Surface hydrophobization of pulp fibers in paper sheets via gas phase reactions

Hydrophobization of cellulosic materials and particularly paper products is a commonly used procedure to render papers more resistant to water and moisture. Here, we explore the hydrophobization of unsized paper sheets via the gas phase. We employed three different compounds, namely palmitoyl chloride (PCl), trifluoroacetic anhydride/acetic anhydride (TFAA/Ac2O)) and hexamethyldisilazane (HMDS) which were vaporized and allowed to react with the paper sheets via the gas phase. All routes yielded hydrophobic papers with static water contact angles far above 90 degrees and indicated the formation of covalent bonds. The PCl and TFAA approach negatively impacted the mechanical and optical properties of the paper leading to a decrease in tensile strength and yellowing of the sheets. The HMDS modified papers did not exhibit any differences regarding relevant paper technological parameters (mechanical properties, optical properties, porosity) compared to the non-modified sheets. XPS studies revealed that the HMDS modified samples have a rather low silicon content, pointing at the formation of submonolayers of trimethylsilyl groups on the fiber surfaces in the paper network. This was further investigated by penetration dynamic analysis using ultrasonication, which revealed that the whole fiber network has been homogeneously modified with the silyl groups and not only the very outer surface as for the PCl and the TFAA modified papers. This procedure yields a possibility to study the influence of hydrophobicity on paper sheets and their network properties without changing structural and mechanical paper parameters. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

Hydrophobization of unsized paper sheets via the gas phase using compounds like palmitoyl chloride, trifluoroacetic anhydride/acetic anhydride, and hexamethyldisilazane yielded hydrophobic papers with static water contact angles above 90 degrees. While the PCl and TFAA approach negatively impacted mechanical and optical properties, the HMDS modified papers showed no differences in relevant paper technological parameters. XPS studies revealed low silicon content in HMDS modified samples, indicating the formation of submonolayers of trimethylsilyl groups on fiber surfaces in the paper network.