The aim of this work was to improve the mechanical performance of CNF film with a post-crosslinking chemistry leading to a fully cellulosic film structure. Typically, pure CNF films have poor wet-strength performances due to the inherent hygroscopicity of cellulose nanofibrils (CNF). This wet-performance can be improved with added polymeric materials that can mechanically bridge fibrils, or with added substances that can glue or coat the film matrix. The all-cellulose concept is a vital approach to increase the extent of permanent fibril-fibril linkages in a CNF film, when it is targeted to a fully cellulosic film structure. In this study, we utilize the partial dissolution approach with N-methylmorpholine-N-oxide (NMMO), which is a powerful cellulose solvent. NMMO was impregnated into the CNF film structure from a methanol solution followed by a heat activation in dry conditions using simple hot-calendering approach. The study shows that the fibril structure of the CNF film existed after the NMMO dissolution. It was observed that a simultaneous heating and compression step was required to achieve embedding of fibrils during regeneration. After heat activation, the treated CNF films were purified with methanol to remove NMMO from the film structure. The used treatment elevated the mechanical performance of the CNF-films significantly. The dry strength of the reinforced CNF film was increased from 122 MPa up to 195 MPa. The wet strength of the reinforced CNF film was up to 75 % from the dry strength of a pure CNF film. The investigated robust and fast method can be utilized to produce CNF films for applications where improved water resistance and fully cellulosic structures are required characteristics.    <br/>

Partial dissolution as a reinforcing chemistry for CNF films

253rd National Meeting (2017)

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