Curing Properties of Urea-Formaldehyde and Melamine-Modified Urea-Formaldehyde Resinswith Dynamic Mechanical Analysis

摘要

Dynamic mechanical analysis (DMA) method was used to study the curing parameters of urea-formaldehydern(UF) and melamine-modified urea-formaldehyde (MUF) resins. Catalyst level,rnresin formulation, melamine level, curing temperature and time interval between catalystrnaddition and DMA tests were examined. The gelation in UF resins preceded the vitrification by arnrelatively long, low modulus period, indicating that gelations occur perhaps very early due torncertain UF polymer resin fractions formed in resin synthesis. The gel time and the cure time ofrnUF resins measured by DMA were well correlated with the catalyst level and the resinrntemperature, and the cure rate was strongly affected by the time interval between catalystrnaddition and DMA tests. Cure times of MUF resins were longer than those of UF resinsrnincreasing with melamine levels. The higher extent of polymerization attained of UF base resinsrnin MUF resin synthesis increased the cure rate. The rigidity and thermal stability of cured MUFrnresins were higher than those of UF resins, especially at higher curing temperatures. The rigidityrnand cure rate of MUF resins were highly affected by melamine levels and formaldehyde/urearn(F/U) mole ratios.