Design of Apparel Fabrics: Role of fibre, yarn and fabric parameters on its functional attributes

Transcription

1 REVIEW Journal of Textile Engineering (2008), Vol.54, No.6, The Textile Machinery Society of Japan Design of Apparel Fabrics: Role of fibre, yarn and fabric parameters on its functional attributes Rabisankar CHATTOPADHYAY Department of Textile Technology, Indian Institute of Technology, Delhi New Delhi , India Received 21 October 2008; accepted for publication 10 November 2008 Abstract The concept of design is not new for textile apparel products. Traditionally the designers have heavily relied on their intuition and experience. However, today s consumer demands products with improved functionalities and quality. With the progress in science, new fibres, technology and finishing techniques traditional designing knowledge has become inadequate to fulfill the need of the consumers. A methodical approach to designing has become necessary. A systematic approach to the design of apparel fabrics and the role of fibre yarn and fabric parameters on functional attributes of the product has been discussed. Key Words: Textile design, Apparel fabrics, Product design, Functional attributes 1. Introduction Textile products are being designed and manufactured for centuries for daily use and ceremonial purposes. Products such as ropes, wicks, and sailing cloth had been the part of our civilization. No formal design methodologies were in practice in those days. The entire design activities were carried out by skilled artisans. The manufacturing techniques had been refined based on practical difficulties and availability of raw material. Artistic temperament, an urge to create innovative products and patronage from kings had led to the creation of new designs and products. The experience-based knowledge had been passed on from generation to generation. However, with the advent of machines and technology things started changing. The manufacturing revolution started in Manchester and people started looking into manufacturing activities more scientifically. However, design remained experienced based for a long time. Textile products can primarily be categorized into three groups: apparel, home textile (including soft furnishing) and technical. In all types of product, both functional and aesthetic design aspects are important. The basic purpose of clothing is to protect the human body from heat, cold, rain, snow, dust, wind and injury. All are essentially functional requirements. The clothing at the same time has to be comfortable to the wearer and pleasant in look. In home textiles such as towels, napkins, curtain, tablecloth, seat covers etc. functional requirements are water absorption, softness, and resistance to sunlight penetration, stain resistance, abrasion resistance. Aesthetic appeal also plays a decisive role in creating a good ambience in the house. Technical products such as filter fabrics, ropes, parachute cloth, geo-textiles, barrier fabrics etc. are primarily designed to satisfy the technical performance criterion. Aesthetic issues are secondary. Where as functional requirements are more objective in nature and measurable, the aesthetic demands are more complex as it depends upon the taste of the people. The taste in turn varies with cultural background, social status and region. The design possibilities for meeting the aesthetic need are therefore enormous. Designing of textile product has mostly been carried out based upon intuitive knowledge, skill and trial and error approach, which is heavily dependent on experience and personal judgment. Hardly any calculation or fundamental design principles are involved in it. Today, however, development of new fibres, finishes, manufacturing techniques and an understanding of relationship between fibre properties and functional performance is opening up new opportunities to produce products to suit the varied requirements. Textiles today are being used in wide variety of fields where traditional Corresponding author: rchat@textile.iitd.ernet.in, Tel: , Fax:

2 Rabisankar CHATTOPADHYAY experienced based knowledge does not exist. Therefore the necessity to have a systematic approach to design textile products is felt today. An understanding of the role of physical and chemical properties of fibres, their dimensional parameters, construction and structures of yarns on functional attributes of the product is important. This would help the designer to choose the right fibre or fibre combinations, yarn and fabric structure for designing apparel or technical product appropriate to the environment and end use. 2. Design Design means formulation of a logical plan of a chain of activities to produce something that satisfies human need. In engineering, it is a process in which scientific principles and tools of engineering - mathematics, computers, and graphics are used to produce a plan which once carried out results in a useful product. A designer is supposed to design a product based on available technology, raw material and human resources. Design is, therefore, always subject to problem - solving constraints such as cost, time etc. In contrast to scientific and mathematical problems, design problems have no unique answer. A good answer may turn out to be unsuitable tomorrow, if there is a growth of knowledge and development in technology. In this context one should also know that product development and product design are not necessarily the same. Product development has a broader base than product design and design is only a part of product development. 3. Types of design Textile products can be classified into two broad categories apparel and non apparel as shown in Fig. 1. The non-apparel can be further classified as home and technical textile. The logic involved in the design process will be different for these products. For apparel products, the design objective is to satisfy predominantly aesthetics attributes (i.e. colour, pattern, appearance, texture etc.) followed by functional aspects (i.e. coolness, warmth, sweat transport, stretchiness, reduction in drag against fluid etc.) In home Fig. 1 Types of textile products. textile both functional (sun light penetration resistance, water absorbency, abrasion resistance etc.) and aesthetic attributes are important. For technical products the main objective is to satisfy the functional attributes such as strength, impact resistance, modulus, resilience etc. Therefore technical products design is based more on scientific logic whereas apparel products need a different logical structure. According to Matsuo [1] textile product design can be classified into the following four categories such as A. Aesthetic design, B. Functional design, C. Exploratory or creative design and D. Incremental design A. Aesthetic design: It deals more with visual appearance and fashion aspects of products that includes motif, colour, pattern preparation etc. An infinite combination of motif and their arrangement, which is aesthetically pleasing, is involved here. B. Functional design: It involves conceptualization, research and development, design, manufacturing, testing, maintenance and marketing. B.1 Partial design approach: It refers to the design of a product to satisfy only one or a set of special functions: for example, strength of fabric or dimensional stability or permeability etc. In other field the usual practice is to design a product part by part and finally combine the parts into one. The major drawback of this is that the interdependent interaction levels between structures and functions cannot be exploited [1]. It is not effective in textiles due to complex dynamic behaviour of structures and functions. B.2 Total design approach: It starts from conceptualization to manufacturing method. It involves a huge amount of information, good organization and complete understanding from raw material to finish stage. The role of raw material and process on the final properties or attributes of the product needs to be understood. C. Exploratory or creative design: It deals with development of new type of product based on their functional requirements. Here the logic structure would be more creative. Examples of this are usually found in technical products. D. Incremental design (or adjust mental procedure): Apparel fabric manufacturer often carries it out. The procedure is to adjust only one parameter or a set of structural or functional parameters for a new design with reference to some existing products. It involves redesigning technique. This design also uses different databases, which tend to accelerate the use of CAD leading to systematic designing procedure. 180

3 Journal of Textile Engineering (2008), Vol.54, No.6, Design process The design process involves a series of systematic steps to be followed prior to actual manufacturing of the product. Dastoor [2] has visualized the manual design procedure as depicted in Fig. 2. A rough procedure is followed for synthesizing a fabric structure through several sub tasks from top - down resolution of the overall design task. Based on the property constraints, the designer chooses the fibre type for interlacing yarns, keeping in mind cost, physical properties etc. The yarn count, its strength is then determined based on the specified fabric tensile strength. Fine adjustment of yarn properties is made by manipulating yarn twist followed by yarn density (ends and picks/inch). The fabric weave is then selected depending on the tearing strength, thickness, fluid permeability etc. According to Hearle [3] in a traditional procedure, the existing design is modified based on expert opinion on fabric sample and/or consumer reaction on fabric or product. The macromechanics relating fabric performance to fabric properties and micro-mechanics involving fabric construction to fibre, yarn and fabric properties which was earlier absent has been the part of modern day design procedure. Matsuo [4] proposed FASE (Fibre Assembly Structural Engineering) for designing textile products. FASE is a kind of configurational, structural, phenomenological knowledge system. FASE has four parts (i) design logic of textile products consisting of aesthetic/functional design effect, basic structure design and basic manufacture design Fig. 2 Manual design procedure [2]. Fig. 3 Designing textile products and its manufacturing methods [4]. (ii) design logic of textile manufacturing method (iii) data base for textile product design and (iv) data base for textile processing The design logic procedure has been depicted in Fig. 3. Design concept is carried out in work step1 for aesthetic and functional design effect. Work step 2 realizes the content of the above aesthetic and functional design. Here the relationship between the structure and aesthetic and functional effects are drawn from the database. The selection of manufacturing method is carried out in the next step 3. The processability of the material has to be looked into and if necessary the basic structure design has to be modified. The detail designing of the process is carried out in sep 4 by referring data base of textile processing which is know how for the industry. According to the author, the design process should actually start from the recognition of need and thereafter follow the logical steps as schematically represented in Fig. 4. These steps are elaborated below: 4. 1 Need for design Fig. 4 Design steps. A need analysis is extremely important for any design. There cannot be a new design without a need. The need for a new design may come from: market pulls, such as fashion, legislation, seasonal factors etc. Reliance on market pull however, can result in low risk products and imitations at the risk of innovations. direct request from a big organistaion such as defence, buying house etc. technology push (new finishing technique, development of new fibres such as bamboo fibre). 181

4 Rabisankar CHATTOPADHYAY situation opportunity - taking advantage of new manufacturing method e.g. compact spinning, nano technology. It may not have a great impact on sale but the market may have a preference for an existing product made from improved quality new type yarn Product definition The product definition must state the product title, purpose of the product, and need for it, potential market and anticipated performance. An example is given in Table 1 for two products Design specification Design specification also known as statement of requirements sets the goal to the designer as to what is expected in the designed product. A list of attributes of apparel products proposed by Matsuo [5] is shown in Fig. 5. The seven attributes originally suggested by Matsuo has been categorized into four viz. visual, tactile, functional and garment making up capability. From the product attributes a list of specifications has been derived. These are dimensional, constructional, aesthetics, performance including service life, cost, safety and disposal (Fig. 6). While some specifications (dimensional, constructional and performance) can be quantified others may be specified in qualitative way or on the basis of an arbitrary scale between 0 and 10. The technical experts of the design team must have a thorough understanding of the quantitative or qualitative role of fibre, yarn and fabric construction, chemical processing and finishing process on the different specification of the product. Fig. 5 Attributes of apparel products [5]. Table 1 Product definition. Fig. 6 Textile product specification. The buyer usually dictates these specifications. At times standards or specifications are also available from standard institution such as ASTM, DIN, BIS, IS etc. The specifications may be partly quantitative and partly qualitative. A typical example of specification is given in Table 2. If the performance specifications are tightened up the client may not be able to afford it. When the client does not know the level of performance required, they may over 182

5 Journal of Textile Engineering (2008), Vol.54, No.6, Table 2 Typical woven and knitted fabric specification for standard apparel [6]. ring, rotor or air jet spun, textured or intermingled etc.) Fabric type (woven, knitted or non-woven, pile, possible interlacement pattern, layered structure or not etc.) Finish type (shrink proof, anti crease, permanent press, anti static, rot proof, raised, etc.) Product outline i.e. sketch (in case of new product where buyer specification does not exists), various components, assemblies etc Detail design specify the performance requirement. Usually some dimensional and constructional parameters of the design are also specified along with technical performance. It is important that certain design specification should be specified with a tolerance. When material and other constructional parameters are specified, it becomes really increasingly difficult for the designer to meet the performance and other specifications as the choice of playing with material and constructional parameters becomes limited. It is desirable to write the performance parameters in order of increasing or decreasing importance. Because in some cases, the designer may not be able to satisfy all the specifications fully and a compromise may be necessary. At times the specification is developed based on customer feed back. The users may not be able to specify his requirement in technical terms or may not be able to quantify it. In such situation it becomes necessary to translate the customer s requirement in to design speciation in a qualitative or quantitative way. In the detail design, one has to work out the details of fabric yarn and fibre parameters. This is toughest part of the design process for technical products as one has to match the performance and property specifications. A through understanding of the role of fibre, yarn and fabric parameters on the properties and performance behaviour of the product should be known. Established mathematical relationships (Tables 3 and 4) between different measurable characteristics of the product and independent parameters related to the raw material, yarn and fabric and the processes should be used as far as possible. These relationships could be used to choose some of the basic parameters of fibers, Table 3 Relationship between fibre and yarn property [7] Conceptual design Keeping in mind the product definition and its intended use, one can identify the following broad parameters at the conceptual design phase: Fibre/fibres to be used and its form (natural, synthetic, blended, form i.e. staple or filament etc.) Yarn type (filament, spun, carded or combed, 183

6 Rabisankar CHATTOPADHYAY Table 4 Relationship between yarn and fabric property. fabric it could be, yarn count, its properties amount of size required, warping speed, EPI, PPI, weave type, type of loom and its speed etc. The process ability of the fibers or yarns, their availability, quality, machine conditions etc. may at times lead to adjust some raw material or manufacturing process parameters. For example, one may not get the exact combination of properties required in the fibre, which fulfils the performance aspect of the design specification. In case of cotton, length and fineness of a fibre may match but not the strength or maturity. Similarly for yarn strength, and extension may match but not the modulus. The required machine may not be available to process the fibres or the quality of the yarn may not suit the attainable loom speed potential. Therefore compromise may be required at different levels due to various constraints. One has to choose the suitable process parameters to process the fibres or yarns in a most optimum way to arrive at the desired yarn or fabric quality attributes Evaluation yarns and fabrics to meet the specification of the fabric. The selection of fibre, yarn and fabric parameters is an iterative process and will progress step by step. There may be multiple options available and one has to look for the right combination of parameters through a carefully designed process of elimination. However, in the absence of such definite relationship, a qualitative understanding about the interaction between different parameters could be very handy to initiate the design process. Fabric properties have been shown to change significantly after finishing [10]. One has to look for design data from various research papers, reports or textbooks. Each industry can have their own database. Unfortunately such design databases are not available in a consolidated form at one place. In case, an exact relation ship between structure properties is not available one can make use of a qualitative relationship developed by many to start the design process. One must remember at this stage that there could be various design options for meeting the criterion fully or partially. One has to pick up the best options based on cost-performance characteristics. The design process may go through a series of iterations after the evaluation stage to fine tune the manufacturing process so as to meet the design specification Sample manufacture Design parameters need to be translated into manufacturing parameters, which the production people will need for manufacturing the product. For manufacturing a The sample produced should be evaluated immediately for its properties and performance and compared with the design specification. The ranking of the specifications, which are not met, are to be noted down and the degree of departure from the desired values are to be calculated. Based on this, corrective actions have to be initiated either in the detail design, raw material or processing stage. A thorough understanding of the technology and fibre, yarn and fabric structure-property relationship will be of immense use to arrive at the right solution. At times, there may be conflicting demand on a particular parameter or action. As an example, speed of a particular machine element may need to be increased from one consideration and decreased from the other. In such cases one needs to optimize. Based on the modified process or design parameter new samples are to be manufactured and tested again. This process should continue few times till we are satisfied with the product and go for mass production. For new products first a conceptual design is made on paper and after some iteration when the idea crystallizes detail design is worked out starting from raw material, specification of intermediate products to process details. Based upon the detail design a sample is produced. The sample is evaluated to find out how far it conforms to the desired specifications. Any significant departure on any attribute is analysed in details to identify the reasons, and suitable correction is initiated in the process or in the design itself till the sample satisfies the specification. Once satisfied mass scale manufacturing is undertaken. 184

7 Journal of Textile Engineering (2008), Vol.54, No.6, Role of fibre, yarn and fabric parameters on different attributes 5. 1 Aesthetic attribute Aesthetic attributes are a function of surface profile, texture, pattern, colour and its combination, lusture, fancy or mélange effect, handle and drape of fabric. Colour combination is governed by the aesthetic imagination of the designer. High degree of fibre orientation and low fibre protrusion from yarn surface (combed, compact yarns, singed yarn) gives a smooth and lustrous appearance to the fabric. Whereas disoriented fibres on yarn surface and high unevenness will lead to rough appearance (carded and rotor yarn). When hairy surface is desired, fibres from fabric surface are raised mechanically. Filament yarn gives too smooth an appearance and to counter it, textured filament yarns are used. Yarns made from finer fibres will be lustrous having large surface area and also make the fabric drape well being more flexible. Micro-denier fibres are known to give fluid like drape. Round and trilobal fibres are lustrous than other non-circular cross section. Coarser yarns give prominent surface profile due its high bending rigidity. High twisted yarns maintain their identity in the fabric due its compact structure and higher bending rigidity and therefore create a clear distinctive look. A soft twisted yarn on the contrary will give a smudged look because of flattening of component yarns. The fabric surface will appear more planer after compression. High ends and picks or wales and courses per inch give a compact appearance whereas low end and pick or wales and course density give an open look. The texture of the fabric gets changed depending upon the way the ends and picks are interlaced. Plain, twill (its derivatives), satin, sateen weaves has distinctive appearance. Similarly in knitted structure, plain, rib, purl interlock give a distinctive look. Fibre, yarn and fabric parameters that affect Table 5 Fibre, yarn and fabric parameters affecting aesthetics appeal. fabric aesthetic attributes are mentioned in Table 5. The coercive couple M 0 and F 0 in fabric and shear has been shown to affect drape. The elastic resistance to bending and shear has been quantified by the slope of the straight line curve denoted by G in bending and B in shear. The ratio of M 0 : B should be 0.3 cm 1 for soft handle and between cm 1 for a crisp handle and above 0.6 cm 1 for harsh handle [11]. The relation between M 0 and F 0 with yarn and fabric parameters has been shown to be M 0 = μ 1 VdL / 2l F 0 = 3 μ 2 Vd c / 16 (p 2 l 1 + p 1 l 2 ) (1) where, μ 1 : coefficient of friction between fibers, μ 2 : coefficient of friction between yarns, V: total force acting between yarns at any cross section, d: yarn diameter, d c : diameter of contact area between yarns, l: length of yarn in unit repeat of woven structure, p: distance between intersection L: distance between twist reversals (i.e. length per unit twist) 5. 2 Tactile attribute The tactile effect is the sensation a person receives when he touches, feels or squeezes a fabric. The tactile effect therefore depends upon compression, friction, shear and bending properties of the fabric. It is also defined by hand or handle of a fabric. These properties in turn depend upon constituent fibre, yarn and fabric parameters (Table 6). A fabric made from yarns having finer fibres and yarns with low packing coefficient (i.e. spun with low twist, low spinning tension, fibres with irregular fibre cross section, textured or bulked yarn) will be easily compressible. On the contrary fabrics made from high twisted yarns will make it difficult to compress. Compressibility will also depend upon crimp level of yarn in fabric, ends and picks density and weave type. Fabrics with less crimp or interlacing will be harder to compress. A jammed fabric will be difficult to Table 6 Fibre, yarn and fabric parameters affecting tactile property. 185

8 Rabisankar CHATTOPADHYAY compress. Frictional properties mainly depend upon fabric surface profile (type of weave) and yarn surface characteristics. Filament yarns are usually smoother than their spun counterparts. Within filaments monofilaments are smoothest followed by twisted multifilament and textured yarns. Textured or bulked yarns have rough surface [12]. Fabrics made from finer soft twisted yarns will be smoother than those made from coarse hard twisted yarns. Fabrics having long floats i.e. less interlacement (sateen) will be smoother than plain (more interlacement). Fine gauge knitted fabrics made from monofilament or filament yarn also will have smooth surface. Coarse, bulked, folded yarns result in textured surface. Yarns having haphazard arrangement of fibres on its surface(rotor, carded yarns) will increase friction than the one having ordered arrangement of fibres on its surface or less hairy (combed yarn, compact yarn, singed yarns). Chemical processing can substantially change fabric surface friction. Shear modulus depends upon weave type, thread density and yarn bending rigidity which in turn depends upon yarn count, twist and fibre parameters (fineness, cross sectional shape, surface friction). Bending rigidity of fabrics depends upon bending rigidity of constituent yarns and level of interlacements. Both shear modulus and bending rigidity increases with yarn linear density, twist, thread density (EPI and PPI) and number of interlacing point (weave type) Functional attributes Easy care/performance properties Table 7 shows the important fibre, yarn and fabric parameters on performance property of the fabric. Tensile properties: The tensile strength of fabric is governed by strength of constituent yarns and fabric structure. If the fabric structure does not distribute the load equally between yarns, but allows stress to concentrate Table 7 Fibre, yarn and fabric parameters affecting performance properties. locally on certain yarns, the fabric strength will reduce due to asymmetric distribution of stress. Weaker yarns also result in weaker fabrics. Coarser yarn and higher yarn twist will increase strength up to a certain extent and beyond that it will fall. Similarly with increase in end density an optimum can be observed. When the thread density becomes too high, it prevents the yarn from straightening out when load is applied and as a result strength cannot be realized fully. Low initial modulus is preferred form comfort point of view. Crimps in warp and weft yarns results in low initial modulus of fabrics. Incorporating extendable yarns can reduce the initial modulus. In knitted structure plain, interlock and rib structure lead to moderate extensibility in length direction (20%), whereas purl leads to very high extensibility. In width wise direction, interlock structure leads to moderate extensibility, plain and purl high (30-50 %) and rib give very high (50-100%). Tear strength and bursting strength: Tear occurs when the stress on fabric results in concentration of stress at a point leading individual yarns to fail in a staggered manner. Frictional resistance at the yarn interlacement points and yarn extensibility can increase resistance to tearing. Tearing strength increases with the strength of the individual yarns, their extensibility and the ease with which the yarns can bunch together in the fabric matrix while tear propagates. In plain weave construction, too many interlacements restrict yarn movement and hence result in low tearing strength. Twill or satin weave on the contrary facilitates yarn movement because of less number of interlacements and allows yarns to come together and thus arrest tearing force together. Rip - stop yarns of greater strength increases tear resistance. Crease/wrinkle resistance: It primarily depends on the type of fibre. Polyester and nylon have better crease resistance in comparison to cotton. The creasing tendency of the fabric increases as the fibre becomes finer. This is all due to lower bending stiffness and strength of finer fibres. Abrasion resistance: Fabric abrasion resistance and resiliency also reduces with fine fibres. Coarser and high twist yarns improve abrasion resistance. High twist restricts the wear off of fibres from fabric surface. Tighter fabric construction also improves abrasion. Pill resistance: Pills are micro balls of entangled fibres attached to the fabric surface. Loose fibres on the fabric surface or ease of plucking of fibres from yarns facilitate pilling. Pilling is a function of fibre strength and yarn structure. Pilling tendency also increases as the fibres become finer due its low bending rigidity, which encourages 186

9 Journal of Textile Engineering (2008), Vol.54, No.6, fibre ends to get entangled easily. Strong fibres also lead to pill formation, which does not shed off, easily from fabric surface. Low yarn twists either in staple or filament yarn encourages pill formation. Table 9 Fibre, yarn and fabric parameters for wearing comfort Microclimate control Table 8 shows the important fibre, yarn and fabric parameters on microclimate control of fabric. Warmness/coolness: Fibers of low density are used where light weight and bulky material is used [13]. Yarns made from finer fibres will be compact and will hold less air in between the fibre interstices. As a result the fabric is expected to be less warm. Yarns made from noncircular fibers will be voluminous and as result will make the fabric warmer. Air and water vapour permeability: It mainly depends upon the pores within fabric and their distribution. Woven fabric has well defined pores. It can be changed by changing thread density, yarn count and yarn surface characteristics. Tight construction, bulk or textured yarns or soft twisted yarns will reduce pore size. In Knitted fabrics the pores are at an angle with respect to the fabric plane i.e. the length of pores are more. Non woven fabrics have a wide range of pores whose upper and lower limit depends upon the method of production and fabric thickness. Thinner fabrics with larger pores lead to increase in permeability. Reduction in sweaty humidity and stickiness: Finer fibres produce finer capillaries, which would make the wicking faster due to higher capillary pressure. Hence sweat removal form skin is expected to be faster with finer fibres. However too fine fibres would make the capillaries so fine that wicking will be slower due to higher resistance to the flow of liquid through the capillaries. While hygroscopic fibres absorb and retain the sweat or water, synthetic fibres do not retain but transmit the sweat or water faster. Water proofing: A compact fabric made from micro fibre can make the fabric waterproof, as water droplets can t penetrate so easily through it. Pore size is also important in water repellency. A tight structure leading to small pores does not allow water to penetrate easily. Table 8 Fibre, yarn and fabric parameters for microclimate control Wearing comfort The relevant fibre yarn and fabric parameters affecting wearing comfort are shown in Table 9. Stretchiness: Stretchiness primarily depends upon fibre extensibility and its recovery behaviour. Products made from nylon, polyester and wool are well known to be stretchy. Knitted structures are more stretchable than woven structures. Filament yarns are also stretchable than equivalent spun yarns. Yarns having elastomeric fibers in the core will be highly stretchable. Lightness: To make a product light once can use low density fibre or finer yarns keeping cover factor same or manipulate ends or picks per inch. Low twist yarns can also reduce fabric GSM as it gives an opportunity to reduce ends and picks per densities at the same fabric cover factor. The other way could be to play with fibre type. Low density fibres make the fabric light without affecting cover factor if replacement is permissible. Otherwise one can check the possibility of mixing low density fibre with normal fibre. Use of bulk yarn can also be an alternative. 6. Selection of fibre The selection of raw material is based upon the suitability of the basic property of the fibre for its intended end use. A property matrix (Table 10) relating fibres to the performance properties of apparel based on a qualitative scale could be of immense use to the designer to choose the right fibre for a given end use [14]. Polyester fibre has the highest rating in the highly desirable category followed by nylon, acrylic, cotton and wool. Polyester fibre has excellent wash and wear performance, wrinkle resistance and has very good abrasion resistance and strength and moderate pill resistance. Hence polyester should be suitable for apparel and home furnishing. The high rank of acrylic in some what desired and unimportant categories such as good resistance 187

10 Rabisankar CHATTOPADHYAY Table 10 Qualitative comparison of performance properties of textile fibres for apparel [7]. to sun light makes it suitable for curtain. Excellent abrasion resistance and strength of nylon makes it suitable for military uniform and work pants. These properties combined with good dye fastness to sunlight and adequate resilience makes it suitable for home furnishing including carpet and furniture cover. Acrylic fibre has intermediate properties in highly desirable category. It is poorer than polyester and nylon but superior than wool and cellulose. Acrylic is deficient to polyester in strength abrasion resistance and wash and wear and wrinkling resistance. The later two properties can be compensated by loose structure in knitted construction compared to dense compact woven fabric construction Acrylic due its greater bulk, resilience and natural-like aesthetics (compared to polyester) sweater, socks, fleece wear. For warmth one has to choose wool, acrylic, nylon silk etc. Cost will always be a consideration for both types of products. All the fibers have their own merits and demerits and this obviously leaves scope to the designer to offer a variety of products to the consumer. It is the consumer who decides where his/her priorities are. surface character and physical characteristics of the yarn but also some important mechanical properties such as strength, elongation, modulus, snag resistance etc. The role of twist in qualitative terms is shown below [15] : Low twist softer and bulkier look, less strength Unbalanced twist nodular effect in yarn and fabric Over twisting novelty and rough surface effect, less strength Twist initially increases strength of yarn followed by decrease. It also increases bending stiffness of yarns. Yarn count range being used for some typical fabric is given in Table 11. It is possible that yarn structural features can get masked and modified or magnified by finishing treatments. In brushed fabric, textural features of constituent yarns tend to get masked where as in clear finished fabrics, textural features of yarns tends to get emphasized. A qualitative relationship between yarn, its structural features and general Table 11 Yarn counts for various types of fabric. Table 12 Yarn type, structural features and expected character. 7. Selection of yarn The yarn selection is closely associated with fabric attributes desired. The parameters to be looked into yarn before selection are: Yarn count, count CV% and twist Type of yarn: carded, combed, rotor spun, air jet spun, compact, textured, bulked etc. Uniformity Strength and elongation Imperfections, hairiness etc. Twist plays important role as it decides not only the 188

11 Journal of Textile Engineering (2008), Vol.54, No.6, characteristics is mentioned in Table 12. Such table can help in selecting suitable yarn type to match the desired property or character expected in the fabric. Table 13 Various weaves and general character of fabric. 8. Selection/designing of fabric Fabric designing is based on three criterions: 1. General physical properties to be satisfied which mainly depends upon it s application 2. Choice of fibre type which mainly depends upon the requirement of the final product and 3. Fabric structure (knitted, woven or non-woven) required meeting the requirements. Knit fabrics because of their loose construction and the ability of its loop to move and adjust itself in the fabric matrix have better wash-wear performance and wrinkle resistance compared to woven structures. Characteristics of woven, non-woven and knitted fabrics are given below: Woven fabric: Yarns are orthogonal to each other, strong, high initial modulus, tensile modulus more than shear modulus, less stretchable in both warp and weft direction, less deformable. Non woven: Fibers are randomly placed one over the other, closely inter-locked, stable, porous. Knitted fabric: Yarns looped around each other, more isotropic than woven fabric, low modulus, weak, stretchable, loops can easily deform to take any complex shape, does not need ironing, soft handle, compressible. Warp knitted fabrics are multi-layer and generally fall between woven and weft knitted fabrics, firm, stable, smooth moderate extensibility. Woven and knitted fabrics are usually used in apparels because of their easy formability capabilities i.e. they can easily shear and bend to match the complex body contour. Non-woven fabrics lack these important characteristics because of being rigid in both bending and shear deformation. The stretch ability characteristics of weft knitted fabrics make them extremely suitable for skin contact and body hugging products (brief, vests, lingerie etc.). Between various weave types, plain weave is mostly used being easy to manufacture. However, one can choose a particular weave to suit any specific requirement. As an example for smooth and lustrous surface satin weave is preferred. Influence of various weaves on general character of the fabric is mentioned in Table 13 as a guideline for the designer. 9. Incremental improvement in functional attribute The various functional attributes have already been mentioned. A designer must have a good qualitative understanding about the mechanism or theory involved about the attribute to be improved. Various technological options related to raw material, process, and assembly structure or finishing available to improve an already existing design should be known. An option, based on cost minimization, ease of implementation, availability of the technology can then be exercised. If the result is not up to Table 14 Reasons and technological options to counter peeling. Reasons 1. Presence of projected fibre ends from Fabric surface 2. Ease of entanglement between projected fibre ends 3. Ease of plucking of fibre ends from yarn surface 4. Higher bending and torsional rigidity of fibres 5. High tenacity and breaking energy of fibres Technological options to counter peeling 1. Compact yarn, singing 2. Low friction surface finish 3. Long fibres, moderately twisted yarns, tighter fabric construction 4. Fibres with lower bending and torsional rigidity 5. Low tenacity and breaking energy of fibres 189

12 Rabisankar CHATTOPADHYAY the expectation, the designer has to analyze the entire process and take suitable corrective actions. In the absence of a quantitative relationship between functional design objective and the fibre properties, assembly structure and finishing process one has to rely upon the intuition and judgmental capability of the designer or the expert. Researcher is trying to develop such relationship, which can be used by the designer. Let us take as an example, the improvement of peeling resistance of a fabric. Peeling Mechanism It results from the strong entanglement of projecting hairs/fibres on fabric surface, which refuses to shed off easily. Various reasons and corresponding technological options are mentioned in Table 14. One may not be able to exercise all the options due to possible negative effect on some important characteristics of the product, processing difficulties or cost considerations. As an example, if the product is sweater we cannot use a high or moderately twisted yarn since it will reduce the bulk and therefore thermal resistance. If the product is made from blended fibres, the length of the synthetic component cannot be increased too much as it will affect process-ability on spinning machines. Keeping in mind such constraints one has to choose the most appropriate one. Matsuo [5] has suggested similar method for improving warmness and reduction of sweaty stickiness. 10. Conclusion The design of textile products needs a methodical approach. It is especially so for products for which traditional knowledge does not exists. The development of technology, new fibers, finishes and production methods has made it more relevant today. The design can no longer be left to trial and error approach but should be carried out in a more objective way to reach the goal. Comprehensive knowledge starting from fibre to finishes and manufacturing techniques will be extremely handy for the designer. A designer needs not to be master in all aspects of the technology as he/she can always seek expert s help whenever required in a narrow domain of technology. Analysis of consumer need, translating it into some qualitative and quantitative specification and then selecting an optimized design option from various suggested ones is the key to the successful design. References [1] Matsuo T (1997) Textile Progress, 27, 2 4 [2] Dastoor PH, Ghosh TK, Batra SK, Hersh SP (1994) J Text Inst, 85, [3] Hearle JWS (1994) Textile Horizon, 14, [4] Matsuo T (1993) J Text Mach Soc Japan (predecessor journal of J Text Eng), 39, [5] Matsuo T (2004) Textiles Magazine, 4, [6] Mehta Pradip V, Bhardwaj Satish K (1998) Managing quality in apparel industry, pp , New Age International Publishers, New Delhi [7] Hearle JWS, Grossberg P, Backer S (1969) Structural mechanics of fibers, yarns and fabrics, Vol. 1, pp65 99, pp , New York, Wiley Interscience [8] Hu J (2004) Structure and mechanics of woven fabrics, p98, The Textile Institute, Woodhead Publishing limited, Cambridge, England [9] Kilbey WF (1963) J Text Inst, 54, T9 T27 [10] Postle R (1983) Proc of 2 nd Australia - Japan bilateral science and technology symposium on objective evaluation of apparel fabrics, Edited by R. Postle, S. Kawabata, M. Niwa, pp1 14, The Textile Machinery Society of Japan [11] Grossberg P (1977) Surface characteristics of fibers and textiles, Part II, Edited by M.J. Scheck, pp , Marcell & Dekkar [12] Lloyd DW (1994) Synthetic fibre materials, Edited by H. Broody, pp32 51, Longman Scientific & Technical [13] Holme I (1994) Synthetic fibre materials, Edited by H. Broody, pp94 131, Longman Scientific & Technical [14] Lulay A (1995) Acrylic fiber technology and applications, Edited by James C. Mason, pp , Marcel Dekker Inc, New York [15] Goswami BC, Martindale JG, Scardino FL (1977) Textile Yarns: Technology, Structure and Applications, pp , John Wiley & Sons, New York 190