Synthetic plastic thermoplastics

Engineering polymers generally comprise a high performance segment of synthetic plastic materials that exhibit premium properties. In this paper, engineering thermoplastics developed for advanced applications, and particularly for enhanced thermal stability are considered. 

What was the first synthetic plastic Although some nineteenth-century experiments should be mentioned, such as the 1869 molding process for cellulose nitrate discovered by John and Isaiah Hyatt, probably the first major breakthrough came in 1910 with Leo Baekeland s discovery of phenol formaldehyde resins (Bakelite ). These are still the leading thermoset plastics made today. The pioneering work of Wallace Carothers at Du Pont in 1929 produced the nylons now used primarily as fibers but known as the beginning of thermoplastic resin technology. 

John Hyatt was the first to make plastics. He made celluloid in 1868. Leo Baekeland made bakelite. Synthetic plastics are made from petroleum products. There are two types of plastics thermoplastics and thermosetting plastics. 

Phenol-Formaldehyde. Phenolic plastics were the first commercial synthetic plastics in 1908, and were the leading commodity plastic for 40 years, until the growth of vinyl and styrenic thermoplastics (Table 15.15). Now quite mature, they remain the second largest family of thermoset plastics. 

Just as in the manufacture of sheet natural rubber and the asphaltic sheet linings, the basic material as the sheet lining manufacturer receives it from the plantation (rubber) or from the refiner or importer (asphalt), the manufacturer of the synthetic lining materials will receive his synthetic elastomer, thermoplastic or other basic resin from the company that produces it-and will have to blend it with fillers, stabilizers, plasticizers, and other materials to make a suitable compound which will-as a lining—perform its function satisfactorily under the anticipated conditions, and for an economical length of time. The actual amount of the basic resinous material in the compound may be as low as 70% of the total weight. 

The first synthetic polymers were produced as by-products of various organic reactions and were regarded as unwanted contaminants. Thus the first preparations of many of the polymers now regarded as essential to our modern lifestyle were thrown away in disgust. One chemist who refused to be defeated by the "tarry" products obtained when he reacted phenol with formaldehyde was the Belgian-American chemist Leo H. Baekeland (1863-1944). Baekeland s work resulted in the first completely synthetic plastic (cal led Bakelite), a substance that when molded to a certain shape under high pressure and temperature cannot be softened again or dissolved. Bakelite is a thermoset polymer. In contrast, cellulose nitrate is a thermoplastic polymer that is, it can be remelted after it has been molded. 

Until 1950, cellulose esters, which are thermoplastics derived from cellulose, were the most important group of thermoplastic materials. Like cellophane, they have been, for the most part, displaced by synthetic plastics with their superior performance and lower cost. They still maintain some niche markets, however. 

It was not until the commercialization of synthetic plastics resins in the 1930s that an almost unlimited variety of base materials became available for compounding into adhesives and sealants. Most of the thermoplastic resins were soluble in organic solvents and were used as solvent adhesives for molded plastic articles of the same base composition and sometimes for other materials. Poly(vinyl chloride) (PVC), a thermoplastic developed in 1927, is used today in solvent formulations to bond PVC articles such as coated fabrics, films, foams, and pipe. In the early 1930s, phenolics came into importance as adhesive resins. Before that time they were used as coating varnishes [9, p. 239). About 1931 development of the use of a new phenolic resin for plywoods and veneers began [9, p. 239]. 

Recent basic research has turned up new approaches for innovative materials combining elements of, and integrating the advantages of, wood and synthetic plastics. Lignin is one of the main components of this new class of plastic-like, wood-like biocomposites. The resulting mixture of lignin, natural fibers, and additives is a compound processable as a thermoplastic. The processed materials are short fiber composites. Arboform is a trade name for this class of compounds. 

Braconnet in 1833, is the oldest of the synthetic plastics. It is made by treating fibrous cellulose with a mbcture of nitric and sulfuric acids, and was first used in the form of a lacquer (See collodion). In 1870, John Wesley Hyatt and his brother patented the use of plasticized cellulose nitrate as a solid, moldable material, the first commercial thermoplastic (celluloid). Camphor was the first (and is still the best) plasticizer for CN, although many camphor substitutes have been developed. Alcohol is normally used as a volatile solvent to assist in plasticization, after which it is removed. Molded products of CN are extremely tough, but highly flammable and subject to discoloration in sunlight. CN is amendable to many decorative variations. Its principal uses today are in knife handles, table-teimis balls, and eyeglass frames. A mixture of nitric and sulfuric acids converts cellulose into cellulose nitrate pyroxylin is a less nitrated material and it has been useful for photographic film, collodion, and celluloid plastics. 

Although an early synthetic plastic derived from cellulose was introduced in Europe in the nineteenth century, it was not until the twentieth century that the modem plastics industry was bom, with the introduction of Bakelite, which found apphcations in the manufacture of telephones, phonograph records, and a variety of varnishes and enamels. Thermoplastics, such as polyethylene, polystyrene, and polyester, can be heated and molded, and bUhons of pounds of them are produced in the United States annually. Polyethylene, a low-weight, flexible material, has many applications, including packj ing, electrical insulation, housewares, and toys. Polystyrene has found uses as an electrical insulator and, because of its clarity, in plastic optical components. Polyethylene terephthalate (PET) is an important polyester, with applications in fibers and plastic bottles. Polyvinyl chloride (PVG) is one of the most massively manufec-tured synthetic polymers. Its early apphcations were for raincoats, umbrellas, and shower cmtains, but it later found uses in pipe fittings, automotive parts, and shoe soles. 

Some 50 years later in 1868 the first synthetic plastic was produced by John W. Hyatt. He was a printer by trade and his driving motivation was to produce an ivory substitute for billiard balls. His hope was to win a large prize that had been offered. The poor guy didn t win the prize, but the thermoplastic material that he produced called cellulose nitrate was of much greater use than that which he sought. It has been used for many purposes such as windows in early automobiles, toys and novelties and film for motion pictures. It s problem was that it was highly flammable and as time went on it was gradually replaced by plastic materials that didn t burn as easily. 

Cellulosic is a family name that applies to a wide group of thermoplastics. They are not synthetic plastics but rather are made from a natui y occurring polymer, cellulose, which is obtained from wood pulp and cotton linters. Cellulose can be made into a film as cellophane or a fiber, rayon, but it must be chemically modified to produce TPs. Because it can be compounded with many different plasticizers in widely varying concentrations, its property range is broad. These plastics are normally specified by their flow, according to ASTM D 569, which is controlled by the plasticizer content. Cellulosics are all processed by conventional TP methods. They include the following types. 

Biodegradable polymers made from cyclic esters have received increasing attention as resorbable biomaterials as well as commodity thermoplastics. Although the CAGR amounts to 20-30%, it is still a niche market accounting for around 1% of the synthetic plastics. Among the monomers, lactic acid, either produced by fermentation or chemical processes, gives access to polylactides (Scheme 21.16)... 

Acrylonitrile is currently the second largest outlet for propylene (after polypropylene). It is used as a monomer for synthetic fibers and acrylic plastics (thermoplastics and food packaging mainly), AS (acrylonitrile-styrene) resins, and ABS (aerylonitrile-butadiene-styrene) thermoplastics, as well as in the synthesis of acrylamide, adiponitrile, and nitrile elastomers. The manufacture of acrylonitrile is exclusively based on the one-step propylene ammoxidation process. Originally developed by Sohio, Standard Oil Company (now part of BP America), the conventional method used since 1957 employs a fluidized-bed reactor and multicomponent catalysts based on Mo-containing mixed-metal oxides. Over the years, the industrial... 

The two types of plastics are thermoplastics and thermosetting plastics. Thermoplastics can be softened melt and recyclable. Recyclable plastics include Polyethylene Terephthalate (PET), Low Density Polyethylene (LDPE), High Density Polyetltylene (HDPE), and Polypropylene (PP). Thermosets can melt and take the shape only once and not used for repeated work. Sometimes, they are termed as non-recyclable plastics, and include polycarbonate, bakelite, nylon, and so on. Table 3shows synthetic polymer properties and their uses in packaging. 

Thermoplastics Thermosetting plastics Thermoplastic elastomers Thermosetting elastomers synthetic rubbers... 

Thermoplastic starch (TPS) is a relatively new concept and today, it is a primary researchy focus for the manufacture of starch-based biodegradable materials (Averous, 2004). Native starch is not thermoplastic, but in the presence of a plasticizer (water, glycerol, sorbitol, etc.), high temperature, and pressure, it melts and fluidizes, enabling its use in injection, extrusion and blowing equipment, just like synthetic plastic materials. 

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