Melamine-formaldehyde microcapsules encapsulating HEDP for sustained scale inhibition

Adding scale inhibitors is an efficient and economical solution to the troublesome scale deposition in various industrial productions. However, the direct use of liquid scale inhibitors often fails to provide long-term effective control and will cause a large amount of waste of scale inhibitors. Encapsulating the scale inhibitor into microcapsules is an advisable new approach to solving this problem. In this work, a water-soluble scale inhibitor (1-hydroxy ethylidene-1,1-diphosphonic acid, HEDP) was encapsulated into melamine formaldehyde microcapsules for the first time by in-situ polymerization using inverse emulsion (W/O emulsion) as a template. The influence of synthesis parameters (water-to-oil ratio, the amount of HEDP, stirring speed) on the morphology and particle size was investigated, and microcapsules with smooth surface, regular spherical shape and good dispersibility were obtained. The microcapsules possessed encapsulation efficiency exceeding 80% and good sustained-release properties (release time up to 63 h) ensuring sustainable scale inhibition. The scale inhibitor released from the microcapsules could inhibit the growth of calcium carbonate crystals and result in lattice distortion, which contributed to high scale inhibition efficiency (about 86%). The prepared microcapsules have broad application prospects in the field of industrial scale inhibition.