Resins, modem

Phenolic adhesives are structural adhesives with specific applications, e.g. where wide gap bonding is required and where large structures need to be bonded. Phenolic resins are the product of a special reaction ratio of a phenol and formaldehyde in the presence of an organic catalyst. There are two main types of phenolic resins phenol or methylol terminated. The phenol terminated are called novalacs, while the methylol terminated are called resoles (one step resins). Modem phenolic resins are prepared in the presence of metal carboxylates and these resins contain a large number of benzylic ether linkages and have open para positions which have good temperature stability and are usually of low viscosity. 

Mallet, M.A.J., Polyamlnoblsmalelmlde Resins, Modem Plastics, June 1973 ppg. 78-81. 

A. S. Wood, Unmatched Performance Sparks a Buildup in Ketone Resins , Modem Plastics, pp. 46-48, April 1987. 

The medium is the binder which provides for the adhesion of pigments. The most important types are the temper media (glue, egg, and gum), the oils, and wax. In addition, for wall painting there is the tme fresco technique, where the pigments are laid down in a fresh, wet plaster preparation layer. Several other media have been used, but much less frequendy, eg, casein temper. In modem paints, a number of synthetic resins are used for this purpose. Contemporary artist paints are often based on acryhc polymers (see Acrylic ester polymers Paints). 

After the resin is appHed to the paper, the wet treated web enters a drying oven where most of the solvent is evaporated off. Modem treaters, such as that shown in Figure 1, have air flotation ovens so that the web is never touched by hot conveyor bars that may cause streaks noticeable in the final product. 

Whereas the eadiest fluorescent-dye pigments would last only 20 days outdoors in a screen-ink film, fade resistance has been improved to such an extent that some modem daylight-fluorescent coated panels stiU have useful color after nine months or mote in Florida sunlight in a 45° exposure tack facing south. The fluorescent layer is usually coated with an acrylic film containing a uv absorber. Indoor-accelerated exposure equipment is, of course, invaluable in the development of such systems. Better dyes and resins very likely will make possible fat mote stable coatings in the future. 

Modem furniture pohshes are designed for a wide variety of surfaces, eg, plastics, metals, and synthetic and natural resin coatings. Furniture pohshes impart shine and provide protection from abrasion, marring, and spills. The formulations clean weU in many cases. In common with most other pohshes, furniture pohshes are characterized by ease and speed of apphcation and of buffing, and by either the absence of objectionable odors or the addition of pleasing ones. 

Natural resins have been collected by hand throughout recorded history and used with minimal processing. They are reported to have been used in the arts, both in paints and for polishing sculptures, as early as 350 BC. Amber, the hardest of these resins, has been used as a gemstone from early Greek history to modem times. The electrical properties of amber were first recorded about 300 BC. Following is a description of commercial natural resins that are available in the United States. 

The modem interest in composite materials can be traced to the development of BakeHte, or phenoHc resin, in 1906. BakeHte was a hard, brittle material that had few if any mechanical appHcations on its own. However, the addition of a filler— the eadiest appHcations used short cellulose fibers (2)—yielded BakeHte mol ding compounds that were strong and tough and found eady appHcations in mass-produced automobile components. The wood dour additive improved BakeHte s processibiHty and physical, chemical, and electrical properties, as weU as reducing its cost (3,4). 

Sticky waxes are generally composed of resins and wax. A high resin content gives viscosity to the melt, a long plastic range, and a brittle fracture when cooled. No modem formulas are available, but the older recipes usually had rosin, beeswax, and gum dammar as the essential constituents. 

In modem manufacturing methods the oil is sometimes reacted directly with the glycerol to form a monoglyceride and this is then reacted with the acid to form the alkyd resin. When the resulting surface coating is applied to the substrate the molecules are substantially linear. However, in the presence of certain driers such as lead soaps there is oxidative cross-linking via the unsaturated group in the side chain and the resin hardens. 

In addition to shellac a number of other natural resins find use in modem industry. They include rosins, copals, kauri gum and pontianak. Such materials are either gums or very brittle solids and, although suitable as ingredients in surface coating formulations and a miscellany of other uses, are of no value in the massive form, i.e. as plastics in the most common sense of the word. 

Because of this continued emphasis on adhesive bonding technology development over the years, the airframes of modem front-line aircraft such as the B-2 bomber and the F-117 and F-22 fighters are largely structurally bonded advanced composites. They tend to be comprised of materials that are more advanced (expensive) than commercial aircraft such as carbon and boron fiber reinforcements with cyanate esters, bismaleimides, polyimides or other high-temperature resin matrices and adhesives. 

Plastics, in the modem meaning, are synthetic materials capable of being molded. The Greek word plastikos means to form. Natural products, while plastic, are usually excluded. Resins may be natural or synthetic. The distinction between plastics and resins is arbitrary - many synthetic materials are both. Historically, the term resin was applied to synthetic substitutes for the natural product plastic was applied to compositions involving molding in their fabrication. Cuslomarily, the fiber industry is considered to be distinct from the plastics industry, although it uses the same ra v materials - polyamides (nylon), cellulose, and cellulose acetate. 

Tracers. To a mixt of 34 parts of Laminae resin, 4 of benzyl ale, 2 of Co naphthenate, and 4 of me et ketone peroxide is added an equal wt of a mixt of 1 part of powd Mg and 2 of K perchlorate, The mixt is formed and cured to give a tracer for following visibly the path of rockets (Ref 24). In Ref 16, p 275 are given formulations for mixts contg K perchlorate which is used in tracer ammo for automatic small arms. Tracer compns contg powd Zr which are suitable for modem HV small arms are discussed in Ref 30... 

Carbon zeolites could be regenerated by acid and were forerunners to modem SAC(H) resins. They proved useful at removing iron, as well as calcium and magnesium, and did not contribute any silica to the water. 

The situation is confused, however, by the case of certain chemicals. Styrene, for example, was known from the mid-nineteenth century as a clear organic liquid of characteristic pungent odour. It was also known to convert itself under certain circumstances into a clear resinous solid that was almost odour-free, this resin then being called metastyrene. The formation of metastyrene from styrene was described as a polymerisation and metastyrene was held to be a polymer of styrene. However, these terms applied only in the sense that there was no change in empirical formula despite the very profound alteration in chemical and physical properties. There was no understanding of the cause of this change and certainly the chemists of the time had no idea of what had happened to the styrene that was remotely akin to the modem view of polymerisation. 

Unlike phenol-formaldehyde polymers, the amino resins are not themselves deeply coloured, but are of a naturally light appearance. They can be easily pigmented to give a variety of shades, which leads to application in uses where good appearance is highly valued, for example in decorative tableware, laminated resins for furniture, and modem white electrical plugs and sockets. 

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