Industrial Crops and Products 74 (2015) 158–164 Contents lists available at ScienceDirect Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop The effect of the composition of spruce and pine tannin-based foams on their physical, morphological and compression properties Matjaˇ z ˇ Cop a , Clément Lacoste b , Marjetka Conradi c , Marie-Pierre Laborie d , Antonio Pizzi b,e , Milan Sernek a,∗ a University of Ljubljana, Biotechnical Faculty, Department of Wood Science and Technology, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia b LERMAB, University of Lorraine, Epinal, France c Institute of Metals and Technology, Physics and Chemistry of Materials, Ljubljana, Slovenia d Chair of Forest Biomaterials and Freiburg Materials Research Center, Albert-Ludwig University of Freiburg, Freiburg, Germany e King Abdulaziz University, Jeddah, Saudi Arabia a r t i c l e i n f o Article history: Received 28 November 2014 Received in revised form 31 March 2015 Accepted 3 April 2015 Keywords: Bark Compressive strength Foam Scanning electron microscopy Spruce tannin a b s t r a c t Tannin-based foams were successfully prepared, using Norway spruce and maritime pine tannins. Var- ious parameters, including the amount of procyanidins, were varied in order to observe the effect of changes in the density of the foam, on the structure its pores, and on the homogeneity, compressive strength, and compressive modulus of the foams. It was found that an optimum amount of spruce tan- nin exists, which results in a foam with the lowest density whereas the amount of cross-linker affects homogeneity, and the foam morphology is defined by the surfactant. A partial replacement of pine tannin with spruce tannin decreased the foaming temperature and led to decreased compressive strength and a decreased compressive modulus of the foams. The main attribute affecting the reaction was the amount of polyphenols, or the amount of impurities (cellulosic sugars) present in the tannin extract. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The development of new materials derived from bio-based sources has become a necessity (Mohanty et al., 2002). When searching for new and better materials, all relevant ecological guidelines (requiring the replacement of petroleum-based prod- uct), have to be taken into consideration (Bozell and Petersen, 2010). Tannins from trees, an abundant resource that is safe for the environment and human health, are one option (Raquez et al., 2010; Sánchez-Martín et al., 2013a). Tannin from spruce bark is an untapped resource, with a structure similar to that of the commercially available pine tannin. Due to complicated and under- developed extraction and cleaning processes, this very promising material has remained largely unexploited. The use of tannin extracts from different wood species (e.g., Castanea sativa, Quercus sp., Acacia sp., etc.) is common in nutri- tion and pharmaceutical and veterinary medicine (Chiarini et al., 2013). Tannin extracts can also be used as binding agents for parti- cle and fiberboards (Tiˇ sler et al., 1986; Roffael et al., 2000) or in the ∗ Corresponding author. Tel.: +386 1 320 3623; fax: +386 1 257 2297. E-mail address: milan.sernek@bf.uni-lj.si (M. Sernek) manufacturing of insulation materials (Meikleham and Pizzi, 1994; Tondi and Pizzi, 2009; Lagel et al., 2014). Tannin can be used in the production of foam, as an insula- tion material obtained by the polycondensation of polyflavonoid tannins and furfuryl alcohol (Pizzi et al., 2012). Some of this end product’s impressive features can easily be adapted (Tondi and Pizzi, 2009). Due to their low conductivity coefficient (Celzard et al., 2010; Lacoste et al., 2014a), these foams, with a high level of natu- ral compounds, are comparable to more established polyurethane foams. The resulting thermosetting material can be used as a ther- mal or sound insulator, an absorber of metal ions, (Sánchez-Martín et al., 2013b), or a material with sufficient resistance to chemicals and fire comparable to that offered by phenol-formaldehyde foams (Tondi et al., 2009). Foams have been prepared from tannin extracts obtained from deciduous trees, e.g., quebracho wood (Schinopsis balansae and lorentzii) (Basso et al., 2014; Martinez de Yuso et al., 2014) or aca- cia bark (Acacia mearnsii) (Tondi and Pizzi, 2009; Szczurek et al., 2013) with the predominantly prorobinetinidin/profisetinidin type of tannin. They have also been prepared from the bark of conifer- ous trees (Pinus radiata and pinaster) (Lacoste et al., 2013a, 2014a), in which a much more reactive procyanidin/prodelphinidin type of tannin is usually found. http://dx.doi.org/10.1016/j.indcrop.2015.04.009 0926-6690/© 2015 Elsevier B.V. All rights reserved.