[Krlos99]

I am looking for an answer to a problem that I have had in the laboratory, which I do not understand. I have made resins from urea and 50% formaldehyde. However, by replacing 50% formaldehyde (liquid) with 90% paraformaldehyde (solid). It strikes me that adding water, paraformaldehyde and soda to regulate the pH (basic), then starting to heat <50 ° C the mixture begins to become pasty; as opposed to using 50% formaldehyde. Do you know the reason?