Formaldehyde resin, фенолформальдегидная resin
We all have some time to deal with resin, but we probably did not think about where and how it is formed. Under the word resin, we represent a very thick, viscous substance with a characteristic odor, black or yellowish color we are accustomed to. Indeed, the resin can be obtained from the cuts of trees (eg pines). Resin is an excellent building material and therefore, it has been used and is still used for building needs. Of course, not being able to synthesize synthetic resins, natural ones were used before: amber (in fact, it is a frozen natural resin!), rosin (used for soldering), natural rubber, dug. All of these resins are of plant origin. But there are also resins of animal origin, such as shellac. Shellac used to be widely used in the manufacture of turntable records, and a solution of this resin in alcohol was used to varnish trees. In fact, a couple of centuries ago, shellac was considered a very expensive material. This followed from the great complexity of the process of processing it from the resulting natural material. The high cost of manufacturing made it necessary to buy it from the inhabitants of the southeastern countries (India, Indochina). It wasn't until the late 19th century that chemists began looking for a solution to this problem. And of course, a substitute for shellac was found - phenol-formaldehyde resin! Phenol-formaldehyde resin is a substance obtained by heating a mixture of formaldehyde (formalin) and phenol. For the first time such a chemical reaction was carried out by the German scientist Adolf Bayer in 1872. In the process of the chemical interaction of formaldehyde and phenol, a polymer and a water molecule were formed. Of course, this reaction also had a drawback, which was that the resin was brittle, and the reaction itself was carried out at a temperature of 140 ... 1800 C. Therefore, the water that was formed during the reaction all turned into steam.< img alt = "Phenol-formaldehyde resin" src = "http://www.kristallikov.net/Page46/P46-1.JPG" /> This resulted in blisters and voids. The American chemist Leo Hendrik Bakeland (1863-1944) was one of the first to find the solution to all problems. Between 1905 and 1909, he discovered that the brittleness of a polymer can be reduced by adding 40-60% wood flour to the reaction mixture before hardening. Subsequently, wood flour and other solids insoluble in the resulting polymer, which improve its properties, began to be called fillers. The American chemist found that if the synthesis is carried out at elevated pressure, then even at a reaction mixture temperature above 100 ° C, water does not turn into steam, which has a positive effect on the strength of the resin. Since there are no air bubbles in the resin, the resin does not contain voids. Bakelite began to be produced industrially earlier than other synthetic resins - in 1910. In honor of this American chemist, the resin is named - Bakelite. Bakelite has high strength and rigidity. The property of Bakelite not to conduct electric current is widely used in the production of electrical equipment: sockets for bulbs, plugs and sockets. Izbakelite can be made with getinax (pressed laminated material, impregnated with phenol-formaldehyde resin, which is based on paper). To obtain it, the paper is first impregnated with resin, then dried and pressed under a pressure of 10 ... 15 atmospheres and a temperature of 150 ... 160 ° C. The resulting solid material - getinax, if heated - is charred, but not softened! But if you replace paper with fabric, we will also get a fairly hard material - textolite (from Latin textum - “fabric” and Greek “lithos” - “stone”). This material, as well as getinax, is widely used in electrical engineering. If it is necessary to obtain a material with very high thermal insulation, use asbestos fabric or fiberglass (fiberglass).
Obtaining phenol-formaldehyde resinTo obtain phenol-formaldehyde resin, we need a 40% formalin (or methanal) solution and crystalline phenol (if this is not available, you can use a concentrated solution of phenol, it is commercially available in the form of carbolic acid). When working with these substances, you need to remember that these are poisons. So, to obtain phenol-formaldehyde resin, we need to mix 2 g of crystalline phenol (or 4 ml of concentrated solution of carbolic acid) with 3 ml of prepared formalin. Then add 3 drops of concentrated hydrochloric acid HCl to the mixture. We observe how the mixture heats up and boils, while turning into a viscous glassy mass. You can slightly cool the reaction flask (the reaction will slow down a little when cooled). We take a sample of the glassy mass with a glass rod and try to dissolve it in various solvents (water, alcohol). We see that the mass dissolves. At this stage, short chains of molecules are formed, forming a resole substance. As the reaction proceeds further, a very viscous mass is obtained. Now, if you take a sample and try to dissolve it, it won't dissolve. The mass has acquired plasticity due to the formation of large chains of molecules. This substance is called resitol.
At the end of the reaction, we place a test tube with a viscous mass in a container with boiling water. Gradually, the phenol formaldehyde resin hardens more and more and turns into stone. You can get it by breaking the test tube. It has a reddish color and does not melt or dissolve. If a piece of phenol-formaldehyde mole is placed in an open flame, it will burn very slowly, char, sparkle slightly and turn the flame yellowish. When burning, the smell of phenol is felt.
You can stop the reaction of phenol-formaldehyde resin formation at any stage by adding alkali to the mixture (in an alkaline medium, the reaction slows down significantly).
Formaldehyde (from Latin formīca "ant") is a colorless gas with a pungent odor, good soluble in water, alcohols and polar solvents. Irritant, toxic.
Application An aqueous solution of formaldehyde (methanediol) stabilized with methanol - formalin - causes denaturation of proteins, therefore it is used as a tanning agent in tanning and gelatin tanning in film production. Due to the strong tanning effect, formaldehyde is also a strong antiseptic, this property of formalin is used in medicine as an antiseptic (formidron, Formagel and similar preparations) and for the preservation of biological materials (creation of anatomical and other preparations).
An aqueous solution of formaldehyde (methanediol) stabilized with urea - UFC - is one of the most important sources of formaldehyde and urea in the production of urea formaldehyde, melamine carbamide formaldehyde resins and for the treatment of urea against caking; used in the woodworking and furniture industries for the production of plywood, chipboard, etc.
The main part of formaldehyde is used for the manufacture of thermosetting polymers (phenol-formaldehyde, urea-formaldehyde and melamine-formaldehyde resins), it is also widely used in industrial organic synthesis ( pentaerythritol, trimethylolpropane, etc.).
During storage (at temperatures below 9 C), the formaldehyde solution becomes cloudy, a white precipitate (paraformaldehyde) precipitates.
- FORMALDEHYDE ;
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|Form of raw material which is supplied||Viscid mass|
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