Synthetic Thermoplastic Polymers

The first of the thermoplastic synthetic polymers to be developed was celluloid, made by combining nitrated cellulose (pure cotton subjected to nitric acid) and camphor (C10H16O), a plasticizer. The motivation was a search for a replacement for the ivory used in making billiard balls. It became a commercial product circa 1865, and is still used for making ping-pong balls. 

Adhesive Emulsions. Thermoplastic, synthetic polymers can be prepared as emulsions for use as adhesives. For example, while EVAc hot-melt adhesives described in the previous section contain less than 40% VAc, when the content of VAc in the copolymer is increased to 60%, and the copolymer is prepared in the form of aqueous emulsions, a very useful and versatile adhesive polymer is obtained. Although the VAc homopolymer, poly(vinyl acetate), is a brittle solid, with a Tg = 28 °C, the ethylene units present in the EVAc copolymer act as an internal plasticizer, and lower the Tg to below room temperature. The plasticization results from the reduction of interchain interaction of the VAc polymer chains by the ethylene units interspersed among the strongly interacting VAc units. This reduction of the Tg has important consequences because the formation of a flexible adhesive film from the emulsion depends upon the Tg of the polymer. 

G. Shipper, D. 0rstavik, F.B. Texeira, M. Trope, An evaluation of microbial leakage in roots filled with a thermoplastic synthetic polymer-based root canal filling material (Resilon), J. Endod. 30 (2004) 342-347. 

PMMA is a transparent thermoplastic synthetic polymer of methyl methacrylate. PMMA may be synthesized via emulsion polymerization, solution polymerization, and bulk polymerization (Figurel2.1). When a radical polymerization is used, the obtained PMMA is atactic and completely amorphous. 

Thermoplastic synthetic polymers are used for preparing semipermeable medical membranes owing to their good mechanical resistance and low density, which make it possible to easily prepare thin self-supporting hollow-fiber membranes, and their low energy requirement and processing costs. In the following, the main features of the commercial semipermeable medical membranes made of synthetic polymers are briefly discussed. 

Photodegradable plastics are thermoplastic synthetic polymers into which light-sensitive chemical additives or copolymers have been incorporated for the purpose... 

In practice, synthetic polymers are sometimes divided into two classes, thermosetting and thermo-plMtic. Those polymers which in their original condition will fiow and can be moulded by heat and pressime, but which in their finished or cured state cannot be re softened or moulded are known as thermo setting (examples phenol formaldehyde or urea formaldehyde polymer). Thermoplastic polymers can be resoftened and remoulded by heat (examples ethylene polymers and polymers of acrylic esters). 

Fabrics composed of synthetic polymer fibers are frequendy subjected to heat-setting operations. Because of the thermoplastic nature of these fibers, eg, polyester, nylon, polyolefins, and triacetate, it is possible to set such fabrics iato desired configurations. These heat treatments iavolve recrystaUization mechanisms at the molecular level, and thus are permanent unless the fabrics are exposed to thermal conditions more severe than those used ia the heat-setting process. 

The discovery and development of polypropylene, the one genuinely new large tonnage thermoplastics material developed since World War II, forms part of what is arguably the most important episode in the history of polymer science. For many years it had been recognised that natural polymers were far more regular in their structure than synthetic polymers. Whilst there had been some improvement in controlling molecular architecture, the man-made materials, relative to the natural materials, were structurally crude. 

The latex of the Sapota achras yields a thermoplastic material, chicle, consisting of about 17.4% hydrocarbon, 40% acetone soluble resin and 35% occluded water. The hydrocarbon appears to contain both trans- and c/s-polyisoprene. Although originally introduced as gutta pereha and natural rubber substitutes, deresinated chicle has become important as the base for chewing gum. Like other polyisoprenes, it is meeting competition from synthetic polymers. 

Thermoplastic polyurethane (TPU) is a type of synthetic polymer that has properties between the characteristics of plastics and rubber. It belongs to the thermoplastic elastomer group. The typical procedure of vulcanization in rubber processing generally is not needed for TPU instead, the processing procedure for normal plastics is used. With a similar hardness to other elastomers, TPU has better elasticity, resistance to oil, and resistance to impact at low temperatures. TPU is a rapidly developing polymeric material. 

This chapter discusses synthetic polymers based primarily on monomers produced from petroleum chemicals. The first section covers the synthesis of thermoplastics and engineering resins. The second part reviews thermosetting plastics and their uses. The third part discusses the chemistry of synthetic rubbers, including a brief review on thermoplastic elastomers, which are generally not used for tire production but to make other rubber products. The last section addresses synthetic fibers. 

The chemistry of synthetic polymers is similar to the chemistry of small molecules with the same functional groups, but the physical properties of polymers are greatly affected by size. Polymers can be classified by physical property into four groups thermoplastics, fibers, elastomers, and thermosetting resins. The properties of each group can be accounted for by the structure, the degree of crystallinity, and the amount of cross-Jinking they contain. 

Blending of the lowest price commodity polymers from synthetic and carbohydrate polymer families [e.g., poly(ethylene) and starch] would appear to follow these laws. Although each polymer class is produced in large volume (first law), the production rate for com starch/synthetic polymer blends is much lower than that for the synthetic polymer this slower extrusion rate directly affects the final cost. Ignoring this limitation, the film properties of the blend are significantly poorer than those of the synthetic polymer film. Both deficiencies are related to the poor thermoplastic properties of water-soluble polymers such as cora-starch. 

Biodegradable plastics have been used on an industrial scale since the end of the 1990s when BASF launched Ecoflex . This is a fossil-based, man-made polyester but yet is completely biodegradable due to its chemical structure. This structure is also the reason why Ecoflex combines excellent mechanical properties with the good processability of synthetic thermoplastics. Ecoflex is the preferred blend partner for bio-based and biodegradable polymers, which typically do not exhibit good mechanics and processability for film applications by themselves. Ecoflex therefore is a synthetic polymer that enables the extensive use of renewable raw materials (e.g., starch). 

During the manufacture of appliance cabinets, a thermoplastic synthetic resin sheet, usually made of PS, is either co-extruded with a barrier layer or laminated to a barrier layer to make the inner liner. To successfully recycle the trim or scrap, the protective polymer film... 

This polymer film composition can be extruded into a polymer film sheet laminated to or co-extruded with a thermoplastic synthetic resin sheet to make a thermoformable inner liner. The ther-moformable inner liner is thermoformed, trimmed, and nested in a spaced relationship within an outer wall element, after which a polymer foam is injected to the space between the inner liner and the outer wall element. 

The above results shown in Figs. 12 and 13 can be discussed in connection with the application of the thermoplasticized wood. The thermoplasticized wood can be used as material for molding, and as one way of utilization, can be used as blend composites with synthetic polymers. If this blending is made by grafting as shown above, two benefits can at least be pointed out (a) the thermoplasticity of wood materials is enhanced. (Better results can be obtained with esterified wood.) (b) the compatibility of the plasticized wood with synthetic polymers increases by the grafting. These factors are considered to be advantageous for preparing molded composites with excellent final properties. 

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