Nanocomposite-based lignocellulosic fibers 3: polyelectrolyte adsorption onto heterogeneous fiber surfaces

Wood and natural fibers are composed of multiple polymeric components. Lignin, one primary component, is typically removed to various degrees during paper-making, but is present on thermomechanically isolated fibers. The effect of the residual lignin on the adsorption of poly(diallyldimethylammonium) chloride (PDDA) onto lignocellulosic fibers was investigated under varying solution conditions (electrolyte concentration and pH). Using nitrogen elemental analysis it was shown for the samples containing the highest concentration of lignin, PDDA adsorption to the fibers was reduced for all solution conditions. Upon extracting the alkali-soluble lignin, the samples showed the greatest amount of PDDA adsorption, achieving ~1.6% (w/w), under neutral solution conditions without the presence of added electrolyte. Furthermore, the influence of polyelectrolyte loading and electrokinetic potential on subsequent multilayer formation of PDDA and montmorillonite clay was quantified. It was revealed that electrokinetic potential of fiber after PDDA adsorption, rather than the amount of adsorbed PDDA layer, controlled the subsequent clay adsorption. Significant mass of PDDA/clay (up to ~75% of starting dry fiber mass for only 4 bi-layers) can be adsorbed onto steam-exploded wood fibers through the multilayer assembly process. This paper provides insight into how non-covalent modification of heterogeneous fibrous substrates offers a novel route for the creation of organic/inorganic fiber materials.