Dry grinding of chitosan powder by a planetary ball mill

Dry grinding of chitosan powder was carried out using a planetary hall mill for its applications to drug carriers. Eighty grams of zirconium oxide balls of 1 - 5 mm diameter and 1 - 4 g of 100% deacetylated chitosan were loaded into a 45 mi agate pot and then ground at 440-723 r.p.m. The particle size was analyzed by a laser scattering diffraction method. When surface grinding was induced by lower rotation speeds and smaller beads, except for 1 mm balls, the chitosan powder was ground at a lower rate, but to a smaller size. The median diameter of the powder ground without any additives was minimized to 5.0 mu m at 440 r.p.m. rotation speed using 2 mm balls. Further, various additives were tested to find an effective material as a grinding aid. Hydrophobic compounds, including fatty acids with a long acyl chain and cholesterol, and hydrophilic polyethylene glycol 4000 were effective to reduce the particle size. Lauryl compounds with the same number of carbons exhibited almost the same size reducing effect as a grinding aid, regardless of polar head groups, consisting of carboxylic acid, alcohol or amine. The optimal content was 10-20% in the case of lauric acid. Fatty acids with a longer acyl chain were more effective as a grinding aid. Among the additives studied, stearic acid was most effective and reduced the median diameter to 1.8 mu m.