Rapid preparation of smooth nanocellulose films using spray coating

Spraying of nanocellulose (NC) on a solid surface to prepare films is an alternative technique to vacuum filtration, which requires a long drainage time and produces films which can sometimes be difficult to separate from the filter. This letter reports a rapid preparation technique for nano-cellulose films using a bench scale system spray coating nanocellulose suspension onto stainless steel plates. After spraying NC suspension onto a smooth steel plate travelling on a constant velocity conveyor, the films can be dried directly on the plates using standard laboratory procedures, saving processing time and effort. By adjusting the suspension consistency, we were able to reproducibly make films with a basis weight ranging from 52.8 ± 7.4 to 193.1 ± 3.4 g/m² when spraying on to a plate moving at a velocity of 0.32 cm/s. The operator preparation time for the nanocellulose film was 1 min, independent of the sample basis weight, which compares to production times reported in the literature of 10 min using filtration techniques. The films made by spray coating showed higher thickness, but comparable uniformity, to those made by vacuum filtration. Optical profilometry measurements showed that over a 1 cm × 1 cm inspection area that the surface roughness (RMS) of the NC film is only 389 nm on the spray coated side in contact with the steel plates, compared to 2087 nm on the outside surface. Thus, the reduction in preparation time for producing the nanocellulose film recommends this spray coating technique as a rapid and flexible method to produce NC films at the laboratory scale.