Encapsulation of a pressure-sensitive adhesive by spray-drying: microparticles preparation and evaluation of their crushing strength

Abstract

An industrial pressure-sensitive adhesive was microencapsulated by spray-drying using an aqueous colloidal ethylcellulose dispersion (Aquacoat® ECD) plasticised by triacetin to form the wall material. Unloaded (0:100) and adhesive-loaded (25:75) particles were produced in a Büchi B-191 mini spray-dryer with product yields of 62% and 57%, respectively. Microparticles were spherical and narrow sized with mean D_3,2 diameters of 3.165 ± 0.001 and 5.544 ± 0.105 µm, respectively. The microparticles were found to redisperse well in water and exhibit enough stability in neutral and alkaline aqueous media to be further used in a coating slip. Crush tests on single microparticles with diameters ranging from 2 to 12 µm were performed using a nanoindenter. They revealed that the crushing force of both kinds of microparticles increased linearly with their diameter and that the adhesive loading reduced the mechanical strength of the prepared microparticles.

• microencapsulation
• mechanical characterisation
• nanoindenter
• ethylcellulose