Thermal decomposition of resins of urea- and melamine-formaldehyde were studied in order to yield data fundamental for improvement in fire-retardation and combustion toxicity-safety of wood-based materials. The part I of the reports describes weight losses of the urea-formaldehyde resin for the TG and isothermal heating in helium and air atmospheres. The sample used was ordinarily prepared in the laboratory. The kinetic parameters of an aparent first-order reaction were derived from the weight-time curves. The active weight loss is interpreted to be controlled by chain mechanisms which consist of reactions accelerating the weight loss and stabilizing the structure, consequently ret-. arding the weight loss. In the kinetic analyses the overall weight loss was obviously shown to undergo a series of, at the least, three stages. The obtained Arrhenius parameters suggest with the different temperature dependences that a major stage at the low temperature is able to be overcome by the minor ones with the increase in the temperature. It is desirable to clarify the chemical mechanisms of the stages.

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