Water vapor mass transport across nanofibrillated cellulose films: effect of surface hydrophobization
In this paper, porous nanofibrillated cellulose (NFC) films were utilized to produce water-resistant, porous cellulose films. Film porosities of ~ 50% were achieved through solvent exchange from water to acetone, and the resulting films were hydrophobized with an epoxy modifier in non-swelling conditions in acetone, yielding films that were non-wettable by water but permeable to water vapor. The mass transport mechanisms of gaseous and liquid water were studied by water vapor transfer rate (WVTR), water vapor uptake and water contact angle measurements to unfold how these properties were achieved. Surface hydrophobization was found to decrease the moisture uptake but it did not prevent it completely. The WVTR values were in effect similar for the initial and hydrophobized films, even if the water contact angles were higher in the latter. We anticipate that the porous and hydrophobic NFC films presented in this paper may find applications in sportswear, medical, or personal hygiene products.
KeywordsCellulose films Nanofibrillated cellulose Surface hydrophobization Water mass transport Water vapor transport rate
The VINN Excellence Centre SuMo Biomaterials is gratefully acknowledged for financial support. The authors also acknowledge Anders Mårtensson for skillful SEM work and Anne Wendel for support in the BET measurements. Furthermore, the authors thank Prof. Gunnar Westman for fruitful discussions and Chris Bonnerup for providing the NFC.
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