Caseins and hydrophobins as novel green flame retardants for cotton fabrics Jenny Alongi a, * , Riccardo Andrea Carletto b , Francesca Bosco b , Federico Carosio a , Alessandro Di Blasio a , Fabio Cuttica a , Vincenza Antonucci c , Michele Giordano c , Giulio Malucelli a a Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Viale Teresa Michel 5,15121 Alessandria, Italy b Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Corso Duca degli Abruzzi 24,10129 Torino, Italy c IMCB, Istituto per i Materiali Compositi e Biomedici, Consiglio Nazionale delle Ricerche, Piazzale Vincenzo Tecchio, 80-80125 Napoli, Italy article info Article history: Received 2 September 2013 Received in revised form 21 October 2013 Accepted 24 November 2013 Available online 4 December 2013 Keywords: Cotton Green flame retardants Caseins Hydrophobins Flammability Combustion behaviour abstract Despite the use of toxic and not environmentally-friendly chemicals, some proteins derived from animal or microbial sources have been investigated as novel green flame retardants for cotton fabrics. In particular, phosphorus- and sulphur-rich proteins (i.e. caseins and hydrophobins) have been homoge- neously deposited on cotton fabrics starting from protein aqueous suspensions/solutions. These surface treatments, based on the use of species able to favour the dehydration of cellulose instead of its depo- lymerization, have strongly enhanced the production of a thermally stable carbonaceous structure (char), hence significantly enhancing the flame retardancy of the fabrics, as assessed by thermogravimetry and flammability tests. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction In the last four decades, both industrial and academic re- searchers have focused their efforts to design and develop chem- icals able to prevent the combustion of polymers or at least to delay the spread of fire after ignition. The most efficient flame retardants (FRs) have been identified as those containing halogens and halogen-based derivatives, phosphorus, nitrogen, aluminium and magnesium, boron, antimony, molybdenum, or recently developed nanofillers [1]. Although very efficient and widely used, some molecules employed in the formulation of the halogen-based FRs such as pentabromodiphenyl ether, decabromodiphenyl ether (or oxide) and polychlorinated biphenyls, have proven to be persistent, bioaccumulative, and/or environmentally toxic for animals and humans [2]. Among the currently commercial available flame re- tardants, phosphorus-based compounds represent a suitable alternative to halogen-based FRs. Furthermore, as far as fabrics are concerned, the current attention is focused either on the production of effective halogen-free substituents for coatings and back-coated textiles or on the use of hydroxymethylphosphonium salts (Proban Ò ) and N-methylol phosphonopropionamide de- rivatives (Pyrovatex Ò ) for cellulosic textiles. A historical and comprehensive review of the progress achieved during the second half of the twentieth century has been recently published by Hor- rocks [3]. In the continuous seek for novel cost-effective and environmentally sustainable FRs, the use of biomacromolecules like proteins and nucleic acids may represent a worthy alternative to the traditional approaches. To this aim, our group has already demonstrated that whey protein isolate (WPI) and herring sperm DNA can be deposited on cotton fabrics, achieving a homogeneous coverage. The WPI treated fabrics have shown an increased total burning time, together with a reduced burning rate [4]; further- more, DNA has conferred a flame suppressant character to the treated cotton fabrics [5,6]. These systems have demonstrated that biomacromolecules may represent a challenging, innovative and promising “green” finishing treatment for cellulosic substrates. In addition, their origin from renewable natural sources represents a further advantage from an environmental point of view. Among the proteins derived from animal or microbial sources, caseins and hydrophobins, which contain phosphorus and sulphur elements, * Corresponding author. Tel.: þ39 0131229337; fax: þ39 0131229399. E-mail address: jenny.alongi@polito.it (J. Alongi). Contents lists available at ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab 0141-3910/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymdegradstab.2013.11.016 Polymer Degradation and Stability 99 (2014) 111e117