Preparation of a UV-attenuating agent using a mechanochemical reaction

This paper describes a mechanical preparation method of an ultraviolet (UV)-attenuating agent with a high transparency for visible light using a high-speed elliptical-rotor-type powder mixer (HEM). Ultra-fine zinc oxide particles are used to attenuate UV radiation. To stabilize homogeneous dispersion of zinc oxide particles in a suspension, they were uniformly immobilized on the surface of silica particles by a mechanochemical reaction between zinc oxide and silica, and the composite particles were incorporated into a polymer medium. The optimum processing time in the immobilization was determined by means of a proposed model considering both the activation energy of the mechanochemical reaction and the mechanical energy applied to the particles in the minimum clearance region of the HEM. The relative change in the number of hydroxyl groups on the surface of the silica particles confirmed that a processing time based on the number of zinc oxide particles was suitable for immobilization. The suspension in which the composite particles were dispersed showed more effective UV attenuation performance and had a higher transparency for visible light in comparison with a suspension containing only a mixture in which the zinc oxide and silica particles were simply blended.