Liyuan Zhang

Cellulose nanofibre is an abundant green nano material. Its potential for sustainable industrial applications has attracted great interest globally. This thesis focuses on developing a new and economical method for preparing cellulose nanofibres from softwood pulp, a novel approach to characterize dimensions of cellulose nanofibres, and a rapid and facile procedure of applying cellulose nanofibres in the production of cellulose nanofibre paper.

This study has demonstrated the possibility of producing high quality cellulose nanofibres from softwood pulp by ball milling. Ball milling has been used to prepare cellulose nanoparticles as a top-down nanofabrication method. However, to produce cellulose nanofibres, rather than nanoparticles by ball milling, a number of challenges must be overcome. In this study, a single factor approach was used to study several major factors that affect the diameter and the aspect ratio of cellulose nanofibres. These factors include the mass ratio of milling balls to cellulose pulp, milling time, size of the balls and also the effect of alkaline pretreatment on nano-fibre yields. The most significant factors influencing the production of cellulose nanofibres are the ball size and the mass ratio of balls to cellulose pulp. This finding has been discussed in terms of contact area between balls and cellulose fibres during milling. Another finding is that alkaline pretreatment did not contribute significantly to the reduction of energy consumption, nor to the quality of the resultant nanofibres. Therefore, ball milling, which does not require any chemical pretreatment, has an advantage in nano cellulose production efficiency over other methods.

When characterizing cellulose nanofibre dimensions, difficulties were encountered when fibre dimensions were at nano scales with large aspect ratios. The currently employed microscopy techniques, such as SEM, TEM and AFM, were unable to characterize both length and diameter of nanofibres with a large aspect ratio. The nanofibre diameter distribution was also found to be questionable because the surface of a large pulp fibre has a similar appearance to a network of oven-dried cellulose nanofibres. These problems have been discussed and solutions have been proposed in this thesis. To characterise the nanofibre diameters and their distributions properly, a series of SEM images have to be taken at both low and high levels of magnification. The area of samples has been included in the frequency calculation of fibre diameter distribution. Besides the common fibre diameter distribution from the frequency statistics, the fibre diameter distribution by fibre weight has also been examined in this study. The results show that a few large fibres influence a certain properties of cellulose nanofibre based materials significantly. However, due to the scale, microscopy techniques cannot solve the problems in determining the ends of nanofibres. For characterizing nanofibre length, the sedimentation method was applied to estimate the cellulose nanofibre aspect ratio instead of nanofibre length for the first time. The aspect ratio plays an important role in the subsequent applications of cellulose nanofibres in nanofibre paper making.

A large quantity of cellulose nanofibre has been prepared by ball milling in this study. A rapid and economical way of making large flat cellulose nanofibre sheets using a moving belt sheet former with commercial mesh fabric has been developed. The effect of cellulose nanofibre dimensions (especially the aspect ratio) on nanofibre paper formation through filtration has been studied. A translucent strong nanofibre paper has been obtained, and the properties have been discussed.

This study has laid a solid foundation for large-scale production and application of cellulose nanofibres. The cellulose nanofibre paper may be produced by a roll-to-roll process one day for important applications, in areas such as filter media and green functional materials.

Thesis publications

Liyuan Zhang, Warren Batchelor, Swambabu Varanasi, Takuya Tsuzuki and Xungai Wang, Effect of cellulose nanofiber dimensions on sheet forming through filtration, Cellulose, Volume 19 (2012), 561-574

Liyuan Zhang, et al., Eco-friendly production of cellulose nanofibres, the 2010 International Conference on Nanoscience and Nanotechnology, Sydney Convention and Exhibition Centre, Sydney, 22~26th February 2010

Liyuan Zhang, et al., Production, characterization, and application of cellulose nanofibre from softwood pulp by soft mechanical decomposition, ARNAM/ARCNN 2010 Workshop, Flinders University, Adelaide, 19~23rd July 2010

Liyuan Zhang, et al., Preparation and characterization on cellulose nanofibre film, the 7th Pacific Rim International Conference on Advanced Materials and Processing (PRICM 7), Cairns Convention Centre, Cairns, Australia, 2~6th August 2010

Liyuan Zhang, et al., Preparation and characterization on cellulose nanofibre paper, the 2010 International Conference on Nanotechnology for the Forest Products Industry, Espoo, Finland, 27~29th September, 2010

Liyuan Zhang, et al., Characterization on cellulose nanofibre non-woven from natural resources, the 2011 China Textile Academic Conference, Shanghai, China, 20~22nd Oct, 2011