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FACTORY TECHNOLOGIES AT HOME - SIMPLE RECIPES
Bakelite. Simple recipes and tips
Directory / Factory technology at home - simple recipes Bakelite - insoluble artificial resin for plastics. He learned his name from the name of the inventor Wakeland (New York). This was followed by the discovery of a number of new resins with Bakelite-like production patterns. Bakelite is obtained by the condensation of phenol with formalin in the presence of alkaline condensing substances. Bakelite is a solid, resinous substance that in various forms has the appearance of celluloid, amber, ivory, ebonite, and in many respects surpasses the properties of these products. This is a strictly defined chemical compound with special properties, of which the most valued in technology are its insolubility, infusibility and high dielectric capacity.
All components are placed in a vessel of a suitable size. With a sufficient amount of condensing substance, the reaction can begin at ordinary temperature, and the mixture is divided into two layers: a watery layer, consisting of separated water and substances dissolved in water, and an oily layer containing the initial condensation products. This initial condensation product is called saliretin resin. In practice, the process is carried out at approximately 50-80 °C. To avoid loss of volatile components from the mixture, heating is carried out in a closed vessel equipped with a reverse-positioned refrigerator: the vapors, rising up a water-cooled tube, condense into a liquid and flow back into the reaction boiler. As it heats up, the viscosity of the oil layer increases. Some practice separating the water from the initial condensation product, after which the saliretin resin is poured into molds. When heated to 120-140 °C in molds, saliretin resin is converted into the final infusible and insoluble condensation product. There is no need to separate the oily liquid from the watery layer - everything can be evaporated together until the mass reaches a consistency suitable for a particular purpose. The most interesting and valuable property of bakelite is that it can be obtained in three different forms (depending on the degree of condensation). These species are known as "A" Bakelite, "B" Bakelite, and "C" Bakelite. Bakelite "A" is the initial condensation product. At ordinary temperatures, it remains in a liquid, easily mobile, viscous, pasty or solid form. Hard Bakelite "A" at normal temperature is brittle like rosin. Let's dissolve in alcohol, acetone, glycerin, phenol and in soda lye, and mixes up with these substances in all proportions. If a solid product is carefully (with low heating) melted, then it cools down and turns back into a solid product, while retaining the ability to dissolve in the solvents listed above. Bakelite "A" is colorless to yellow. If Bakelite "A" is heated more strongly, then it turns into Bakelite "B", which is an intermediate product to obtain an infusible and insoluble product. Bakelite "B" - Under ordinary conditions, it is hard and brittle, but somewhat stronger than hard "A" Bakelite. It differs from Bakelite "A" in that it does not dissolve in the above solvents. In acetone, phenol and terpeneol it only swells. When heated, it does not melt, but softens greatly, turning into a rubbery plastic mass, which, when cooled, becomes hard and brittle again. In heated forms, this mass is in a plastic state, with further heating under certain conditions, it hardens again, and reaches the final degree of condensation, giving an infusible and insoluble product - Bakelite "C". Bakelite "C" - the final product of condensation, infusible, insoluble in all solvents. If the primary condensation product is heated to 100 °C, a violent reaction will occur with the release of gaseous products, and the resulting Bakelite “C” will be in the form of a spongy or bubbly mass and, therefore, unsuitable for many technical purposes. Therefore, heating must be done carefully. Typically, the resulting Bakelite "A" in solid form is ground into powder and mixed with appropriate fillers and molded in heated hydraulic presses. Fillers can be sawdust, mica, graphite, sand, asbestos, and various fibrous materials in general, as well as lamp black, pigments, paints, mineral materials, pumice, etc. Fillers will reduce bakelite shrinkage and the possibility of cracks. Bakelite compositions with fibrous materials acquire especially valuable properties. In addition, fibrous materials can be impregnated with liquid Bakelite "A", and the Bakelite binds to it, and does not remain on their surface, as is the case with rubber or celluloid, resulting in stronger compositions. Compositions with powdered fillers are much more difficult to impregnate with liquid Bakelite and therefore more brittle. Filling substances can be added in an amount of from 60 to 80°. Pressing takes place in iron molds under a hydraulic press, and the temperature of the molds is increased to 160-180 °C. When the mold is carefully filled, Bakelite “A” completely adheres to the filling substances and, under the influence of heat, transforms into Bakelite “B”. This product fills the mold well and is no longer fusible. Molded pieces of Bakelite "B" can be converted to Bakelite "C" by heat. The transition is made without forms. If heating is carried out under normal conditions, then many bubbles form in the bakelite. To avoid the formation of bubbles, the molded pieces are placed in a special device called a “bakelizer,” i.e., in an autoclave in which increased pressure is created by supplying compressed air or carbon dioxide. You can also heat the bakelite mass in a hermetically sealed vessel, in which pressure is generated by itself. It should be noted that a bakelizer is not always needed: some types of bakelite are obtained by heating under atmospheric pressure. Bakelization is usually carried out for 2-3 hours at a temperature of about 160 °C and a pressure of about 8 atmospheres. Ready bakelite in its pure form (without fillers) is a solid mass (sp. 1,25), odorless, colorless to golden yellow. Depending on the purity, i.e., depending on the amount and type of filling substances, Bakelite can be transparent white, ivory-colored, and in general can be made of any color. A fingernail does not leave a mark on bakelite. Bakelite is a poor conductor of heat and resists pressure, friction, shock and shock. The elasticity is close to celluloid. Can be easily machined on a lathe. A good insulator, its dielectric constant is from 5,6 to 8,85, i.e. higher than that of gutta-percha, and as high as that of mica. Water, diluted alkalis and acids have no effect on bakelite; only hot concentrated nitric and sulfuric acids decompose it. Bakelite is stable up to 300 °C; at higher temperatures, charring occurs and complete combustion does not occur. Bakelite is widely used in technology for the production of buttons, mouthpieces, billiard balls, handles, knobs, in electrical engineering: as an imitation of amber, ivory, etc. Bakelite impregnates wood, cardboard; it is so hard that it can be engraved, etc. It can fix the bristles in shaving brushes, toothbrushes, etc. Soluble types of Bakelite are used for the production of varnishes.
Author: Korolev V.A.
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