AIR PERMEABILITY OF POLYESTER NONWOVEN FABRICS. Guocheng Zhu, Dana Kremenakova, Yan Wang, Jiri Militky

Transcription

1 AIR PERMEABILITY OF POLYESTER NONWOVEN FABRICS Guocheg Zhu, Daa Kremeaova, Ya Wag, Jiri Mility Deartmet of textile material egieerig, Techical Uiversity of Liberec, Liberec, Czech Reublic, Studetsá 140/, Tel: , Abstract: Keywords: Air ermeability is oe of the most imortat roerties of o-wove fabrics i may alicatios. This aer aims to ivestigate the effects of thicess, orosity ad desity o the air ermeability of eedle-uched o-wove fabrics ad comare the exerimetal values with two models which are based o hydraulic radius theory ad drag theory, resectively. The air ermeability of the samles was measured by a air ermeability tester FX3300. The results showed that the air ermeability of o-wove fabrics decreased with the icrease i thicess ad desity of samles, icreased with the icrease of orosity, ad the air ermeability was ot directly roortioal to the ressure gradiet. Meawhile, the redictio model based o hydraulic radius theory had a better agreemet with exerimetal values tha the model based o drag theory, but the values were much higher tha the exerimetal results, esecially for higher orosity ad higher ressure gradiet. air ermeability; o-wove fabric; orosity; thicess Itroductio Air ermeability describes the rate of flow of a fluid through a orous material, ad the mathematical exressio is give by q Q At Where q is rate of flow (m/s), Q is volume of flow of fluid through the samle (m 3 ), t is time (s) ad A is the cross-sectioal area (m ). No-wove fabrics stad out as a uique class of orous media, which cotai relatively high volume of air ad very comlex structure due to the radom arragemet of fibres. Air ermeability is oe of the most imortat roerties of owove fabric i may alicatios, Numerous researchers have wored o the air ermeability of o-wove fabrics i both exerimet [1-3] ad aalytical redictio [4-7]. I geeral, two theories are alied for redictig the air ermeability of orous materials: the first based o hydraulic radius theory, ad the secod based o drag theory. Darcy derived a equatio for calculatig the air ermeability based o hydraulic radius theory, which states that rate of flow is directly roortioal to the ressure gradiet causig the flow[8]. The equatio is as follows: Or htt:// q µ L Q A t µ L (1) () (3) Where q is the rate of flow (m/s), is the flow ermeability coefficiet (m ), is the ressure gradiet (a), μ is the viscosity of the flow (a s), L is the thicess of samle (m), Q is the volume flowig i time (m 3 ), A is the cross-sectio area (m ) where flow goes through, t is time (s). The ey arameter for redictig air ermeability is the ermeability coefficiet. Kozey ad Carma[8] roosed aother equatio to determie the ermeability coefficiet for homogeeous orous materials havig orosity less tha 0.94, ad the Davies [9] exted this wor ad emirically derived a mathematical exressio for redictig the air ermeability coefficiet of o-wove fabrics havig orosity i the rage of Mohammadi[5] modified the Kozey formula by itroducig Davies ermeability coefficiet to redict air ermeability of layered o-wove fabrics. The mathematical exressio of ermeability coefficiet is give by 3 d ε 16 µ 1 ε D ( ) Where d is fibre diameter (m), ε is orosity, μ is the viscosity of the flow (a s), D is the Davies costat, which is give by ε ( 1 ε ) ( 1 ε ) (5) D ( 1 ε ) From a differet oit of view, the drag theory leads to a differet exressio for the deedece of resistivity o orosity tha that give by the hydraulic radius theory. Some researchers[7] reorted that the drag theory ca exlai the air ermeability of orous materials. The air ermeability of orous materials is give by [7] ( ρ ρ ) d 1 f l Re q 9.4 L µ ρ.4 l R 8 Uautheticated e (4) (6)

2 Where q is the rate of flow (m/s), is the ressure gradiet (a), ρf ad ρ are the fibre ad o-wove fabric desities (g/ m 3 ), d is the fibre diameter (m), L is the thicess of samle, μ is the viscosity of the flow (a s), Re is Reyolds umber, which is give by Re ρ vd µ (7) Where ρ is fluid desity (g/m 3 ) ad v is fluid velocity (m/s). I this wor, some o-wove fabrics with various arameters such as desity, orosity ad thicess were reared i a cardig machie ad a eedle-uched machie. The air ermeability of o-wove fabrics was measured i a air ermeability tester FX3300. The exerimetal results were comared with aalytical models based o these two theories, ad the effects of some arameters o the air ermeability were discussed. Exerimet Polyester hollow fibres (sulied by Sioec Yizheg Chemical Fibre Comay Limited) were used to reare o-wove fabrics i cardig machie ad eedle-uchig machie at our laboratory. After eeig o-wove fabrics at a costat temerature ad costat humidity box for 4 hours, the owove fabrics were measured. The rofiles of hollow fibres ad o-wove fabrics were observed by scaig electro microscoy (SEM). The thicess was measured by a Alambeta istrumet, which eables quic measuremet of the samle thicess uder a 00 Pa cotact ressure[10]. The air ermeability was measured by air a ermeability tester FX3300, which measures airflow rate uder costat air ressure dro. Five samles from each o-wove fabric were measured ad a average value was determied. Results ad discussios Determiatio of the structural characteristics of owove fabric I o-wove fabrics, ores of all geometrical shaes are ossible because of the radom arragemet of fibres. Some researchers stated that the air ermeability of o-wove fabrics is related to the fibre diameter, orosity, ore size ad ore shae or tortuosity factor [11, 1]. Accordig to the images of the fibres (figure 1), the mea fibre diameter was aroud 45 ± 5 μm, hollow diameter was ± 3 μm, ad the air volume cotet was 7 ± 8%. Hollow fibre desity was 1034 g/m 3, which was calculated by m ρ f π r r l ( 1 ) Where ρf is fibre desity (g/m 3 ), reresets the umber of fibres, m reresets mass of sigle fibre (g), r1 ad r rereset fibre diameter ad hollow diameter (m), l reresets legth of sigle fibre (m). The orosity of o-wove fabric is give by ρ ε 1 100% ρ f Where ε is the orosity of o-wove fabric, ρ ad ρf are the desities of o-wove fabric ad fibre (g/m 3 ), resectively. (8) (9) Figure 1. Images of hollow fiber ad owove fabric htt:// 9 Uautheticated

3 The mea effective ore diameter of o-wove fabrics is give by Verschoor[13]: π d D 4 1 ( ε ) (10) Where D is the mea effective ore diameter (m), d is the mea fibre diameter (m) ad ε is the mea orosity of the samle. The relatio of desity ad orosity Obviously, the desity of o-wove fabric is iversely roortioal to the orosity of o-wove fabric accordig to equatio (9), ad figure also shows the relatioshi betwee the desity ad orosity of o-wove fabrics. The desity had a wider chage with resect to the chage of orosity. The effect of thicess o air ermeability Accordig to equatios () ad (6), the air ermeability would decrease with icrease i thicess of o-wove fabrics, ad the exerimetal results showed the same treds (figure 3). However, the redicted values were much higher tha the exerimetal values, esecially for model, which is based o drag theory. Meawhile, the redictio of models becomes worse with the icrease i ressure gradiet. Higher redicted values from model 1 might be due to the assumtio that the o-wove fabrics are ordered structures, which is differet from reality. The mea hydraulic radius caot be easily defied. Higher redicted values from model might be due to the much higher Reyolds umber, which is the ey factor associated with a itrisic variatio of drag. For model, the Reyolds umber is limited aroud 1[7]. Therefore, aalytical determiatio of air ermeability of owove fabrics is still very challegig. The effect of orosity o air ermeability Air ermeability of o-wove fabrics icreases with the icrease i orosity, ad the redicted values from model 1 are higher tha the exerimetal results, esecially whe the orosity ad the ressure gradiet are icreasig (figure 4). The redicted values based o model were ot give due to the limitatio of Reyolds umber. Model 1 stated the correlatio betwee ermeability ad orosity. However, some researchers[14, 15] cocluded that there is o simle correlatio betwee ermeability ad orosity because of the strog deedece of flow rate o the width, shae ad tortuosity of the coductig chaels. Pieaar[11] ad Clareburg[1] oit out that the tortuosity factor, the ratio of the effective or tortuous chael legth ad the samle thicess are imortat arameters i determiig flow through o-wove fabrics. The effect of desity o air ermeability Figure. The relatio of desity ad orosity Accordig to figures ad 4, it is obvious that the air ermeability of o-wove fabrics would decrease with the icrease i desity, ad the exerimetal results gave the same treds (figure 5). Therefore, desity might ot be a imortat arameter as it ca be relaced by orosity. Besides, desity caot rovide ay detail iformatio about the ore size ad ore shae. Figure 3. Effect of thicess o air ermeability of owove fabrics with desity 15.34±0.16g/m3. (A) 100Pa ressure gradiet ; (B) 00Pa ressure gradiet. htt:// 10 Uautheticated

4 Figure 4. Effect of orosity o ermeability of owove fabrics with 7.58±0.05mm thicess (A) 100a ressure gradiet; (B) 00a ressure gradiet. Figure 5. Effect of desity o ermeability of owove fabrics with 7.58±0.05mm thicess (A) 100a ressure gradiet; (B) 00a ressure gradiet. The effect of ressure gradiet o air ermeability Model 1 imlied that the air ermeability would be directly roortioal to the ressure gradiet, but the exerimetal results demostrated that the air ermeability of samles uder a 00 Pa ressure gradiet was 1.6 times higher tha the air ermeability of samles uder a 100 Pa ressure gradiet. Coclusio Air ermeability of o-wove fabrics with differet structures was ivestigated i this study. Some coclusios ca be made based o the results: (1) the air ermeability of owove fabrics decreased with the samle s thicess ad desity, icreased with the icrease of orosity ad the air ermeability was ot directly roortioal to the ressure gradiet; () the redictio model based o hydraulic radius theory had a better agreemet to exerimetal values tha the model based o drag theory; but the values were much higher tha the exerimetal results, esecially for higher orosity ad higher ressure gradiet. Therefore, more wor is eeded for imrovig the accuracy of redictio model Figure 6. The effect of ressure gradiet o air ermeability which may be eeded to tae ore size ad ore shae ito cosideratio. htt:// 11 Uautheticated

5 Acowledgemet This wor is suorted uder Studet Grat Scheme (SGS 48013/115) by Techical Uiversity of Liberec, Czech Reublic. Refereces [1] Kothari, V.K. ad A. Newto, Air-Permeability of No- Wove Fabrics. Joural of the Textile Istitute, (10): [] Mohammadi, M. ad P. Bas-Lee, Air ermeability of multilayered owove fabrics: Comariso of exerimetal ad theoretical results. Textile Research Joural, 00. 7(7): [3] Debath, S. ad M. Madhusoothaa, Thermal resistace ad air ermeability of jute-olyroylee bleded eedleuched owove. Idia Joural of Fibre & Textile Research, (): [4] Kulicheo, A.V., Theoretical aalysis, calculatio, ad redictio of the air ermeability of textiles. Fibre Chemistry, (5): [5] Mohammadi, M. ad P.B. Lee, Air ermeability of multilayer eedle uched owove fabrics: Theoretical method. Joural of Idustrial Textiles, 00. 3(1): [6] Sog, W.F. ad W.D. Yu, Fractal calculatio of air ermeability of owove fabrics. Joural of the Textile Istitute, (8): [7] Iberall, A.S., Permeability of Glass Wool ad Other Highly Porous Media. Joural of Research of the Natioal Bureau of Stadards, (5): [8] Carma, P.G., ed. Flow of Gases through Porous Media. 1956, Butterworth Scietific Pubicatios: Lodo. [9] Davies, N.C. The searatio of airbore dust ad articles Lodo: Proceedigs of istitute of mechaical egieers. [10] Lubos Hes ad I. Dolezal, New method ad equimet for measurig thermal roerties of textiles. Joural of the textile machiery society of Jaa, : [11] Pieaar, H.W. ad Clarebu.La, Aerosol Filters - Tortuosity Factor i Fibrous Filters. Chemical Egieerig Sciece, (1): [1] Clarebu.La ad H.W. Pieaar, Aerosol Filters.I. Theory of Pressure Dro across Sigle Comoet Glass Fibre Filters. Chemical Egieerig Sciece, (7): [13] Verschoor, D.J. ad Greebler, Heat Trasfer by Gas Coductio ad Radiatio i Fibrous Isulatio. Tras. ASME, : [14] Scheidegger, A.E., ed. The Physics of Flow through Porous Media. 1957, Uiversity of Toroto Press: Toroto, Caada. [15] Hillel, A., ed. Fudametals of Soil Physics. 1980, Academic Press: New Yor. htt:// 1 Uautheticated