Abstract
An attempt was made to evaluate the stability of generation on formaldehyde gas at a level typical of an indoor environment by a permeation tube method using paraformaldehyde. The permeation tube was prepared by filling a cylindrical polyethylene tube with paraformaldehyde. The permeation rate (Pr) of formaldehyde gas from the tube was evaluated at 50°c by measuring both the weight loss of the whole tube, which is a normal way to derive a standard permeation rate of a permeation tube, and the amount of formaldehyde at the outlet of a gas generator. The results showed that Pr obtained by formaldehyde gas analysis (Prf) successfully became constant after 40 days when the tube was placed in the gas generator at 50°c, and kept stable for more than a year. Meanwhile, at the beginning of the gas generation, the rate of weight loss of the tube (Prw) was about 10 times greater than the Prf and decreased continuously to meet the Prf with 60.0 ng/min for about 210 days. These results indicate that impurities contained in paraformaldehyde are also generated from the tube and caused the excess rate obtained by the previous weight loss method.
