CHAPTER 3 MATERIALS AND METHODS

Transcription

1 CHAPTER 3 MATERIALS AND METHODS 3.1 INTRODUCTION This Chapter presents the details of materials and methods utilized for analysing the performance of yarns and fabrics along with the description of apparatus, procedures and techniques. The methodology adopted for this study is presented in the form of a flow diagram, as given in Figure 3.1. Figure 3.1: Flow Diagram of Methodology Adopted for the Study I. Staple Fibres Bamboo (100%) Cotton (100%) Modal (100%) Viscose (100%) Bamboo/Cotton (50:50) Ring Spinning II. Production of Spun Yarns (40 Ne) Bamboo/Cotton (50:50) Blended Yarn 100% Modal Yarn 100% Viscose Yarn 35

2 III. Fabric Production (Production of Weft Knitted Fabrics with Variations in Loop Length) Bamboo/Cotton (50:50) Modal (100%) Viscose (100%) 1x1 Rib Interlock 1x1 Rib Interlock 1x1 Rib Interlock 0.31cm 0.31cm 0.31cm 0.31cm 0.31cm 0.31cm 0.29cm 0.29cm 0.29cm 0.29cm 0.29cm 0.29cm 0.27cm 0.27cm 0.27cm 0.27cm 0.27cm 0.27cm IV. Preparation of Weft Knitted Fabrics Desizing + Scouring + Bleaching Dyeing With Cold Brand Reactive Dye Relaxation Treatments Given for Weft Knitted Fabrics Dry Relaxation Wet Relaxation Full Relaxation 36

3 V. Objective Evaluation Yarn Testing Fabric Testing Physical Properties Physical Properties Count and Twist Strength and Elongation Evenness and Imperfections Hairiness and Yarn Quality Index (YQI) Mechanical Properties Yarn to Yarn Dynamic Friction Yarn to Metal Dynamic Friction Yarn Abrasion Yarn Flexural Rigidity Yarn to Needle Static Friction Comfort Properties Related to Moisture Management Yarn Wicking Loop Length Tightness factor Fabric Weight Fabric Thickness Mechanical Properties Bursting Strength Abrasion Resistance Bending Length Flexural Rigidity Surface Friction Comfort Properties Related to Moisture Management Wettability Sinking Time Absorptive Capacity Vertical Wicking Aesthetic Properties Fabric Drape 37

4 VI. Instrumentation Fabric Analysis Yarn Analysis Simple Low Cost Manual Drape Elevator Fabric Surface Friction Tester Yarn Friction Tester Yarn Flexural Rigidity Tester VII. Investigating the Drape Formation of Weft Knitted Fabrics (with three different loop lengths, relaxation stages and with two types of stitches and linings variation) Conventional Method Simple Low Cost Manual Drape Elevator Method Image Analysis Method Samples without variation Samples with variation Samples without variation Samples with variation Samples without variation Samples with variation Stitch Variation Lining Variation Stitch Variation Lining Variation Stitch Variation Lining Variation Type I Type II 40 s 80 s Type I Type II 40 s 80 s Type I Type II 40 s 80 s 38

5 3.2 MATERIALS AND METHODS The materials and methods selected for the research work are discussed below. Bamboo, cotton, modal and viscose staple fibres of cellulosic origin were selected for the study. Fifty percent of bamboo and fifty percent of cotton fibres were blended together in the blow room and were ring spun into blended yarn of 40 Ne. Similarly 100 percent modal and 100 percent viscose fibres were individually ring spun into 40 Ne yarn. The physical and mechanical properties of fibres used in the study are given in the Table 3.1. Fibre Type Average Fibre Length (mm) Table 3.1 Properties of Bamboo, Cotton, Modal and Viscose Fibres Fibre Fineness (dtex) Initial Modules (cn/tex) Dry Tenacity (cn/tex) Wet Tenacity (cn/tex) Elongation at Break (%) Moisture Regain (%) Bamboo Cotton Modal Viscose YARN PRODUCTION The step by step process followed for producing 40 Ne yarn of 50:50 bamboo/cotton blend, 100% modal and 100% viscose yarns is given in the form of a flow chart as shown in Figure

6 Fibres (Bamboo/Cotton, Modal and Viscose) L.R. Blow Room (Opening, Blending and Cleaning) Carding Draw Frame Draw Frame Simplex Ring Spinning 40 Ne Yarn Figure 3.2 Flow Diagram of Yarn Production In the process of yarn production, the fibres were passed through a Platt s blow room consisting of two blended hopper bale opener, type 490 air stream cleaner and MB 23 single scutcher lap unit equipped with Kirschner beater. The scutcher lap from the blow room was processed on 40 inch cards. Normal speeds and settings were used for bamboo/cotton, modal and viscose fibres. All the samples were processed through two passages on LR high speed draw frame model Do/2 with polar drafting system followed by LR can fed inter model G.S. After two passages of drawing, slivers of bamboo/cotton, modal and viscose were processed in Lakshmi Rieter, Simplex and spun into yarns of number 40 Ne on ring spinning machine using a spindle speed of 10,500 RPM. Three types of yarns namely (50:50) bamboo/cotton blend, (100%) modal and (100%) viscose 40

7 were produced. The nomenclature of yarn samples are presented in the following Table 3.2. Sample No Table 3.2 Nomenclature of Yarn Samples Description of Samples Sample Code Yarn Count (Ne) Bamboo/cotton yarn (50 : 50) Modal Yarn (100%) Viscose Yarn (100%) BCY MY VY 40 (14.76 tex) 40 (14.76 tex) 40 (14.76 tex) 3.4 FABRIC PRODUCTION In this study, spun yarns of bamboo/cotton blend, modal and viscose were utilized to produce weft knitted fabrics of 1x1 rib and interlock. The weft knitting machinery details, loop length and tightness factor selected, are given in Tables 3.3 and 3.4 respectively. Figures 3.3 (a) and (b) show the graphical representation of weft knitted structures. Table 3.3 Weft Knitting Machinery Details S.No Particulars Rib Interlock 1 Machine Pailung,Taiwan Pailung,Taiwan 2 Model Pl.xd2.5ba/c Pl.xd2.5ba/c 3 Diameter (inches) Gauge Number of feeders Number of needles Speed (rpm)

8 Table 3.4 Loop Length and Tightness Factor Selected for Weft Knit Structures S.No. Weft Knitted Fabrics Sample Code of Knitted Structures 1 1 Rib Interlock Tightness Factor (Tex 0.5 cm -1 ) Loop Length (cm) 1. Bamboo/ cotton Blend (50:50) BCR 1 BCI BCR 2 BCI BCR 3 BCI MR1 MI Modal (100%) MR2 MI MR3 MI VR1 VI Viscose (100%) VR2 VI VR3 VI The numbers 1, 2 and 3, indicated in the sample codes represent the large, medium and small loop lengths such as 0.31cm, 0.29cm and 0.27cm. 1 1 Rib Interlock (a) (b) Figure 3.3: Graphical Representation of Weft Knitted Structures 42

9 3.5 FABRIC PREPARATION As a preparatory step to remove the foreign matters, the weft knitted fabrics were desized, scoured and bleached by making use of the recipe given below: Sodium hydroxide 3% Sodium silicate 3% Hydrogen peroxide 3% Wetting agent -0.1% Material liquor ratio 1:20 Time duration 1 hour Temperature 60 0 c The measured amount of sodium hydroxide and sodium silicate were taken and wetted with wetting agent followed by hydrogen peroxide. Water was added as per the material liquor ratio; the temperature was maintained at 60 o c and was kept for one hour. After pre-treatments, the fabric samples were subjected for dyeing and conditioning. 3.6 DYEING Reactive dye was chosen due to its good colour fastness properties, brilliancy, easy dyeability and which are more suitable for dyeing natural and regenerated fabrics of cellulosic origin. Fabric dyeing was carried out based on normal industrial parameters and by following the dyeing recipe given below, Reactive dyes Yellow F4G- 0.35% Turquoise blue H2GB 0.5% Sodium chloride 40% Soda ash 10% Material liquor Ratio 1:20 43

10 Temperature 60 0 c Time duration 1 hour Shade 5% After the process of dyeing, the fabric samples were soaked in water consisting of soap oil of 5ml per liter for 12 hours at 30 C, and then hydro extracted and flat dried at 60 C. The fabric samples were then conditioned at a standard atmosphere of 27 ± 2 C and with a relative humidity of 65% ± 2% for 24 hours. 3.7 YARN TESTING Prior to yarn testing, yarn samples of bamboo/cotton, modal and viscose were kept in the standard atmospheric conditions of 65% ± 2% relative humidity and temperature of 27 ± 2 C for 48 hours Physical Properties After conditioning the yarn samples, their physical properties such as yarn count, twist, strength, elongation, evenness, imperfections and hairiness were subsequently measured. Table 3.5 gives the details of instruments and standards used for assessing the physical properties of yarns. 44

11 Table 3.5 Instruments and Standards Used for Assessing the Properties of Yarns S.No. Yarn Properties Instruments Testing Standards I Physical properties i. Yarn Count Statex Yarn Count System ASTM D ii. Yarn Twist Electronic Yarn Twist Tester ASTM D 1422 iii. iv. II i. ii. iii. Yarn Strength & Elongation Yarn Evenness Imperfections & Hairiness Mechanical properties Yarn to Yarn Dynamic Friction Yarn to Metal Dynamic Friction Yarn Abrasion Uster Tensojet Tester ASTM D a Uster 5 Evenness Tester ASTM D Lawson-Hemphill Friction Tester Lawson-Hemphill Friction Tester CTT Yarn Abrasion Tester (Constant Tension Transport) ASTM D 3412/041 ASTM D ASTM LH-403 CTT- YAT Measurement of Yarn Count and Twist Yarn count was determined by using Statex yarn count system, which consisted of a combination of electronic balance and computer. Using this system, twenty readings were taken and the mean value and CV percentage were calculated. Yarn twist was assessed on electronic yarn twist tester under a standard tension of 0.5 cn/tex and an average of fifty readings were taken Measurement of Yarn Strength and Elongation The tensile properties of yarns namely breaking strength and elongation were measured by Uster Tensojet Tester using the single strand method. The tenacity and mean elongation, along with respective CV percentage were calculated. 45

12 Measurement of Yarn Evenness, Imperfections and Hairiness Yarn evenness was determined by Uster-5 evenness tester equipped with a quadratic integrator. The imperfection indicator was used in conjunction with the evenness tester for recording the thin places, thick places and neps per kilometre. Average values of twenty observations were reported along with the total imperfections per kilometre of each yarn sample. Yarn hairiness was carried out on Uster yarn hairiness tester with path setting at 3mm.Twenty readings were taken and mean values were calculated. shown below, Yarn Quality Index (YQI) was calculated using Barella s (1976) equation as YQI Yarn Tenacity Elongation = (3.1) U% Mechanical Properties The yarn samples were also tested for yarn flexural rigidity and frictional properties. For the above tests, ten readings were taken and the mean values were calculated and recorded Measurement of Yarn to Yarn Dynamic Friction Coefficient of yarn to yarn dynamic friction was measured using Lawson- Hemphill friction tester according to ASTM D 3412/01 standard. The speed was maintained at 0.02m/min, input tension at 9.81 mn/tex, apex angle at 35 and the speed at 0.02 m/min. From the measured tension, the coefficient of friction was calculated by using the formula given below, T T 1 2 µθ = e (3.2) 46

13 Taking logarithms on both the sides, this equation reduces to T T 1 µ = 0.733log (3.3) 2 Where, µ = Coefficient of friction. θ = Angular contact in radians (θ = π = 3.14 radians) T 1 = Output tension T 2 = Input tension Measurement of Yarn to Metal Dynamic Friction Coefficient of yarn to metal friction was measured using Lawson-Hemphill friction meter as per ASTM D standard. The speed of yarn was maintained at 100 m/min, with wrap angle of 180.The standard friction surface of 12.7 mm diameter chrome-plated steel of 4-6µm roughness. The coefficient of friction was calculated from the measured input and output tensions as the yarn runs at constant speed over the rod Measurement of Yarn Abrasion In this test method, the yarn was made to run over a standard abrasion wire. When the wire breaks, the test stops. The amount of yarn that is required to break the wire is noted and compared with other sample yarns abrasion test results. In this comparison test, the higher number indicates less abrasive yarn Measurement of Yarn Flexural Rigidity Flexural rigidity is the resistance of yarn to bending. There is no affordable and standard method available for measuring the flexural rigidity of yarns. This property has been measured by making use of custom built yarn flexural rigidity tester developed for this study which is shown in Figure 3.4 (a) and its schematic diagram in Figure 3.4 (b). 47

14 Figure 3.4 (a): Custom Built Yarn Flexural Rigidity Tester F D A B E C G Figure 3.4 (b): Schematic Diagram of Yarn Flexural Rigidity Tester A Sample Yarn B Rider C Measuring scale D Yarn loop Holder Pin E Measuring Scale Holder F Transparent Glass Chamber G Glass Tube to form Yarn loop 48

15 The sample yarn was formed into a loop with a radius of 0.8 cm and hung on a yarn loop holder pin situated near the measuring scale. A known load(w) of 0.03gf in the form of a rider was applied and the deflection value(d) was measured and the mean values of average of ten samples were recorded. The yarn flexural rigidity was calculated, using the formula given below, Flexural Rigidity = kwl 2 (cosθ/tanθ ) (mn.mm 2 ) (3.4) Where, K = Constant value (0.0047) W=Applied load (gf) L= 2πr and θ = 493 d/l d = Deflection value in cm Specific flexural rigidity is obtained by dividing flexural rigidity by tex Measurement of Yarn to Needle Static Friction Coefficient of yarn to needle static friction was measured using a simple custom built yarn friction tester as shown in Figure 3.5(a) and its schematic diagram in Figure 3.5(b). Figure 3.5(a): Custom Built Yarn to Needle Static Friction Tester 49

16 Yarn samples of 250mm (25cm) in length were taken. A metal needle with a constant weight of gm was threaded on the sample yarn and the ends of yarn was tied on to metallic hooks provided at both ends of the sliding beam. The friction of yarn was measured similar to inclined plane method. B 1 A B 2 C D E Figure 3.5 (b): Schematic Diagram of Yarn to Needle Static Friction Tester A Sliding Beam C Metal Needle (Traveller) D Protractor B 1 and B 2 Metallic Hooks E Protractor Holding Stand The deflection angle at which the traveler starts to slide is noted from the protractor. For each yarn sample of bamboo/cotton blend, modal and viscose, ten readings were taken, mean values were calculated and the coefficient of yarn friction was calculated by making use of the formula given below, µ = tan θ (3.5) Where, µ = coefficient of yarn friction θ = angle This method is based on the method used by Howell and Mazur (1953). 50

17 Yarn Wicking Wicking behaviour of yarn samples was assessed by making use of an apparatus developed for measuring the vertical wicking of weft knitted fabric samples, which is shown in Figure 3.6, based on DIN standard. Figure 3.6: Instrument Developed for Measuring Vertical Wicking of Fabrics The yarn samples of bamboo/cotton blend, modal and viscose of 15cm in length were suspended with its lower end immersed in a reservoir of distilled water and wicking height was monitored at a regular time interval of every minute upto a maximum of 10 minutes. The readings of ten samples were recorded and the mean values were calculated. 3.8 RELAXATION TREATMENTS GIVEN FOR WEFT KNITTED FABRICS Rib and interlock structures of bamboo/ cotton, modal and viscose of three different loop lengths which were dyed and subjected to three stages of relaxation such as dry, wet and full by following BS 4931 and BS 4923 standard methods respectively. 51

18 3.8.1 Dry Relaxation Weft knitted fabrics, knitted in tubular form were laid free from constraints on a flat surface to relax in dry state in a standard testing atmosphere of 27 0 ± 2 0 C and a relative humidity of 65% ± 2% for 24 hours Wet Relaxation Fabric samples were put into a large stainless steel tub containing water maintained at a constant temperature of 40 C for twelve hours. Then the material was hydro extracted and then allowed to dry for three days and conditioned in a standard testing atmosphere of 65% ± 2% relative humidity and 25 ± 2 C for 24 hours. The samples were subjected to relaxation treatments as recommended by STAR FISH method Full Relaxation In order to achieve fully relaxed state, the wet relaxed samples were further subjected for full relaxation. This was achieved by soaking the fabric samples at 40 C for 24 hours followed by hydro extraction and tumble drying for 1 hour at 70 C. This treatment cycle was repeated for three times and finally the samples were conditioned in a standard testing atmosphere of 65% ± 2% relative humidity and 25 ± 2 C for 24 hours. The nomenclature of weft knitted fabric samples is presented in Table

19 Table 3.6 Nomenclature of Weft Knitted Fabric Samples S.No. Description of Samples Sample Code Loop Length (cm) 1 Bamboo/Cotton Rib 1 BCR Bamboo/Cotton Rib 2 BCR Bamboo/Cotton Rib 3 BCR Bamboo/Cotton Interlock 1 BCI Bamboo/Cotton Interlock 2 BCI Bamboo/Cotton Interlock 3 BCI Modal Rib 1 MR Modal Rib 2 MR Modal Rib 3 MR Modal Interlock 1 MI Modal Interlock 2 MI Modal Interlock 3 MI Viscose Rib 1 VR Viscose Rib 2 VR Viscose Rib 3 VR Viscose Interlock 1 VI Viscose Interlock 2 VI Viscose Interlock 3 VI The numbers 1, 2 and 3 indicated in the sample codes represent the large, medium and small loop lengths such as 0.31 cm, 0.29 cm and 0.27 cm. 3.9 FABRIC TESTING Prior to objective evaluation, the dry, wet and full relaxed 1x1 rib and interlock structures of bamboo/cotton, modal and viscose were conditioned in a standard testing atmosphere of 27 o ± 2 o C and 65% ± 2% relative humidity to facilitate accuracy in physical testing. 53

20 3.9.1 Measurement of Physical Properties Loop Length To compute the loop length of dry, wet and full relaxed weft knitted fabrics, ten samples from each with a size of 100mm x 100mm were cut. Ten courses were then unraveled from each sample and measured for course length using Shirley crimp tester under a pre-determined tension of 0.1gf/tex. The mean values of course length were calculated and this was divided by the number of needles of the respective cylinder yielding the loop length of the respective sample. The actual loop length and the corresponding measured values of yarn linear densities were used to calculate the actual tightness factor according to the formula given below, Where, K = l = Loop length in centimetre tex l K= Tightness Factor (Tex 0.5 cm -1 ) A number of ten observations were made for each fabric sample. (3.6) Fabric Weight Weft knitted fabric samples of 10cm in diameter were cut using Techno GSM cutter based on ASTM 3776 standard and were weighed using Samsung Electronic precision balance. The mean weight in grams was multiplied by 100 to obtain the fabric weight in grams per square metre Fabric Thickness MAG thickness tester was used to measure the thickness. Samples with 100mm x100mm in size were cut and each specimen was placed between the anvil and presser 54

21 foot of the thickness tester gauge. The fabric thickness was then noted from the dial readings of the tester. The mean values were calculated and expressed in millimetres Measurement of Mechanical Properties The mechanical properties related to fabric stiffness, bursting strength, abrasion resistance and surface friction were determined for dry, wet and full relaxed weft knitted fabric samples. The mean values of ten samples were calculated Bursting Strength MAG bursting strength tester based on IS was used to determine the bursting strength. Ten readings from each fabric sample were taken. A specimen with 30mm in diameter was clamped over an expandable diaphragm. The diaphragm gets expanded by fluid pressure to the point as the specimen ruptures. The difference between the total pressure required to rupture the specimen and the pressure required to inflate was reported as bursting strength. The mean values were calculated and expressed in kg/cm Abrasion Resistance The abrasion resistances of weft knitted fabrics of bamboo/cotton, modal and viscose subjected for dry, wet and full relaxed states were assessed using Martindale abrasion tester based on BS 5690 standard. A standard size of 38mm diameter sample was held by a modified specimen holder by a pinned ring. A flattened rubber ball pushes the samples as the holder was tightened thus stretching it. The holder was then mounted on the Martindale tester with a 12kPa pressure and the test was carried out. The sample was inspected at suitable intervals until the material develop an unacceptable level of thinning. The sample weight was then measured in gm/1000 rubs and mean values were calculated respectively. 55

22 Bending Length and Flexural Rigidity Shirley stiffness tester based on BS 3356 standard was used to measure the bending stiffness of fabrics. The test specimens with 25mm in width and 200mm in length were cut both in wale and course directions. The bending stiffness was determined by allowing the samples to bend to a fixed angle under its own weight. The length of the fabric required to bend to that angle was measured as the bending length. Four readings were taken from each sample, one face up and one face down on first end and then the same for the second end. Finally the mean bending length was calculated using the formula, C= lf ( θ) 1 Where, C = bending length l = length of the fabric θ = angle of inclination and 1/3 cos1/ 2 θ f 1 θ = = 8 tan θ 0.5 (3.7) (3.8) Flexural rigidity of the fabric was calculated from bending length (C) and weight using the formula, Flexural rigidity (G) = WC 3 x 10 3 mg.cm (3.9) Where, W = fabric weight in gm/cm 2 C = bending length in cm Measurement of Aesthetic Properties Aesthetic properties are one among the broad classification of fabric properties, in which fabric drape is closely associated with it. It is difficult to categorize exclusively different properties under each category because they are related to one another. The 56

23 property of drape is one such property that falls under the psychological comfort as well as aesthetic properties of fabrics. The DC values of weft knitted fabrics were assessed by Conventional Method (CM), Simple Low cost Manual Drape Elevator Method (SLMDEM) followed by Image Analysis Method (IAM). A comparison between the DC values of these three methods has been done without any variation and with two type of stitches and linings variation. Apart from the assessment and comparison of DC values, various non-standard drape parameters were also measured Measurement of Fabric Drape by Conventional Method In the conventional method the drape coefficient was measured according to BS EN standard using MAG drape tester. It consists of a draping chamber (I) and an exposing chamber (II) as shown in Figure 3.7 (a) and its schematic diagram in Figure 3.7 (b) respectively. A circular weft knitted fabric specimen of 25cm in diameter was concentrically sandwiched between two smaller horizontal discs with a diameter of 12.5cm and the unsupported annular ring of fabric sample was allowed to hang down under the action of gravity. A circular light sensitive ammonia paper with a diameter similar to that of fabric specimen was placed under acrylic sheet just below the circular specimen support present in the draping chamber. A planner projection of the draped image shadow gets recorded on the circular light sensitive ammonia paper due to the influence of 2000 watts mercury light, ammonium vapours from the concentrated ammonium solution kept in a bowl in the exposing chamber. The light sensitive circular ammonia paper with the exposed draped profile was folded and weighed to give the initial weight (W 1 ). 57

24 Figure 3.7 (a): Conventional MAG Drape Tester I A I. Draping Chamber II. Exposing Chamber B D C E F H G Figure 3.7 (b): Schematic Diagram of Conventional MAG Drape Tester A Mercury Light B Smaller Specimen Supporting Disc (a) C Smaller Specimen Holding Disc (b) D Fabric Sample E Circular Specimen Support F Transparent Acrylic Sheet G Thick Wire Mesh H Glass Bowl I Switch and Cord with Plug Pins 58

25 The paper was then cut along the outline of the shadow of the draped profile and was weighed to give the final weight (W 2 ). Drape coefficient was calculated using the equation given below, Drape Coefficient (%) = W 2 / W 1 x 100 (3.10) Where,W 1 = Initial weight of the circular ammonia sheet W 2 = Weight of the ammonia sheet after cutting it along the outline of the draped profile. The folds present along the contour of the draped profile are referred to as nodes. The numbers of nodes formed were recorded for each sample Measurement of Fabric Drape by Image Analysis Method In image analysis method, the instrument set up consisted of a simple low cost manual drape elevator, a digital camera to capture the draped image of the mounted fabric specimen, a computer to analyse the captured image and translate it into suitable output. Image analysis set up for the measurement of fabric drape is shown in Figure 3.8. Digital Camera Simple Low cost Manual Drape Elevator UPS Figure 3.8: Schematic Diagram of Drape Measurement Using Image Analysis Method Computer 59

26 A circular fabric sample with a diameter of 25cm is mounted and executed similar to that of conventional method. The difference is that, after allowing the sample to fall, the image of the draped configuration was captured using a digital camera. Then the captured image was transferred to the computer and the raw image was cropped, calibrated by setting the dimension of the circular ring for 25cm and then the draped configuration of the image was selected using Magnetic Lasso tool in Adobe Photoshop, which attaches a boundary to select the dark region based on pixel value, reducing the variation in the selection process. The drape coefficient of the fabric was calculated using the image pixels and the image resolution of the draped specimen. The following equation given below was used to determine the drape coefficient values. Total selected Pixels Pixels per cm 2 - Area of supporting disc (cm 2 ) DC % = x 100 Area of the specimen (cm 2 ) - Area of supporting disc (cm 2 ) OR A s - A 1 DC % = x 100 (3.11) A 2 - A 1 Where, A s = the area of draped fabric image A 1 = the area of supporting disc A 2 = the area of circular fabric sample Apart from measuring the drape coefficient values of original samples without variation, two types of stitches and linings were introduced to measure and assess the influence of stitches and linings in measuring the drape coefficient of weft knitted fabrics. Details concerning sewing requirements with stitches and lining materials are given in Tables 3.7 and 3.8 respectively. 60

27 Table 3.7 Details of Sewing Requirements and Stitches S.No Machine Details Single Needle Lock Stitch Machine 3-Thread Flat Lock Machine 1. Brand Name Juki Siruba 737 E 2. Made Taiwan Taiwan 3. Feed Mechanism Drop feed Differential feed 4. Needle System Db 1 Db 1 5. Machine Power ¼ HP ¼ HP 6. Sewing Thread Cotton Cotton 7. Thread ticket No Thread ply No Needle Medium ball point Medium ball point 10. Needle size Sewing thread type Z Twist Z Twist 12. Number of spools Sewing thread size T27 T Thread ply 2ply 2ply 15. Stitches per inch Stitch tension Medium Medium 17. Stitch size 3mm 3mm 18. Stitch classes Class 301 Class

28 S.No Sample Code Count Lining-1 (Bleached 100% Cotton) Lining-2 (Bleached 100% Cotton) Table 3.8 Details of Lining Materials Warp (cm) Weft (cm) GSM Thickness (mm) 40 s s Unlike conventional method in the image analysis technique using simple low cost manual drape elevator, the drape coefficient values of weft knitted fabrics with stitches and lining variation were also measured. The simple low cost manual drape elevator fabricated for the study was utilized to capture the draped image. By making use of digital camera, the image was grabbed and processed by using Magnetic Lasso tool in Adobe Photoshop software, as explained in image analysis method. In analysing the drape profile of series of weft knitted fabrics, image analysis enabled to assess further more non standard drape parameters such as Drape Distance Ratio (DDR), Fold Depth Index (FDI) and Amplitude to Average Radius Ratio (ARR) apart from DC and NN. For estimating the digital image and to make it clear, the image was converted into binary image, which was then utilized to calculate the non-standard drape parameters, as shown in Figure 3.9. These new parameters were determined based on the theoretical equations suggested by Behera and Pattanayak (2008), in their study on measurement and modeling of drape using digital image processing. Figure 3.9 shows that draped fabric image indicating the angle and radius needed for the estimating the non-standard drape parameters. 62

29 (Source: Behera and Pattanayak 2008) Figure 3.9: Draped Fabric Image indicating the Angle and Radius Needed for Estimating the Non-standard Drape Parameters From the Figure 3.9, x i = r i cos θ i and y i = r i sin θ I (3.12) Average radius is r a = (1/n) Σr i (3.13) Area for the triangle (A) of (0, 0), (X i, Y1) and (X 2, Y2) points can be denoted by following relationship: 1 = r1 r sin θ 2 A 2 (3.14) and the total area for the boundary curve(s) can be given by the following relationship; S = n= 1 i= r r i i+ 1 sin θ (3.15) Where, r 1 and r 2 are the radii of the supporting disc and undraped fabric sample respectively. The angle and radius at different points are needed to measure the area. For this, all the centre point of the binary image is located and then it is rotated by a constant 63

30 angle and radius is calculated at all points. For the calculations, boundary of the fabric image is approximated by 1 and so that there are 360 points on the boundary of the image. Therefore, θ = 1 and n = 360, with these parameters the various drape parameters such as DC, NN, average radius (r avg ), maximum radius (r max ), minimum radius (r min ), Drape Distance Ratio (DDR), Amplitude to Average Radius Ratio (ARR) and Fold Depth Index (FDI) were determined using the following relationships given below, As A1 DC(%) = 100 (3.16) A A 2 1 r2 ravg DDR(%) = 100 (3.17) r r 2 1 rmax rmin FDI(%) = 100 (3.18) r r 2 1 rmax rmin ARR = cm (3.19) 2 Where, A s the area of draped fabric image A 1 the area of fabric supporting disc A 2 the area of undraped fabric sample r 1 the radius of fabric supporting disc r 2 the radius of undraped fabric sample r max the maximum radius of draped fabric image profile r min the minimum radius of draped fabric image profile r avg the average radius of draped fabric image profile Determination of Comfort Properties Related to Moisture Management Fabrics meant for apparel manufacturing must possess good moisture transmission property which influences the comfort properties. Clothing worn next to skin should absorb the moisture from the body as well as transmit it to the atmosphere. Apart from 64

31 absorption behaviour, there are other moisture related properties that impart thermo physiological comfort of fabrics like drying time, air permeability and wicking behaviour Wettability A series of weft knitted 1 1 rib and interlock fabrics of bamboo/cotton (50:50), modal (100%) and viscose (100%) of cellulosic origin was examined for absorbency tests such as wettability, sinking time, absorptive capacity, vertical wicking and air permeability to assess the comfort properties related to moisture management by following standard test methods. Finally, a comparison was made between yarn and fabric wicking. The arrangement setup for measuring the property of wettability is shown in Figure Figure 3.10: Wettability Test The wettability test was carried out based on BS 4554 standard method. The test specimen was clamped on to an embroidery frame of 150mm in diameter so that it was held taut and away from any surface. A burette with a standard tip size was clamped 6mm above the horizontal surface of the sample. The fabric was illuminated at an angle 65

32 of 45 and was viewed at 45 from the opposite direction. At the start of the test, a drop of liquid was allowed to fall from the burette and the timer started. When the diffuse reflection from the liquid vanishes the timer was stopped. Five areas on each specimen were tested and then the average values were determined Sinking Time This is a simple test for assessing the water absorption capacity of the textile materials. The arrangement setup for measuring the sinking time is shown in the Figure Figure 3.11: Sinking Time Test A fabric specimen of 25 mm x 25 mm in size was taken and was dropped from a height of 25mm, onto the surface of distilled water and the length of time taken by the fabric to sink was measured. Ten readings were taken and the mean values were calculated Absorptive Capacity Absorptive capacity provides a measure of the amount of liquid held within a test specimen after specified times of immersion and drainage, report Das et al., (2009). The test for absorptive capacity was conducted by following the principles of test described in ASTM D standard. Ten specimens of 76mm x 76mm from each fabric sample were weighed and immersed in distilled water at 20 o C for a specified time, taken out and 66

33 the excess water was drained prior to weighing. The liquid absorptive capacity was given as a percentage of the original mass of the test specimen, by making use of the equation given below, ( B A) Water absorbency (%) = x100 A (7.1) Where, A = Specimen weight before immersion B = Specimen weight after immersion The mean percentage absorption was then calculated Vertical Wicking The vertical wicking of weft knitted fabrics was determined by measuring the wicking height against gravity along the course and wale directions. The test was conducted using a vertical wicking tester based on DIN standard. The apparatus used for vertical wicking is given in Figure A fabric strip of 150 mm x 25 mm was suspended vertically with its lower end immersed in a reservoir of distilled water. Figure : 3.12 Vertical Wicking of Weft Knitted Fabrics 67

34 The duration of each test was 10 minutes and the height reached was noted in centimetres with respect to the clamped scale. Each experiment was carried out for ten samples and average was calculated Air Permeability Air permeability is a property of textile materials of how well it enables the passage of air through it. It is the volume of air passing through unit per second and is normally represented as cm 3 /cm²/ sec. The Prolific air permeability tester was used for testing based on IS 11056: 1984 standard. The test fabric samples were preconditioned in a standard atmosphere of 65% ± 2% relative humidity and 27 ± 2 C temperature for 24 hours. The air permeability tester consists of an arrangement to hold the test specimen between two flat faces so as to expose a known area to the flow of air through it, a vacuum system to draw air through the exposed area of the test specimen, arrangement to measure the volume of air flowing through the test specimen and arrangement to measure the pressure drop between the two faces of the test specimen as a result of flow of air. The test specimen is held between two annular ring shaped grips. The grips are lined with rubber gaskets to reduce flow of air through the edges. The two grips can be brought in contact with each other with the help of a hand operated screw arrangement. The test area can be altered by placing adaptor discs of different openings in the grips. The vacuum needed to draw air through the exposed area of the test specimen is created with the help of a vacuum pump supplied with the equipment. The volume of air passing through the test area is measured with the help of a set of rotameters. The mean values were then calculated STATISTICAL ANALYSIS The test results were analysed statistically with the view to finding out the samples having better correlation, significant differences and for analysing the deviations between the three different types of weft knitted fabrics. 68

35 Regression analysis was used to analyse the relationship between wickability of yarns and time in respect of weft knitted fabrics. Correlation coefficient was employed to find out the relationship between drape coefficient and mechanical properties of weft knitted fabrics. ANOVA was used to check the significant difference of fabric friction. Standard deviation was used for analysing the deviation of drape coefficient values measured by conventional and simple low cost manual drape elevator methods followed by image analysis. 69