Repeated impacts tests and nanoindentation as complementary tools for mechanical characterization of polymer-coated particles.

Polymercoated particles have been produced by applying two grades of hydroxypropyl methylcellulose and one grade of polyvinyl alcohol onto sodium benzoate PuroxS core particles by using topspray fluid bed coater and then stored under two different conditions, namely ambient conditions 23°C, 55 RH and in the freezer −18°C, 25 RH. Surface morphology has been firstly analyzed using scanning electron microscope and atomic force microscope. Resistance to attrition and viscoelastic properties have been measured by repeated impact tester RIT and nanoindentation, respectively. The resistance to attrition have been discussed as function of type of coating materials, breakage mechanisms, and storage temperature, and then compared with uncoated PuroxS. The storage conditions is not influencing the morphology, whereas is strongly affecting the resistance to attrition. Coated particles stored at −18°C were found to be more resistant to attrition than ones stored at room conditions. Such differences negligible at low energies low numbers of impacts increase as soon as the number of impacts and the energy rise. The improvement in the resistance to attrition was related to the plasticizing effect of water content. Displacement, storage modulus E′, loss modulus E″, and damping factor tan δ have been measured for all coated particles. Quasistatic and dynamic nanoindentation were found to agree very well with each other. Comparison of the nanoindentation results and the RIT results showed that tan δ, as measure of viscoelasticity and flexibility of the polymeric coating material, is related to the attrition behavior. It was found, in fact, that a higher tan δgives more resistance to attrition. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [ABSTRACT FROM AUTHOR]