Fine-powdering of fibrous cellulose by mechanical milling

Fibrous cellulose was mechanically milled in a vibratory ball mill under several conditions and the obtained powders were characterized. Water or organic solvent adsorbed on amorphous regions of cellulose significantly affected the crystallinity and particle size of the obtained powders. From the vacuum-dried samples which contained < 0.1 wt% water were obtained fine powders with low crystallinity. This may be due to an increase in internal strain of dry cellulose which results in the fragility against a mechanical stress, and due to a decrease in agglomeration of cellulose powders promoted by water. On the other hand, by milling the air-dried samples which contained 7 wt% water at = 100 degrees C were obtained the fine powder with the same particle sizes as in the case of the vacuum-dried samples. These powders exhibited higher crystallinities than in the case of the vacuum-dried samples. This suggests that preferential breaking up of the amorphous regions of cellulose maintains the crystalline regions. Adsorption of organic solvents such as acetone on cellulose induced the finer powders of cellulose with relatively higher crystallinity. The addition of 20 wt% acetone to the vacuum-dried cellulose was most effective for the preparation of the fine cellulose powder.