Wetting and hydrophobic modification of cellulose surfaces for paper applications

The use of papers in packaging and development of novel technological applications for paper substrates largely depends on the control of the hydrophilic properties of the cellulose fibres and improvement of the water-repellent properties. This review provides an actual summary of available literature on theoretical concepts and practical methods to improve the hydrophobicity of cellulose fibres and paper webs. In the first part, the interaction of water with cellulose fibres and paper webs is described at different levels ranging from the molecular scale over the micro- to macroscale fibre properties towards the interactions with porous substrates. The concepts for hydrophobicity and superhydrophobicity applied to cellulose fibres are reviewed, considering the surface chemistry and topographical features. In the second part, current techniques for hydrophobization based on sizing or direct fibre surface functionalization are described. Besides traditional sizing procedures, novelties in nanoparticle applications as hydrophobic sizing agent are reviewed. Novel trends in physical, chemical and nanotechnological fibre surface modifications or surface coatings are reviewed to turn the wetting properties into the superhydrophobic regime. The main future concern in controlling cellulose wettability lies in the development of sustainable modification techniques based on renewable resources such as biopolymers and green chemistry.