Preparing Compositions Based on Aminoresins

In the production of composite plastics based on aminoresins those with the greatest popularity are resins based on carbamide, melamine and their mixtures. These resins are solidifying binders with the highest production volumes. 

Carbamide- and melamine-formaldehyde resins are synthesized in aqueous solutions by using, as a rule, 1.5-2 mol of formaldehyde to 1 mol of carbamide or 2.9-3.0 mol od dormaldehyde to 1 mol of melamine in a weakly-alkaline medium. When using carbamide and melamine mixtures their ratio must be 1 1 or 2 1. 

Combining aminoformaldehyde resins with the fillers in the production of composite materials is achieved by impregnating the filler with the aqueous solutions of resins with a low degree of condensation with subsequent drying and prehardening. 

The optimum temperature of polycondensation of urea with formaldehyde is 30-40°C. 

In preparing compositions use is made of organic and mineral fillers. The most important organic filler is bleached wood pulp. The pulp fiber length depends on the type of wood thus, pulp produced from beech has 1 mm-long fibers, whilst that obtained from conifers -3 mm-long fibers. 

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