Factors influencing particle size of polyamide microcapsules synthesized via interfacial polycondensation

Abstract

Synthesis of 1-100 micrometers of polyamide microcapsules by interfacial polycondensation between diacid chlorides and diamines was carried out. The synthesis was started by dissolving the diacid chloride. in an oily-like material to be encapsulated in microcapsules and then mixing this solution in an aqueous solution of an emulsifier or a protective colloid. The mixture was agitated into emulsion by a high-speed homogenizer at the propeller speeds between 2,000-10,000 rpm., and the agitation times between 30-150 sec. This emulsion was poured into the aqueous solution of a diamine and an acid-receiver. Polycondensation occurred at the interface between the tiny oil droplets and another liquid layers and produced a thin film of polyamide as a shell of the microcapsules which encapsulated the oily-like material in the core. Sebacoyl chloride and terephthaloyl chloride as diacid chlorides; and hexamethylene diamine and para-phenylene diamine as diamines were selected as monomer pairs to synthesize the polyamide microcapsule shell. Sodium dodecyl benzene sulfonate and poly (oxyethylene Tuaryl ether) as surface active agents; and sodium salt of styrene maleic anhydride and poly (vinyl alcohol) as protective colloids were selected to be emulsifying agents. Sodium hydroxide used as an acid-receiver during polycondensation. Butyl acetate and dibutyl phthalate were used as encapsulated materials in microcapsules. Based on the experiments, it was found that dibutyl phthalate was appropriate as encapsulated material than butyl acetate; poly (vinyl alcohol) was the most effective emulsifying agent and sodium dodecyl benzene was as more sulfonate could be used as a co-emulsifying agent with poly (vinyl alcohol) to produce microcapsules with various diameters. Furthermore, it was found that all diacid chloride and diamine combinations could be applied as monomer pairs to synthesize the polyamide microcapsule shell having a wide range of chemical and physical properties; the speed of the propeller, the agitation time of the homogenizer, and the amount of diacid chloride and emulsifying agent affected the characteristics of the microcapsules: increasing the speed of propeller decreased the average diameter of the microcapsules; longer agitation time produced more equal-sized microcapsules; increasing the concentration of emulsifying agent produced stable emulsion Which reduced the average diameter of the microcapsules; the amount of diacid chloride had a direct effect encapsulation efficiency, concentration of which must be adjusted properly so as to produce a perfect shell of the microcapsules.