Available online at http://www.urpjournals.com International Journal of Fiber and Textile Research Universal Research Publications. All rights reserved ISSN 2277-7156 Original Article Influence of Wet Processing on Properties of Single Jersey Knitted Fabrics Murugesh Babu. K * and Selvadass. M Department of Textile Technology, Bapuji Institute of Engineering and Technology, Visvesvaraya Technological University, Davangere – 577004, India *Corresponding author: [email protected] Received 04 March 2013; accepted 15 March 2013 Abstract The physical, dimensional and dyeing properties of the single jersey knitted fabrics were investigated after different wet processing stages and sequences. For this purpose, 2/40’s, 100%, organic cotton single jersey greige knitted fabric was developed. The greige fabric was subjected to pretreatment processes involving combined scouring/bleaching and mercerization. The pretreated fabrics were then dyed and finished to ready to stitch (RTS) fabrics. At the end of each process stage, samples were collected and analyzed for various physical properties. The change in the colour of the fabric was also investigated at end of each process stage. Simillarly, the influence of process sequences on fabric properties was studied by varying the wet processing sequences during the development of RTS fabrics. The results show that the properties of the fabric changes to a considerable extent after each stage of wet processing. It is observed that the pretreatment of the greige fabric has greater influence on the fabric properties. Further, the process sequence adopted has definite influence on fabric properties. The preparatory process sequence that includes mercerisation process has greater influence on fabric properties compared to scouring process alone. The dyeing process also influences fabric properties. These include the dyeing method adopted and the strength of colour developed. The finishing process, where the dyed fabric is padded with softener and dried in a drier alters fabric properties to a considerable extent. It improves fabric handle and imparts a soft feel to fabric. The results of dimensional stability analysis of RTS fabrics after repeated washing show that mercerized RTS fabrics has higher length wise shrinkage compared to scoured RTS fabrics. The dyeing behavior of RTS fabric show that fabric dyed with mercerized RFD fabric has greater colour strength compared to RTS fabric dyed with scoured RFD fabric. © 2013 Universal Research Publications. All rights reserved Keywords: organic cotton; knitted fabrics; wet processing; physical properties; dyeing properties 1. Introduction Single jersey knitted fabrics is generally used to make outerwear garments such as T-shirts. The knitted fabrics undergo a series of different processing treatments like scouring, bleaching, dyeing, softener padding and relax drying. These processes are carried out to impart a particular property related to that process like scouring for absorbency, bleaching for whiteness, dyeing to impart colour to fabric and finishing for improving softness and handle of the fabric. The properties of the knitted fabrics are influenced by various parameters like raw material, yarn structure, fabric structure, processing stages and finishing. The process adopted affects the fabric properties and its overall performance. The amount of changes occurred in the properties of the fabric due to pretreatment, dyeing and finishing process makes the subject complex. During the finishing process, internal stresses stored during spinning, knitting is removed and the fabrics attain an almost fully 18 relaxed state. By adopting different processes and finishing methods, different kinds of end products in a sense of aesthetic and utility properties can be produced from the same unfinished fabrics [1]. Further, the determination of the changes in physical and dyeing properties during different stages of wet processing is important for the control of process parameters to get the final product as per the requirements of the customer. There have been a number of studies on the influence of different fiber types, fabric structure and processing parameters on various properties of knitted fabrics [2-5]. However, limited number of studies on influence of wet processing stages and process sequences on the physical, demensional and dyeing properties of the cotton knitted fabrics has been reported so far [1,6]. In this study, the influence of the wet processing stages and sequences on the physical, dimensional and dyeing properties of organic cotton knitted fabrics are investigated in order to see the differences, the results are then International Journal of Fiber and Textile Research 2013; 3(1): 18-30 compared. In order to study the influence of wet processing stages on fabric properties, 2/40’s, 100%, organic cotton single jersey greige knitted fabric was developed. The greige fabric was subjected to pretreatment processes involving the combined scouring/bleaching and mercerization to develop scoured and mercerized to ready for dyeing (RFD) fabrics. The pretreated knitted fabrics were then dyed using reactive dyes. The dyed fabrics were then finished to ready to stitch (RTS) fabrics. At the end of each process stage, samples were collected and analyzed for various physical properties. Further, the change in the colour of the fabric was also investigated at end of each process stage. The physical properties include the fabric weight (grams per meter square), loop density, tightness factor, thickness, drape, air permeability and bursting strength. The dyeing properties include colour, colour strength and colour difference values. Simillarly, the influence of process sequences on fabric properties was studied by varying the wet processing sequences during the development of RTS fabrics. 2 Experimental 2.1 Influence of process stages on fabric properties Global Organic Textile standards (GOTS) approved 40’s count, 100% organic cotton single yarn supplied from Armstrong Spinning Mills, Erode, India was purchased from M.P.Shan Tex, Tirupur, India. The single yarn purchased (100 kg) was twisted as double yarn at Selvam Twisting, Tirupur, India using two-for-one twisting machine. The yarn was knitted to greige fabric at M.P.Shan Tex, Tirupur, India using 24 gauge, 4 track, Mayer &Cie, single jersey knitting machine. The greige fabric was scoured and finished to RFD fabric at Victus Dyeing, Tirupur, India. The process involved the demineralisation and combined scouring/bleaching using 100 kg Thies softflow dyeing machine. The fabric is then squeezed in a Bianco SPA squeezer & padding machine and dried using Santex CH9555 relax dryer machine. This fabric is known as the scoured RFD fabric. The scoured RFD fabric was divided into two parts. One part of the scoured fabric was kept aside. The other part of the scoured RFD fabric was mercerized using a Dornier tubular knitted fabric mercerization machine. The mercerization process consists of cold mercerization, two hot wash, neutralization and a cold wash. The scoured mercerized fabric was then dried in monforts dynair 5000 dryer machine. This fabric is known as the mercerized RFD fabric. The recipes of demineralization, combined scouring/bleaching and mercerization process is presented in Table 1. Table 1: Chemicals and auxiliaries used in demineralization, combined scouring/bleaching and mercerization process Process Chemicals Product name Quantity Water 1:06 Demineralization Wetting agent Ciba Ultra 1EL 1gpl Demineralization agent Invertex SA 2gpl Water 1:06 Wetting agent Ciba Ultra 1EL 0.5 gpl Sodium hydroxide Caustic soda flaks 2.0 gpl Scouring Hydrogen peroxide 2.0 gpl Peroxide stabilizer Clarite CBB 0.2gpl Acetic acid 2.0 gpl Wetting agent 1gpl Mercerization Sodium hydroxide Caustic soda flaks 0.1 kg/kg fabric Acetic acid 2gpl The scoured and mercerized RFD fabrics were dyed separately to develop three colours. Dyeing was done using 10 Kg Thies softflow dyeing machine present in D.K.T.E. Society’s Textile and Engineering Institute, Ichalkaranji, India The fabric was finished in open width form by padding the fabric with the silicon softener and dried in an stenter machine. The quantity of dyes used in dyeing process was kept constant for both the scoured and mercerized fabrics. The dye bath recipes used in the dyeing process is presented in Table 2. Table 2: Dye bath recipes for dyeing scoured (S) and mercerized (M) organic cotton knitted fabric with reactive dyes using salt and alkali by exhaust dyeing process Sample Colour S5 / M5 Maroon S6 / M6 T Blue S7 / M7 D Green 19 Dye Navacron Yellow HRN Navacron Red HB Navacron Navy H2G Navacron Yellow HRN Navacron Blue HRN Navacron T Blue Navacron Yellow HRN Navacron Blue HRN Navacron T Blue Qty (gpl) 1.85 4.27 1.00 0.21 2.30 0.45 0.90 1.10 4.00 Total qty (gpl) salt (gpl) soda (gpl) 7.120 80 20 2.960 80 20 6.000 80 20 International Journal of Fiber and Textile Research 2013; 3(1): 18-30 To determine the physical and dyeing properties of knitted fabrics, samples were collected immediately at the end of a particular process stage. The samples collected include greige fabrics, scoured and mercerized RFD fabrics, dyed unfinished (UF) fabrics and dyed finished (F) fabrics. The samples were tested for the physical and dyeing properties at room temperature and atmosphere after allowing it to dry relax for one hour. 2.2 Influence of process sequences on fabric properties 2.2.1 Procurement of organic cotton hosiery yarn Global Organic Textile standards (GOTS) approved 2/40s, 100% organic cotton super combed hosiery yarn was obtained from Sambandam Spinning Mills Limited, Salem, India with the help of Shahi Exports Pvt. Ltd. (Knits division), Bangalore, India. Initially 200 kg of yarn was purchased for knitting. At the later stage, 250 kg of 40s, 100% organic cotton single yarn supplied from Armstrong Spinning Mills, Erode, India was purchased from M.P.Shan Tex, Tirupur, India. The yarn was twisted as double yarn at Selvam Twisting, Tirupur, India using two-for-one (TFO) twisting machine. The yarn obtained from the Sambandam Spinning Mills Limited was knitted to greige fabric at Shahi Exports Pvt. Ltd., Tirupur, India using 4 track Mayer & cie single jersey knitting machine. The yarn supplied by Armstrong Spinning Mills, Erode, India was knitted at M.P.Shan Tex, Tirupur, India using 4 track, Mayer &Cie, single jersey knitting machine. 2.2.2 Development of readyto stitch fabrics The greige fabric knitted at Shahi Exports Pvt Ltd, Tirupur was sent for processing at Brindhaa Textile Processing Mills, Tirupur, India. The greige knitted fabric was divided into two parts. One part of the fabric was demineralised and scoured using Thesis Softflow dyeing machine. The fabric was then squeezed in Bianco SPA pad & squeezer machine and dried using Santex CH9555 relax dryer machine. This fabric is scoured RFD fabric. The other part of the greige fabric was mercerised using Dornier tubular knitted fabric mercerisation machine. The mercerisation process consists of cold mercerisation, two hot wash, neutralisation and a cold wash. The greige mercerised fabric was then dried in monforts dynair 5000 dryer machine. The dried greige mercerised fabric was then taken to demineralisation and combined scouring/bleaching process in a softflow dyeing machine. The fabric was then squeezed in Bianco SPA pad & squeezer machine and dried using Santex CH9555 relax dryer machine. This fabric is greige mercerised scoured RFD fabric. The greige fabric knitted at M.P.Shan Tex, Tirupur, India was scoured/bleached and finished to RFD fabric at Victus Dyeing, Tirupur, India. The scouring process is similar to development of scoured RFD fabric discussed in previous section. Then half the quantity of scoured fabric was taken for mercerisation at Brindhaa Textile Processing Mills, Tirupur, India to develop scoured mercerised RFD fabric. The tubular scoured and mercerised fabrics were converted to open width fabrics using a slit opening machine. The tubular scoured and mercerised RFD fabrics were dyed seperately to develop seven colours. Dyeing was done using softflow dyeing machine. The fabric was finished in tubular form by padding the fabric with silicon softener and drying in relax dryer machine. Similarly, the open width scoured and mercerised RFD fabrics were dyed seperately to develop three colours using non-silicate cold pad batch (CPB) dyeing method. The fabric was finished in open width form by padding the fabric with silicon softener and drying in stenter machine. The shade and recipe for dyeing of light colour samples using an 10 kg industrial softflow dyeing machine (exhaust dyeing) is presented in Table 3 for scoured (S1 – S4) and mercerised (M1 – M4) fabric. The dyeing was done at Victus Dyeing, Tirupur. For dark shades, 3 colours were selected. The recipe for dyeing scoured (S5 – S7) and mercerised (M5 – M7) organic cotton knitted fabric is presented in Table 4. The dyeing was done using 10 Kg softflow dyeing machine at DKTE Society’s, Textile & Engineering Institute, Ichalkaranji, India. The fabric was finished at Loyal Super Fabrics, Cuddalore, India. Navacron H series regular dyes were used. The recipes for dyeing samples using non-silicate CPB dyeing method for scoured (S8 – S10) and mercerised (M8 – M10) knitted fabric in open width form is presented in Table 5. The dyeing and finishing was done at Loyal Super Fabrics, Cuddalore, India. Table 3: Dye bath recipes for dyeing scoured (S) and mercerised (M) organic cotton knitted fabric with low impact reactive dye using salt and alkali by exhaust dyeing process Sample Colour S1/M1 Yellow S2/M2 Stone S3/M3 D violet S4/M4 Brown 20 Dye Levafix Brill Yellow CA Levafix orange CA Levafix Blue CA Remazol Yellow RR Remazol ultra caramine RGB Remazol Blue RR Remazol ultra yellow RGB Remazol ultra caramine RGB Remazol Blue RGB Remazol yellow RR Remazol ultra caramine RGB Remazol Blue RR Scored (S) Qty Total qty (gpl) (gpl) 0.4190 0.0572 0.501 0.0245 0.1180 0.0546 0.260 0.0876 0.4980 0.5190 2.077 1.0600 0.9330 0.2950 1.758 0.5300 Mercerised (M) Total qty Qty (gpl) (gpl) 0.3660 0.0546 0.442 0.0216 0.1090 0.0515 0.249 0.0889 0.3630 0.3410 1.438 0.7340 0.6370 0.2070 1.245 0.4010 International Journal of Fiber and Textile Research 2013; 3(1): 18-30 Salt (gpl) Soda (gpl) 20.0 6.0 12.5 5.0 40.0 10.0 35.0 9.0 Table 4: Dye bath recipes for dyeing scoured and mercerised organic cotton knitted fabric with low impact reactive dye usingsalt and alkali by exhaust dyeing process Sample Colour Dye Qty (gpl) Total qty (gpl) salt (gpl) soda (gpl) S5 / M5 Maroon Navacron Yellow HRN 1.85 Navacron Red HB 4.27 7.120 80 20 Navacron Navy H2G 1.00 S6 / M6 T Blue Navacron Yellow HRN 0.21 Navacron Blue HRN 2.30 2.960 80 20 Navacron T Blue 0.45 S7 / M7 D Green Navacron Yellow HRN 0.9 Navacron Blue HRN 1.10 6.000 80 20 Navacron T Blue 4.0 Table 5: Dye bath recipes for dyeing scoured and mercerised organic cotton knitted fabric with low impact reactive dye usingsalt and alkali by cold pad batch dyeing process Sample Colour Brand Qty (gpl) Total qty (gpl) Soda (gpl) Caustic (ml/l) S8 / M8 Royal Blue Drimarine Royal Blue HFCD 40.00 40.00 20.00 5.50 Remazol ultra yellow RGB 6.00 S9 / M9 24.00 20.00 3.25 Red Remazol ultra caramine RGB 15.00 Levafix Azure CA 3.00 S10 / M10 Black Remazol Black GSA 50.00 50.00 20.00 80.00 The process sequences adopted for development of RTS is further summarized in Table 6. Table 6: Process sequences adopted for development of scoured and mercerised RTS fabric Cotton cultivation Yarn & gray Ginning fabric Spinning development Knitting Fabric S1-S4 S5-S7 S8-S10 M1-M4 M5-M7 Demineralisation Slit opening Mercerisation Demineralisation, Fabric preparation Drying combined scouring & Open width fabric bleaching scouring/bleaching Pretreatment Combined Demineralisation, processes scouring & combined Demineralisation Drying bleaching scouring & bleaching Stenter drying Mercerisation Dyeing Exhaust dyeing using softflow dyeing machine Non-silicate CPB dyeing Finishing Relax drying Stenter drying The developed RTS fabrics were tested to study the influence of process sequences on physical, dimensional and dyeing properties. 2.3 Testing methods The properties of the fabrics were measured in accordance with the relevant standards: fabric weight, ASTM D377696; loop density BS 5441: 1988; fabric thickness, ASTM D1777 – 96(2011)e1; fabric drape, BS 5058:1973; air permeability, ASMT d737-04(2008)e2; bursting strength, ASTM D3786 – 2006. The tightness factor (TF) was determined using the formula TF = [(T) 1/2 / l], where T is the linear density of yarn (Tex) and l is loop length in cm [7, 8]. The colour specification, colour strength and colour difference of fabric samples were determined by Minolta CM-3301d spectrophotometer that uses JAYPAK 4808 quality control system software. The colour measurement 21 M8-M10 Slit opening Fabric preparation Combined scouring & bleaching Demineralisation Stenter drying Mercerisation Stenter drying Exhaust dyeing using softflow dyeing machine Softner padding Relax drying Compacting Non-silicate CPB dyeing Stenter drying was done using standard formula CIE 76, 10 deg observer and D65 source. 3. Results and Discussions 3.1 Influence of wet processing stages on physical properties 3.1.1 Fabric weight The influence of wet processing stages on the fabric weight (grams per square meter) of the organic cotton knitted fabrics is presented in Fig.1.The results show that the weight of greige fabric increases after the pretreatment processes. Similarly, the weight of the scoured and mercerized RFD fabrics increases after dyeing and finishing process. Further, it can be observed that the weight of the mercerized fabrics is slightly more compared to the scoured fabrics at the end of all processing stages. The fabric weight (GSM) is determined by two factors that International Journal of Fiber and Textile Research 2013; 3(1): 18-30 interact in the knitted fabric, i.e. the loop size and the yarn size. Keeping these two factors constant, the changes observed in the fabric weight at different processing stages are primarily due to the pretreatment processes adopted and the fabric shrinkage observed during the processing. During pretreatment of the greige fabric, there is a certain amount of weight loss in the material. The weight loss observed in the greige fabric during pretreatment process is due to removing of impurities present in the fabric. Greige knitted cotton fabric made of cotton fibres consists of approximately 10% by weight noncellulosic substances such as lipids, waxes, organic acids, proteins/nitrogenous substances, non-cellulosic polysaccharides, and other unidentified compounds. The presence of these non-cellulosic materials imparts poor water absorbency [9-12]. In order to remove these noncellulosic materials or impurities from the fabric/fibres, scouring is normally carried out with strong alkali at high temperature for a certain specified time [13-15].The total amount of impurities to be removed is less than 10 % (about 5 to <10 %) of the total weight [16]. On the other hand, bleaching removes any unwanted colour from the fibres which significantly impair the inherent white appearance of cotton cellulose. This process also eliminates any traces of other impurities remaining from the previous preparation steps and improves the absorbency of the material for the dyeing and printing process [17]. In the pretreatment of the cotton knit fabrics, the scouring and bleaching is done as a single process known as combined scouring &bleaching. Here, the scouring process is accelerated in the presence of hydrogen peroxide (H 2O2) and less time is generally required to achieve good absorbency of the material. The advantages of this process are an increased production with the reduction of labor cost and reduced treatment time, the loss in weight and strength 22 of material is less. H2O2 is a powerful oxidizing agent that rapidly destroys the natural coloring matters present in cotton without undue oxidative damage to the fibres [16]. The amount of raw material after the scouring process is reflected by the weight (grams per meter square) of fabric, which must be maintained for the garments. If excessive weight loss occurs during the scouring/bleaching process, then the GSM of fabric will be reduced significantly that it will affect the garment quality. Again, if the weight loss is less than the standard mentioned, then impurities will remain in the substrate which can create quality problems such as improper or uneven dyeing. Further, during pretreatment process, the fabric also shrinks. This increases the GSM of the pretreated fabrics. The weight of the fabric is also influenced by mercerization process. The scoured fabric subjected to the mercerization process shrinks to a large extent. Further, mercerization process removes the loose and protrudingfibres from the surface of the fabric. This gives the mercerized fabric a neat surface finish and increase the luster considerably. All these have influence on fabric weight. Further, the fabric weight is also affected by the shrinkage during the processing stages. The more the number of processing stages, the higher will be the degree of shrinkage. This results in higher knit density and consequently higher weight of the fabric. The depth of colour developed in dyeing process whether light or dark colour influences the fabric weight. It is observed that fabrics dyed to dark colour have slightly higher fabric weight compared to fabrics dyed to light color. The softener padding process impact softness, improve handle and volume of the fabric. Normally, the increase in fabric volume through the softening depends on the type and percentage of the softener. International Journal of Fiber and Textile Research 2013; 3(1): 18-30 3.1.2 Loop density The influence of wet processing stages on the course per inch (CPI), wales per inch (WPI) and loop density (Loops/inch2) of the organic cotton knitted fabrics is presented in Figs. 2, 3& 4. The results show that after pretreatment of the greige fabric, the CPI, WPI and loop density changes to a large extent in the resultant fabrics at the end of each processing stage. The fabric structure becomes more compact. The CPI of the greige fabric increases after pretreatment process. Further, the CPI of the scoured and mercerized RFD fabrics after the dyeing process shows slight variation whereas it decreases after the finishing process. However, when the scoured and mercerized fabrics are compared at the end of various process stages, the CPI of the scoured fabric is slightly less compared to the mercerized fabrics. The WPI of the greige fabric increases after the scouring/bleaching process whereas decreases after the mercerization process. The WPI of the scoured RFD fabric decreases after the dyeing and finishing process whereas the wpi of the mercerized fabrics remains almost same. Further, it can be observed that wpi of the scoured fabrics is more compared that of the mercerized fabrics after different process stages. The loop density of the greige fabric increases to large extent after pretreatment process. The loop density of the scoured and mercerized RFD fabrics varies after the dyeing & finishing process. Further, when the scoured and mercerized fabrics are compared, it is observed that the scoured fabrics have slightly higher loop density compared to mercerized fabrics. The change of loop density in wet processing is perhaps due to anisotropic swelling behavior of cotton fibres. During all wet processing as well as laundering, cotton fibers swell about 40 % by volume, but very little longitudinal swelling accounting for only about a 1–2 % increase in fiber length occurs. This anisotropic swelling behavior is explained by the fact that the crystalline, microfibrillar structures in cellulosic fibers are not 23 penetrated by water. Swelling therefore occurs only between microfibrillar structures and consequently their orientation in the fiber determines the swelling anisotropy. During this process in knitted cotton fabrics, the shape and orientation of the loops change to minimum energy conformation. The loops usually become rounder in shape causing shrinkage in the wale direction, especially when the fabric has been previously dried under tension. In order to release the stresses imposed by bending twisted yarns into loops, the loops themselves tend to twist out of the plane of the fabric. This causes shrinkage in the course direction and often produces significant differences in twist level in the two legs of the knitted loops [18]. 3.1.3 Tightness factor The tightness or cover factor indicates the relative tightness or looseness of a plain knit structure. The general definition was that a ratio exists between the area covered by the yarn in one loop to the area occupied by that loop. A detail discussion of tightness factor of the knitted fabrics is present in literature [19-22]. The influence of wet processing stages on the tightness factor of the organic cotton knitted fabrics is presented in Fig.5.The results show that the tightness factor of the greige fabric after pretreatment process varies to a great extent. Further, the tightness factor of the scoured RFD fabrics increases after the dyeing process and decreases after the finishing process. The tightness factor of the mercerized RFD fabrics varies after the dyeing process and decreases after the finishing process. When the scoured and mercerized fabrics are compared, mercerized fabrics show slightly higher tightness factor compared to that of scoured fabrics. The tightness factor is influenced by linear density of yarn and the loop length. The linear density of yarn can change slightly due to various processing stages. The changes in the loop length can be attributed to change in the dimensional properties of fabric such as cpi, wpi and loop density due to shrinkage at the end of each processing stages. International Journal of Fiber and Textile Research 2013; 3(1): 18-30 3.1.4 Fabric thickness The influence of wet processing stages on the thickness (mm) of the organic cotton knitted fabrics is presented in Fig.6. The result shows that the thickness of the greige fabric decreases slightly after the pretreatment processes. The thickness of the scoured RFD fabrics increases slightly after the dyeing process and then decreases after the finishing process. The thickness of the mercerized RFD fabrics follows similar trend as that of scoured fabrics. When the scoured and mercerized fabrics are compared, the thickness of the scoured fabrics is slightly high compared to that of the mercerized fabrics. The fabric thickness is influenced by fibre specific gravity and yarn linear density [23, 24]. Further, fabric thickness for a particular yarn is directly related to the yarn diameter in fully relaxed state of fabric [25]. The thickness of the fabric is also influenced by the course spacing which is directly related to course density. The change may be due to shrinkage of the fabric at various stages of processing. Further, all dyed and bleached fabrics undergo change in thickness, which could be due to further tightening of the structure as a result of increased adhesion between fabric structural elements. 3.1.5 Fabric drape The influence of wet processing stages on the drape of the organic cotton knitted fabrics is presented in Fig.7. The results show that the drape coefficient of the scoured RFD fabrics increases after dyeing process and then decreases after the finishing process. The drape coefficient of the mercerized RFD fabrics also follows same trend as that of the scoured fabrics. When drape coefficient of the scoured and mercerized fabrics are compared, it is observed that the mercerized fabrics show higher drape coefficient value compared to that of scoured fabrics. Drape is an important factor when presenting the aesthetics and functionality of both, the fabric and the created garment. Drapeability can be described as a phenomenon of fabric-fold formation, which arises when a fabric hangs down without the influence of external forces. It depends on the fabric’s parameters such as structure, yarn type, fibre content, as well as its finishing treatments [26]. The change in drape of fabrics observed after different processing stages can be attributed to higher relaxation shrinkage and higher loop density. The high drape coefficient of mercerized fabrics is mainly due to mercerization process adopted. After combined scouring/bleaching, the fabric is mercerized. This makes the fabric stiffer and less stretchable than a normal scoured/bleached fabric. The fabric also shrinks after mercerization process. The dyeing process further makes the fabric stiff and the drape coefficient increases to a large extent. The dyeing process is followed by the finishing process where the dyed fabric is padded with a softener. After the finishing process, the drape coefficient of the dyed fabric decreases since the application of softener reduces the inner friction between the fibres and yarns in the fabric structure. In finishing, the type and concentration of the softener used is important and has significant influence on the drape properties. 3.1.6 Air permeability The influence of wet processing stages on the air permeability (cc /cm2.sec) of the organic cotton knitted fabrics is presented in Fig.8. The results show that after the pretreatment process of the greige fabrics, the air permeability decreases to a large extent in the resultant RFD fabrics. The air permeability of the scoured RFD fabrics decreases after the dyeing and finishing process whereas, air permeability of the mercerized RFD fabrics increases after the dyeing process and decrease after the finishing process. When the air permeability of the scoured and mercerized fabrics is compared, it is observed that the mercerized fabrics show higher value compared to that of the scoured fabrics. Air permeability is mainly affected by two parameters, porosity and fabric thickness [27]. When all fabric parameters are kept constant, the air permeability is influenced by the yarn type and twist factor. In recent studies, it has been proved that the loop length has an obvious effect on air permeability when the other parameters such as density and fabric thickness are constant [28]. The air permeability of the mercerized fabrics increases compared to the scoured fabrics. This may be due to the fibre arrangement in the cross-section of the yarn. After mercerization of the scoured fabric, which is done by stretching, the fibres present in the yarn are better arranged in the cross-section than before mercerization. This reduces the loose fibres between the loops. 3.1.7 Bursting strength The influence of wet processing stages on the bursting strength (kg/cm2) of the organic cotton knitted fabrics is presented in Fig.9. The results show that after the pretreatment process of greige fabrics, the bursting strength decreases slightly in the resultant RFD fabrics. The bursting strength of the scoured RFD fabric remains more or less same after dyeing and finishing process. The bursting strength of the mercerized RFD fabric increases slightly after the dyeing process and further increases after the finishing process. When bursting strength of the scoured and mercerized fabrics is compared, it is observed that the mercerized fabrics show higher bursting strength compared to the scoured fabrics. The major reason for the increased bursting strength in the mercerized fabrics can be due to reduction of internal stresses and the deconvolution of the fibres in the fabric during the swelling process. 3.2 Influence of wet processing stages on dyeing properties The colour specification, colour strength and colour difference of the greige and RFD fabrics is presented in Table 7: Comparison of colour specification, colour strength and color difference of gray and RFD fabrics Sample Colour L a b c h K/S Gray Gray 14.04 84.34 1.14 13.99 85.30 0.758 Scoured RFD Off white 4.94 94.51 -0.30 4.94 93.49 0.131 Mercerised RFD Off white 7.82 92.96 -0.17 7.81 91.25 0.218 24 International Journal of Fiber and Textile Research 2013; 3(1): 18-30 dE 3.250 Table 7. It is observed that the pretreatment of the greige fabric changes the colour of resultant RFD fabrics. This is due to combined scouring/bleaching process where the surface chemical compounds imparting greige colour to the fabric is removed. The comparison of colour specification of the scoured and mercerized RFD fabrics shows that the colour of the mercerized RFD fabric varies slightly when compared to that of the scoured RFD fabric. The mercerized RFD fabric is darker, greener (less red), yellower and brighter than the scoured RFD fabric as shown by the colour difference values. The colour specification, colour strength and colour difference of the scoured and mercerized unfinished and finished dyed fabrics is presented in Table 8. Finished (F) Unfinished (UF) Table 8: Comparison of colour specification, colour strength and color difference of scoured (S) and mercerized (M) unfinished (UF) and finished (F) dyed fabrics Sample Colour L a b c h K/S dE S5 Maroon 23.52 19.09 3.32 19.38 9.86 9.398 S6 T Blue 36.19 -10.74 -15.27 18.67 234.85 6.955 S7 D Green 30.52 -21.29 1.75 21.36 175.29 17.810 M5 Maroon 15.97 12.35 3.28 12.78 14.89 21.038 10.43 M6 T Blue 30.83 -9.78 -16.12 18.86 238.73 10.109 5.65 M7 D Green 27.03 -20.87 3.15 21.11 171.41 23.763 3.74 S5 Maroon 23.25 19.09 3.08 19.33 9.16 9.506 S6 T Blue 37.69 -10.78 -15.46 18.85 235.09 6.302 S7 D Green 30.48 -22.32 2.03 22.42 174.82 20.657 M5 Maroon 15.05 12.44 3.02 12.8 13.64 22.934 10.55 M6 T Blue 31.32 -9.62 -16.45 19.05 239.66 9.594 6.55 M7 D Green 26.91 -21.47 3.13 21.7 171.71 25.188 3.83 It can be observed that the mercerized dyed fabrics show 3.3 Influence of wet processing squences on physical high colour strength values compared to the scoured dyed properties of fabrics fabrics. The high colour difference values observed further The influence of process sequences on fabric weight is confirms this point. The high colour strength of the presented in Fig. 10. The result shows that tubular and open mercerized fabrics is due to changes in the chemical and width scoured fabrics has less weight compared to that of structural properties of organic cotton fibres during the mercerised fabrics. Further, it can be observed that the mercerization process. This results in high dye uptake from fabric dyed to dark colours has higher fabric weight the dye bath.The colour specification, colour strength and compared to fabrics dyed with light colours. Thus, the colour difference of the scoured and mercerized dyed weight of the fabric is primarly influnced by preparatory finished fabrics shows similar results as that of the dyed processes adopted, the colour strength of the dyed fabric unfinished fabrics. Further, it can be observed that the and the fabric state wheather the fabric is processed in finishing process does not affect the colour of dyed fabrics. tubular rope or open width form. 25 International Journal of Fiber and Textile Research 2013; 3(1): 18-30 The influence of process sequences on the course per inch (CPI) and wales per inch (WPI) of the organic cotton knitted fabrics is presented in Figs. 11 & 12. It can be observed mercerised fabrics have high CPI compared to scoured fabrics. Similarly, the results of WPI analysis shows that scoured fabrics have slightly high WPI compared to mercerised fabrics. Further, the CPI of open width fabrics is less compared to tubular fabrics. The influence of process sequences on tightness factor is presented in Fig. 13. The result shows that the tightness factor of scoured fabric is less compared to mercerised fabrics. Simillary, the tightness factor of open width fabrics is more compared to tubular fabrics. In general, the results show that mercerised fabrics probably due to shrinkage during pretreatment process has high influence on weight of fabric, CPI, WPI and tightness factor. Further, these properties are also influenced by the fabric state whether tubular or open width. The influence of process sequences on fabric thickness, drape, air permeability and bursting strength is presented in Figs. 14, 15, 16 & 17. The results show that thickness and drape of mercerised fabrics is less compared to scoured fabrics. However, air permeability and bursting strength of mercerised fabrics is more compared to scoured fabrics. In general, the results show that as the process sequences is varied, the physical properties of the fabric also varies. The pretreatment process adopted, the fabric state whether tubular or open width and the depth (strength) of colour developed has greater influence on fabric properties. 3.4 Influence of wet processing squences on dimensional properties The dimensional stability of RTS fabric is analyzed as length and widthwise shrinkage after repeated washing and tumble drying. The dimensional stability of RTS fabric after first wash, fifth wash and tenth washed, tumble dried fabric is summarized in Figs. 18 & 19. The results show that lengthwise shrinkage of scoured and mercerized RTS fabric dyed with light colour varies whereas that of mercerized RTS fabric dyed with dark colour is more compared to that of scoured RTS fabric. The results of widthwise shrinkage varies and it is less compared to lengthwise shrinkage. Further, it can be observed that width wise shrinkage of all RTS fabric decrease after fifth and tenth washes. 26 Fig. 18 - Comparison of lengthwise (L) shrinkage of RTS fabric after first wash(A), fifth wash (B) and tenth wash (C) International Journal of Fiber and Textile Research 2013; 3(1): 18-30 Fig. 19 - Comparison of widthwise (W) shrinkage of RTS fabric after first wash(A), fifth wash (B) and tenth wash (C) 3.5 Influence of wet processing squences on dyeing behavior The colour specification, colour strength and colour difference of scoured and mercerized RTS fabric without washing is summarized in Tables 9 & 10. The colour specification of scoured and mercerized RTS fabric varies. The colour strength of mercerized RTS fabric is more compared to scoured RTS fabric. Further, the dyeing of samples IS1 / IM1 – IS4 / IM4 was done to get same colour strength. Hence, no major change in colour specification is observed between them. The dyeing of scoured and mercerised samples IS5 / IM5 – IS10 / IM10 was done with same dye recipe but the dyed and finished samples show major change in colour specification and colour strength values. The high colour strength of mercerized RTS fabric is probably due to high dye uptake from the dye bath. Table-9: Comparison of colour specification and colour strength of scoured and mercerized RTS fabric (unwashed samples-I) Sample Colour L a b c h K/S S RFD IS1 IS2 IS3 IS4 IS5 IS6 IS7 IS8 IS9 IS10 M RFD IM1 IM2 IM3 IM4 IM5 IM6 IM7 IM8 IM9 IM10 Off white Yellow Stone D Violet Brown Maroon T Blue D Green R Blue Red Black Off white Yellow Stone D Violet Brown Maroon T Blue D Green R Blue Red Black 5.57 74.08 62.30 31.72 40.16 23.25 37.69 30.48 38.04 30.91 15.70 91.88 72.41 60.89 28.67 36.37 15.05 31.32 26.91 34.4 27.23 12.75 92.8 1.09 5.10 4.41 5.12 19.09 -10.78 -22.32 0.08 29.91 -0.31 91.35 2.63 5.12 4.53 5.12 12.44 -9.62 -21.47 1.57 29.67 -0.03 -0.32 33.64 5.02 0.11 8.83 3.08 -15.46 2.03 -38.19 13.14 -2.90 -0.26 35.66 5.41 -0.36 9.26 3.02 -16.45 3.13 -40.36 13.58 -2.25 5.56 33.66 7.16 4.42 10.21 19.33 18.85 22.42 38.19 32.67 2.92 8.23 35.75 7.45 4.54 10.58 12.8 19.05 21.7 40.39 32.63 2.25 93.34 88.11 44.50 1.42 59.87 9.16 235.09 174.82 270.15 23.70 263.78 91.88 85.75 46.54 355.4 61.04 13.64 239.66 171.71 272.27 24.58 269.31 0.168 0.561 0.579 3.774 2.378 9.506 6.302 20.657 4.006 5.886 13.468 0.258 0.667 0.619 4.434 2.958 22.934 9.594 25.188 5.313 8.037 19.338 Table 10: Comparison of colour difference of mercerized and scoured RTS fabric Sample Colour dL da db dc dH dE IM1 vs IS1 IM2 vs IS2 IM3 vs IS3 IM4 vs IS4 IM5 vs IS5 IM6 vs IS6 IM7 vs IS7 IM8 vs IS8 IM9 vs IS9 IM10 vs IS10 Yellow Stone D Violet Brown Maroon T Blue D Green R Blue Red Black -1.67 -1.41 -3.05 -3.79 -8.20 -6.37 -3.57 -3.64 -3.68 -2.95 1.54 0.02 0.12 0.00 -6.65 1.16 0.85 1.49 -0.24 0.28 2.02 0.39 -0.47 0.43 -0.06 -0.99 1.10 -2.17 0.44 0.65 2.09 0.29 0.12 0.37 -6.53 0.20 -0.72 2.20 -0.04 -0.67 -1.43 0.26 -0.47 0.21 1.23 1.51 -1.20 1.45 0.50 0.25 3.04 1.46 3.08 3.82 10.55 6.55 3.83 4.49 3.71 3.03 Table 11 show colour specification, colour strength and colour difference values of RTS fabric after ten washes. The results show that colour specification and colour strength of RTS fabric after ten washes does not show 27 major changes when compared with RTS fabric that is not subjected to washing process. The colour difference values presented in Table 12 show only minor differences that further confirm the above point. International Journal of Fiber and Textile Research 2013; 3(1): 18-30 Table 11: Comparison of colour specification and colour strength of scoured and mercerized RTS fabric after ten washes Sample Colour L a b c h K/S AS1 Yellow 71.27 0.43 31.51 31.51 89.19 0.665 AS2 Stone 58.72 5.19 4.45 6.83 40.58 0.762 AS3 D Violet 30.26 4.50 -0.20 4.50 357.41 4.177 AS4 Brown 39.06 5.39 8.17 9.79 56.58 2.568 AS5 Maroon 23.27 18.98 2.77 19.18 8.29 9.568 AS6 T Blue 35.19 -9.10 -14.74 17.32 238.28 6.893 AS7 D Green 28.12 -19.89 1.12 19.92 176.78 23.282 AS8 R Blue 38.97 -0.27 -38.59 38.59 269.56 3.770 AS9 Red 31.98 29.47 12.23 31.91 22.54 5.251 AS10 Black 15.94 -0.73 -3.63 3.71 258.57 12.907 AM1 Yellow 70.67 1.96 32.89 32.95 86.56 0.733 AM2 Stone 59.26 5.31 4.65 7.06 41.23 0.747 AM3 D Violet 29.22 4.49 -0.50 4.52 353.59 4.411 AM4 Brown 36.88 5.31 8.50 10.02 58.00 2.946 AM5 Maroon 15.13 12.71 2.93 13.04 12.96 22.707 AM6 T Blue 28.51 -8.29 -15.84 17.87 242.35 11.275 AM7 D Green 25.49 -18.83 2.02 18.94 173.87 26.183 AM8 R Blue 35.68 1.15 -40.34 40.36 271.67 4.939 AM9 Red 27.30 29.18 13.12 31.99 24.19 8.005 AM10 Black 13.16 -0.19 -2.54 2.55 265.61 18.544 Table 12: Comparison of colour difference between scoured and mercerized RTS fabric without washing (I) and after ten washes (A) Sample Colour dL da db dc dH dE IS1 vs AS1 Yellow -2.87 -0.46 -2.15 -2.12 0.57 3.62 IS2 vs AS2 Stone -3.60 0.14 -0.57 -0.30 -0.51 3.65 IS3 vs AS3 D Violet -1.46 0.09 -0.31 0.09 -0.31 1.50 IS4 vs AS4 Brown -1.11 0.33 -0.66 -0.41 -0.61 1.33 IS5 vs AS5 Maroon 0.01 -0.09 -0.32 -0.14 -0.30 0.33 IS6 vs AS6 T Blue -2.45 1.65 0.84 -1.49 -1.09 3.07 IS7 vs AS7 D Green -2.36 2.71 -0.86 -2.74 0.74 3.69 IS8 vs AS8 R Blue 0.90 -0.18 -0.50 -0.45 -0.27 1.04 IS9 vs AS9 Red 1.05 -0.43 -0.92 -0.76 -0.69 1.47 IS10 vs AS10 Black 0.21 -0.37 -0.77 0.75 -0.41 0.88 IM1 vs AM1 Yellow -1.81 -1.81 -0.43 -2.77 0.45 3.34 IM2 vs AM2 Stone -1.65 -1.65 0.24 -0.76 -0.71 1.83 IM3 vs AM3 D Violet 0.54 0.54 -0.09 -0.14 -0.15 0.57 IM4 vs AM4 Brown 0.50 0.50 0.21 -0.76 -0.55 0.93 IM5 vs AM5 Maroon 0.08 0.08 0.29 -0.08 -0.15 0.31 IM6 vs AM6 T Blue -2.76 -2.76 1.29 0.70 0.94 3.13 IM7 vs AM7 D Green -1.43 -1.43 2.96 -1.06 0.78 3.45 IM8 vs AM8 R Blue 1.28 1.28 -0.42 0.00 -0.41 1.35 IM9 vs AM9 Red 0.06 0.06 -0.49 -0.48 -0.24 0.69 IM10 vs AM10 Black 0.39 0.39 -0.13 -0.32 -0.19 0.52 4 Conclusions The results show that the properties of the fabric changes to a considerable extent after each stage of wet processing. It is observed that the pretreatment of the greige fabric has greater influence on the fabric properties primarily due to shrinkage of material. The pretreatment process adopted also has greater influence on the dyeing properties. Hence, it is observed that mercerized fabrics shows high colour strength value than the scoured fabrics due to greater dye uptake. The various pretreatment and dyeing processes make the fabric firm, compact and rougher. The finishing process using softener padding imparts softness to the 28 fabric and improve fabric handle. Further, the results show that process sequence adopted has definite influence on fabric properties. The preparatory process sequence that includes mercerisation process has greater influence on fabric properties compared to scouring process alone. This can be observed by comparing finished scoured and mercerized RFD fabric properties. The mercerisation process makes the fabric surface free of fuzzy fibres and gives neat fabric surface without any surface fibres. This improves the fabric appearance. It further improves the luster of fabric significantly. The unfinished dyed fabric and the finished dyed fabric that has International Journal of Fiber and Textile Research 2013; 3(1): 18-30 adopted mercerisation process at preparatory stage maintain the luster even after repeated washing. The dyeing process also influences fabric properties. These include the dyeing method used and the strength of colour developed. The dyeing process has greater influence on fabric handle properties. This can be seen by comparing scoured and mercerized unfinished dyed fabric. The fabric drape is less indicating that the fabric has become stiff after dyeing process. It also has a very harsh feel. Further, it can be observed that fabric dyed with light colour has less weight compared to fabric dyed to dark colour. Finally, the finishing process where, the dyed fabric is padded with softener and dried in a drier alters fabric physical properties. It improves fabric handle and imparts a soft feel to fabric. The results of dimensional stability analysis of RTS fabric after repeated washing show that mercerized RTS fabric has higher length wise shrinkage compared to scoured RTS fabric when dyed to dark colours. Similarly, the widthwise shrinkage of mercerized RTS is less compared to scoured RTS fabric. The dyeing behavior of RTS fabric show that fabric dyed with mercerized RFD fabric has greater colour strength compared to RTS fabric dyed with scoured RFD fabric. Further, the finishing process adopted after dyeing does not alter the colour strength and the colour difference observed is not large. Acknowledgements The authors would like to thank the management of Shahi Exports Pvt. Ltd. (Knits Division), Bangalore, India for supporting the work. 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Source of support: Nil; Conflict of interest: None declared 30 International Journal of Fiber and Textile Research 2013; 3(1): 18-30
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