Vacuum 81 (2006) 265–271 Experimental study of the behaviour of leather under vacuum conditions R. Barni, S. Zanini, M. Piselli, C. Riccardi à Dipartimento di Fisica G.Occhialini, Universita` degli Studi di Milano-Bicocca P.za della Scienza 3 I-20126 Milano, Italy Received 14 October 2005; received in revised form 31 March 2006; accepted 10 April 2006 Abstract A characterization of the device-pumping behaviour of our vacuum reactor for plasma treatment of materials at low pressure is presented. The analysis of the pumpdown curves measured both in the viscous and in the molecular regimes was made to study the outgassing flowrates of several leather materials. Estimates of the relevant flowrates in different pressure ranges and measurements of the flow composition have been obtained. Such data can be interpreted in the framework of simplified desorption models and could be used in order to design the pumping system needed for vacuum treatment of such materials. We have also measured other related quantities such as the moisture uptake and the weight loss. r 2006 Elsevier Ltd. All rights reserved. PACS: 07.30.Bx; 81.05.Lg; 52.80.Vp Keywords: Outgassing; Leather; Molecular; Drying 1. Introduction Surface properties of solid polymeric materials have strong effects on most of their practical applications. Indeed many properties, such as adhesion, gloss, wett- ability, permeability, dyeability, printability and antistatic behaviour are related more to the surface than to the bulk of the material. Treatments of material surfaces under vacuum conditions are known since many years. Processes like etching of particular surface components, grafting of new functional groups, deposition of films or coatings and even polymerization are actively studied [1–3]. However applications to quite complex natural materials such as leather are scarce [4]. Our research group has a quite long record on the surface modifications of textile fabrics and fibres with low-pressure plasmas [5–7]. We also started research on the surface modification of leather products. In order to apply these leather treatments in a technologically feasible process it is necessary to keep stable vacuum conditions in large device volumes in the presence of a large amount of leather materials. This requires detailed information of the behaviour of leather under vacuum conditions. Moreover, vacuum can be used for the drying step in the leather processing. In fact, hide proteins, mainly collagen, have been associated with a large amount of water. The drying operation is a critical leather-making step to attain the required physical properties for leather products. It is well known that drying operations carried out in different conditions cause variations in leather exterior properties, which is the most critical point of leather manufacturing. There are various drying methods (air drying, drying tunnel, toggle dry, radio frequency and microwave drying) currently being used in leather manu- facturing [8]. Besides these processes vacuum drying is also actively investigated. Existing studies for chrome-tanned leather exploit the relationship between drying variables and residual water content, as well as the rate of drying. It was also reported that drying variables affect the dimen- sional stability of leather and its mechanical properties such as stiffness [9]. Despite such interest, in-vacuo behaviour and outgassing phenomena in biological, organic and in general polymeric materials are poorly known. We have already performed a ARTICLE IN PRESS www.elsevier.com/locate/vacuum 0042-207X/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2006.04.002 à Corresponding author. Tel.: +39 02 6448 2314; fax: +39 02 6448 2367. E-mail address: claudia.riccardi@mib.infn.it (C. Riccardi).