Published: March 1976
Thermosetting resins are the most diverse and widely used of all man-made materials. They are easily poured or formed into any shape, are compatible with most other materials, and cure readily (by heat or catalyst) into an insoluble solid. The cross-linking reaction during cure is irreversible and, unlike the thermoplastics, thermosets cannot be softened by heating. Thermosetting resins are also excellent adhesives and bonding agents.
This report is primarily concerned with processes for making thermosetting condensation polymers by reacting formaldehyde with phenol, urea, or melamine. Related products based on derivatives of phenol, urea, melamine, and mixtures thereof are also considered.
Phenol-formaldehyde (PF) resin is the oldest and the most widely used thermosetting resin still in use. Urea-formaldehyde (UF) resin and melamine-formaldehyde (MF) resin are the most important aminoplasts, that is, thermosetting condensation polymers made from the reaction of formaldehyde with an organic compound containing reactive -NH, groups. Other important thermosetting resins include the unsaturated polyesters [covered in Process Economics Program (PEP) Report No. 261, epoxy resins (covered in PEP Report No. 38), alkyd resins, and silicones.
The PF, UF, and MF resins are available as pellets, powders, lumps, or flakes of 100% resins; as molding pellets of filled resin; and as solutions in water (syrup), alcohol (varnish), or an organic solvent (lacquer). They are produced in a wide variety of formulations and grades, tailored to individual applications. End-uses vary from bonding resins and adhesives to molded articles, coatings, and textile treating resins.
This report describes the batch processes for producing several forms of each resin, but does not evaluate resins for individual applications. Only certain processes known to be in commercial use are evaluated with respect to economics.