. 7.2 ).

The advantages of this type of construction lay in the high reversible com-pression, the decoration possibilities for both sides, and the high strength of



the material, depending on the processed fi bre materials used. It is possible to create more functions such as heating with electrical conductive fi bres or pneumatic structures by airtight coating. Knitted spacer textiles normally show a higher elastic tenacity when compared with warp-knitted fabrics and woven structures.

Hydroentanglement for design

Due to developments in improving strength and mechanical durability, non-wovens are becoming more and more attractive for the clothing industry. These types of product are economical as they have protective properties, which help them to withstand deterioration during washing procedures. Using hydroentanglement processes it is possible to create new ways of pat-terning nonwovens. For example, for spun-lace fabrics hydroentanglement offers an interesting range of patterning and aperturing solutions. In combi-nation with calenders or sleeves, high production speed is possible. Modern sleeves are able to produce logos and artwork in 3D design with high quality details.

7.2 Advances in finishing, coating and digital printing technologies

The following sections look at the many and various techniques and applica-tions used in the fi nishing and coating of textiles, as well as the rapid devel-opments that have occurred over recent years in the fi eld of digital printing on textiles.

7.2 Spacer warp knitting.



7.2.1 Metalization

Functionalization of fi bres and textiles requires auxiliaries to be integrated into the bulk of the material or added to the surface of the textile. For light refl ection, antistatic behaviour and electrical conductive elements, thin layers of metals or metal oxides can be applied using the physical vapour deposition (PVD) process, in which atoms or molecules are vaporized and subsequently condense on a substrate as a solid fi lm. Cathodic sputtering is the favoured technology for the coating of textiles with metals. This tech-nology offers considerable additional potential for the creation not only of metallic fi lms but also of ceramic fi lms. Potential applications of this tech-nology include management of heat transfer, solar radiation, heat radiation, electrical conductivity and more. Few companies offer this special coating as a service.

7.2.2 Plasma treatment for improved functionalization

Another technology used for the functionalization of textiles and fi bres is that of plasma treatment systems. This technology has already been success-fully installed and utilized by some textile companies, and further develop-ment is ongoing in R&D centres regarding plasma processes for coatings with thin polymer layers, under low and atmospheric pressure. Plasma-based modifi cations are, in principle, dry processes and, therefore, form an interesting economical alternative to the traditional wet textile fi nishing systems.

Atmospheric pressure plasma systems can be easily integrated into con-tinuous-running textile productions and fi nishing lines. If the energy supply is controlled in such a way that the plasma gas temperature is kept around room temperature, it is called cold or low-temperature plasma. The techno-logical basis for the wide applicability of atmospheric pressure processes in the textile industry is the enhancement of the established corona technol-ogy, by coating both electrodes with the help of dielectric material (dielec-trical barrier discharge, DBD) using an intermittent electrical power supply and by enabling the use of defi ned gas mixtures.

Activation of the surface of textile materials has been shown to have the following potential benefi ts:

increase of adhesive force: lamination, coating, taping up to 100% • considerable enhancement of yarn wetting and complete yarn penetra-• tion by liquid coating systems for textile constructions.

Plasma treatment has the ability to change the properties of fabrics, such as the friction coeffi cient and surface energy or antistatic behaviour. Plasma



treatment under pressure requires closed systems and a vacuum chamber. Despite the higher investment costs, it can extend the application possibil-ities for thin coatings on fi bres substantially. Encapsulated plasma devices are necessary for the plasma polymerization processes. A continuous pro-cess, however, is still possible if there is an uncomplicated gas-lock at the air inlet of the reactor chamber. It is possible to produce water- and oil-repellent layers on textiles using plasma polymerization.

The main advantages of plasma treatment are the following:

modifi cation of surface properties without changing the properties of • the fi bre bulk water-free processes with a minimum consumption of chemicals and • elimination of energy-intensive drying processes highly environmentally friendly processes • generally applicable to nearly all kinds of fi bres. •

The use of liquid aerosols in plasma technology increases the application spectrum of suitable chemicals considerably. Liquid chemicals, solutions and dispersions can be used, to a certain extent, in plasma treatment of tex-tiles for surface modifi cation with the help of aerosols under atmospheric pressure or using under-pressure systems. The following are examples of the potential benefi ts which can be achieved through the combination of aerosols and plasma surface treatment:

physical surface modifi cation, for example, creation of permanent elec-• trostatic properties (electret) on fi lters chemical functionalization for hydrophobic/oleophobic properties • minimum application of chemicals for energy-saving fi nishing • chemical and topographical nanostructuring. •

7.2.3 Digital printing

Digital printing is a technology which is highly fl exible and has great poten-tial in the patterning and design of textiles. Flexible digital inkjet systems have been developed which are specifi cally designed for decorating applica-tions. They can produce high quality, multicolour printing, onto two opposing vertical sides. Through computer-based control of patterns this technology provides enormous potential for customized products. The technological development of printing heads and peripheral components has been accom-panied by the improvement of full colour management systems and software tools for design, creation, texture mapping and colour-way creation. In some systems the pre-treatment is integrated inline. Some post-treatments, such as



thermocure, can also be added, using hot air applications or UV radiation. Due to advances in technology, the potential production speeds which can be achieved have increased dramatically in the last few years. Actual productiv-ity numbers show a printing production speed of 8000 m 2 /h, with a resolution of up to 2400 dpi. 3

Parallel to the development of faster printing ink technologies, there has been rapid progress in the development of the ink itself to provide more functions than just colour. Using electrically conductive inks it is possible to produce smart textiles which can be used as heating elements, shield against electromagnetic waves or simply to guide electrons. Rapid proto-typing is a process that uses curable polymers in printing systems. Three-dimensional elements can be produced with almost limitless freedom of design. Meanwhile, the fi rst textiles are now on the market that have been entirely digitally manufactured. They can use precise body geometry to pro-duce this kind of wearable technology.

7.2.4 Laser treatment for patterning

New fi nishing effects can be achieved using laser treatment units. The free patterning effect is created when the laser beam burns or melts the fi rst layer of the textile material. Lasers can also be used as a cutting device. Remarkable working fl exibility can be achieved when this technology is combined with the utilization of a robot arm. The way in which the laser burns the surface of the material is fully computerized. This kind of technol-ogy can be used to treat running fabric as well as sewed pieces of cloth. In all processes, an effective suction of the air and air treatment is required.

7.2.5 Sol-gel technologies

The fi rst sol-gel products came onto the market a few years ago. A combi-nation of inorganic and organic materials with sol-gel technologies can be used to form functional fi lm coatings on fi bres. Silicon alkoxides or metal alkoxides are transformed into stable silicon or metal oxide nanosol dis-persions by acid or base catalysed hydrolysis. These can then be applied to fabrics using traditional textile processes. Subsequent condensation/aggregation results in the formation of a so-called lyogel fi lm which dries to form a porous xerogel fi lm. Sol-gel technology offers many possible appli-cations for the functionalization and fi nishing of textiles. The incorporation of highly fl uorinated silane compounds, for example, yields oleophobic dirt-repellent layers, while the incorporation of ammonia compounds results in antistatic layers. The fi lm around the fi bre is fl exible enough for the demands of different textile materials. By fi nishing with solgel it is possible to create



highly abrasion-resistant textiles. In combination with suitable additives, a whole range of functions are possible, such as anti-soiling or easy-to-clean properties.

7.2.6 Dual-side coating in one step

The machine industry can offer further possibilities for the functionaliza-tion of textiles using coatings. For example, special application units for the direct coating of fabrics are integrated in the stenter entry during the processing of bi-elastic knitted fabrics. In this way it is possible to perform almost tension-free processing of tension-sensitive knitted textiles. In addi-tion to this, an application unit for the coating of the underside of the textile web has been developed. Both units in combination allow for the simultane-ous coating of the top and bottom of the textile web in one dryer passage. 4

7.2.7 Hotmelts as an alternative coating system

The application of hotmelt and powder-coating systems have been devel-oped due to a move away from the use of solvents and thoroughly dried watery media in the textile industry. Powder-coating systems can be ther-moplastic polymers or thermoset polymers. Other than the advantage of being solvent-free, hotmelts also have high production speeds as well as low thermal pollution of the materials.

Hotmelts are being developed with increasingly versatile applications in textile fi nishing. In the meantime, applications in the areas of interlining, furniture, technical composite materials, shoes, automotive interiors, sound insulation materials, medical and hygiene products, geotextiles, protective and functional clothing, the use of hotmelt applications is standard. Almost unlimited combinations of various materials and styles can be achieved.

Hotmelts are an alternative to fl ame lamination of foams. Thermoplastic or reactive adhesives such as reactive polyurethane, thermoplastic polyes-ter, polyamides, EVA polymers, as well as non-wettable polyurethanes, have been well established as usable materials in this fi eld. The manufacturers of coating plants have followed this trend and offer many corresponding application modules.

7.2.8 Foam coatings – a lightweight and low energy option

According to the view of producers of auxiliary materials and plant manu-facturers, there is a growing trend towards the use foam applications in the processing of water-based application systems. The benefi ts of utilizing foam



over other methods are the positive energy aspects, easy manageability, the ability to adjust the solids content, the ability to apply the process to a small area and the high material effi ciency which can be achieved. Between unsta-ble and stable foam, the transition of wet fi nishing to coating is quick and smooth. The confi guration of breathable coatings using foam processes is becoming more popular.

7.3 State-of-the-art nanotechnologies

In the past few years, intensive efforts have been made to open up new markets for the textile industry with regard to the big technological and economical potential of nanotechnologies. This can be observed across the world, from basic research to industrial production. A whole series of textile materials with specifi c functions gained through the processing of nanopar-ticles are already on the market. For example, established ‘nanofi nishings’ offer functions such as the absorption of UV radiation by titanium dioxide nanoparticles, antimicrobial effects through the use of silver nanoparticles and self-cleaning properties through the nanoparticle-induced increase of surface area roughness in combination with water-repellent coating systems.

The defi nition of nanotechnologies is as follows: nano (Greek: dwarf): according to the defi nition of the Federal Ministries of Education and Research, Germany (BMBF), nanotechnology describes the testing, imple-mentation and manufacturing of structures, molecular materials and sys-tems with a dimension or production tolerance typically below 100 nm.

For textile technology, nanotechnologies offer various opportunities including:

the generation of extremely fi ne nanoscale fi bres (nanofi bres) • the incorporation of nanoscale particles in the fi bre matrix (‘nanocom-• posite fi bres’) the functionalization of the fi bre surface through nanoscale functionar-• ies (‘nano-surface functionalization’) with very thin layers or through the familiarization of nanoparticles.

These manufacturing options are used in the production of nanofi bres for fi lter applications, nanostructured textiles for biomedical products and of self-cleansing and electrical-conducting textiles.

Today functional textiles are, for the most part, promoted with dirt-repel-lent and self-cleaning properties based on nanotechnological coatings, as well as with hygienic, antibacterial functions through the use of nano silver particles. Clean, outdoor clothing despite adverse weather conditions, and the prevention of unpleasant odours after physical exercise, is an attractive



sales angle. Because of these advantages, many notable suppliers of outdoor clothing and sports gear have included nano products in their line of mer-chandise. However, nanoparticles in fi bre polymers and in coatings have already accomplished a large amount. From fi re prevention to heat and UV protection, as well as chemical protection and optimized surgical textiles, a wide range of functional abilities have already been achieved.

Parallel to these developments in nanotechnology, an intensive scientifi c and public discussion about the ecological and health dangers of nanopar-ticles is underway. A substantial uncertainty by both consumers and textile producers has been noted, with regard to the extent of the dangers ema-nating from nanoscale materials. However, this level of uncertainty does not necessarily correlate with the actual risks posed. All materials have the potential for nanoscale materials to be released from them through mechan-ical or chemical infl uences, or through ageing. But how likely is the release? Is the release probability higher for textiles modifi ed through nanoparticle technologies compared to conventional non-nano textiles? It is noticeable that due to this uncertainty the use of the term ‘nano’ in advertisements is in decline. How much does one have to worry about possible health risks for workers or consumers?

Those who develop, process or deliver nanomaterials into circulation for the production of technical textiles have to be aware of the public view of nanotechnology, and the direct infl uence this may have on upcoming regu-lations, the consequences of which could limit or modify the way in which nanotechnologies develop and the uses for them. Public funding agencies at state, federal and European Union level, and the vast majority of the com-panies which produce or process nanoparticles, realized long ago that it is necessary to examine the possible dangers associated with nanotechnologi-cal developments. It is important to identify and quantify the real risks, as well as to minimize the risks by appropriate safety measures. It is necessary to apply precautionary principles in order to produce safe products and to maintain the commercial exploitation of the developments.

At the Institute of Textile Technology and Process Engineering (ITV) Denkendorf 5 in Germany a test method has been developed to answer these questions with regards to product safety and quality. Using this tool, air-carried nanoparticles which can potentially be released from fi bre-based materials during processing or usage can be determined and quantifi ed. Information can be obtained regarding particle concentrations, particle size distribution, particle chemistry and particle form. These four important properties need to be defi ned in order to assess the potential risks posed by a process or a material.

The test for determining the potential release of nanoparticles is an important tool which enables an assessment of the health risks posed by nanotechnology-modifi ed textiles to be made. The extent to which synthetic



nanomaterials are released into the environment from innovative textile products is ultimately connected to the quality of the fi nishing. This test can assist in the development of materials, towards nanoparticle emission-free textiles, thus reducing the risk to consumers. Tests demonstrated that rele-vant emissions from nanoparticle-based coatings can be prevented through the correct setup of textile auxiliaries and processing technology.

7.4 Protective textiles

Textiles are required to have certain properties to protect health and life against environmental attacks. The simplest task is to keep the human body warm. But insulation is not the only desirable property for high-tech materi-als, as a number of other environmental infl uences can affect human life and comfort. This kind of functionality can be described as a ‘barrier’ function. The defi nition of a ‘barrier’ function can be given as ‘Textiles with blocking properties against …’. The barrier function is one of the most important requirements for textiles with regard to protection during applications such as sport and other physical activities.

The barrier is divided into the following types of environmental impact:

mechanical: cutting with knife or saw, stab impact (penetrating, piercing, • pricking), bullet resistance thermal: protection against cold or heat • fl ame retardancy: protection against burning/fl ames • chemical: fl uid chemicals, solid and particle form, gases, gases in combi-• nation with heat, radioactive contamination/radiation weather infl uence: water- or wind-proof. •

For each protection property a detailed construction of the textile material, including the joining methods used, has to be considered. It is often nec-essary to add different materials with the support of technologies such as coating, lamination or welding.

Special application textiles – for example, materials used as a barrier against electromagnetic waves – can require the integration of electrically conductive elements into the textile materials. Electromagnetic waves cover a wide range of frequencies, and only a small portion of these fre-quencies are visible as light to the human eye. Most electromagnetic waves can only be detected by a technical appliance. Electromagnetic waves are radiated by a multitude of electrical and electronic devices. The radiated waves can have a disturbing effect on other devices and can also infl uence people’s health and life quality, as well as the environment. With regard to environmental pollution and risk to human beings who are permanently



exposed to strong electromagnetic fi elds (EMF), the term ‘electromagnetic pollution’ is often used.

There is a selection of different materials available for the construction of textiles with shielding properties. In principle, electrically conductive materials, such as stainless steel, silver, nickel, copper and carbon, as well as some newly developed plastics, can be used to create a shielding effect against electromagnetic waves. The types of textiles may also have parallel applications which have to be considered. For example, some of these mate-rials could cause allergic reactions (like nickel) or they could be care and wash resistant. However, some of the derivative effects could be positive – for example, protection against electrostatic charge (professional clothing, technical applications).

The shielding effect is dependent on the textile construction. At higher fre-quencies (GHz-range) fi ne structures show a decrease in the shielding effect. 6 The direction of insertion (warp/weft direction) in the textile fabric, the use of staple fi bres or fi laments and electrical contact are also of importance. Shielding effects over 99% effective are available and are used as inserts for a mobile phone in suit jackets, as pyjamas and curtains, as well as mattress covers.

7.5 Bionics, modelling of textile structures, e-textiles and interactive fabrics

Looking into nature can give inspiration for innovations in textile-based mate-rials. There is great potential for improvement. The word ‘bionics’ comprises the two words ‘biology’ and ‘technical’, and expresses the creative transfer of knowledge from the fascinating world of nature to technical products or sys-tems. The basis for such a development can emanate from biological knowl-edge (biopush) or can be driven by technical necessities (techpull).

One of the most famous bionical textile products, which many millions of people use every day, is Velcro®. In 1948 the Swiss George de Mestral discovered the principle; every time he returned from hunting with his dog, they were both covered in burrs. Under the microscope he detected the retaining mechanism of the burrs and rebuilt it using polyamide fi bres, which were very new at the time.

Innately, textile process technologies offer good potential for bionical developments. Similar to growth processes in nature, which use atoms and molecules as building blocks, in textile engineering large systems are cre-ated from small to tiny fi bres. Compared to the processes often used in tech-nology, such as the production of large semi-fi nished products (e.g., steel plates), the subsequent comminution (e.g., cutting, drilling, rotating and milling) and the following assembly (e.g., machine fi ttings), textile engineer-ing is low energy and easy on materials.



There are number of examples where fi brous or hairy structures are developed by plants and animals (e.g., silk worms, or wool from sheep). Fibrous structures can be found on the top and bottom surface of leaves, on the feet or heads of insects, as the sealing or gliding element between the shells of insects, in the feathers of birds and the fur of animals, as well as in the form of threads in a spider’s web. They are the foundation for many functions and mechanisms, the intricacies of which are only partly understood.

In nature, there are fi bre-reinforced materials in many facets and shapes. Fibre-reinforced composite materials can be found in soft and hard forma-tions in bones, plant stems, leaves and other surfaces; they can consist of both organic and inorganic elements. Fibre-reinforced materials are the foundation of effi cient structures, which can come under high pressure at the same time as still being very light.

An example that has already been transferred to uses in textile engi-neering is self-cleaning surfaces. These can be found on plants, as well as on animals, and show remarkable self-cleansing properties utilizing water drops which pick up dirt, bacteria and fungi along the way. This phenom-enon is known as the lotus effect. In the past couple of years it has been demonstrated that a few key parameters need to be considered for well-functioning technical implementation of the lotus effect. As with many good bionical developments, it is far from simply just a copy of the natural model. Nature generates the self-cleaning properties with two typographical hier-archical levels: micro structures in the area of 10–50 µm and nanostructures in the area of 20–200 nm. For textile materials both hierarchical levels can be developed through single fi bre dimensions and nanotechnological fi nish-ing, which can help to achieve a structure on the nanometre level. In addi-tion, a macro structure supports the self-cleaning through the hierarchical level of the textile surface generation – for example, when weaving using the warp and weft joining method. Good self-cleaning surfaces often suc-ceed with continuous yarns, so-called multifi laments, in combination with the roughness of hydrophobic surfaces.

In contrast to the surface of leaves, most technological surfaces have to allow for the cleaning of oils and fats, so surfaces require more than just wax coatings. It is sometimes necessary to use oleophobic coatings as well. This is achieved with the help of fl uorocarbons. Technical materials are often required to last longer than many materials in nature, which regenerate themselves – such as the leaves of a plant or the fur of animals that can regrow over time. For this reason, the effects of UV also need to be taken into account with regard to technical materials. In technol-ogy, abrasion stability has to meet certain requirements, particularly as the regeneration properties of surfaces seen in natural models has not yet been developed.



In the textile sector, the fi rst products with the lotus effect are now on the market. The ITV Denkendorf has developed a quality seal for self-cleaning textiles on the basis of the lotus effect, which can be applied to products that successfully pass the strict testing ( Fig. 7.3 ). Using this method of coating, the requirement to remove oily and sooty dirt from the surface of the prod-uct can be achieved by rubbing the surface using only water.

One of the fi rst products that were allowed to carry this quality seal were the awnings of a German manufacturer. 7 In contrast to the materials nor-mally used, the awnings were developed with multifi lament yarns, in combi-nation with a weather-proof, suffi ciently abrasion-resistant nanostructured fi nish, rather than with staple-fi bre yarns.

7.5.1 Modelling

The development of textile structures for new areas of application is based on experimental research involving a number of different fi bre shapes and mixtures. With the help of computers and adapted software, the properties of textiles for technical and protection applications can be determined in advance. Specifi c properties should be tested in combination in order to develop the best product possible.

In order to understand the 3D composition of the fi nal product and the infl uence of geometric variations on the dynamic properties, techniques have been developed involving two-dimensional (2D) or 3D image analysis and modelling of textiles, with the simulation of dynamic features such as fl ow resistance, tensile strength and elongation, as well as particle barrier. The tech-nology of microstructure simulation establishes the connection between the microscopic and macroscopic properties of the microscopically heterogeneous

7.3 Sign of approval.



materials. The basis of the technology is the simulation of fl ow in highly com-plex geometries such as foams and fi bre materials at a microscopic and mac-roscopic level. Specifi c mathematical tools help researchers to manage the enormous computing demands and to study the fl ow interactively. The fi rst step of microstructure simulation is to model an existing material and to per-form calculations on this model. The actual process of virtual material design can only begin after successful validation of measurements. 8

In addition to the functional side of a textile, the aesthetic impression can be visualized by rendering. Textile rendering and simulation are soft-ware tools with options dedicated to designers who are specialists in textile rendering and animation of virtual prototypes. It is possible to create very realistic simulations using software tools for stitching and trench effects, kinematics animation, dynamic camera tours and photo-realistic rendering. Using such software for modelling purposes, product development time can be reduced dramatically.

For some textile production processes, such as weaving, specialized soft-ware is already available for the intermediate to advanced designer of woven fabrics. The software can provide realistic fabric rendering, direct design creation and full-fabric fl oat analysis and correction. In addition to design generation, software tools offer a combination of possible weave constructions and process parameters in production.

7.5.2 E-textiles and interactive fabrics

Electronic combined textiles, so-called e-textiles – also known as electronic textiles or smart textiles – are fabrics which enable computing, digital com-ponents and electronics to be embedded in them. This development of wear-able technology is known as intelligent clothing or smart clothing because it allows for the incorporation of built-in technological elements in everyday textiles and clothes. Electronic textiles do not strictly encompass wearable computing because emphasis is placed on the seamless integration between the fabric and the electronic elements, such as cables, microcontrollers, sen-sors and actuators.

The fi eld of e-textiles can be divided into the following main categories of integration:

E-textiles with classical electronic devices such as conducting wires, inte-• grated circuits, light emitting diodes (LEDs) and conventional batteries embedded into garments. This is the most common type of e-textile. E-textiles with modern electronics directly on the textile fi bres. This can • include either passive electronics such as pure wires, conducting textile fi bres or more advanced electronics such as transistors, diodes and solar



cells. The fi eld of embedding advanced electronic components onto tex-tile fi bres is sometimes called fi bretronics. The deepest integration form is the construction of a fi bre itself as a sen-• sor or actuator.

Just as in classical electronics, the construction of electronic capabilities on textile fi bres requires the use of conducting and semiconducting materi-als such as a conductive textile. There are a number of commercial textiles today that include metallic fi bres mixed with textile fi bres to form conduct-ing elements that can be woven or sewn. However, because both metals and classical semiconductors are stiff materials, they are not very suitable for textile applications in which fi bres are subjected to much stretch and bending during use. They are only able fulfi l the requirements in small geo-metrical dimensions.

A new class of electronic materials that is more suitable for e-textiles is organic electronics materials. These materials can be conductors or semi-conductors, and they can be incorporated into inks and plastics. Some of the most advanced functions that have been demonstrated in the lab include:

organic fi bre transistors: • 9,10 the fi rst textile fi bre transistor that is com-pletely compatible with textile manufacturing and that contains no met-als at all organic solar cells on fi bres • 11 organic LEDs on textiles. •

7.4 Baby body, ITV Denkendorf.



A number of these applications could be useful, especially in the area of protecting human life, therefore it is likely that this will be the fi rst area to see e-textiles coming onto the market. E-textiles used in, for example, a shirt or suit that could observe vital parameters such as heart rate, breathing rate or skin temperature could allow for the monitoring and protection of human life in dangerous situations ( Fig. 7.4 ). R&D in this area can be seen, for example, in the design of a suit for babies to detect warning signs for cot death. These applications could further be extended to policemen, fi remen or soldiers. Sensors and communication technology embedded in clothing could reduce risks and help to improve emergency response capabilities by measuring environmental parameters and vital signs, as well as by warning against overstraining and external hazards.

7.6 References 1. Raghavendra, R., Hegde, Dahiya, A. and Kamath, M. G. (2004). Fiber and fi ber con-

sumption in nonwovens, University of Tennessee 2004. 2. Outlast Technologies, Inc. (2011). Available from: www.outlast.com [Accessed 15

February 2012]. 3. Schneider, R. and Frick, S. (2011). Lecture on the ITMA-Nachlese, ITV Denkendorf,

October. 4. Stegmaier, T., Arnim, V. V., Blichmann, J. and Planck, H. (2011). Double-sided coating

of knittings in one step. Lecture on the 6th European Coating Congress ‘Surf on the Waves of Innovations in Coating and Lamination’, Gent, 8–9 September.

5. Institute of Textile Technology and Process Engineering Denkendorf (2012). Textile Innovations for the Industry . Available from: www.itv-denkendorf.de [Accessed 15 February 2012].

6. Stegmaier, T., Schmeer-Lioe, G. and Abele, H. (2008). Shielding effect of textiles against electromagnetic waves – new high-frequency test device. Technische Textilien , E128, March.

7. Schmitz-Werke, Emstetten, Germany, http://de.swela.com/faq/faq.php 8. Stegmaier, T., Finckh, H. and Planck, H. (2004). FEM zur numerischen Simulation

statischer und dynamischer Eigenschaften von Schutzbekleidung. Technische Textilien , August: 146–9.

9. Wiley Online Library (2009). Electronic Textiles: Embedded Electrolyte-Gated Field-Effect Transistors for e-Textiles . John Wiley & Sons, Inc., 22 January.

10. Hamedi, M., Forchheimer, R. and Inganäs, O. (2007). Towards woven logic from organic electronic fi bers. Nature Materials . Nature, 4 April.

11. Lee , M. R., Eckert , R. D., Forberich , K., Dennler , G., Brabec , C. J., and Gaudiana, R. A. (2009). Solar power wires based on organic photovoltaic materials. Science , American Association for the Advancement of Science, 10 April. 324(5924): 232–235.

Documents

The Global Textile and Clothing Industry || Recent advances in textile manufacturing technology