Plastics, as a class

This manuscript deals with plasticizers as a class of additives. 

Plastics, as a class of material, is a truly exceptional one in that within a short span of less than a single lifetime it has pervaded nearly all aspects of modem life in all parts of the civilized world. Examples of successful replacement of conventional materials by plastics are far too numerous to list. What is important to note, however, is that nearly all of these substitutions survived in the marketplace and often continue to increase their market share in the relevant sectors. These obviously provide good value for the money because successful applications of plastics deliver performance comparable to (or better than) the materials they replaced but at a lower cost. A valid argument might be made that the market cost of plastics seriously underestimates the true cost, which reflects the use of common resources and externalities associated with their production. The same, however, holds tme for competing materials as well. The available (albeit incomplete) data suggest that even a comparison based on the true cost of materials would find plastics to be an exceptional value. 

There is a health benefit associated with hindering hydrogen bonding. Alkylphenols as a class are generally regarded as corrosive health hazards, but this corrosivity is eliminated when the hydroxyl group is flanked by bulky substituents in the ortho positions. In fact, hindered phenols as a class of compounds are utilized as antioxidants in plastics with FDA approval for indirect food contact. 

Polyurethanes, as a class of materials, are one of the most versatile available. By varying the reactants, their amounts and the reaction conditions, one can obtain millable elastomeric gums, hard rigid plastics, reactive liquids, and foams. The versatility is such that it is very difficult to provide a brief summary. 

Semisolids dosage forms, as a class, are plastic in behavior, i.e., they retain their shape until acted upon by an outside force, in which case they deform and the deformations are permanent. The common denominator to all semisolid systems which gives them their special rheological character is that they all have a permanent three-dimensional structure. This structure is sufficient when undisturbed to impart solid-like properties but which is easily broken down and realigned under some strain or applied force (4). The semisolid systems used pharmaceutically include... 

A likely set of compounds to consider for similar assay development are the nitroaromatic compounds shown in Figure 1 which are related to nitrobenzene (1). As a class, nitroaromatic compounds are of environmental concern since, as Figure 1 shows, they have been documented at as many as 30 of the 818 final EPA National Priority List (NPL) of waste sites in the United States ( ). The nitroaromatics most frequently found as environmental contaminants are 2,4-dinitrotoluene (2) and 2,6-dinitrotoluene (3) used in plastics, dyes and munitions production nitrophenols (4,5) used in pesticides and munitions wastes such at... 

Engineering plastics are so called because of their significantly better mechanical properties than the commodity plastics. They are also more expensive to produce. As a class their production volume is about one-tenth of that of the commodity plastics (Table 22.2). 

This particular manufacturer created a composite panel consisting of a glass-fiber reinforced plastic outer shell backed with a rigid polyurethane foam. The product looks like a cluster of hand split wood shakes. When installed, the panels interlock and look exactly like a shake shingle roof to the casual observer. These panels have been tested and qualify as a Class A built-up roof covering. In addition, they provide a much greater resistance to the transmission of heat than wood shake shingles. The panels are fast and easy to install and quite durable. 

A material added to a polymer during the final synthesis stages or in subsequent processing to improve or alter some characteristics of the polymer. Additives, as a class of materials, are not intended to increase strength properties. Examples of additive include pigments, lubricants, antistatic agents, flame retardants, and plasticizers. 

In this field PUs seek to replace silicone rubber, plasticized PVC, polyethylene, PTFE, polyester and nylon. As a class, PUs have been found to be relatively biocompatible materials. Originally polyesters were used but now, due to hydrolysis problems, polyethers predominate. Various commercial PUs have been made available and are given later. 

Because of their high reactivity, these 2K acrylic adhesives are used in many situations where fast ambient cure is important. Since the incorporation of the redox couple catalysts, acrylic adhesives have advanced their use on metals as well as plastics, woods, and ceramic substrates. As a class, they tend to be fairly accommodating of oily metal and imprepared plastics and composites. Offensive odors often accompany the common forms that use the less expensive lower alkyl acrylates. Colors of these materials are clear, off-white, white, and amber. They are not often intentionally pigmented, although they may be tinted by functional metal additives or aluminum powders. 

As a class the polyesters find wide application as fibres, as laminating resins for glass-fibre reinforced cars and boats, in moulding compositions, in surface coatings, as adhesives and as plasticizers for PVC. Elastomeric polyesters may also be prepared. Providing that the molecule is flexible (for example by primarily consisting of a carbon-carbon aliphatic backbone with small substituents on the carbon atoms, does not crystallize or has a very low melting point) then the presence of a few ester links, which increase interchain attraction and reduce rubberiness, is not too adverse on the rubbery properties of the polymer. 

At the other extreme the so-called engineering plastics such as poly(aryl ether ether ketone), poly(tetrafluoroethylene), and poly(2,6-dimethoxy-l,4-phenylene oxide) have high melting temperatures and more extended chain stmctures with correspondingly lower entropies of fusion. Cellulose derivatives are another case in point. As a class of polymers, they are characterized by very high melting points and low heats of fusion. The low entropy of fusion must result from the highly extended nature of the chain. 

Those compositions having polystyrene as the continuous phase form, as a class, impact-resistant plastics. Those having the rubbery oil as the continous phase are softer, and behave as reinforced elastomers. In the latter case, the PS takes the place of the carbon black as the reinforcing component. 

Fibre-reinforced plastics form a class of materials whose properties are only attained as the component is moulded. Any strategy for quality assurance must therefore take this primary factor into account. 

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