AN EFFECT OF WASHING ON DURABILITY OF HYDROPHOBIC FINISHES OF MEMBRANE LAMINATES Mateusz Kowalski, Renata Salerno-Kochan Cracow University of Economics – Faculty of Commodity Science and Product Management, Sienkiewicza 4, 30-033 Cracow, Poland, kowalskm@uek.krakow.pl; salernor@uek.krakow.pl 1. Introduction The main function of outer layer of clothing made of laminated materials is to protect against adverse weather factors, among which precipitation is the most invasive one. Rain and melted snow can cause wetting of the outer layer and in consequence may lead to water penetration into deeper layers. Wet clothing can lead to disruption of body thermal balance, thus causing signifcant deterioration of user comfort [14]. To prevent it, the outer layers of clothing should be resistant to water (waterproofng) that includes two basic material properties, namely, water tightness and wetting resistance (hydrophobic abilities/water repellency) [12]. Water tightness is reached, among other things, by using membrane materials, which prevent the penetration of water into the inner layers of clothing and shed rain droplets or melted snow on its surface, while water repellency is most often an efect of shell materials of appropriate dense structure based on the hydrophobic fbers. The manufacturers more often use also hydrophobic fnishes that form a waterproof coating on the material surface that helps to strengthen the product’s barrier to water [7,11,12-13,15]. These fnishes are called as DWR (durable water repellent) coatings. Their main goal is to create a thin membrane on its surface preventing the spilling of liquid droplets and wetting the inner clothing layers [16]. The mechanism of action of such coating, illustrating the behavior of water droplets on its surface, is presented in Figure 1. It is possible to achieve hydrophobicity by enabling liquid droplets of the highest possible contact angle to be formed that promotes its rundown without causing the wetting of material by using coatings of a surface energy lower than the surface tension of water. Any liquid of lower surface tension can spill over the surface of solid body of higher surface tension, while an inverse phenomenon is impossible. A solid body (textile material) of low surface energy gained with a DWR fnish is comprised mainly of non-polar groups, while water is a polar solvent; thus when these two bodies contact each other, a repulsion phenomenon occurs. This is why water dropping on the material forms no wet continuous layer on it but “transforms” into individual droplets (similar to pearls) that can be easily removed from the surface of a material without leaving any wet traces [10]. Wettability of a material depends on the contact angle. The contact angle (θ) is the angle between the tangent to the test droplet outer surface and the solid surface where the liquid is present at interface of three phases: solid (S), liquid (L), and vapor (gaseous) (V). The relationship between these phases under equilibrium conditions is expressed by the Young equation, which is the basis for describing all wetting phenomena [2,9]: γ SV - γ SL = γ LV · cosθ, where γ SV is the surface tension in a solid–gas system (here: air), γ SL is the surface tension in a solid–liquid system, γ LV is the surface tension in a liquid–gas system, θ is the wetting contact angle. Abstract: The aim of the study is to show how the washing process, while considering the type of washing agent and number of wash cycles, determines the durability of hydrophobic fnishes of laminated fabrics. The samples of material were subject to multiple wash cycles in clear water and with the use of two types of washing agents, namely, an ordinary washing powder and a detergent recommended by manufacturers of functional clothing. The washed materials were subject to spray test and its waterproofng and degree of surface wetting were evaluated. The tests have shown that waterproofng of membrane laminates with DWR (durable water repellent) coating become deteriorated during washing treatment and the use of special detergent does not guaranty the maintenance of better coating properties than an ordinary washing agent. Keywords: hydrophobic fnishes, fabric washing, water repellency, membrane laminates Figure 1. The mechanism of hydrophobic coatings activity [17] http://www.autexrj.com AUTEX Research Journal, Vol. 18, No 2, June 2018, DOI: 10.1515/aut-2017-0028 © AUTEX 137