Formaldehyde Resins

摘要

Urea-formaldehyde (UF) resins can present a swollen colloidal phase when dispersed within a continuous water phase containing soluble oligomers. The main goal of the present investigation was to clarify the physical and chemical nature of these two phases and elucidate their impact on the bonding process. Optical and electronic microscopy provided information on the morphology of the colloidal phase, showing primary particles and particle agglomerates. Mechanisms are suggested for the colloidal stabilisation and dilution-induced flocculation. Three commercial urea-formaldehyde resins with different F/U molar ratios were studied using particle size distribution analysis. The results showed the influence of trie resin's degree of condensation and the aging status on the size of the colloidal structures. Gel permeation chromatography analysis was performed on samples of different resins and of the respective continuous and dispersed phases, separated by centrifugation.