Nanoscale surface modification of wood veneers for adhesion
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Surface chemistry of wood is based on the exposed cut surface that is the combination of intact (lumen wall) and cut cell wall material. It is inherently complex and changes with history of processing. Modification of wood surface through noncovalent attachment of amine containing water soluble polyelectrolytes provides a path to create functional surfaces in a controlled manner. Furthermore, modification of the surface can be performed using layer-by-layer (LbL) assembly, where the adsorption of polyelectrolytes or nanoparticles in sequential steps yields a multilayer film with a defined layer sequence on a given substrate. The objective of this study was to quantify adsorption of polyelectrolytes onto wood surface and use these polyelectrolytes as adhesives. In this study, optimal pH conditions for modifying wood surfaces, by anchoring adsorbing polyelectrolytes, were detected using zeta- ( )-potential measurements. Positively charged wood surfaces were also detected by the same technique after a layer of poly(diallyldimethylammonium chloride) (PDDA) or poly (ethylenimine) (PEI) was adsorbed. Both X-ray photoelectron spectroscopy (XPS) and Carbon-Nitrogen-Sulfur analyzer (CNS) were used to quantify the amount of charged polymer on wood surfaces to elucidate optimal pH and ionic strength for polyelectrolyte adsorption. Confocal laser scanning microscopy (CLSM) and Environmental Scanning Electron Microscope (ESEM) were used to characterize adsorbed LbL multilayers of poly(acrylic) acid (PAA) and poly(allylamine hydrochloride) (PAH). Cross-linking between PAA and PAH at various temperatures was studied by Fourier Transform Infrared Spectroscopy (FTIR) and the evaluation of multilayer as bonding agents was carried out by compression shear test following ASTM D905 standard.
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