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Curing mechanism of urea-formaldehyde under ambient temperature
Pages: 169-172
Year: Issue:  6
Journal: Journal of Nanjing Forestry University(Natural Science Edition)

Keyword:  urea-formaldehyde resinGPCmolecular weight distributioncuring mechanism;
Abstract: This article investigates the change of viscosity, gel time and molecular weight distribution of urea-formalde?hyde ( UF) resin with curing agent ammonium chloride ( NH4 Cl) under ambient temperature by measuring gel time and gel permeation chromatography ( GPC) analysis. It was found that the viscosity of UF resin with 2?0% NH4 Cl changed slightly at the beginning, but sharply increased from 99 mPa·s to 10 020 mPa·s after 8 hours. The resin thickened and clustered at this stage. After 10 hours, UF resin took shape and became hard and its gel time decreased to 40 s from 137 s for the un?cured resin. Number average molecular weight and weight average molecular weight increased signifi?cantly, and small molecular disappeared gradually while molecular of medium and high weight accounted for higher pro?portion. The molecular uniformity of UF was improved degree of dispersion dropped from 1.11 to 1.08. The degree of ge?lation increases and the activity of applicable UF resin decreases with longer elapsed time.
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