Thermosetting aminoplasts

Mambish EJ et al. Granulation of thermosets (aminoplastics) (1979) Ser. Plastics and Synthetic Resins NIITEKhIM, Moscow, p 7... 

The term amino resin is usually appHed to the broad class of materials regardless of appHcation, whereas the term aminoplast or sometimes amino plastic is more commonly appHed to thermosetting molding compounds based on amino resins. Amino plastics and resins have been in use since the 1920s. Compared to other segments of the plastics industry, they are mature products, and their growth rate is only about half of that of the plastics industry as a whole. They account for about 3% of the United States plastics and resins production. 

Thermosets are formed by crosslinking (curing) of reactive linear and branched macromolecules and can be manufactured by polycondensation, polymerization and polyaddition. Thermosets can therefore be processed once only with the application of heat and pressure to form semi-finished products or finished articles and cannot be recovered their processing is irreversible. Amongst the most familiar thermosets are the combinations of formaldehyde with phenol, resorcinol etc. (phenolics), urea, aniline, melamine and similar combinations (aminoplastics). 

At the present time aminoplasts comprise moulding compounds based on amine resins (thermosetting condensation products of formaldehyde with carbamide or melamine or a combination thereof) and organic or mineral fillers or a combination thereof doped with dyestuff and modifying substances (plasticizers, stabilizers, crosslinking agents, and the like). 

Amine-resin thermosetting materials (plastics) are manufactured in all industrially developed countries. Aminoplasts are still one of the most common types of polymeric materials although production of novel plastics is rapidly growing. 

Increased demand for granulated thermosetting materials and their effective use necessitated the selection and utilization f the efficient methods known in the art or provision of new rational techniques for granulation of aminoplasts, development and introduction of highly productive equipment to meet the aforementioned requirements. 

A continuously manufactured sheet consisting of layers of fibrous sheet material (for example, paper) impregnated with phenolic and/or aminoplastic and/or polyester thermosetting resins, assembled and bonded together by means of heat and pressure, the outer layer or layers on one side having decorative colours or designs. 

N6 Data for the three important thermosetting materials (phenolics, aminoplastics and epoxide resins) were not covered in the 1998 review on which the 1997 data was based. The 1987 figures for these materials do include a substantial percentage of use in adhesive, surface coating and laminate applications. 

U.S. Pat. Nos. 3,407,154 [16] and 3,407,155 [17] describe thermosetting urea-formaldehyde and aminoplast resinous molding composition comprising fusible reactive urea-formaldehyde and aminotriazine-formaldehyde resin, respectively, and purihed a-cellulose hbers (14-25% by weight) as a hller. 

Formaldehyde is employed in the production of aminoplasts and phenoplasts, which are two different but related classes of thermoset polymers. Aminoplasts are products of the condensation reaction between either urea (urea-formaldehyde or UF resins) or melamine (melamine-formaldeliyde or MF resins) with formaldehyde. Phenoplasts or phenolic (phenol-formaldehyde or PF) resins are prepared from the condensation products of phenol or resorcinol and formaldehyde. 

The principal feature that distinguishes thermosets and conventional elastomers from thermoplastics is the presence of a cross-linked network structure. As we have seen from the above discussion, in the case of elastomers the network structure may be formed by a limited number of covalent bonds (cross-linked rubbers) or may be due to physical links resulting in a domain structure (thermoplastic elastomers). For elastomers, the presence of these cross-links prevents gross mobility of molecules, but local molecular mobility is still possible. Thermosets, on the other hand, have a network structure formed exclusively by covalent bonds. Thermosets have a high density of cross-links and are consequently infusible, insoluble, thermally stable, and dimensionally stable under load. The major commercial thermosets include epoxies, polyesters, and polymers based on formaldehyde. Formaldehyde-based resins, which are the most widely used thermosets, consist essentially of two classes of thermosets. These are the condensation products of formaldehyde with phenol (or resorcinol) (phenoplasts or phenolic resins) or with urea or melamine (aminoplastics or amino resins). 

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