Phenolic resins are obtained with the condensation of phenol with formaldehyde in the presence of alkaline catalysts. The best catalyst is NaOH, used in the form of a 40%solution. Resins have a dry residue up to 70-80% and do not form water emulsions.
To obtain water-emulsion resins that are most acceptable in the manufacture of wood-based plates, a method developed by an engineer Tarasov is usually used. According to this method, the resin is condensed in two phases: in the presence of an sour catalyst in the first phase and alkaline – in the second. In the first phase, a threaded molecule of several (up to 9) phenol molecules is formed, and in the second phase, in the presence of an excess of formaldehyde, the filamentary molecules are saturated with methylular groups, which give the resins the water-emulsion character and increase the adhesive properties of the resin. In water-emulsion resins per molecule of phenol, there are about one methylol group.
Crystalline phenol – a scarce product, is used for the production of many synthetic products, and therefore phenolic resins B and SP -2 in the coming years, obviously, will be widely used in the production of chips.
Upon receipt of resins from the total phenols, it is necessary to slightly change both the recipe of the mixture, and the resin condensation regime on pure phenol proposed by Tarasov. These changes are caused by the need to align the velocities of the formaldehyde reaction with various phenols that make up the total mixture. If you do not leve -the noise of the reaction, then more active isomers will bind not one or two, but several formaldehyde molecules. At the same time, less active isomers will remain in the mixture in the form of ballast – free phenol, which without appropriate functional groups, cannot be considered as a binder.
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