1. Improve initial viscosity
To improve the initial viscosity of urea formaldehyde resin, modifiers such as polyvinyl alcohol, polyethylene glycol, and hydroxymethyl cellulose can be added, but these substances are relatively expensive. Therefore, starch based substances can be used, especially when starch is added at the beginning of urea formaldehyde resin synthesis for better results. During the synthesis process, starch may undergo hydrolysis to produce various types of dextrins. Due to the high relative molecular weight of starch and its high viscosity after dissolution, adding a small amount can produce urea formaldehyde resin with high viscosity. At the same time, hydroxyl groups, hydroxymethyl groups, and aldehyde groups generated by hydrolysis on starch molecular chains may participate in the synthesis reaction of urea formaldehyde resin, which not only improves the initial viscosity, but also enhances the adhesive strength and storage stability.
2. Reduce contractility
Urea formaldehyde resin has a high curing shrinkage rate, which is prone to cracking and internal stress in the adhesive layer, resulting in a decrease in viscosity and strength. In order to reduce the shrinkage rate of urea formaldehyde resin during curing, some fillers such as flour, starch, blood powder, a-cellulose powder, wood powder, soybean powder, etc. are usually added to the resin solution.
3. Reduce brittleness
In order to reduce brittleness and improve toughness, polyvinyl alcohol, polyvinyl formal solution, polyvinyl acetate lotion, VAE solution, etc. can be added, and the initial viscosity and aging resistance can also be improved.
4. Improve water resistance
Adding small amounts of melamine, phenol, resorcinol, alkylamines, sugar aldehydes, etc. during the synthesis of urea formaldehyde resin can effectively improve its water resistance. Adding aluminum sulfate, aluminum phosphate, and other crosslinking agents can also significantly improve water resistance. Adding fillers such as wood flour, flour, soybean flour, iron oxide, expansive soil, etc. during the glue mixing process can also improve water resistance.
Phenol modified urea formaldehyde resin is used to introduce a benzene ring structure into the resin, which blocks the water absorbing groups of the resin and significantly improves its water resistance and aging resistance. The water resistance can also be improved by adding resorcinol or melamine into the curing agent components, and by blending acrylate copolymerization lotion with urea formaldehyde resin.
5. Improve adhesive strength
The use of multiple composite additives such as polyvinyl alcohol and phenol can improve brittleness, enhance water resistance and adhesive strength.
Urea formaldehyde resin can significantly improve its performance by adding modifiers according to different usage requirements.
