Tokuyama Corporation

Makoto Kataoka

Shingo Hiranaka

Kentaro Matsuo

Yuusuke Shimahara

Yasuto Yasuzawa

Gypsum derived from waste gypsum boards is calcined and converted into gypsum granules including hemihydrate and/or anhydrous type III gypsum. The calcined gypsum granules are dropped into water to prepare a gypsum slurry. Then, dihydrate gypsum particles are crystalized in the slurry. The temperature of the gypsum granules just before being dropped into the water is 90&#xb0; C. or higher.

Recycling method of dihydrate gypsum from waste gypsum boards

A method of producing a nonfoamed formed article of a vinyl chloride resin by mixing a hydrated water-containing gypsum powder and a vinyl chloride resin powder together, and heating the obtained mixture at a temperature lower than a temperature at which the vinyl chloride resin starts decomposing thereby to remove the hydrated water of the gypsum and to form the mixture. The method makes it possible to obtain a nonfoamed formed article free of defective appearance by directly adding the hydrated gypsum (specifically dihydrate gypsum) to the vinyl chloride resin without converting it to the anhydrous gypsum, without requiring wasteful energy cost, without causing foaming or defective forming stemming from the hydrated water and maintaining stability.

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Shunan, Japan

Makoto Kataoka