1489 ISSN 1229-9197 (print version) ISSN 1875-0052 (electronic version) Fibers and Polymers 2016, Vol.17, No.9, 1489-1496 Estimation of Pore Size and Porosity of Modified Polyester/PVA Blended Spun Yarn Pawan Kumar, S. K. Sinha * , and Subrata Ghosh Department of Textile Technology, National Institute of Technology, Jalandhar 144011, India (Received December 28, 2015; Revised July 3, 2016; Accepted July 9, 2016) Abstract: The performance of a textile material depends on the arrangement of its constituent fibres. For good mechanical behaviour strong inter fibre cohesion is necessary. In order to impart comfort characteristics, a permeable structure is desired. Staple fibre, by virtue of its limited length and other constraints, cannot produce fully compacted structure. For an optimum performance, a balance between the permeable and cohesive characteristics is necessary. An estimation of the openness of the structure may help in designing product for specific requirement. The degree of openness, however, may be varied through necessary modifications during and post manufacturing stage. In the present study empirical relations have been developed to calculate the equivalent pore diameter and porosity for three different modes of packing in yarns. Theoretical calculation was done for all three possible modes of packing while the experimental evaluations were made using the cross sectional images. The change in pore size and porosity were also estimated for a polyester/PVA blended yarn on removal of PVA component. A comparison of experimentally measured porosity was made with the results obtained theoretically. Hexagonal close packing resulted lowest porosity and experimentally measured values were in close association with the theoretically measured porosity. Keywords: Pore size, Porosity, Hexagonal close packing, Hexagonal open packing, Open packing, Ring yarn Introduction The physical, mechanical and end use characteristics of any yarn largely depend on the properties and the arrangement of its constituent fibres. The arrangement of the fibres plays important role in deciding the level of inter-fibre cohesion and openness in structure. The former influences its mechanical properties while the later influences permeable and fluid transmission behaviour. A relatively open structure should offer good permeable, heat regulation and dye absorption/ retention characteristics but may cause a negative impact on its mechanical behaviour. For optimum performance, a balance between compactness and openness is necessary. The arrangement of fibre in a yarn during its formation depends largely on tension condition in individual fibre, influenced by parameters related to the fibre, yarn and process. To derive comfort characteristics one may prefer an open structure but from the point of view of strength and durability, compacted structure is desirable. The nature of openness in the structure is not only influenced by the size of the pore but also on the geometry and distribution of pores. The geometry of such pores influenced by the arrangement of fibres influences the moisture transportation and permeability, which is important for comfort in a garment. A specific end use requirement can help in deciding the required level of compactness in the structure. Depending upon the end use, the openness of the structure needs to be altered. Such alteration can be brought about either through variation of spinning parameters, mechanical action or by partial or complete removal of a component. Estimation of pore characteristics of a yarn can also be helpful in specifying the application area and designing product out of it. Neckar [1] defined a pore as a channel obtained through arbitrary division of space between fibres in a fibrous assembly. A complete pore was also considered to be composed of a real and a fictive one. The former being defined as the space between the border of a pore and real fibre while the later as the distinguishing lines between pores. Pores in a yarn are generally formed by the fibre walls and result in open channel capillaries unlike a regular capillary channel. Such a condition leads to varying capillary flow in the sections despite the constituent fibres having homogeneous wetting properties [2]. Ito [3] reported that the wicking behaviour is strongly influenced by the size and continuity of the capillary formed within the yarn. Das [4,5] reported the bulked yarns and fabrics in presence of air space in the yarn to affect the overall characteristics of yarns and fabrics. Ogston [6], on the other hand, reported the geometry of spaces in fibre assemblies to be more important in under- standing the mechanics of fluid flow, permeability and filtration characteristics. Komori [7] deduced mathematical expression involving the sizes and geometrical anisotropies of void spaces in a random fibre assembly and reported the width and depth of the space to play dominant role in the mechanics of fluid flow. Width of void was reported to influence the quantity of flow and the length over which a fluid can flow freely was reported to be dependent on the depth of open space. Yoon [8] and Das [9] reported that the liquid and air transportation/transmission properties of the fabric to be more dependent on the yarn geometry. Ogulata [10] on the other hand, reported a strong correlation between fabric and *Corresponding author: sinhask@nitj.ac.in DOI 10.1007/s12221-016-5955-4