ORIGINAL PAPER The S3 layer isolated from carboxymethylated cellulose wood fibers Goeun Sim • Theo G. M. van de Ven Received: 1 September 2014 / Accepted: 6 November 2014 / Published online: 12 November 2014 Ó Springer Science+Business Media Dordrecht 2014 Abstract The innermost S3 layer is isolated from highly swollen, carboxymethylated cellulose wood fibers (CMF). The isolation is attempted by applying gentle magnetic stirring, ultrasonication, and acid hydrolysis, where each treatment has caused the formation of largely variable fiber morphologies. The S3 layer can be partially or completely isolated from CMF by applying gentle shear or a mild acid hydrolysis. The S3 layer isolated from CMF is highly swollen with a volume 5–10 times its original value, and has microfibril angles between 50° and 90°. Surface carboxylates on the S3 microfibrils are available for further chemical modifications. Domi- nant right handedness is observed from 3D recon- structed confocal microscopic images. When air-dried from water, the S3 layer collapses completely onto the substrate, giving an average layer thickness of 83–140 nm. Keywords S3 layer Á Carboxymethylated fibers Á Ultrastructure of the wood cell wall Introduction Wood cell walls are carefully engineered structures that are capable of providing optimum stiffness, strength, and hardness to trees. In order to thoroughly understand the properties of the wood base products, the structures of the wood cell walls have been studied extensively on different levels—macro- scopic, microscopic, nanoscale and molecular (Booker and Sell 1998; Zhong and Ye 2009; Moon et al. 2011). The three major chemical components in wood fibers are cellulose, hemicellulose, and lignin. Since cellulose fibers have advantages in superior strength-to-weight ratio, corrosion and fatigue resis- tance, and abundance, utilizing cellulosic materials has been attracting much attention for the past few decades (Tabet and Aziz 2013). As cellulose chains are synthesized, accumulated and crystallized in nature, they form bundles of nano-, and then microfibrils (Isogai et al. 2011). The microfibrils are arranged in specific angles (microfibril angles, MFA), which provide distinctiveness between the sublayers of the secondary (S) layer, namely, S1, S2, and S3 layers (Barnett and Bonham 2004). The S2 layer is typically 40 times thicker than the other two secondary layers, hence its properties and functions have been well studied (Sell and Zimmer- mann 1993; Fahle ´n and Salme ´n 2003; De ´jardin et al. 2010). A recent literature review reveals a contro- versy over the cellulose microfibril orientations in the S3 layer, as some report a cross-fibrillar structure G. Sim Á T. G. M. van de Ven (&) Department of Chemistry, Pulp and Paper Research Centre, McGill University, Montreal, QC, Canada e-mail: theo.vandeven@mcgill.ca G. Sim Á T. G. M. van de Ven Centre for Self-Assembled Chemical Structures, McGill University, Montreal, QC, Canada 123 Cellulose (2015) 22:45–52 DOI 10.1007/s10570-014-0503-0