As a result of the polycondensation reaction, linear polymers and more complex resin -shaped compounds with the spatial structure of macromolecules are formed. Small-shaped products are a complex mixture of low- and high molecular weight substances that are not amenable to separation, and have the properties of colloidal solutions of various concentrations and viscosity.
To obtain adhesive resins, it is necessary that the molar ratio of urea and formaldehyde is in the range from the preparation of the adhesive solution located in the workshop of the chips.
The reactionary mixture is prepared in advance in two stainless steel tanks with coils, in which cold water or steam circulates, allowing to maintain a given temperature. The first king’s power is carried out using a dosage pump.
After a certain time, the mixture on the First Tsaria by gravity (or pump) shimmers into the second, and 1.5 to 1: 2. However, with an increase in the amount of formaldehyde, its content in the finished product in a free form grows. To reduce the content of free formaldehyde in the resin, they use the method of two -phase condensation. Excess formaldehyde, obtained at the first stage, is connected by the additional introduction of urea at the second stage.
With an increase in the acidity of the medium, the speed and completeness of the polycondensation reaction increase, the resins are quickly conveyed and poorly dissolve in water. With condensation in the alkaline environment, urea resolves that have an alkaline reaction that quickly turn into a pasty mass are soluble in water. With two -phase condensation, the reaction in the first phase is carried out in an alkaline environment, and on the second — in acidic.
With this method, soluble in water and long -lasting resins are formed. The reaction is carried out at a temperature of 80-90 °. According to the readiness of the resin, the reaction stops by introducing ammonia water into the resin to transfer the acidic environment into an alkaline.
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