A novel sol-gel multi-layer approach for cotton fabric finishing by tetraethoxysilane precursor C. Colleoni a , I. Donelli b , G. Freddi b , E. Guido a , V. Migani a , G. Rosace a, ⁎ a Dipartimento di Ingegneria, Università di Bergamo, Viale Marconi 5, 24044 Dalmine, Bergamo, Italy b INNOVHUB, Stazioni Sperimentali per l'Industria, Divisione Stazione Sperimentale per la Seta, Via G. Colombo 83, 20133 Milano, Italy abstract article info Article history: Received 28 April 2013 Accepted in revised form 10 July 2013 Available online 18 July 2013 Keywords: Sol-gel Cotton fabric Tetraethoxysilane Multi-layer Dibutyltindiacetate The way of producing functional textile finishings by the sol-gel process using a multistep approach, consisting of consecutive depositions of sol layers on cotton fabric, for obtaining architectures with a different number of layers (namely, 1, 3 or 6 layers) is discussed. To this aim, tetraethoxysilane (TEOS) has been used as a precursor and the role of such architectures has been deeply investigated and correlated with the sol concentration and with the presence of the condensation catalyst DBTA (Dibutyltindiacetate). The multi-layer coatings were ap- plied by padding using sols containing appropriate molar ratios of the precursor, anhydrous ethanol, catalyst and hydrochloric acid. The effects of the catalyst during the alkoxide reaction and the silica amount applied by sol-gel treatment on the thermo-oxidative behavior of the treated fabrics were deeply studied. FT-IR ATR spec- troscopy, SEM analysis, thermal and thermo-oxidative stability, washing fastness, flammability and mechanical properties of the sol-gel treated cotton fabrics have been also investigated. The results obtained should be interpreted according to the properties investigated. The higher the concentration and the number of layers of the inorganic matrix, the higher the heat protection of textile samples. However, the resulting coating was so rigid that it modified the mechanical properties and particularly it decreased the wear resistance according to Martindale test. To improve the mechanical properties the best results were obtained by modulating a lower concentration of the matrix using a layered approach. In all cases, high adhesion of the coating to the textile fabrics was observed. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Chemical finishing techniques are extensively used to improve some properties of natural and synthetic fibers and fabrics. For this purpose, textile materials are treated with different functional finishes, such as repellent, durable press, soil release, flame retardant, antistatic and anti- microbial. The choice of the type of finishing process (batch versus con- tinuous, method of preparation, dyes and method of dyeing, finishing agents and how they are applied), as well as the combination with mechanical and thermal treatments (sanding, sueding, brushing, calen- dering, sanforizing, etc.) plays an important role on the wearing and per- formance characteristics of textiles. A survey of up-to-date literature [1] reveals that different chemicals are commonly used as finishes to im- prove fabrics performances but, due to the strong pressure for banning harmful chemicals such as halogen-containing flame retardants, various attempts to reduce/replace environmentally and safety questionable chemicals have been made. Furthermore, the choice of the finishing pro- cess contributes to influence the industrial closing costs, thus becoming another parameter to be taken into consideration. In recent years the sol-gel process, which leads to the formation of self-assembled (nano) layers on the fiber surface, has remarkably proved its exceptional poten- tial regarding the synthesis of new coatings with a high degree of homo- geneity at molecular level and with outstanding physical–chemical properties. The sol-gel represents a versatile synthetic route based on a two-step reaction (hydrolysis and condensation), usually starting from (semi) metal alkoxides (e.g. tetraethoxysilane, tetramethoxysilane, tita- nium tetraisopropoxide), that leads to the formation of completely hybrid inorganic or organic–inorganic coatings at or near room temper- ature [2,3]. These coatings are capable to protect the polymer surface by creating a physical barrier acting as insulator, thus improving the ordinary performances of the treated materials, such as flame retardancy [4–6], antimicrobial or UV radiation protection [7,8], dye fastness [9,10], anti-wrinkle finishing [11], super-hydrophobicity [12–14] and bio- molecule immobilization [15]. Recently, sol-gel has been also stud- ied for innovative applications regarding hydrogen production by water photosplitting [16] and the development of textile materials with self-cleaning [17] and sensing [18,19] properties. Sol-gel tech- niques based on a tetraethoxysilane (TEOS) precursor are promising and practical to prepare the silica films, due to their low-temperature and cheap processing and because they are suitable to obtain homoge- neous films on a large area substrates. The gelation process of TEOS in the presence of typical catalysts such as acids or bases [20,21] has been widely studied through examination of its viscoelastic behavior during the sol-gel transition. However, the use of strong acidic or basic Surface & Coatings Technology 235 (2013) 192–203 ⁎ Corresponding author. Tel.: +39 0352052021. E-mail address: giuseppe.rosace@unibg.it (G. Rosace). 0257-8972/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.surfcoat.2013.07.033 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat