All we ever had to deal with resin, but probably not wonder where and how it is formed. We now the resinis very dense, viscous substance with a characteristic smell, familiar black or yellowish color. Indeed, the resin can be got from cuts of trees (e.g., pines).
Resin is an excellent building material, and therefore, it was used now for construction purposes.
Of course, not being able to synthesize resin, previously used natural: amber (actually is fossil natural resin!), rosin (use when soldering), natural rubber, copal.
All of these are resin of vegetable origin. But there are also resin of animal origin, such as shellac. The shellac widely used to manufacture of plates for turntables, and an alcohol solution of this resin was applied to lacquer trees.
Actually a couple of centuries ago, the shellac was considered a very expensive material. This followed from the high complexity of its processing derived from natural material. High cost of production forced to buy it from the inhabitants of the South-Eastern countries (India, Indochina).
Only in the end of 19th century, chemists began the search for a solution to this problem. And of course, a substitute for shellac was found - phenol-formaldehyde resin!
Phenol-formaldehyde resin is a substance is got by heating a mixture of formaldehyde (formalin) and phenol. For the first time that a chemical reaction was carried out by a German scientist Adolf Bayer in 1872. In the process of chemical interaction of formaldehyde with phenol were formed polymer and a water molecule. Of course, when this reaction was a drawback, which was that the resin was fragile, and the reaction was carried out at a temperature of 140...1800 C. Therefore, the water that was formed during the reaction – all passed in pairs.
This this was the cause of the emergence of bubbles and voids. American chemist Leo Hendrik Bakeland (1863-1944) one of the first found the solution to this problems. From the 1905 to 1909, he found that the brittleness of the polymer can be reduced if add of 40— 60% wood flourin to the reaction mixture before solidification . Subsequently, the wood flour and other insoluble solids in the resulting polymer, which improve its properties, became known as fillers. American chemist found that if the synthesis is carried out at elevated pressure, even when the temperature of the reaction mixture above 100 ° C, water does not turn into vapor, which positively influences for the strength of the resin. Since air bubbles are not available in the resin, such a resin does not contain voids. Bakelite was produced industrially in 1910 is before other synthetic resins. In honor of this American chemist the resin named – bakelite.
Bakelite has high strength, rigidity. Property of bakelite not conduct electric current, is widely used in the manufacture of electrical equipment: ammunition for light bulbs, plugs and sockets. From bakelite can produce getinaks (pressed plated material impregnated with phenol-formaldehyde resin, which is based on a paper). To get it the paper is first impregnated with resin, then dried and pressed with a pressure of 10 to 15 atmospheres and a temperature of 150...1600C. The resulting solid material – getinaks in case of heat it – charred, but not softened! But if the paper be replaced by fabric – we will get also quite solid material - textolite (from Latin. textum — "cloth" and Greek "lithos" — stone). This material, as well getinaks widely used in electrical engineering. If you need to get material with very high thermal insulation using asbestos cloth or glass fibre (fiberglass).
Getting phenol-formaldehyde resin
To get a phenol-formaldehyde resin we need a 40% formalin solution (or methanal), and crystalline phenol (if this is not available, you can use a concentrated solution of phenol, it is available as carbolic acid). When working with these substances is necessary to remember that it poisons.
So, to get a 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 the prepared formalin. Then to the mixture add 3 drops of concentrated hydrochloric acid HCl. Watching as the mixture is heated and boils, turning into a viscous glassy mass. You can slightly cooling the flask with a flowing reaction (when cooling, the reaction will slow down a bit).
With glass rod take a sample of the vitreous mass and try to dissolve in various solvents (water, alcohol). Watching that the mass is dissolved. At this stage the short chain moleculesthe are formed, and new substance resol is formed.
In the further we get a very viscous mass. Now, if we take a sample and try it to dissolve – it will not dissolve. The substance became ductility due to the formation of large chains of molecules. This substance is called resitol.
At the completion of the reaction, put the tube with viscous substance to container of boiling water. Gradually phenol-formaldehyde resin increasingly hardens and turns into stone. To get it by breaking the test tube. It has a reddish color, does not melt or dissolve. If a piece of phenol-formaldehyde resin place in an open flame, it will be very slow to burn, char, a little sparkle and paint the flame in yellow color. When burning the smell of phenol. You can stop the reaction of formation of phenol-formaldehyde resin at any stage by adding alkali to the mixture (in alkaline solution the reaction is much slower).