Urea-formaldehyde resins: production, use and properties

Urea-formaldehyde resins are widely used in construction, woodworking and some other sectors of the national economy. The industrial way to produce them was first started in the USA in 1927. Such resins are somewhat inferior in water resistance and strength to polyester and epoxy materials. But their manufacture is much cheaper.

How to produce

Get CFS resin, as can already be judged by the name, by polycondensation of formaldehyde with urea. They are a non-combustible aqueous suspension, the degree of viscosity of which and color may vary depending on the brand. The production of urea-formaldehyde resins usually involves the use of special, equipped with a jacket and a special mixing device. In total, the manufacturing process of such products includes three main stages:

• polycondensation;

• acid condensation;

• drying.

The polycondensation of the resin is carried out in an alkaline medium at a pH of the reaction solution of 7.5-8. In the manufacturing process, make sure that the molar ratio of urea: formaldehyde is 1: 1.6-1.9.

Acid condensation is carried out in a medium with pH = 4.5-4.8. At this stage, due to an increase in molecular weight, the viscosity of the solution begins to increase sharply. At the end of the acid condensation reaction, another portion of urea is added to the resin. The required amount of this substance is calculated so that the molar ratio of components in the finished solution is 1: 1.3-1.4. At the drying stage, the resin is adjusted to the desired viscosity values. At the final stage, the product is cooled and modified in order to reduce its toxicity.

Scope of use

Urea-formaldehyde resin (formula N = CH2 C = O and NH2 HOCH2NH C = O NH2) can be used in the production of:

• Fiberboard and particleboard;

• plywood;

• putties, varnishes and paints;

• moisture resistant paper and cardboard (impregnation);

• polystyrene foam.

Urea-formaldehyde resin (KF-MX2) is also often used in drilling. In this case, it is used as the basis for grouting mortars. The latter, in turn, are viscous mixtures capable of rapidly hardening in air. Grouting mortars are used mainly to fix casing strings and to protect them from corrosion.

CFS based glue

In enterprises of the woodworking industry in its pure form, FFS is rarely used. More often serves as the main element in the urea-formaldehyde resin used in carpentry. The main varieties of such products made on the basis of CFS, there are five:

• KF-B - quick-hardening adhesive;

• KF-O - general purpose (formaldehyde content not higher than 0.25%);

• KF-MT - low toxicity, used for the production of fiberboard and particleboard;

• KF-Zh - with increased viability;

• KF-BZ - combining the advantages of the KF-B and KF-Zh brands.

Quick-hardening adhesives KF-B at the enterprises of the woodworking industry are mainly used in the production of plywood and for facing furniture panels on single-span presses. The low-toxic product KF-O is used at most only for gluing paper. Also, such glue can be used in the manufacture of plywood. Particleboard and fiberboard with its use are not manufactured. For the production of boards based on shavings or fiber, a product of the KF-MT brand is used.

Adhesive with increased vitality is great for joining all kinds of furniture parts. In construction, in some cases, it can also be used to strengthen soft soils. KF-BZ universal adhesives are most often used in the manufacture of plywood and furniture. They can also be used in the manufacture of various kinds of joinery products. Depending on the type of hardener, all adhesives based on KFS can be used for both hot and cold bonding.

Sometimes in construction, woodworking, etc., special adhesives with various kinds of modifying additives find application.

Properties of resin KF-MT

Technical characteristics of urea-formaldehyde resins depending on the scope of application may be different. From the table below you can get information about the properties of the most popular resin KF-MT used in the manufacture of fiberboard and particleboard.

From other grades of KF resins, KF-MT is distinguished primarily by its reduced viscosity with a relatively high solids content. Such characteristics allow it to be introduced into airless spray mixers. The use of such equipment, in turn, makes it possible to significantly reduce the moisture content of resin-treated wood particles and, accordingly, reduce the pressing time of the boards.

Impregnating Resins (SCFP)

This variety of CFS is used in the manufacture of moisture-resistant cardboard and paper. Sometimes it is also used for the impregnation of decorative rolled films, chipboard and fiberboard plywood. The table below shows the specifications of this product.

Characteristics of the resin used for the manufacture of coatings

For this purpose, a product of the brand K-421-02 is usually used. It is a melamine urea formaldehyde resin a clear liquid and has the following properties:

Properties of KF-MX2

Urea-formaldehyde resins used for the production of cement slurries must also fully comply with GOST.

Urea-formaldehyde foam: area of ​​use

This product is mainly used in construction as an insulating material. It can be used to isolate from the cold:

• walls;

• subroof space;

• floors and ceilings.

Compared with conventional polystyrene foam, KFS has one important advantage. This material is completely non-combustible. Urea-formaldehyde resins belong to the group of thermoactive substances. That is, reverse reactions cannot occur in them by definition. Accordingly, KFS-foam does not form a melt during a fire. The only thing is that under the influence of high temperatures it loses a little in mass, releasing nitrogen and carbon dioxide, which are harmless to human health. The service life of the foam of this variety is about the same as that of extruded polystyrene foam - about 80 years. This material can be used both in the form of plates, and in a liquid state. In the latter case, the mass is simply poured into the cavities of various building structures.

How to make foam KFS

This interesting material first appeared in the late 30s in Germany. In Europe, the construction of buildings and structures it is used very widely. In 30% of cases, when warming various kinds of building envelopes, this material is used. Recently, CFS foam has become increasingly popular in Russia.

The manufacturing technology of this insulation is relatively simple. There is even special, relatively inexpensive equipment on sale, which anyone can buy, in principle. Such installations work as follows:

• an aqueous solution of phosphoric acid and a foaming agent is poured into one of the containers;

• the urea-formaldehyde resin itself is placed in another container;

• taps open in a barrel.

A powerful pump is used to mix material components. The urea-formaldehyde resin and the foam stream are distilled into a special mixer. The mass obtained in this tank is poured into the cavity of building structures through a hose with a nozzle.

Properties of the resin used for the production of foam

For this purpose, a product of the KFZh-PV brand is usually used in construction. This is a liquid resin of white or light brown color, the technical characteristics of which must exactly meet the requirements of GOST.

How CF resins are labeled

Thus, urea-formaldehyde resin has found very wide application in industry and construction. This product is labeled according to the requirements of GOST-14192. On the label of the container with CFS or in the consignment note must be present:

• the name of the manufacturer with its trademark;

• Net weight;

• brand of resin;

• production date;

• batch number;

• designation of the standard itself.

How should the resin be packaged

Large woodworking and construction companies usually purchase this product in very large quantities. In this case, the urea-formaldehyde resin KF is delivered to the destination in railway tanks. Smaller batches are poured into steel barrels. The latter before use, according to GOST-13950, must be thoroughly washed. Standards allow resin to be poured, including multi-turn drums with small external defects.

Test methods

Urea-formaldehyde resins are accepted at enterprises in batches (with the same characteristics and a weight of not more than 200 tons). To verify the quality of the product tests are carried out. At the first stage they produce:

• sampling of point samples with a metal tube;

• connection of all samples with placement in a glass jar;

• labeling with date and place of sampling.

Actually, the tests themselves may include visual inspection, as well as determination in laboratory conditions:

• dry mass of each sample;

• mass fraction of free formaldehyde;

• concentration of hydrogen ions;

• gelatinization time;

• miscibility with water;

• ultimate strength.

How to transport and store

Urea-formaldehyde resin (hazard class of this substance - II) can be transported on all modes of transport. At air temperatures below 0 ° C, only containers with heat exchangers or heat-insulating coatings may be used. In the latter case, heating is done by supplying hot water to the tank jacket. The temperature of the CFS after this procedure should not exceed 25 ^° C. It is forbidden to heat the product with steam.

In summer, at t of air from 25 ° C, the resin can be transported no longer than for 10 days. Store the product at a temperature not lower than 5 ° C and not higher than 20 ° C in a tightly closed container. It is not permitted to keep barrels or tanks with resin in direct sunlight. GOST also prescribes to store containers with this product under a canopy, avoiding exposure to atmospheric precipitation.

Urea-formaldehyde resin: manufacturers and brands

Today, Russia produces about 500 thousand tons of CFS per year. The largest domestic companies involved in the production of these products are:

• "Ugra Forestry Holding";

• "Shatura";

• Volga region plywood and furniture factory;

Our country also manufactures products such as urea-formaldehyde resin, Russian-Finnish manufacturers. Specializes in the production of this material, for example, the company "Kronostar-East", part of the European concern Swiss Krono Group. In addition, KFS is one of the varieties of products manufactured by such giants of the chemical industry as PJSC Acron (Veliky Novgorod) and PJSC Metafraks.