Calculation on the Shortening of the Time for the Bleaching Reaction of Japan Wax Particles

Abstract

Japan wax is often bleached in the sunlight in the form of flakes or particles. In the midcourse of the bleaching process, they are usually melted and the concentration of colored materials unchanged in the particles is made uniform. This molten wax is, then, made again into particles, which are exposed to the sun and bleached furthermore. The midcourse melting of the Japan wax particles, called "nakani" in the works, brings about the shortening of the time required for bleaching. In this paper, we discuss theoretically the kinetics of the two bleaching reactions before and after nakani to obtain the reduction and suitableness of the total bleaching time.
Light intensity at the raw wax/bleached wax interface in a particle was considered to play an important role in the bleaching reaction. A simple, idealized model was, therefore, devised for the bleaching reaction in the particle, to set importance on the local light intensity in the particle. The Japan wax particles subjected to bleaching were dispersed with various size and the log-normal size distribution was assumed for these particles. Rate expressions for the two reactions were derived from the model and solved numerically for the total bleaching time with a digital computor.
The total time for the two bleaching reactions was found in our work to be almost always shorter than the time required for the same conversion by only a single bleaching reaction. This fact suggests the effectiveness in the range considered. It was found furthermore that the total bleaching time vs. coversion curve had a minimum. The minimal value of the total bleaching time is the optimal one. It was not recommended to expose the particles after nakani longer than the time spent for bleaching before nakani. As either the values of logarithmic standard deviation or molar absorptivity increased, the minimal bleaching time decreased in our work and consequently the nakani procedure became more effective.