Carbohydrate Polymers 126 (2015) 32–39 Contents lists available at ScienceDirect Carbohydrate Polymers j ourna l ho me pa g e: www.elsevier.com/locate/carbpol In-situ glyoxalization during biosynthesis of bacterial cellulose Cristina Castro a,1 , Nereida Cordeiro b , Marisa Faria b , Robin Zuluaga a,∗ , Jean-Luc Putaux c,2 , Ilari Filpponen d , Lina Velez a , Orlando J. Rojas d , Piedad Ga˜ nán a a School of Engineering, Universidad Pontificia Bolivariana, Circular 1 no. 70-01, Medellín, Colombia b Competence Centre in Exact Science and Engineering, University of Madeira, 9000-390 Funchal, Portugal c Centre de Recherches sur les Macromolécules Végétales (CERMAV-CNRS), Affiliated with Université Joseph, BP 53, F-38041 Grenoble Cedex 9, France. d Biobased Colloids and Materials group (BiCMat), Department of Forest Products Technology, Aalto University, School of Chemical Technology, P.O. Box 16300, 00076 Aalto, Espoo, Finland. a r t i c l e i n f o Article history: Received 7 November 2014 Received in revised form 3 March 2015 Accepted 4 March 2015 Available online 14 March 2015 Keywords: Bacterial cellulose Gluconacetobacter medellensis Crosslinking Glyoxal Surface energy a b s t r a c t A novel method to synthesize highly crosslinked bacterial cellulose (BC) is reported. The glyoxalization is started in-situ, in the culture medium during biosynthesis of cellulose by Gluconacetobacter medellensis bacteria. Strong crosslinked networks were formed in the contact areas between extruded cellulose ribb- ons by reaction with the glyoxal precursors. The crystalline structure of cellulose was preserved while the acidic component of the surface energy was reduced. As a consequence, its predominant acidic char- acter and the relative contribution of the dispersive component increased, endowing the BC network with a higher hydrophobicity. This route for in-situ crosslinking is expected to facilitate other modifica- tions upon biosynthesis of cellulose ribbons by microorganisms and to engineer the strength and surface energy of their networks. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Bacterial cellulose (BC) is an extracellular biopolymer pro- duced by microorganisms belonging to the Gluconacetobacter genus. These bacteria extrude cellulose ribbons that form a three- dimensional network at the air–liquid medium interface. Cellulose chains are assembled into sub-elementary fibrils of 1.5 nm width that further associate to form cellulose nanofibrils (2–4 nm width) and nanofibril bundles or ribbons (20–100 nm width) (Iguchi, Yamanaka, & Budhiono, 2000). BC is highly pure and crystalline and exhibit good water-holding capacity, mechanical strength and degradability (Bielecki, Krystynowicz, Turkiewicz, & Kalinowska, 2005). As a consequence, recent investigations have considered BC as a reinforcing constituent in advanced thermoplastic and ther- mosetting polymer matrices, resulting in composite materials with unique properties and morphologies (Laborie, 2009). The hydrophilicity of cellulose is related to the presence of three different OH groups in the repeating units of the polymer ∗ Corresponding author. Tel.: +57 4 4488388; fax: +57 4 2502080. E-mail addresses: cristina.castro@upb.edu.co (C. Castro), robin.zuluaga@upb.edu.co (R. Zuluaga). 1 Tel.: +57 4 4488388; fax: +57 4 2502080. 2 Member of Institut de Chimie Moléculaire de Grenoble and Institut Carnot PolyNat. which are capable of forming inter- and intra-chain hydrogen bonds. The resultant surface hydrophilicity of cellulose fibrils limits their compatibility with nonpolar matrices. As a result, sev- eral functionalization strategies have been attempted, including esterification, polycondensation, etherification, and acetalyzation reactions (Heinze, & Liebert, 2001). Likewise, cellulose can be chem- ically modified with crosslinking agents to covalently bond the fibrils (Schramm & Rinderer, 2002; Yu, Lee, & Bang, 2008). One of the most commonly used crosslinking agents include formaldehyde- based chemicals but their use has been undermined by reported carcinogenic effects (Schramm, & Rinderer, 2000). Thus, alterna- tive crosslinking agents are needed such as polycarboxylic acid and dialdehydes, which have been used since the late 1980s (Xu, Yang, & Deng, 2001; Lee, & Kim, 2005). Among crosslinking agents, gly- oxal has been one of the few readily available non-formaldehyde agents capable of crosslinking cellulose (Schramm & Rinderer, 2002; Welch, 1983; Head, 1958). Glyoxal is the simplest of the dialdehyde group. It is produced by gas-phase oxidation of ethylene glycol, liquid-phase oxidation of acetaldehyde or by lipid autoxi- dation (Kielhorn, Pohlenz-Michel, Schmidt, & Mangelsdorf, 2004). Moreover, upon release into the environment, glyoxal is rapidly converted enzymatically to glycolate by microorganisms as bacte- ria and fungi (Kielhorn et al., 2004; Quero et al., 2011). Reactions with glyoxal have commonly been used to impart durable properties to cellulose-based materials, including textiles and paper (Schramm & Rinderer, 2002; Yu et al., 2008). Surface http://dx.doi.org/10.1016/j.carbpol.2015.03.014 0144-8617/© 2015 Elsevier Ltd. All rights reserved.