Urea-formaldehyde resin modification

Because urea-formaldehyde resin has the disadvantages of poor initial viscosity, large shrinkage, large brittleness, water resistance, aging, release of formaldehyde, solidification and formaldehyde emission, and damage to health, it must be modified to improve performance and expand application. The simple method of modification is as follows:

1, improve the initial viscosity

To improve the initial tack of urea-formaldehyde resin, modifiers such as polyvinyl alcohol, polyethylene glycol, and hydroxymethyl cellulose can be added, but these materials are expensive, so starch materials can be used, especially starch starts at the synthesis of urea-formaldehyde resin. Just join, the effect is better. During the synthesis process, starch may be hydrolyzed to form various dextrin. Because of the relatively high molecular weight of the starch, the viscosity after dissolution is also large. A small amount of urea-formaldehyde resin can be obtained by adding a small amount. At the same time, the hydroxyl group on the molecular chain of the starch, the methylol group and the aldehyde group produced by hydrolysis may participate in the synthesis reaction of the urea-formaldehyde resin, which not only improves the initial tackiness, but also improves the bond strength and storage stability.

2, reduce shrinkage

Urea-formaldehyde resin has a large curing shrinkage rate, is prone to cracks, and internal stress is generated in the rubber layer, so that the viscosity strength is lowered. In order to reduce the shrinkage rate of the urea resin when it is cured, some fillers such as flour, starch, blood meal and a-cellulose powder, wood powder, soy flour, and the like are usually added to the resin glue.

3, reduce brittleness

In order to reduce brittleness and improve toughness, polyvinyl alcohol, polyvinyl formal solution, polyvinyl acetate emulsion, VAE solution, etc. may be added, and initial tack and aging resistance may also be improved.

4, improve water resistance

When a urea-formaldehyde resin is synthesized, a small amount of melamine, phenol, resorcinol, alkylamine, uronic acid, etc. can effectively improve the water resistance of the urea-formaldehyde resin. The addition of aluminum sulfate, aluminum phosphate or the like as a crosslinking agent can also significantly improve the water resistance. Adding fillers such as wood flour, flour, soy flour, iron oxide, and expansive soil during the adjustment of the rubber can also improve the water resistance.

The phenol-modified urea-formaldehyde resin is used, and a benzene ring structure is introduced into the resin to block the water-absorbing group of the resin, so that the water resistance and aging resistance of the resin are remarkably improved. Resorcinol or melamine may also be added to the curing agent component, and the acrylate copolymer emulsion may be blended with the urea resin to improve water resistance.

5, improve the bonding strength

The use of multi-component additives such as polyvinyl alcohol and phenol improves brittleness and improves water resistance and bond strength. The neutral-weak acid-weak alkali compounding process is used to carry out the reaction at medium temperature, and the obtained urea-formaldehyde resin has a shear strength 10 times or more of that of the urea-formaldehyde rubber, and the water resistance and boiling resistance are greatly improved.

Urea-formaldehyde resin can significantly improve performance according to different application requirements after adding modifier.