Attrition strength of water-soluble cellulose derivatives coatings

The aim of this paper was to compare the attrition strength of microparticles coated with various water-soluble cellulose derivatives coatings using the repeated impact tester (RIT). As a core material glass beads of diameter 650-850 mu m were used. Four water-soluble cellulose derivatives have been investigated as coating materials: methylcellulose (MC), two types of carboxymethylcellulose (CMC - low and high viscous type) and hydroxypropylcellulose (HPC). Within the research coatings of 5 mu m and 20 mu m thickness were attrition tested. For all tested cellulose derivatives coatings, attrition occurred according to the layer fatigue submechanism. Overall, HPC coatings were found to be the strongest since they did hardly show any coating mass loss during attrition testing. Most of the low viscous CMC coatings were resistant to fatigue for a low number of impacts, only, and they have shown the lowest strength against attrition. Attrition data showed the relationship between coating uniformity and coating strength in that uneven and irregular surfaces resulted in a lower strength against attrition. Coating thickness also influenced the results of the repeated impact tests: thicker coatings generally presented a higher attrition strength compared to 5 mu m coatings. Testing two different carboxymethylcellulose types showed the influence of molecular weight on the coating strength. High viscous CIVIC, having a higher molecular weight, also presented a higher strength against attrition. (C) 2009 Elsevier B.V. All rights reserved.