Facile fabrication of superhydrophobic paper with improved physical strength by a novel layer-by-layer assembly of polyelectrolytes and lignosulfonates-amine

Abstract

Interest in superhydrophobic paper is growing, and efforts have been made to prepare superhydrophobic paper with an improved physical strength property. This study reported a facile method for fabricating a superhydrophobic paper with enhanced physical strength through layer-by-layer self-assembly of poly(allylamine hydrochloride) (PAH) and lignosulfonates-amine (LSA) on cellulose fiber surfaces, followed by a heat treatment at 160 °C for 30 min. The formation of PAH/LSA multilayers on cellulose fiber surfaces was confirmed by X-ray photoelectron spectroscopy (XPS), zeta potential measurement and atomic force microscopy (AFM). The XPS results showed that the contents of the two characteristic elements (i.e., Cl and S) increased with increasing bilayer numbers. The zeta potential of modified fibers was regularly inversed after each layer deposition. The AFM phase image revealed that the surface root-mean-square roughness of modified cellulose increased along with the increasing bilayer number. Moreover, the wetting properties and physical strength of handsheets prepared from modified cellulose fibers with and without heat treatment were tested, respectively. The result showed that the water contact angle was higher when LSA was in the outermost layer than when PAH was in the outermost layer, and the heat treatment improved the hydrophobicity for all the handsheets. The non-heat-treated handsheet prepared from (PAH/LSA)5 multilayer-modified fibers gave a water contact angle of 120.3o, and then after heat treatment, the contact angle reached up to 151.7o, indicating that high temperature treatment induced the most hydrophobic long chain groups in LSA macromolecules orientated to the multilayer-air interface. The tensile strength properties of both non-heat-treated and heat-treated handsheets made from PAH/LSA-modified fibers were significantly enhanced. When a (PAH/LSA)5 multilayer was deposited on the cellulose fiber surface, the tensile strength increased by 33.9 % for non-heat-treated handsheets and by 57.8 % for heat-treated handsheets compared to that of handsheets made from original fibers, respectively.