Gas-filled plastics

Gas-filled plastics are polymer materials — disperse systems of the solid-gas type. They are usually divided into foam plastics (which contain mostly closed pores and cells) and porous plastics (which contain mostly open communicating pores). Depending on elasticity, gas-filled plastics are conventionally classified into rigid, semi-rigid, and elastic, categories. In principle, they can be synthesized on the basis of any polymer the most widely used materials are polystyrene, polyvinyl chloride, polyurethanes, polyethylene, polyepoxides, phenol- and carbamideformaldehyde resins, and, of course, certain organosilicon polymers. 

Berlin, A. A., Shutov, F. A. Strengthened Gas-Filled Plastics. Moscow Khimia, 1980 (Russ.)... 

Telegina, E. B., et al. USSR Conf. Gas-Filled Plastics, Vladimir USSR, 1978, p. 177... 

Increase of the output of gas-filled plastics is cormected first of all with the development of new types of compositions and of new h y efficient production methods. These materials are produced both under industrial conditions on transfer lines and directly at locations by casting or spraying. 

It should be noted that up to now, quantitative estimates of the uniformity of gas-filled plastics have not been carried out, although the importance of this concept for the estimation of the morphology of foamed plastics is obvious. Indeed, for researchers and technologists the quantitative determination of the uniformity of foams should become one of the basic criteria of the quality of articles, along with other morphological parameters. On the other hand, for theoretical calculations, it should be remembered that the coefficient of uniformity is a brutto characteristic of foam heterogeneity and incorporates the total non-uniformity of the dis-... 

Studies of the moisture absorption (hygroscopicity) and water absorption (hydro-scopicity) of gas-filled plastics are of considerable practical importance, since foamed polymers always contain moisture (with the exception of their use in space or under extremely rare conditions on Earth) n4iich noticeably affects all physico-mechanical characteristic of materials, in particular electrical and heat insulation properties. 

Berlin, A A, Shutov, F. A Strengthened gas-filled plastics. Moscow, Chemistry 1980 (In Russian) Berlin, Heidelberg, New York, Springer (in translation), in preparation... 

Berlin, A. A Production of gas-filled plastics and elastomers. Moscow GosKhimizdat 1953 (in Russian)... 

If, on the other hand, a system is produced by a random conglomeration of a large number of individual elements (porous or nonporous), the result will be an addition system. They also include both natural and man-made materials sand, gravel, woven fabrics, powders, fibrous materials, paper. Addition systems also include a special type of gas-filled plastics, the so-called syntactic foams. 

Berlin, A, A., Shutov, F. A. Strengthened Gas-Filled Plastics. Moscow Khimiya 1980 (Russ.) Berlin, A. A., Shutov, F. A. Morphology of Oligomeric Plastic Foams, in Physico-Chemistry and Chemistry of Reactive Oligomers. Alma-Ata AN Kaz. SSR Publication 1979, pp. 50 (Russ.)... 

Gas-filled plastics for tribo-engineering purposes are antifrictional materials that liberate vapors of Cl in the course of wear and thus protect friction joints from mechano-chemical wearing under operation in hostile media and during stoppage. 

Typically, large-scale gas filling makes the main characteristics of foam plastics — coefficients of heat and temperature conductivity, dielectric permeability, and the tangent of the dielectric loss angle — totally independent of the chemical structure of the original polymer [1],... 

The window material is beryllium (approximately 0.9-mm thick), the material of choice for low-energy x- and y-radiation. Aluminum windows can be used but must be strong enough to withstand a vacuum hence a significant sacrifice in transparency must be made. Suitable plastic windows, restricted to low atomic number materials, leak slightly, and the presence of any oxygen or water will reduce the resolution performance of a detector of this kind. It is essential that the gas fill used be of the highest possible purity and that it remain so. 

Syntactic foamed plastics (from the Greek ovvxa C, to put together) or spheroplastics are a special kind of gas filled polymeric material. They consist of a polymer matrix, called the binder, and a filler of hollow spherical particles, called microspheres, microcapsules, or microballoons, distributed within the binder. Expoxy and phenolic resins, polyesters, silicones, polyurethanes, and several other polymers and oligomers are used as binders, while the fillers have been made of glass, carbon, metal, ceramics, polymers, and resins. The foamed plastic is formed by the microcapsular method, i.e. the gas-filled particles are inserted into the polymer binder1,2). 

On the other hand, syntactic materials may also be thought of as reinforced or filled plastics, with the gas-containing particles being the reinforcing component. This classification is also justifiable in view of the manufacturing technology. The matrix is not foamed chemically, but is filled mechanically with the hollow spheres. Syntactic foamed plastics are thus called physical foams 6,7). 

At present, hundreds of various elastic and rigid gas-filled materials used literally in all branches of industry are produced on the basis of reactive oligonwrs and high polymers. The production of these materials is rapidly expanding. Thus, in 1970 the world output of plastic foams was 2 million tons, in 1975 3.5 million tons, 1980 it will be 5-6 million tons, and in 1985 about 20% (6% in 1975) of all plastic materials will be gas-filled ... 

In the last decade several novel types of gas-filled polymers appeared which belong to the second generation integral (structural) plastic foams syntactic foams reinforced polymer foams multilayer foams (foamed laminates), metallized plastic foams mineral and metallic foamed materials obtained on the basis of foamed polymers laminated constructions on the basis of foamed polymers and monolithic (unfoamed) plastics, metals, paper, leather, etc. 

Also, the preparation of honeycomb plastics and gas-filled fibrous materials does not require foaming. Formation of gas cavities in the former is carried out by glueing of previoudy prepared sheet materials or by extmsion of thermoplastics through special nozzles in the latter case by glueing or filling with polymeric binders of fibrous substances containing capillaries and pores. 

Finally, in the preparation of gas-filled materials on the basis of polymer-oligomer compositions, oligomers which are plasticizers or lubricants of the corresponding high polymers are used. Such compositions ensure miscibility of components with blowing agents, fillers, stabilizers, etc. and subsequent foaming of polymers is usually... 

Freely foamed oligoester plastics are being increasingly used as light fillers in load-carrying structures, as heat, sound and electrical insulating and buoyant materials. This type of gas-filled material finds application in building, furniture and other industries. 

Another study of foamed polymers uses modern physicochemical methods of structure elucidation of gas-filled polymers and more accurate mathematical descriptioa These studies have considerably contributed to the understanding of the general character of the spatial structure of plastic foams. Thus, quantitative estimations of the effect of each morphological parameter (specific gravity, size and shape of ceUs, type of communication between ceUs, cell distributbn in the bulk, etc.), on the properties of a given material could be made. 

Moisture absorptfon of plastic foams is closely connected with cell properties, including thermal insulation properties. Investigation of heat insulation of plastic foams containing a liquid phase helps to elucidate the mechanisms of moisture and mass transfer as weU as of heat transfer in gas-filled materials. 

The rapidly expanding industrial production of gas-filled polymers is considerably affecting the structure of both production and consumption of synthetic materials. Foamed plastics are now used practically in all branches of industry, replacing traditional natural materials (wood, glass, metals) and finding novel applications " ... 

Shutov, F. A The gas-structure element and a new classification of plastic foams. All-Union Conference on Gas-Filled Polymers, Vladimir/USSR, 1974 (in Russian)... 

Domkin, V. S. Electrical properties of gas-filled polymers. All-Union Seminar on Plastic Foams, Leningrad USSR, 1975 (in Russian)... 

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