Abstract
A novel rapid method for high throughput production of smooth nanocellulose (NC) films by spray coating was communicated recently. In this method, we employed spray coating to produce wet films on stainless steel plates moving on a conveyor, forming free-standing films with interesting structural, mechanical and surface properties upon drying. In this research, we investigate the range of mechanical and physical properties of nanocellulose films prepared by spraying. Furthermore, a comparison with NC films prepared via conventional vacuum filtration was conducted to evaluate the suitability of this method as an alternative film preparation process. One set of experiments was completed where the solids concentration of the suspension was fixed at 1.5 wt% and the conveyor velocity was varied, while two series of experiments were completed where the solids concentration of the suspension was varied and the conveyor speed was fixed at either 0.32 or 1.05 cm/s. By varying speed and solids concentration, spray-coating was found to allow efficient production of films with basis weights ranging from 38 to 187 g/m2, with film thicknesses ranging from 58.4 to 243.2 μm, respectively. There was a universal linear relationship between the thickness and basis weight, independent of the process conditions. The optical uniformity of film was also noticeably dependent on the spraying process. The optical uniformity index of films, relative to vacuum filtered films, increased with conveyor speed at 1.5 wt% solids concentration and was independent of solids concentration at low speed. Forming at the higher speed of 1.05 cm/s produced a maximum in optical uniformity in the range 1.5–1.75%, with these films being more uniform than conventional films produced through vacuum filtration. The most uniform films produced by spraying also had a similar tensile index to films made via vacuum filtration. With an understanding of these parameters and effects, we demonstrate this method to be a more time efficient alternative method to produce uniform films where the properties can be tailored to the required application.
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Acknowledgments
The financial support from the Australian Research Council, Australian Paper, Carter Holt Harvey, Circa, Norske Skog and Visy through the Industry Transformation Research Hub Grant IH130100016 are acknowledged for this research work. The authors are grateful to the facilities used with the Monash Centre for Electron Microscopy. K. S. is grateful to Monash University, Bioresource Processing Research Institute of Australia and Bioprocessing Advanced Manufacturing Initiative and Faculty of Engineering International Postgraduate Research Scholarship for his doctoral studies. The Optical Profilometry of NC films were performed in part at the Melbourne Centre for Nanofabrication (MCN) in the Victorian Node of the Australian National Fabrication Facility (ANFF). K. Shanmugam acknowledges Dr. Hemayet Uddin, Process engineer at Melbourne Centre for Nanofabrication for the optical profilometry investigation of nanocellulose film.
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Shanmugam, K., Doosthosseini, H., Varanasi, S. et al. Flexible spray coating process for smooth nanocellulose film production. Cellulose 25, 1725–1741 (2018). https://doi.org/10.1007/s10570-018-1677-7
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DOI: https://doi.org/10.1007/s10570-018-1677-7