Shrink-Resist Treatment of Wool with Epoxy-Functional Acrylic Emulsions—Polyethylene Polyamines as Curing Agents

Abstract

Wool can be effectively shrinkproofed by an epoxy-functional polyacrylate emulsion, provided that a small proportion of a moderately high molecular weight polyethylene polyamine (e.g., polyethylenimine) is included as a crosslinking agent. Other types of polyamines or alternative epoxy resin curing agents are ineffective. The shrink-resist effectiveness increases with molecular size of the polyamine to a limit of MW 600, and this is accompanied by a considerable fall in the optimum polyamine concentration. Volatile organic acids have the effect of reducing the optimum polyamine concentration, but this effect is diminished with increasing size of the polyamine. The rate of cure is reduced for polyamine molecular weights above 600 and is not enhanced by an alkaline catalyst, though curing can be prevented entirely by either strong acids or organic acids of low volatility. The paper proposes that crosslinking is promoted in an alkaline environment and also by greater polyamine mobility, the latter being dependent on molecular weight. Increasing the size and ionic charge of the polyamine molecule enhances the effective polyamine concentration at the fiber surface by restricting diffusion into the fiber, thus enabling the formation of a strongly adherent multiphase film.