Urea-formaldehyde polymers development

Melamine was first isolated by Leibig in 1834 from the mixture obtained by heating ammonium thiocyanate. A technically feasible route to melamine was developed in 1935 by Ciba AG (Switzerland) and at the same time Henkel patented the production of resins from melamine and formaldehyde. In general, melamine-formaldehyde polymers resemble urea-formaldehyde polymers but they have improved resistance to heat and water. The two materials have therefore found application in similar areas, melamine-formaldehyde resins now being widely used in the production of moulding powders, laminates, adhesives, surface coatings and textile finishes. 

As polymer chemistry advanced in the 1930s and 1940s, stronger and more durable synthetic adhesives such as early phenol, resorcinol and urea formaldehydes began to supplant natural glues in wood aircraft manufacture. Around this time however, metal began to replace wood as the dominant material for aircraft manufacture. Aerospace adhesives research and development moved on to focus on metals, primarily aluminum, as the substrates of interest. 

A series of compounded flame retardants, based on finally divided insoluble ammonium phosphate together with char-forming nitrogenous resins, has been developed for thermoplastics.23 These compounds are particularly useful as intumescent flame-retardant additives for polyolefins, ethylene-vinyl acetate, and urethane elastomers. The char-forming resin can be, for example, an ethyle-neurea-formaldehyde condensation polymer, a hydroxyethyl isocyanurate, or a piperazine-triazine resin. Commercial leach-resistant flame-retardant treatments for wood have also been developed based on a reaction product of phosphoric acid with urea-formaldehyde and dicyandiamide resins. 

Cellulose nitrate is derived from cellulose, a natural polymer. The first truly man-made plastic came 41 years later (in 1909) when Dr. Leo Hendrick Baekeland developed phenol-formaldehyde plastics (phenolics), the source of such diverse materials as electric iron and cookware handles, grinding wheels, and electrical plugs. Other polymers — cellulose acetate (toothbrushes, combs, cutlery handles, eyeglass frames) urea-formaldehyde (buttons, electrical accessories) poly(viryl ehloride) (flooring, upholstery, wire and cable insulation, shower curtains) and nylon (toothbrush bristles, stockings, surgical sutures) — followed in the 1920s. 

In Chapter 2 we indicated that the formation of a polymer requires that the functionality of the reacting monomer(s) must be at least 2. Where the functionality of one of the monomers is greater than 2, then a cross-linked polymer is formed. Thermosets like phenol-formaldehyde, urea-formaldehyde, and epoxy resins develop their characteristic properties through cross-linking. In this section our discussion is confined to those polymeric systems designed with latent cross-linkability that under appropriate conditions can be activated to produce a polymer with desirable properties. 

The first completely synthetic plastic, phenol-formaldehyde, was introduced by L. H. Baekeland in 1909, nearly four decades after J. W. Hyatt had developed a semisynthetic plastic—cellulose nitrate. Both Hyatt and Baekeland invented their plastics by trial and error. Thus the step from the idea of macromolecules to the reality of producing them at will was still not made. It had to wait till the pioneering work of Hermann Staudinger, who, in 1924, proposed linear molecular structures for polystyrene and natural rubber. His work brought recognition to the fact that the macromolecules really are linear polymers. After this it did not take long for other materials to arrive. In 1927 poly(vinyl chloride) (PVC) and cellulose acetate were developed, and 1929 saw the introduction of urea-formaldehyde (UF) resins. 

The major industrial developments in organic chemicals initiated in the 1930-1940 period have continued since that time. Most important of all is the introduction of purely synthetic polymers. Table 4.1 shows the growth in importance of these materials over the period 1950 to 1988. Although much of this growth was due to the increased demand for the polymers introduced in the 1930s and 1940s—urea-formaldehyde resins, nylon, polyethylene (low-density), poly(vinyl chloride), and butadiene co-polymers—new polymers... 

The first completely synthetic plastic material was made from the condensation of phenol and formaldehyde in the presence of a catalyst. The production of this material was perfected by Leo Hendrik Baekland (1863-1944), a Belgian chemist working in the United States, and it was marketed from 1909 under the name Bakelite. Bakelite is a highly crosslinked three-dimensional thermosetting polymer, and in the 1920s and 1930s a number of similar materials were developed such as urea formaldehyde and melamine formaldehyde. 

On the other side of the Atlantic, B. F. Goodrich started production of PVC in 1927. The resin was extruder-blended with polyacrylic ester and sold as Troluloid an Astralon. By the early 1930 s the production of polymethylacrylate, PMA (in 1928), urea-formaldehyde resin, UF (in 1929), and PS (in 1930) began as well. In 1931, development of silicone polymers got underway at Corning Glass Works. Polyamides, PA-66, PA-6,10, PA-10,6 and PA-6,66 were invented in 1937 at E. I. du Pont de Nemours Co. by Wallace H. Carothers and almost immediately introduced to the market [Mark and Whitby, 1940]. The commercialization dates of selected polymers are listed in Appendix II. 

Pizzi A 1979 The chemistry and development of tannin/urea-formaldehyde condensates for exterior wood adhesives. J Appl Polym Sci 23 2777-2792... 

Baekeland in 1909. Before the end of the 1920s a large number of other synthetic polymers had been created, notable examples being the development of polyvinyl chloride in 1927 and urea formaldehyde in 1929. Today there are literally hundreds of synthetic polymers commercially available with ranges of properties making them suitable for applications in many industries including the electrical and electronics industries. For every material commercially available many more have been synthesised, examined and discarded as of no present use for various technical or economic reasons. The year of introduction and typical electronics applications for various plastics are shown in Table 1.1. 

Open pore urea-formaldehyde structures have unique properties, and their spherical and pore sizes can be controlled to make them suitable for many applications. Filtration structures, chromatographic columns, porous urea-formaldehyde pigmented polystyrene, smog dispersal agents, moisture retentive fertilizers, fruit coatings, and porous polymer-bound multicomponent corrosion inhibitors have been prepared. Development of technologies based on open pore urea-formaldehyde structures is a distinct possibility. 

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