Synthetic resin obtained by linear polymerization of furfuryl alcohol. The dark brown to black resins are soluble in acetone, acetic esters and aromatics. They are used as binders in foundries for molds and cores, which cure with acid at room temperature. The base material for all furan resins is pure furfuryl alcohol.
The basic principle of solidification of furan resin molding materials is based on polycondensation, which leads to molecular growth with simultaneous curing. In polycondensation, starting resins are condensed by the action of strong acids (phosphoric acid or para-toluolsulfonic acid) to form irreversible, highly crosslinked, macromolecular resins with elimination of a low-molecular substance (usually water).
In foundry practice, modified furan resins are used, which are produced by condensing the furfuryl alcohol in the presence of urea and formaldehyde. This allows resins with almost arbitrarily adjustable properties. The addition of adhesion promoters (silanes) significantly improves the strength properties of the molding compound.
Molds and cores made with furan resins are characterized by extreme dimensional stability and very high strength. The special composition of these resins (high furfuryl alcohol content combined with the lowest free formaldehyde, nitrogen and water content) ensures environmentally friendly processing.
Glass fiber reinforced furan resins have high resistance to heat and flame.