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  • 1. Indian Journal of Fibre & Textile ResearchVol. 35, June 2010, pp. 139-144 Effect of different processing stages on mechanical and surface properties of cotton knitted fabrics H Hasania Textile Engineering Department, Isfahan University of Technology, Isfahan, Iran Received 14 July 2009; revised received and accepted 4 September 2009 The influence of different processing stages on the low stress mechanical and surface properties of cotton knitted fabrics has been studied. The KES-FB system has been used for the measurements of low stress tensile, shear, bending, compression and surface properties. The results show remarkable changes in mechanical and surface properties of knitted fabrics after processing stages, such as bleaching, dyeing and softening. Keywords: Cotton, Knitted fabric, Mechanical properties, Surface properties1 Introduction knitting mill fabric to the final finished state. In case The tailoring quality of fabrics and the design of of knitted fabrics, the effect of these stages isgarments as well as automated handling are greatly significant. There are very few data available on theinfluenced by the fabric physical and low stress knitted fabrics as well as on the effect of a finishingmechanical properties, such as bending, tensile, shear, and processing procedure on the quality of knits3,4. Incompression and surface properties. Objective the present study, the effect of different processingmeasurement of these characteristics leads to making conditions (bleaching, dyeing and softening) on therational decisions in selecting fabrics in order to fabric mechanical characteristics such as tensile,minimize the tailoring problems and improve the bending, shearing, compression, and surfacequality of finished garment. The KES-FB (Kawabata properties has been studied.Evaluation System for Fabrics) system, primarilydeveloped for an objective evaluation of fabric 2 Materials and Methodshandle, has now been widely accepted for the Fourteen knitted fabrics with similar tightnessinvestigation of low stress mechanical and surface factor were produced on a single jersey circularproperties1. knitting machine (Mayer & Cie, E28, 30”). Cotton In textiles, raw material, yarn structure, fabric yarns of 50 Nm and 750 tpm were also spun on astructure, finishing and processing stages affect the conventional ring spinning machine. The effect offabric hand and its overall performance. During following processing stages on the mechanical andfinishing, internal stresses stored during spinning, surface properties of the cotton knitted fabrics waswarping and knitting are removed and fabrics attain investigated:an almost fully relaxed state. The amount of changes Bleaching process — Knitted fabrics wereoccurred in thickness, loop density, tightness factor bleached in two different conditions, namelyand mechanical parameters of fabric during finishing normal and intensive bleaching.and processing makes the subject complicated. By Dyeing process — Knitted fabrics were dyed afterusing various finishing and processing treatments, bleaching or washing processes using a reactivedifferent kinds of end products in a sense of aesthetic dyestuff.and utility properties can be produced from the same Softening — Knitted fabrics were softened afterunfinished textile fabric2. In order to improve the bleaching and dyeing processes using differentfabric hand and dimensional stability, various softeners; for a specified softener, two differentfinishing and processing stages are undertaken from softener percentages were used.____________ The conditions of processing stages used in thisa E-mail: h_hasani@cc.iut.ac.ir study are shown in Table 1 and details of the treated
  • 2. 140 INDIAN J. FIBRE TEXT. RES., JUNE 2010fabrics are given in Table 2. The basic mechanical anisotropy is a consideration in knitted fabrics, elevenproperties, such as tensile, bending, shearing, of the tests (tensile, bending, shear and surfacecompression, and surface properties of the fabric properties) were measured in both course andsamples were measured by KES-FB system5 using the wale directions. Average values of the wale andset-up of knits standard sensitivity6. For each course measurements were taken for furtherprocessing stage, each measurement was made twice analysis. Specimen preparation, pre-conditioning, andon three separate samples cut from the center of the testing involved standard atmospheric conditionsknitted fabrics, and five resulting values were of 20°C±2°C temperature and 65%±2% relativeaveraged. Standard size samples of 200 mm × 200 mm humidity.were tested in wale and course directions. Because 3 Results and Discussion 3.1 Effect of Processing Stages on Bending Properties Table 1―Processing stages of knitted fabrics Changes in bending characteristics of the cottonProcessing stage Chemical used Temp. Time knitted fabrics through the processing stages are °C min shown in Fig. 1. Bending rigidity reflects theNormal bleaching H2O2 (1.5%) 80 30 flexibility of the fabric and higher bending rigidity (B)Intensive bleaching H2O2 (1.5%) 98 60 values indicate greater resistance to bending motions.Dyeing Bezative orange 60 75 Bending hysteresis indicates the ability of the fabric S-RL 150a to recover after being bent. The smaller the bendingSoftening hysteresis (2 HB) value, the better is the bending(i) cationic softener Tubingal KREb 40 20 recovery ability of the fabric1. For the cotton knitted(ii) non-ionic softener Tubingal 220b 40 20 fabric, there is a large increase in fabric bending(iii) micro-emulsion Tubingal MSQb 30-40 20 softener rigidity values after bleaching and dyeing asa compared to raw knitted fabric. This is explained in Reactive dye.b terms of the relaxation shrinkage in both course and Softener produced by CHT company, Germany. wale directions. The fabric shrinkage gives a smaller space for bending. The results reveal that the dyed Table 2—Details of treated fabrics fabric represents the highest values of bending rigidityCode Stitch Processing stage Softener and bending hysteresis as compared to other fabrics. density/cm² amount, % This can be attributed to higher relaxation shrinkage and higher knit density after dyeing in comparisonA01 247 Knitting mill fabric - with other processing stages. In case of intensiveA02 300 Intensive bleaching - bleaching, the bending properties increase higher thanA03 320 Intensive bleaching + 2 softening (Tubingal 220) in the normal bleaching, because this stage wasA04 320 Intensive bleaching + 2 performed at higher temperature and time. Therefore, softening (Tubingal MSQ) an intensive bleached fabric is stiffer than a normalA05 320 Intensive bleaching + 4 bleached fabric. softening (Tubingal MSQ) The softeners can reduce inner friction betweenA06 320 Intensive bleaching + 2 fibres and yarns in the fabric structure and in this way, softening (Tubingal KRE) the bending properties are greatly reduced. NaturallyA07 300 Normal bleaching -A08 310 Normal bleaching + 2 in this case, the type of softener plays an important softening (Tubingal 220) role. The reduction in bending rigidity and bendingA09 310 Normal bleaching + 2 hysteresis values for softening with Tubingal KRE is softening (Tubingal MSQ) larger than that for softening with Tubingal MSQ andA10 310 Normal bleaching + 4 Tubingal 220. Furthermore, the results reveal that softening (Tubingal MSQ) regardless the fabric bleaching method, the softenerA11 310 Normal bleaching + 2 concentration also affects remarkably the bending softening (Tubingal KRE)A12 315 Washing + dyeing - properties.A13 315 Normal bleaching + dyeing - 3.2 Effect of Processing Stages on Tensile PropertiesA14 315 Normal bleaching + dyeing 2 Tensile properties of cotton knitted fabrics obtained + softening (Tubingal KRE) from KES-FB are shown in Fig. 2, interpreted in term
  • 3. HASANI: MECHANICAL & SURFACE PROPERTIES OF COTTON KNITTED FABRICS 141 Fig. 1―Effect of different processing stages on bending properties of knitted fabrics Fig. 2―Effect of different processing stages on tensile properties of knitted fabricsof tensile linearity (LT), tensile energy (WT), and fabrics < intensive-bleached fabrics < normal-tensile resilience (RT). Tensile linearity reflects the bleached fabrics. The tensile linearity values of theelasticity of the fabric; the higher the LT value the bleached and dyed fabric are found to be higher thanstiffer is the material. Tensile energy is the work done that of the knitting mill fabric. This is associated withduring extending the fabric, and a greater tensile the increase in fabric stiffness.energy value responds to a higher tensile strength of The results show a large increase in tensile energythe fabric. Tensile resilience reflects the recovery values and a reduction in tensile linearity values afterability of a fabric after being extended1. softening as compared to the bleached and dyed The results reveal that the tensile energy and tensile knitted fabrics. It can be explained due to theresilience values of knitted fabrics tend to decrease reduction in friction between the stitches. This meansafter both normal and intensive bleaching and also that the fabrics become more stretchable and moredyeing processes as compared to knitting mill fabric. energy is needed to attain the same tensile load. TheThis means that the fabrics become stiffer as well as increasing order of tensile energy values is: Tubingalless stretchable. It is attributed to higher shrinkage of 220 < Tubingal MSQ < Tubingal KRE. An increase inknitted fabrics after bleaching and dyeing. The softener concentration increases the tensile energyincreasing order of the tensile energy values is: dyed and tensile resilience values. The increase in
  • 4. 142 INDIAN J. FIBRE TEXT. RES., JUNE 2010extensibility which occurs during softening of the 3.4 Effect of Processing Stages on Thickness and Weightknitted fabrics could improve the tailorability, Fabric thickness (T) and weight (W) are shown inespecially from the viewpoint of shaping and sewing. Fig. 4. It is obsereved that the fabric thickness changes slightly after the softening treatment. All3.3 Effect of Processing Parameters on Shear Properties dyed and bleached fabrics undergo minimum decrease Changes in shear characteristics of the cotton in thickness, which could be due to further tighteningknitted fabrics through the processing stages are of the structure as a result of increased adhesionshown in Fig. 3. The shear stiffness and hysteresis are between fabric structural elements. The fabric weightaffected by the slipperiness at loop intersections, the is affected by the shrinkage during the processingcoefficient of friction, the contact length and the knit stages. The more the number of processing stages, thedensity. The shrinkage of the knitted fabrics during higher is the degree of shrinkage. This results inbleaching and dyeing decreases the slippage between higher knit density and consequently higher weight ofyarns or fibres and increases the knit density as well the fabric. The softening process makes the fabricsas the yarn contact in the loop intersections. more voluminous and thicker. Naturally, the increaseTherefore, it is expected that the bleached and dyed in fabric volume through the softening depends on thefabrics lead to a higher shear stiffness and hysteresis type and percentage of the softener.as compared to the raw fabric. The shear stiffness of 3.5 Effect of Processing Stages on Compression Propertiessamples decreases in the order: dyed knitted fabrics > The compressional properties of cotton fabric afterintensive-bleached fabric > normal-bleached fabric. various processing stages are presented in Fig. 5,This is attributed to different stitch densities which considering compression energy (WC), compressionare achieved after processing. resilience (RC) and compression linearity (LC). The The effect of softening is directly related to the compression energy WC reflects the fluffy feeling oflevel of inter-yarn pressure and frictional resistance to the fabric; the fabric will appear fluffier when theshear formation1. The softeners facilitate the slippage value of compression energy is increased7.of yarns in the fabric structure and consequently the Compression resilience is the percentage of the extentshear stiffness (G), shear hysteresis at 0.5° (2 HG) and of recovery or the regain in fabric thickness when theshear hysteresis at 5° (2 HG5) values decrease. The applied force is removed. The greater the RC value,decreasing order of shear properties values for the the better is the retention ability of the fullness of theused softeners is: Tubingal MSQ > Tubingal 220 > fabric after compression8.Tubingal KRE. Naturally, the percentage of the The results reveal that the greatest decrease in WCsoftener affects the shear properties. An increase in and LC occurs during bleaching and dyeing. Thisthe softener concentration decreases the shear means that the knitted fabrics will be less fluffier afterproperties of knitted fabrics. bleaching and dyeing as compared to a knitting mill Fig. 3―Effect of different processing stages on shear properties of knitted fabrics
  • 5. HASANI: MECHANICAL & SURFACE PROPERTIES OF COTTON KNITTED FABRICS 143 Fig. 4―Effect of different processing stages on weight and thickness of knitted fabrics Fig. 5―Effect of different processing stages on compressional properties of knitted fabricsfabric. In contrast, the values of WC and LC increase coefficient of steel/fabric friction (MIU), meanafter softening. This could be due to the slight decrease deviation of MIU (MMD) and geometric roughnessin fabric thickness after dyeing and bleaching and the (SMD). The results reveal that the greatest increase inincrease in fabric volume and thickness after softening. MIU, MMD and SMD occurs during bleaching andKnitted fabrics which were bleached by normal dyeing. This could be explained by the increase inbleaching method and softened represent higher values disturbance in surface fibres as well as fabric surfaceof the compressional characteristics than the knitted irregularities after bleaching and dyeing processes. Infabrics which were bleached by intensive bleaching contrast, the values of MIU, MMD and SMD increasemethod and softened. Regardless to bleaching method, by softening, because the softeners mask thean increase in softener percentage makes the fabrics irregularity of the knitted fabrics. After softeningmore voluminous and consequently they represent treatment the coefficient of friction between fabrichigher compressional properties. surface and slip probe MIU is defined as the ratio of the sliding force to the compressional load and it3.6 Effect of Processing Stages on Surface Properties of Knitted Fabrics increases in all cases. The surface properties of cotton fabric after various Furthermore, the results reveal that an increase inprocessing stages are presented in Fig. 6, considering softener concentration reduces the irregularity of the
  • 6. 144 INDIAN J. FIBRE TEXT. RES., JUNE 2010 Fig. 6―Effect of different processing stages on surface properties of knitted fabricsfabric surface and consequently the values of SMD, properties as well as surface roughness afterMMD and MIU9. The high temperature and relative softening. An overall increase in fabric extensibilitiesmovement between fabric and water in dye bath and compressibility is observed after softening forcreate an effect that contributes to fabric surface knitted fabrics. These changes could improve handleirregularity. Therefore, the dyed knitted fabrics and tailorability of the fabrics. It is also inferred thatrepresent the highest roughness value. the application of a cationic softener can improve handle and tailorability of fabrics more than a non-4 Conclusions ionic softener and micro-emulsion softener. An The results show remarkable changes after different increase in concentration of the softener makes theprocessing stages, such as bleaching, dyeing and fabrics softer, more flexible and smoother, becausesoftening in mechanical and surface properties of the inner friction of fibres and yarns decreases moreknitted fabrics. For the knitted fabrics, there is a in fabric structure.marked increase in both the rigidity and hysteresis inshear and bending properties as well as surface Referencesroughness after bleaching and dyeing. Also, an overall 1 Naujokaityte L & Strazdiene E, Material Sci, 13 (2007) 249.decrease is observed in fabric extensibilities and 2 Frydrych A, Dziworska I & Matusiak M, Fibres Text Easterncompressibility during bleaching for knitted fabrics. Eur, 11 (42) (2003) 31. 3 Matsudaira M & Matsui M, J Text Inst, 83 (1992) 144.These changes could result a few problems from the 4 Kawabata S & Niwa M, J Text Inst, 80 (1989) 19.viewpoint of shaping and sewing of fabric. As a 5 Charles Q & Wenlong Z, Text Res J, 73 (12) (2003) 1057.consequence of these changes, the fabric will be 6 Kawabata Evaluation System for Fabrics Manual (Katostiffer, denser and rougher. Tech. Co. Ltd, Kyoto, Japan), 1989. Three types of softeners namely cationic, non-ionic 7 Sun D & Stylios G, Fibers Polym, 7 (2006) 245.and micro-emulsion were used. It is found that the 8 Hallos R S, Burnip M S & Weir A, J Text Inst, 81 (1990)type of softener plays an important role to create 123. 9 Maekinen M, Meinander H & Luible N, Proceedings, thedesired changes in mechanical and surface properties HAPTEX’05 Workshop on Haptic and Tactile Preception ofof the knitted fabrics. There is a marked reduction in Deformable Objects (Hanover University Press, Hanover),both the rigidity and hysteresis in shear and bending 2005, 8.