Influence of combined mechanical treatments on the morphology and structure of cellulose nanofibrils: Thermal and mechanical properties of the resulting films

• The effect of a second mechanical treatment was evaluated in nanocellulose.
• The morphological, structural, thermal and mechanical features were assessed.
• The second treatment had a slight effect in sample mechanical behavior.
• Further fibrillation decrease the thermal stability and degree of polymerization.
• The most notorious modifications were exerted after the first mechanical treatment.

The deconstruction of the hierarchical structure of cellulose results in the production of cellulose nanofibrils (CNFs). CNFs are commonly obtained by grinding and high-pressure homogenization processes and both treatments can be simultaneously used. Nevertheless, the influence of a two-stage high pressure homogenization of previously ground CNFs on the nanofibril diameter and the physical, thermal and mechanical properties of the resulting films has not been reported. The present study aims at understanding the changes exerted in cellulose after grinding and subsequent passing through the first and second stage of a high-pressure homogenizer. The films prepared from the resulting CNFs were analyzed by electron microscopy, infrared spectroscopy, X-ray diffraction, viscometry, thermal degradation and tensile tests. The data indicate that the initial grinding treatment prompted the most remarkable changes, resulting in enhanced mechanical properties of the films, while decreasing its thermal stability, intrinsic viscosity and crystallinity. Further fibrillation in a high-pressure homogenizer did not have a significant effect, except a decrease in thermal stability and intrinsic viscosity.

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