Basic properties of plastics as a building material

Article from the online resource Manufacture of plastic and polymer products - www.poliolefins.ru

The novelty of plastics as a building material, a complex chemical structure of the polymers and their extreme rigidity work in certain building constructions require comprehensive, deep and scientific study objective behavior problems of plastics in time and their durability.

A valuable property of plastics is their low bulk density. Volumetric weight of various commonly used plastics, including porous sponge ranges from 1 to 2200 kg / m3. Special plastics, for example, radiopenetic with barium sulphate as a filler, can have a bulk density and are much higher. Average, bulk density of plastics, excluding porous plastics, is half that of aluminum and 5-8 times less than that of steel, copper, lead. It is quite obvious that even a partial replacement of these metals, as well as silicate materials with plastics, results in a significant reduction in the weight of the structure, although in cases where plastics are used as a structural wall material, aggregate in skeleton-type buildings and interlayers.

Strength characteristics of plastics are particularly high in plastics with sheet-like fillers. For example, for fiberglass, the tensile strength reaches 2800 kg / cm2 (steel grade St.S. 3800-4500 kg / cm2), in delta wood - 3500 kg / cm2 and for fiberglass anisotropic material (SVAM) -4600 kg / cm2. From the data given, it can be seen that laminated plastics can be used for load-bearing structural elements of buildings. The compressive strength of these materials is also sufficient, namely: for delta-wood 2000, for glass-cloth laminate 1600 and for SVAM 4000 kg / cm2. Interesting and encouraging in terms of the use of plastics in the construction of the ratio of these materials in the limits of compressive strength and tensile strength, namely: delta-wood 0.7, for fiberglass 0.6, for SVAM 0.9, for comparison - for steel 1, for pine 0.4, for concrete 0.1. Thus, the main strength characteristics of plastics in terms of compressive strength and tensile strength are high enough and exceed in this respect many building materials of the silicate group. Strength characteristics of porous plastics, for example, miporas, are very low, but they satisfy the requirements set by it.

The most important indicator for constructive materials is the coefficient of constructive quality of the material, i.e. the coefficient obtained from dividing the strength of the material by its bulk weight. A wide application in the construction of materials with a high coefficient of constructive quality predetermines the correct solution of one of the main tasks of progressive construction - reducing the weight of buildings and construction. According to this indicator, plastics take first place. The coefficient of constructive quality of brickwork is 0.02 (the lowest of all building materials), concrete grade 150-0.06, steel grade St. Z-0.5, pine - 0.7, duralumin-1.6, SVAM - 2,2 and, finally, delta-wood - 2,5. Thus, according to the coefficient of constructive quality, laminated plastics are unsurpassed so far, from which the most durable and lightest structures can be created.

The thermal conductivity of dense plastics ranges from 0.2 to 0.6 kcal / m * h * deg. The lightest porous plastics have a thermal conductivity of only 0.026, i.e. their thermal conductivity coefficient is close to the coefficient of thermal conductivity of the air. It is clear that the low thermal conductivity of plastics allows them to be widely used in construction equipment.

A valuable property of plastics is chemical resistance, due to the chemical resistance of polymers and fillers, which are used for the manufacture of plastics. Chemical resistance should be understood in the broad sense of this term, including resistance to water, salt solutions and to organic solvents. Particularly resistant to acids and salt solutions are plastics based on polytetrafluoroethylene, polyethylene, polyisobutylene, polystyrene, polyvinyl chloride. Chemically resistant plastics can be used as building materials for the construction of chemical industry enterprises, sewage networks, as well as for insulation of containers when storing aggressive substances.

A valuable property of plastics is their ability to be colored in different colors by organic and inorganic pigments. When selecting dyes and pigments for plastics, naturally, the possible chemical interaction between the polymer and the dye must be taken into account. Good colorability of plastics throughout the thickness of the product makes it possible to avoid periodic painting, which is required by many other building materials and that raises operating costs.

The high resistance of plastics to corrosive effects, the even and dense surface of the products obtained during molding, also allow in some cases to refuse staining. To the quality of coloring of plastics used as building material, much higher requirements should be made than to the quality of the coloring of plastics used, for example, in aircraft construction and machine building. This is due to the difficult conditions of service of building materials and the duration of the service of buildings. To paint them must be made high demands in respect of resistance to weathering, in particular, to the most active factor - the effect of light.

Of great interest is the property of plastics, as their low abrasion, i.e., the ability to resist abrasive forces. This opens great prospects for the widespread use of plastic materials in the construction of floors. The testing of floors based on polymers produced good results. Thus, the abrasion of polyvinyl chloride tiles for floors is 0.05, glyptal linoleum 0.06 g / cm2.

The most valuable property of plastics is the ease of their processing - the ability to impart to them a variety of even the most complex forms. The non-grinding processing of these materials (casting, pressing, extrusion) significantly reduces the cost of manufactured products. It is also expedient for technological and economic reasons to machine their processing (sawing, drilling, milling, planing, turning, etc.), which makes it possible to fully use chips and wastes (using thermoplastic polymers).

Ability bonding of plastic products, both among themselves and with other materials such as metal, wood, et al., Holds great promise for the manufacture of various composite laminated building products and supplements.

Easy welding of materials from plastics (for example, pipes) in a jet of hot air allows to mechanize and rationalize certain types of construction work, in particular sanitary and technical.

Easy sealing connection points and interfaces to materials of plastics allows them widely used in waterproofing and thermo-insulating structures. This property is well combined with the light ability of plastics to give thin and strong gas and waterproof films that can be used as a reliable inexpensive and convenient material in waterproofing and gas insulation structures.

The ability of many of these films not to be destroyed by the action of organic solvents makes it possible to use them as an insulating material in the construction of gasoline storages and other storage facilities for light oil products having a very wide distribution in the national economy. The property of plastics to form thin films in combination with their high adhesion to a number of materials makes them an indispensable raw material for the production of varnishes and paints based on them. Paintwork materials among other types of building materials based on polymers will be particularly fast and successfully developed as the least polymer-intensive. The concept of the polymer capacity of a building material is extremely valuable for the long-term planning of the development of the production of building materials based on polymers.

In establishing this concept, one should keep in mind two components of the polymer capacity-the quantitative content of the polymer in a given material and the absolute weight of this material per unit area of ​​the structure (wall, floor, roof). For example, using a polyethylene film 0.085 mm thick with a weight of 80 g for a two-layer waterproofing of 1 m2 requires 160 g of polyethylene, since this film consists of pure polyethylene. Therefore, the polymer capacity of the polyethylene film is 160 g / m2. The polymer capacity of polyvinyl chloride linoleum with 50% polymer, 1 m2 of which weighs 2600 g, will amount to 1300 g / m2. Polymer-based coating compositions have a low polymer content, 50-75 g / m2. Only those building materials based on polymers, which will have a low polymerization coefficient, can be counted on wide implementation.

The disadvantages of plastics as a building material should be attributed to their low ceiling heat resistance (from 70 to 200 ° C). This applies to most plastics and only some types of plastics, for example organosilicon, polytetrafluoroethylene, can operate at slightly higher temperatures (up to 350 ° C). True, this deficiency can be felt only at the lower limit of this heat resistance. Especially important is the heat resistance for roofing materials on the basis of plastics, since on the roof due to radiation the temperature on the surface of materials in some geographical areas can reach 85 ° C.

A significant drawback of plastic masses is their small surface hardness. For plastics with fibrous fillers, it reaches 25, for polystyrene and acrylic plastics-15 kg / mm2. Cellulose plastics (etros) - 4 -5 kg / mm2 (at steel this indicator about 450) differ the lowest hardness. Brinell hardness is equal to (in kg / mm2): paper plastics 25-30, textolite - 35, asbestextolite - 45, delta-wood-20, organic glass - also about 20.

A significant disadvantage of plastics is their high coefficient of thermal expansion. It ranges between (25-120) 10-6, while for steel it is equal to everything) 10 * 10-6. The high coefficient of thermal expansion of plastics should be taken into account in the design of building structures, especially large-sized elements, for example wall panels. The large coefficient of thermal expansion of plastics: in combination with low thermal conductivity causes significant residual internal stresses that can cause cracks in building products due to sudden temperature changes. It is quite obvious that these stresses are particularly significant when reinforcing plastic products with metal.

Do not ignore another negative property of plastics - their increased creep. Even rigid types of plastics with mineral powder fillers, to a much greater extent than for ceramic materials, concretes and metals, have a slowly developing plastic flow-creep, which increases strongly even with comparatively insignificant temperature changes.

A significant disadvantage of plastics is their flammability. However, there is every reason to believe that this shortcoming will be overcome in the near future. Developing new types of polymers - not only carbon-chain ones, that is, those whose main chain consists of carbon atoms, but also heterochain, the main chain of which, along with carbon, also contains other atoms, and primarily silicon, the chemical industry gives construction new types of difficult-combustible plastics.

As a negative property of some plastics, one should note their toxicity. The latter in a number of cases depends not only on the toxicity of the polymers themselves, but also on the toxicity of those components that are included in plastics (stabilizers, plasticizers, dyes). The toxicity of polymer building materials has not been studied enough, and this issue should be given serious consideration, since this is especially important for those plastics that are used in the interior decoration of living quarters and in water supply systems.

The unexplored properties of plastics include their durability. Meanwhile, the issues of the durability of materials, the variability of their properties over time, are decisive and determine the possibility and expediency of their application in construction.