Components of Inhibited Plastics

Inhibited plastics are composite materials (CM) consisting of inhomogeneous components (phases) separated by interfaces. They contain thermoplastics 

When choosing the components of inhibited CM, one should take into account  

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Cyclic amines are the most applicable functional components of inhibited plastics. They are first of all cyclohexyl amine, dicyclohexylamine and their derivatives (nitrosodicyclohexylamine, cyclohexylamine), salts of cyclic amines with inorganic (nitric, chromic and carbonic) acids and organic (s3m-thetic fatty, benzoic, nitric and dinitrobenzoic) acids as well as amines (N-cyclohexyl phenylimine) and their salts (methanitrobenzoate of hexam-ethylenimine). 

There are numerous examples among the carboxylic acids of using S3m-thetic fatty acids (SFA) of various fractions, as well as caproic, pelargonic, oleic, benzoic acids, nitrous and ammonium salts of benzoic and sebacic acids, salts of dicarbonic, nitrous and dinitrobenzoic acids as components of inhibited plastics. 

Characteristics of the most used Cl as components of inhibited plastics are given in Table 1.3. 

The most important requirement imposed on Cl as a component of inhibiting plastics is the thermal stability of the inhibitor at joint processing with the pol3mier. The upper temperature threshold of such processing depends on the phase transition temperature, that of thermal and thermoox-idative destruction of Cl, and intensive evaporation of volatile components of the inhibitive mixture. The chief criteria for Cl adoption expediency as a plastic modifier is minimal loss of the volatile fraction and retained protective... 

Thermodynamic and Process Compatibility of the Components of Inhibited Plastics... 

This non-equilibrium chemical and physical (mechanical) state of inhibited plastics is caused by incorporated Cl and their carriers (PI) in concentrations exceeding the thermodynamic compatibility threshold with the polymer. The thermodynamic non-equilibrium is a useful property of inhibited plastics since it expands their anticorrosion functional features. The greater the deviation from the non-equilibrium state of such systems, the quicker the relaxation processes in them accompanied by the release of excess Cl into the ambient medium and to the object being protected. The structure and properties of the components of inhibited plastics Cl depend on their composition and can be carried to the mated part by either diffusion in the gaseous (thanks to Cl volatility) or liquid phase via its exudation, its mixture with a PI, or washing of water-soluble Cl and diffusion through the material moisture. These processes bring about mechanical relaxation of the polymer matrix. The point at which the inhibited anticorrosion material moves into a state of thermodynamic equilibrium is usually correlated with its protective ability. 

To characterize the thermodynamic compatibility of components of inhibited plastics, the following empirical parameters can be used ... 

Apart from the Cl, some low-molecular components of inhibited plastics can be a source of contamination. For example, materials plasticized by a toxic phosphate of phthalate can present a danger to the environment [13]. An alternative to these PI can be mineral oils, polar PI of the esters of aliphatic dicarboxylic acids and alcohols, amogst others. These esters represent perfect PI of a number of thermoplastics, can dissolve Cl and are, besides, contact inhibitors and water-repellent agents for metal surfaces [22] (e.g. dibutyl se-bacates). 

A broad spectrum of synergetic mixtures of Cl is used to strengthen their inhibiting action and expand the range of metals protected [39,46,47]. To extend the life of inhibited plastics, they are modified by Cl mixtures of different volatility. Highly volatile components of inhibitive mixtures intensify the formation of adsorptive Cl laj ers on hardware surfaces prior to the onset of the corrosion process. Low-volatility Cl are able to prolong the anticorrosion effect of the plastics. 

One of the reasons of defective plastics with low anticorrosion properties (especially films) is phase instability and thermal destruction of Cl and other low-molecular-weight components under elevated temperatures. In this regard, the thermal stability values of LDPE, PI and their blends with PE and some VCI of the PHC series are also cited in Table 1.6 for comparison [50,51]. Above considered low-molecular-weight components have Tdi at or above the LDPE processing temperatures and will not undergo thermal destruction during combination with the polymer binder melt. High thermal stability of VCI of PHC series is one of the merits of inhibited plastics. 

Plastic products formed of the blends of compatible components commonly acquire perfect mechanical properties. Nevertheless, sometimes process peculiarities and specifics of their operation conditions as well as economical reasons force the manufacturer to introduce ingredients that are either incompatible or have restricted compatibility with the polymer binder and other CM components. For instance. Cl of inhibited plastics are, as a rule, highly polar materials poorly compatible with non-polar polymers, including PE, PP, PS and other thermoplastics widely adopted as binders (see 1.3). 

Parts of friction joints and seals are often made from inhibited structural plastics (see Chap. 4). Their main role in metal-polymer friction joints is to abate Mechano-chemical wearing of metal counterbodies. Application of inhibited antifrictional materials is considered to be a promising trend for extending the life of friction joints operating in hostile media. The structural polymers or their blends most often contain plasticizers. Cl, fillers and modifiers as additional components. The inhibited plastics are employed in plain bearings, sealing elements and other members of oil-extracting equipment and vehicles. 

The effectiveness of plastic protection means containing volatile Cl depends much on the liberation kinetics of Cl from the polymer matrix. We have already analyzed (see Sect. 1.5) the problem of binding inhibitors within the plastic structure. The delivery velocity of the required amount of Cl to the metal part surface turned out to be a reliable criterion for estimating the efficiency of inhibited plastics. Some plastic grades do not need to take account of the Cl delivery factor if the inhibiting component is located in the most probable place of corrosion. 

Polymers used in inhibited plastics (polyolefins, polyamides, fluoroplastics and others) are in their majority harmless and friendly to man [7]. Toxicity of this kind of plastics can arise from additives that are impregnated for special purpose or their decomposition products. The extent of the danger to the human organism of inhibited plastics during their production and application (independently of the purpose) depends on the toxicity of the low-molecular components that isolate into the environment. 

Because of its cylindrical shape and hydrophobic character, cholesterol is an important component of the membranes of animal cells. Its rigid structure decreases membrane fluidity, but it also inhibits the crystallization of fatty acid side chains of the membrane lipids and it acts as a sort of membrane plasticizer. 

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