Mechanical properties of cellulose nanofibril films: effects of crystallinity and its modification by treatment with liquid anhydrous ammonia
The influence of cellulose crystallinity on mechanical properties of cellulose nano-fibrils (CNF) was investigated. Degree of crystallinity (DoC) was modified using liquid anhydrous ammonia. Such treatment changes crystal allomorph from cellulose I to cellulose III, a change which was reversed by subsequent boiling in water. DoC was measured using solid state nuclear magnetic resonance (NMR). Crystalline index (CI) was also measured using wide angle X-ray scattering (WAXS). Cotton linters were used as the raw material. The cotton linter was ammonia treated prior to fibrillation. Reduced DoC is seen to associate with an increased yield point and decreased Young modulus. Young modulus is here defined as the maximal slope of the stress–strain curves. The association between DoC and Young modulus or DoC and yield point are both statistically significant. We cannot conclude there has been an effect on strainability. While mechanical properties were affected, we found no indication that ammonia treatment affected degree of fibrillation. CNF was also studied in air and liquid using atomic force microscopy (AFM). Swelling of the nanofibers was observed, with a mean diameter increase of 48.9%.
KeywordsDegree of crystallinity Mechanical properties Swelling Cellulose nanofibrils
This work is performed as a part of the NORCEL Project: The NORwegian NanoCELlulose Technology Platform, initiated and led by The Paper and Fiber Research Institute (PFI) in Trondheim and funded by the Research Council of Norway through the NANO2021 Program (Grant 228147 Research Council of Norway). The Research Council of Norway is further acknowledged for the support to the Norwegian Micro- and Nano-Fabrication Facility, NorFab. Thanks are extended to CELSUR for providing cotton linters. Thanks are further extended to Jasna Stevanic Srndovic for assistance with NMR and WAXS measurements, Kelly McCammon-Ottesen for proof-reading.
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