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PLEASE SCROLL DOWN FOR ARTICLE This article was downloaded by: [Hong Kong Polytechnic University] On: 16 March 2011 Access details: Access Details: [subscription number 912320008] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Journal of the Textile Institute Publication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t778164490 Compression property and air permeability of weft knitted spacer fabrics Yanping Liu a ; Hong Hu aa Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon,Hong KongFirst published on: 26 January 2011 To cite this Article Liu, Yanping and Hu, Hong(2011) 'Compression property and air permeability of weft-knitted spacerfabrics', Journal of the Textile Institute, 102: 4, 366 — 372, First published on: 26 January 2011 (iFirst) To link to this Article: DOI: 10.1080/00405001003771200 URL: http://dx.doi.org/10.1080/00405001003771200 Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdfThis article may be used for research, teaching and private study purposes. 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The Journal of The Textile Institute Vol. 102, No. 4, April 2011, 366–372 ISSN 0040-5000 print/ISSN 1754-2340 onlineCopyright © 2011 The Textile InstituteDOI: 10.1080/00405001003771200http://www.informaworld.com TECHNICAL NOTECompression property and air permeability of weft-knitted spacer fabrics Yanping Liu and Hong Hu* Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong TaylorandFrancis ( Received 26 November 2009; final version received 11 March 2010 ) 10.1080/00405001003771200 This paper presents an investigation of the compression properties and air permeability of weft-knitted spacer fabrics.Twenty spacer fabrics were knitted on a computerized flat knitting machine with different weft knit patterns, spacer yarns, and loop lengths (stitch cam settings). Their compression property and air permeability were tested with theKawabata Evaluation System for Fabrics (KES-F). The influences of different factors were discussed and compared.The results obtained provide some useful information for new spacer fabric development. Keywords: spacer fabrics; knitting; compression; air permeability; KES-F Introduction Spacer fabric is a novel kind of three-dimensionaltextile structure consisting of two separate outer fabriclayers that are joined together but kept apart by spacer yarns. Spacer fabrics can be manufactured by warp knit-ting (Ye, Fangueiro, Hu, & Araújo, 2007), weft knitting(Dias, Monaragala, Needham, & Lay, 2007), weaving(Li, Wang, Zhang, & Wu, 2009), non-woven (Vasile,Langenhove, & Meulemeester, 2006), or even braiding(Milwich, Speck, Speck, Stegmaier, & Planck, 2006)technologies. In the recent years, great attention has been paid to weft-knitted spacer fabrics due to their good transversal compressibility and excellent air permeability. These properties are very important for improving the wearing comfort of spacer fabrics used inapparels and medical care. Despite a great deal of inves-tigations that have been done to exploit the applicationsof weft-knitted spacer fabrics, systematic studies onthese properties are still very limited.Weft-knitted spacer fabrics can be produced withdifferent kinds of fibre materials on both flat knittingand circular knitting machines (Dias et al., 2007; Yip & Ng, 2008). Recently, weft-knitted spacer fabrics madeof monofilaments as the spacer layer and elastic yarnsas the outer layers have found applications in apparelsand medical care due to their good transversalcompressibility and excellent planar elasticity. Yip and Ng (2008) experimentally investigated the physical and mechanical properties of elastic weft-knitted spacer fabrics used for intimate apparels. However, only oneweft-knitted structure was used in their study. Pereira,Anand, Rajendran, and Wood (2007) investigated thestructures and properties of weft-knitted spacer fabricsfor knee braces and compared them with commercial products. They found that weft-knitted spacer fabricswith appropriate elastic and recovery properties havedesirable physical, mechanical, and thermophysiologi-cal characteristics for knee braces. Unfortunately, thefabric structure details were not given in their article.Based on the existing literature, it has been found thatthe relationships between the knit structures and the properties of the weft-knitted spacer fabrics are still notclearly established.This paper presents a systematic study of compres-sion and permeability properties of weft-knitted spacer fabrics. The effects of knitted structure, spacer yarn, and loop length (stitch cam setting) will also be discussed. Experimental Spacer fabrics preparation Twenty kinds of weft-knitted spacer fabrics were manu-factured on a Stoll CMS 822 E7.2 computerized flatknitting machine of gauge 14. While the outer layers of all spacer fabrics were made from nylon/spandex (70D/20D) covered yarn, the spacer layer was made from polyester monofilaments with three different diameters(0.08, 0.09, and 0.1 mm). As shown in Figure 1, four weft knit spacer structures with different connectingdistances of spacer yarns were used (denoted as A, B, C,and D, respectively). The structural parameters of thesefabrics are listed in Table 1. After knitting, all fabricswere firstly steamed on both sides by placing them on asteam table and then were cut into the required sample *Corresponding author. Email:
[email protected] D o w nl o ad ed B y : [ H o n g K o n g P ol y t e ch ni c U ni v e r si t y] A t : 04 :44 16 M a r ch 2011 The Journal of The Textile Institute 367 size (20 cm × 20 cm). All samples were conditioned under the standard condition, BS1051, at 20 ° C and 65%relative humidity, for 24 h before testing. Figure1.Knitpatternandcross-sectionofspacerfabrics. Compression test The KES-FB3-A compression tester was used for test-ing the compression property of the spacer fabrics. Thetesting method used was according to the instructionmanual from Kato Tech Co., Ltd. (Kawabata & Niwa,1996). The parameters obtained from the compressionhysteresis curves are defined in Table 2. The samplesize used in the compression test was 20 cm × 20 cmand the maximum pressure used was 300 gf/cm 2 . Ineach case, 10 specimens were tested and the averagevalues were reported. Air permeability test The air permeability was evaluated using the KES-F8-AP1 air permeability tester. The testing result, expressed as air resistance ( R ), was recorded in kPa · s/m, in whicha larger value of R indicates poorer air permeability of the fabric. The sample size used in this test was also20 cm × 20 cm. In each case, 10 specimens were tested and the average values were reported. ANOVA analysis Analysis of variance (ANOVA) was performed usingthe Statistical Package for the Social Sciences (SPSS)for each dependent variable. The p values within paren-theses in the following text are the significance levels of different dependent variables. The higher the p values,the lower the significance. p ≤ 0.05 means that thedifference is significant. Results and discussion Structure features As shown in Figure 1, tuck stitches are used to connectthe two outer layers together with the monofilaments.Different tuck connecting methods can result indifferent monofilament (spacer yarn) inclination angles.Here, the inclination angle of a spacer yarn is defined asthe angle formed between the outer layer and themonofilament. For the spacer fabrics made from no-elastic yarns, it is normal that the inclination angledecreases when the connecting distance of two tuck stitches increases. However, when elastic yarns are used for the outer layers, the situation becomes quite differ-ent. Instead of decreasing the inclination angle, increas-ing the connecting distance of tuck stitches will result inthe increase in the inclination angle of the spacer yarns,as shown in Figure 1(b) and 1(c). The reason is that highshrinkage of the nylon/spandex covered yarn causes thesurface loop wales to come more close after the fabricis removed from the machine and this leads to a higher inclination angle of the spacer yarns. The maximalinclination angle is 90 ° when the spacer yarns are perpendicular to the outer layers. Increasing the inclina-tion angle also results in the increase in the fabric thick-ness. So, it is possible to knit spacer fabrics withdifferent thicknesses using elastic yarns for the outer layers on the same flat knitting machine. However, if the connecting distance of the tuck stitches is too long,the inclination angle of the spacer yarns decreasesagain, as shown in Figure 1(d). In this case, the too longconnecting yarns cannot totally be recovered from theinclined position to the vertical position.Table 1 lists the details of all the spacer fabricsknitted. It can be found that the thickness of the spacer fabrics made of the same-diameter monofilaments asspacer yarns increases with the increase in the connect-ing distance of the tuck stitches. This confirms again theabove explanation. In addition, the spacer fabric thick-ness increases when thick monofilaments are used asspacer yarns for some knit patterns. The loop length of the outer layers also has an effect on the fabric thick-ness. Here, the loop length is represented by the needle position (NP) value, which indicates the stitch camsetting. The higher the NP value, the more the looplength. A higher NP value (lower density of the fabric)makes the outer layers more prone to shrinkage and thusleads to a higher fabric thickness. However, the effectof the NP value on the fabric thickness for the spacer layer is different from that for the outer layers. For aspacer layer with NP = 9, the thickness of the fabrics ismore than that for a spacer layer with NP = 10 but lesser than that for a spacer layer with NP = 11 for the knit patterns B and C. This is because the tuck stitches withlong connecting distances are easier to incline. Theinclination of the connecting yarns between the tuck stitches can reduce the fabric thickness. However, as theinclination is limited, the fabric thickness gets increased again when the NP value increase.The area density of the fabrics increases with theincrease in the monofilament diameter. Moreover, theouter layers and spacer layer with higher NP values canincrease the area density. The variation trend for bulk density is not clear due to the different effect of fabricthickness.The number of wales per centimeter (WPC) and courses per centimeter (CPC) can be influenced by themonofilament diameter. Two-way ANOVA tests were performed for samples 1–12 to determine whether therewere any significant differences for WPCs and CPCsdue to different monofilament diameters and tuck connecting distances and their interaction. From D o w nl o ad ed B y : [ H o n g K o n g P ol y t e ch ni c U ni v e r si t y] A t : 04 :44 16 M a r ch 2011 368 Y. Liu and H. Hu Table 1 and the ANOVA results, it can be concluded that a smaller monofilament diameter leads to a higher WPC ( p = 0.000) and CPC ( p = 0.000) for the samefabric structure and a higher NP value. Moreover, theeffects of the tuck connecting distance and the interac-tion between the monofilament diameter and the tuck connecting distance both significantly influence theWPCs ( p = 0.000 and 0.000, respectively) and CPCs( p = 0.000 and 0.000, respectively). However, thevariation trends are not clear.A two-way ANOVA was performed for samples13–16 to examine whether there were any significantdifferences in WPCs due to different NP values of theouter layers. Normally, the outer layers with higher NPvalue (longer stitch loops) can result in smaller WPCs.However, in contrast to CPCs, the inverse case wasobserved, as the WPCs of samples 14 and 16 are higher than those of samples 13 and 15 ( p = 0.000). The reasonfor this unusual phenomenon is that the elastic yarnsshrink more easily when the stitch loop gets bigger (higher NP value). Compression property The compression properties of all the spacer fabricsknitted are listed in Table 3. A series of two-wayANOVA tests were performed for each dependent vari-able to determine whether there were any significantdifferences due to different knit patterns and differentspacer yarns. Figure 1.Knit pattern and cross-section of spacer fabrics. D o w nl o ad ed B y : [ H o n g K o n g P ol y t e ch ni c U ni v e r si t y] A t : 04 :44 16 M a r ch 2011 T h e J o ur n a l o f T h eT e x t i l eI n s t i t u t e 3 6 9 Table 1.The details of different spacer fabrics.SampleKnit patternMonofilament diameter (mm)NP1 a NP2 b Thickness c (mm)Area density (g/cm 2 )Bulk density (g/cm 3 )WPC d CPC d Stitches/cm 2 1A0.089113.3638 (0.1356)0.0454 (0.0001)0.1350 (0.0053)9.4 (0.047)22.5 (0.236)211.5 (1.155)2A0.099113.3897 (0.0920)0.0515 (0.0003)0.1520 (0.0034)9.3 (0.047)21.5 (0.333)200.0 (3.883)3A0.109113.7240 (0.1406)0.0561 (0.0004)0.1507 (0.0068)9.2 (0.047)19.0 (0.333)174.8 (3.201)4B0.089113.5606 (0.1080)0.0454 (0.0001)0.1276 (0.0039)9.4 (0.066)22.5 (0.236)211.5 (1.568)5B0.099113.8383 (0.1491)0.0554 (0.0001)0.1443 (0.0056)9.2 (0.081)22.0 (0.236)202.4 (3.525)6B0.109114.0117 (0.1071)0.0557 (0.0001)0.1390 (0.0037)8.5 (0.066)21.0 (0.408)178.5 (3.742)7C0.089114.4551 (0.2322)0.0506 (0.0001)0.1135 (0.0051)9.0 (0.094)22.0 (0.236)198.0 (3.634)8C0.099114.4807 (0.1755)0.0553 (0.0001)0.1234 (0.0047)8.6 (0.047)21.5 (0.236)184.9 (1.014)9C0.109114.5020 (0.1199)0.0553 (0.0001)0.1229 (0.0032)8.5 (0.047)21.0 (0.236)178.5 (2.993)10D0.089115.3681 (0.2103)0.0599 (0.0002)0.1117 (0.0038)9.4 (0.066)22.5 (0.333)211.5 (4.633)11D0.099115.5493 (0.2802)0.0594 (0.0001)0.1071 (0.0051)8.6 (0.047)22.0 (0.236)189.2 (3.064)12D0.109115.6235 (0.2592)0.0617 (0.0003)0.1098 (0.0054)8.4 (0.066)21.0 (0.408)176.4 (4.643)13B0.099103.2808 (0.1926)0.0431 (0.0001)0.1313 (0.0079)7.8 (0.081)25.0 (0.408)195.0 (4.318)14B0.099124.1162 (0.1194)0.0583 (0.0002)0.1415 (0.0042)9.4 (0.081)21.0 (0.471)197.4 (5.978)15C0.099104.0779 (0.1554)0.0477 (0.0001)0.1171 (0.0045)8.0 (0.047)25.0 (0.236)200.0 (0.707)16C0.099124.9357 (0.1219)0.0595 (0.0006)0.1206 (0.0029)8.3 (0.047)22.0 (0.236)182.6 (0.919)17B0.0910113.1876 (0.0593)0.0510 (0.0005)0.1600 (0.0030)9.1 (0.066)22.0 (0.333)200.2 (3.369)18B0.0911114.1367 (0.0958)0.0583 (0.0001)0.1410 (0.0032)8.7 (0.047)23.0 (0.236)200.1 (3.135)19C0.0910114.2983 (0.1113)0.0567 (0.0003)0.1319 (0.0033)8.5 (0.047)23.0 (0.333)195.5 (3.681)20C0.0911114.5234 (0.0941)0.0573 (0.0001)0.1268 (0.0026)8.6 (0.066)23.0 (0.333)197.8 (3.251) a NP1 is the NP of spacer layer; b NP2 is the NP of outer layer; c fabric thickness was tested using KES at a pressure of 0.5 gf/cm 2 ; d WPC is the number of wales per centimeter; CPC is the number of courses per centimeter. Note: Values within parentheses are the standard deviations. Downloaded By: [Hong Kong Polytechnic University] At: 04:44 16 March 2011
