Manufacture of fine cellulose powder from chemically crosslinked kraft pulp sheets using dry milling

The present study concerns the preparation of cellulosic powders with two-stage dry milling of chemically crosslinked birch kraft pulp sheets. Chemical crosslinking of kraft pulp sheets using glyoxal with and without a catalyst (aluminium sulphate) made the pliable, tenacious kraft pulp sheets brittle. Due to the brittleness, the crosslinked pulp sheets could be disintegrated easily and rapidly using a Wiley mill. The length-weighted average fibre length of the crosslinked pulp powders (0.31–0.33 mm) was shorter than the Wiley-milled reference powder (0.44 mm). The notably higher density and less fluffy character of the crosslinked pulp powders enabled their effortless further processing with an air-flow-type ultra-fine microniser. The medium size value (D50) of the micronised crosslinked powders was around 40 μm. The study finds that chemical crosslinking pre-treatment enhances the dry milling of kraft pulps to a fine powder. Chemical crosslinking may offer a new tool for industrial cellulosic powder manufacturing.