Consolidation and dewatering of a microfibrillated cellulose fiber composite paper in wet pressing

• Presenting a new composite paper containing microfibrillated cellulose.
• Novel methodology for the analysis of structure consolidation.
• Micro and nano-scale pore structure was defined.
• Good press dewatering and optical properties of the composite paper.

The emerging research field of bio-based nanomaterials has gained a lot of interest recently. One of the most promising new range of materials are the micro and nanofibrillated celluloses, or nanocelluloses that are based on wood or other natural cellulose sources. While the strength increasing potential of nanocelluloses is evident in light of the current knowledge, the related challenges in dewatering are inevitable due to the hydrophilic nature and the large relative surface area of the material. The target of this work was to characterize the dewatering and structural changes of a high filler content (70 wt% precipitated calcium carbonate) biocomposite containing microfibrillated cellulose in a wet pressing process. Softwood bleached kraft pulp fibers were used as a reinforcement in the composite. Press dewatering performance together with dynamic density measurements were made with a press simulator, and scanning electron microscopy and mercury intrusion porosimetry were used in the structural analysis of the samples. The dewatering of a new type of MFC based composite was shown to be better than traditional softwood based fibers. The high amount of filler in the structure does not contribute to the binding of water and helps to provide channels for water removal. Mercury porosimetry data was able to partially explain the good press dewatering of the composite paper compared to a SBKP reference paper. Based on the results, it can be concluded that the dewatering of the MFC composite is not limited by the wet pressing operation commonly used in the paper manufacturing industry. Excellent optical properties together with potential cost savings supports the use of this type of novel composite in future applications.

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