Heterogeneous formalization of poly(vinyl alcohol)

The distributions of formaldehyde content from the surface to the inner part of poly(vinyl alcohol) (PVA) films formalized in a aqueous solution of sodium chloride and in a methanol/water mixture both containing formaldehyde and hydrochloric acid were investigated using rolled films. The formaldehyde content at the surface was higher than that in the inner part. When the PVA film was formalized in such a reaction condition that the rate of formalization was fast, a PVA film of high formaldehyde content at the surface and of large difference in the formaldehyde content between the surface and the inner part was prepared. Assuming that the formalization occurs in proportion to the amount of diffusing solution for formalization and that the diffusion obeys the F ICK'S Law, the diffusion coefficients of the solution for formalization were estimated from the distribution of the formaldehyde content to be about 1.8 × 10 −6 cm 2 /min at 50°C for the methanol solution containing 5% formaldehyde, 18.1% water and 5% hydrochloric acid and 1.7% × 10 −6 cm 2 /min at 50°C for an aqueous solution containing 1% formaldehyde, 10% sodium chloride and 5% hydrochloric acid.