Print base decorative paper with high-dimensional stability by chemical fiber modification: an experimental and analytical approach

The main structural component of wood fibers is cellulose, which, being highly hydrophilic, interacts with water. Cellulose-based paper has, therefore, the same affinity with water. However, for most products such as decorative paper, this is more of a disadvantage, where water uptake both as liquid and from humid air not only weakens the paper by breaking hydrogen bonds but also alters its dimension and stability over time. The dimensional stability (ability of the paper to retain the size as its moisture content changes) is a critical parameter when the paper is submitted to printing, copying, and converting operations. Humidity can cause sheet wrinkling or warping, thus compromising the processability and the results achievable. The modification of fibers with chemical additives can be a way to improve the performance of paper against water and water vapor uptake. For this reason, several tests of horizontal diffusion of solvents were carried out to evaluate the change in uptake of as-is paper and of papers modified by several different chemical treatments. Solvent uptake tests were performed to assess the interaction of chemically treated and untreated papers with water, dichloromethane, and ethanol. Diffusion mechanisms of the solvents flow within the fiber networks and their movement through the porous solids were analyzed. The chemical treatments of the fiber with silane, siloxane, and polyelectrolyte multilayer were found to considerably influence both solvent contact angles and absorption times of the papers, thus affecting the rate of solvent (more interestingly, of the water) diffusion into the fiber wall. By comparing all the treated and untreated samples, the contact angles with the solvents decreased by performing siloxane, oligo-siloxane, and silane treatments. More specifically, the diffusivity rates of water decreased because of the disappearance of a fraction of the hydrophilic sites and the onset of higher crystallinity regions on the paper sheets.