Rate of Viscosity Change for a Urea-Formaldehyde Resin

The effects of conventional flour extension, foam extension, and inert salt upon the rate of urea-formaldehyde resin polymerization were studied by viscometry. The technique was based upon measuring viscosity change with a modified Gibson viscometer. The reasons for selecting the instrument, based on the free falling sphere principle, and the conditions necessary to apply Stokes formula N = Ns(f) are discussed. The research showed that urea-formaldehyde cures in three stages of which two were actually tested: 1) an initial stage characterized by slightly changing viscosity, and 2) a secondary phase of rapidly changing viscosity. The viscosity during the initial stage of cure was strongly influenced by temperature, type of catalyst, nature of the extender, and the presence of inert materials. Both flour and air extension increased the rate of viscosity change in the initial stage of polymerization. Inert salts in all concentrations studied had no significant influence upon rate of cure, however. During the secondary stage of rapid polymer development, the rate of viscosity change was independent of temperature, type of catalyst, nature of extender, and presence of inert materials.

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