Quantification of hierarchic multimodal pore structures in textiles by the example of knitted fabric structures

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1 Quantification of hierarchic multimodal pore structures in textiles by the example of knitted fabric structures Annette Mark 1, Dr. Boris Bauer 1, Prof. Dr.-Ing. Götz T. Gresser 1 1 Institute of Textile Technology and Process Engineering, Denkendorf (Germany) Abstract Typically, terms used in the clothing industry are corresponding to engineering production processes. Therefore, each engineering step is considered separately, and clothing consists of fibers, yarns and textiles. From the functional point of view, however, clothing consists solely of fibers, which are arranged spatially and thereby forming a system of pores. Pores and pore structure highly effect thermodynamic processes in textiles and clothing. Therfore, mathematical models and physical metrics are deduced in recent research activites for calculating and quantifying the pore structures of yarns and textiles. For demonstration, two materials are chosen: a cotton ring-spun yarn Nm50, knitted to a typical single jersey T- Shirt fabric on an E24 circular knitting machine, and a wool triple twisted ring-spun yarn Nm13, knitted to a typical pullover fabric one-by-one on an E8 flat knitting machine. The comparison of the two different textiles indicates that the pore structure of textiles is strictly bimodal distributed. Yarn pores have usually diameters between about 1 and 50 m and can be defined as meso pores, whereas mesh pores have usually diameters between about 100 and 1000 m and can be defined as macro pores. Introduction According to the current state of the scientific literature, these pores are arranged in fibers (1) (2) (3) (4), yarns (2) (3) (5) (6), textiles (5) (7) and clothing (8) (9) (10) (11) (12). The basis to deduce mathematical models and physical metrics for calculating multimodal pore structures are classical construction values of fibers, yarns and knitting fabrics like the density, mass or diameter determined by the laboratories of the Institute of Textile Technology and Process Engineering. The construction values are used to derive characteristic values in the dimension of length (pore diameter), area (fiber surface) and volume (pore volume). For the calculations, some auxiliary characteristics are also required like the number of fibers in the yarn or the length of the yarns in the textile. Yarn volume balance For demonstration, two high-quality, but fundamental different yarns were choosen, a cotton ring-spun yarn with fineness of Nm50 or 200 dtex, typically used for circular knitting machines (CO50), and a wool twisted ring-spun yarn with fineness of Nm13 or 743 dtex, typically used for flat knitting machines (WV13). The wool fibers of the WV-yarn have considerable higher mass m f of 4,4 dtex and diameters d f of 21 m than the cotton fibers of th CO-yarn with 1,7 dtex or 21 m, respectively (Table 1). ρ f m f d f / cm 3 g -1 / dtex / m CO WV Table 1 Construction values for quantifying yarn pores by the example of cotton yarn CO50 and wool yarn WV13, respectively

2 In the wool yarn, the pore diameters d py with 28 m and fiber surface areas A sf with 109 m 2 10 km -1 are considerable higher than in the cotton yarn with 13 m or 44 m 2 10 km -1 respectively (Table 2). m y n fy n py d y d py A sf / dtex / - / - / m / m / m 2 10 km -1 CO WV Table 2 Characteristic values for quantifying yarn pores The total volume of the yarn V y is calculated on the basis of the mass m y and density ρ y of the yarn and the total volume of the fibers V fy is calculated on the basis of the mass m f and density ρ f of the fibers. The absolute yarn pore volume V py results from the yarn volume balance according to Equation 1. Equation 1 V y = V fy + V py The relative pore volume V pyr of the wool yarn with 0.76 is by a factor 1.1 merely higher in comparison to the cotton yarn with 0.67 and therefore unlikely for characterizing the fundamental different characteristics of both yarns. Conversely, the absolute pore volume V py of the wool yarn with 1759 cm 3 10 km -1 is by a factor 6.6 considerable higher in compairison to the cotton yarn with 268 cm 3 10km -1 (Figure 1). Figure 1 Yarn volume balance by the example of cotton yarn CO50 and wool yarn WV13 Textile volume balance For further experimental procedure the cotton yarn CO50 is knitted on a circular knitting machine with needle gauge 24 to a single jersey fabric, commonly used for confection of a typical T-Shirt (WV13_E8), and the wool yarn WV13 is knitted on a flat knitting machine with needle gauge 8 to a one-by-one fabric typically used for the confection of a pullover (CO50_E24). The wool fabric WV13_E8 has considerable higher thickness h t of 2.79 mm and mass m t of 534 g m -2 than the cotton fabric CO50_E24 with 0.56 mm and 137 g m -2. Other characteristic values like the density ρ t and yarn length l yt are comparatatively equal of both different textiles (Table 3).

3 h t ρ t m t l yt / mm / g cm -3 / g m -2 / m m -2 CO50_E WV13_E Table 3 Characteristic and auxiliary values for quantifying multimodal pore systems in knitting fabrics by the example of cotton CO_E24 and wool WV_E8 fabric, respectively The total volume of the textiles V tf is calculated on the basis of textile thickness h t and the volume of the fibers V tf and yarn pores V pty is calculated on the basis of the yarn length l yt. The volume V ptt of the mesh pores results from yarn volume balance according to Equation 2. Equation 2 V t = V tf + V pyt + V ptt The relative pore volume V pyr of both textiles is with values of 0.86 or 0.89, respectively more or less identical, whereas the absolute pore volume V pt of the woolen textile is with 2385 cm 3 m -2 by a factor 5.1 considerable higher in compairison to the cotton textile with V pt with 470 cm 3 m -2 (Figure 2). Figure 3 Yarn volume balance of the cotton textile CO50_E24 and wool textile WV13_E8 Pore-diameter-volume-distribution Assuming that pores in meshes are cylindrical, the pore diameter of meshes d ptt in the unit µm is calculated from mesh pore volume V ptt and mesh pore number n ptt in textiles. Both, the diameter d ptt and volume V ptt of the meshs pores can be plotted in x-y-graphics together with diameter d py and volume V pty of the yarns. The result shows, pore structures in textiles are strictly bimodal distributed. The diameter of the yarn pores d py and mesh pores d ptt are considerably higher in the woolen textile with 28 or 867 m than in the cotton textile with 13 or 482 m, and the volume of the yarn pores V pty and mesh pores V ptt are also considerable higher in the wool textile with 1264 or 1121 cm 3 m -2 than in the cotton textile with 184 or 286 cm 3 m -2 (Figure 4).

4 Figure 4 diameter-volume distribution of the cotton textile CO50_E24 and wool textile WV13_E8 Conclusion Numerous research projects related to porosity in each of the mentioned scales, however, none approaches textiles as a hierarchical multimodal pore system. Thus, this research offers a new methodical concept to simulate and forecast textile properties. The comparison of the two different knitted fabrics demostrates that the pore structure of textiles is strictly bimodal distributed. Yarn pores have usually diameters between about 1 and 50 m and can be defined as meso pores, whereas mesh pores have usually diameters between about 100 and 1000 m and can be defined as macro pores. The next step is to add clothing and with it mega pores which originate from the fit and drapery of dressed clothing to the meso and macro pores of the textiles. Different thermodynamic processes like MIR-radiation, convection or evaporation prefer different pore size scales. According to this hypothesis, pore function models are to be derived from multimodal pore structure models. Literature 1. Junjie, H., et al., et al. Pore structure development of polyacrylonitrile nascent fibers in water stretching process. Thermochimica Acta. 2013, 569 (10), S Miller, B. und Tyomkin, I. An extended range liquid extrusion method for determining pore size distributions. Textile Research Institute. 1986, 56 (1), S Jakšić, D. und Jakšić, N. Assessment of porosity of flat textile fabrics. Textile Research Journal. 2007, 77 (2), S Mao, Z., et al., et al. States of water and pore size distribution of cotton fibers with different moisture ratios. Industrial & Engineering Chemistry Research. 2014, 53 (21), S Bauer, B., Koch, S. und Mark, A. KF CJ4 Entwicklung von Energieeffizienz Garnen für funktionelle Sommer und Winterbekleidung. Textiltechnik, Institut für Textil- und Verfahrenstechnik. Denkendorf : Arbeitsgemeinschaft industrieller Forschungsvereinigungen, Zwischenbericht (intern). 6. Li, Y., Huang, L. und Yu, J. Study on the pore structure of cotton-like polyester knitted fabrics. Advanced Materials Research. 2013, , S Du, N., Fan, J. und Wu, H. Optimum porosity of fibrous porous materials for thermal insulation. Fibers and Polymers. 2008, 9 (1), S

5 8. Hofenbitzer, G. Bekleidung Schnittkonstruktion für Damenmode. 1. Haan-Gruiten : Verlag Europa-Lehrmittel, Bd Song, G. Clothing air gap layers and thermal protective performance in single layer garment. Journal of Industrial Textiles. 2007, 36 (139), S Ho, C., et al., et al. The effect of added fullness and ventialtion holes in T-Shirt design on thermal comfort. Ergonomics. 2011, 54 (4), S Li, J., Zhang, Z. und Wang, Y. The relationship between air gap sizes and clothing heat transfer performance. The Journal of The Textile Industrie. 2013, 104 (12), S Mark, A. The impact of the individual layers in multi-layer clothing systems on the distribution of the air gap thickness and contact area. St Gallen : Eidgenössische Materialprüfungs- und Forschungsanstalt, Masterarbeit (intern).

Study on heat and moisture vapour transmission characteristics through multilayered fabric ensembles

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