Phenol-formaldehyde plastics

Although the use of simple diluents and adulterants almost certainly predates recorded history, the use of fillers to modify the properties of a composition can be traced as far back as eady Roman times, when artisans used ground marble in lime plaster, frescoes, and po22olanic mortar. The use of fillers in paper and paper coatings made its appearance in the mid-nineteenth century. Functional fillers, which introduce new properties into a composition rather than modify pre-existing properties, were commercially developed eady in the twentieth century when Goodrich added carbon black to mbber and Baekeland formulated phenol— formaldehyde plastics with wood dour. 

One of the earliest commercial plastics was Bakelite , formed by the reaction of phenol with a little more than one equivalent of formaldehyde under acidic or basic conditions. Baeyer first discovered this reaction in 1872, and practical methods for casting and molding Bakelite were developed around 1909. Phenol-formaldehyde plastics and resins (also called phenolics) are highly cross-linked because each phenol ring has three sites (two ortho and one para) that can be linked by condensation with formaldehyde. Suggest a general structure for a phenol-formaldehyde resin, and propose a mechanism for its formation under acidic conditions. (Hint Condensation of phenol with formaldehyde resembles the condensation of phenol with acetone, used in Problem 26-17, to make bisphenol A.)... 

The phenol derivatives figure in the structures of a number of important reactions, including the synthesis of aspirin and the manufacture of phenol - formaldehyde plastics and glues. 

The relation between the cell size and the strength of phenol-formaldehyde plastic foams shows that, for a mean cell diameter of less than 0.2-0.3 mm, their compressive strengths and Youngs moduli increase considerably as compared to foams with large cells, It has been found that for many flexible foam types the tensile strength and ultimate elongation are the higher the smaller the cells ss.ioo)... 

The primary use for phenol is as an intermediary chemical, a compound used in the synthesis of other chemicals. About 40 percent of all the phenol produced in the United States is used to make hisphenol A, while a similar amount is used in the production of a variety of polymers, such as phenol-formaldehyde plastics and nylon-6. The third largest application of phenol is in the manufacture of a host of other chemicals, xylene and aniline being the most important. 

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. 

Baekeland, Leo Hendrik A scientist born in Ghent, Belgium (1863—1944), who did early work in photographic chemistry and invented Velox paper (1893). After moving to the United States, he discovered the phenol-formaldehyde plastic originally called Bakelite (1909). 

While the use of natural polymers dates back to the dawn of civilization, polymer science developed rather recently. Tables 14.11,14.12, and 14.13 delineate three distinct stages in the discovery, invention, and theory. The vulcanization of natural rubber and the synthesis of phenol-formaldehyde plastics... 

It has been suggested that the practical similarities between methanol and ammonia oxidation led to the more rapid development of platinum gauzes for nitric acid production during the 1914-1918 war. Large-scale production of formaldehyde did not become important until the demand for phenol-formaldehyde plastics developed in the 1920s. With so little information available on the production of formaldehyde, it is more likely that the experience gained from ammonia oxidation in the wartime plants was then applied to the manufacture of formaldehyde. 

These phenol/formaldehyde plastics are still around due to their cheapness and good electrical and mechanical properties. They have been joined over the years by other similar materials of which urea/formaldehyde and melamine-formaldehyde must be the best known. The former, for instance, may be seen in the white or light coloured electrical switches and fittings, the latter as hard plastic tableware and decorative laminates of the Formica type. There is little difference in the bonding behaviour of the members of this group. 

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