The frequent occurrence of warm winter in recent years is one of the consequences of global climate change. Only in Central Europe, there are scenes of large-scale snow cover from time to time, but we cannot take it lightly. After all, in the northern hemisphere, winter is still the most in the year. In the colder winter, people tend to stay in a warm and comfortable room during the cold winter. Choosing the right plastic for home building materials helps maintain a more comfortable indoor temperature during the winter, while reducing the cost of indoor heating.
Up to two-thirds of the heat generated by the indoor heating system is lost through the roofs of the exterior walls, basements, and unisolated detached homes, meaning that approximately 2,000 liters of heating fuel is wasted each year. In order to avoid heat loss and reduce energy consumption, we can add a strong modern insulation material to the house.
The insulation effect of this modern material far exceeds the effect of the thickest house wall. A one-meter-thick concrete wall can achieve good insulation, but this is equivalent to a standard insulation of two centimeters. The role. The well-known "passive house" is constructed with a 40 cm thick insulation layer, almost never requiring heating, because its comfortable indoor temperature is mainly derived from the heat generated by the residents themselves.
At present, more insulation materials are used including the following categories:
â— Natural organic materials: such as wood fiber, cellulose, hemp, linen, coconut fiber, reed;
â— Synthetic inorganic materials: such as mineral wool (asbestos and glass wool), and mineral foam (autoclaved aerated concrete, pumice, calcium silicate, foam glass, expanded perlite);
â— Synthetic organic materials: especially rigid foam made of polystyrene or polyurethane.
Renewable natural materials are suitable for thermal insulation in the house, but they cannot be used as outdoor insulation materials because the renewable natural materials are extremely flammable and easily absorb a large amount of water. Another criterion for determining the suitability of insulation materials is the lowest possible level of thermal conductivity. A good insulation material should be highly resistant to thermal energy, which means that good insulation materials must be poor thermal conductors. The unit of thermal conductivity is watts/meter Kelvin, abbreviated W/(mK), and the construction terminology is represented by the Greek letter λ.
Therefore, the lower the thermal conductivity of the material, the higher its ability to insulate it. The following are the thermal conductivity coefficients for various materials.
â— Kapok: 0.09
â— Calcium silicate: 0.065
â— Expanded Perlite: 0.05
â— Coconut fiber: 0.045
â— Mineral wool: 0.04
â— Polystyrene (PS): 0.035
â— Polyurethane (PU): 0.025
â— Polyisocyanurate (PIR): 0.023
The most important synthetic plastic in the field of thermal insulation is polystyrene foam, which is based on styrene (C8H8) and can be prepared from benzene (C6H6) and ethylene (C2H4) in refineries. Under the action of catalyst or high temperature, the monomer will be converted into a macromolecular chain structure, and styrene will be polymerized into polystyrene. This synthetic material is not easily corroded and the water absorption capacity is lowered.
Add a layer of sturdy modern insulation material to the house
Rigid Expanded Polystyrene Foam (EPS) is the most widely used material currently made of polystyrene particles with a pentane (C5H12) blowing agent. When the two materials are heated above 90 ° C, The alkane will evaporate and expand the volume of the polystyrene particles to 20-50 times, and then by further treatment with hot air, the EPS foam can be made into various shapes, such as blocks, plates, or specific parts. shape.
Rigid extruded polystyrene foam (XPS) is prepared by continuous extrusion. The polystyrene is first melted in an extruder, carbon dioxide is added as a blowing agent, and then extruded using a mold of a different shape. By adjusting the width of the extruder opening, the thickness of the foam can be varied accordingly.
Both EPS and XPS are resistant to aging and moisture, and have poor thermal conductivity, thus meeting the most stringent thermal insulation requirements. However, both types of foams need to be shielded from UV radiation because sunlight can make these materials brittle and yellow. Through the research and analysis of the material life cycle, it is found that the use of foaming agent has a negative impact. For example, the use of pentane blowing agents can exacerbate summer smoke pollution, although it has not yet reached the stratosphere of the atmosphere; in the past, the use of partially halogenated chlorofluorocarbons (HCFCs) in the production of XPS plastics, due to its negative effects, Germany is no longer Use this material.
Polystyrene has been a mainstream insulation material since the 1960s, and Styropor was widely known throughout the world as its trade name. Polystyrene is extremely light in weight because it contains up to 98% air in the cells of its material structure. The material was invented in 1949 by Fritz Stastny (1908 – 1985) when he was a chemist at BASF in Ludwigshafen, Germany. BASF recently successfully optimized the performance of EPS materials (trade name Neopor). By adding graphite particles to the raw polystyrene particles, BASF successfully reduced the EPS thermal conductivity level to 0.032 W/(mK). The resulting foamed plastic panel exhibits a shiny silver-gray color that also absorbs infrared radiation, which further reduces the conduction of thermal energy. Therefore, to achieve the same thermal insulation effect, Neopor plates can be reduced by up to 30% thicker than conventional polystyrene sheets, and the thickness of the entire insulating structure can be significantly reduced.
Foam made of polyurethane (C3H8N2O) is also a very popular insulation material in the construction industry. This foam is made by adding a polyisocyanate foaming agent through a diol or a polyol or a mixture of the two. to make. The reaction mixture is poured into a mold, and the final foaming and hardening process of the foam is carried out under the influence of pressure and temperature, and then the foam block is cut into a desired plate shape or sheet shape. Rigid polyurethane foam can be used as a thermal insulation material for flat or sloping roofs. Like polystyrene, polyurethane foams also require UV protection.
The lower the thermal conductivity of the material, the higher its thermal insulation capacity
In 1937, Otto Bayer (1902 – 1982) received a patent for the production of polyurethane, a chemist who worked at the company of Leverkusen, Germany. Polyurethanes have been widely used as insulation materials in construction, cargo containers and refrigerators since the 1950s. In 2007, the global consumption of polyurethane materials exceeded 12 million tons, and it continues to increase.
Polyisocyanurate plastics are similar to polyurethanes but have better chemical and thermal stability, and their diphenylmethane diisocyanate (MDI) content is higher than polyurethane. In addition to this, the reaction partner used in the production of the polyisocyanurate process is a polyester polyol rather than a polyether polyol used in the production of polyurethane. The structural unit of polyisocyanurate consists of the isomers 1,3,5-triazine and 2,4,6-trione. Polyisocyanurate plastics are usually made into rigid foam boards and used as insulation materials in the construction industry. Their thermal conductivity is 0.023 W/(mK), which is the lowest thermal conductivity level, so it is considered to be One of the best classic insulation materials.
Netzwerk Innovative Dämmtechniken is co-sponsoring a joint study with the ARGE-SH Institute in Kiel, Germany, to find more efficient insulation materials by studying materials such as vacuum insulation panels (VIPs). The thermal conductivity of vacuum insulation panels ranges from 0.003 W/(mK) to 0.008 W/(mK), which means that a 20 mm thick vacuum insulation panel can reach its ten times thick polystyrene foam. The insulation effect of the board. The structure of the vacuum insulation panel is similar to that of a thermos flask. The surface is a gas-tight enclosure that encloses a rigid core in which the air is evacuated. For example, an open-cell foam with a lambda value of 0.008 W/(mK) is suitable as the inner core, and a plastic film coated with aluminum by evaporation is a standard outer casing material. Improving the thermal insulation properties of the material depends mainly on the degree of vacuum. If the outer casing is damaged and causes a non-vacuum state, the thermal conductivity level will increase sharply, and the vacuum insulation panel will completely lose its heat preservation effect.
Plastics can be used not only as building materials for indoor insulation, but also for other applications. It keeps people warm in the winter outdoor activities, such as thermal underwear made of synthetic textile fiber, especially polyester material, which does not freeze, is windproof and waterproof, and can transmit human body sweat and condensed moisture. And to evaporate, not only can keep warm, but also keep the body dry. In addition to polyester materials, polyacrylic acid and polyamide (nylon) can also be used to make thermal underwear.
Polyurethane (PVC) is commonly used for surface coatings of raincoats, gloves or boots. The durability and environmental resistance of this material is second to none, whether it is an acidic substance or an extremely cold temperature of minus 50 °C. Will not damage the material. Immediately, PVC materials will celebrate its 100th birthday. In 1912, a chemist named Fritz Klatte (1880 – 1934) successfully polymerized vinyl chloride (C2H3Cl), a chemist who worked at Griesheim. Elektron then went to work at Hoechst AG. However, Klatte's success at the time did not result in the development of a product that could be used for sale, so Griesheim Elektron gave up Klatte's patent in 1926. By the time the inventor Klatte died, BASF succeeded in producing PVC materials that no longer decomposed. After 1945, PVC became the world's hottest and most productive plastic, which can be used in many applications, such as window frames, mulch and phonograph records.
By the way, cold protection is not only a problem to be considered in the winter. For those working in a refrigerated warehouse or a freezing laboratory, it is necessary to wear the DIN EN 342 standard for clothing that is resistant to cold and frost. Special work clothes. Similar metrics are occasionally used in people's usual leisure activities, such as the body suits worn by water sports enthusiasts such as divers and surfers to prevent hypothermia, which is made of polychloroprene. Polychloroprene is well known for its two trade names, DuPont's Neoprene and LANXESS' Baypren. Polychloroprene can be prepared by polymerizing chloroprene (2-chloro-1,3-butadiene, C4H5Cl), and the vulcanization process makes it chemically resistant and weather resistant. Unlike most other unsaturated elastomers, polychloroprene cannot be sulfurized for vulcanization, but instead is replaced by a metal oxide (zinc oxide, magnesium oxide). If the vulcanized rubber is subsequently foamed with the aid of a chemical blowing agent, it will have the desired thermal insulation properties.
As early as 1839, a tough and waterproof vulcanized rubber was used to make dry suits. The inventor of the rubber was named Charles Goodyear (1800 – 1860). The insulation capacity of this material was not important at the time. Because divers can wear wool thermal underwear in this wetsuit to keep out the cold. In 1930, the neoprene wetsuit was invented and put on the market in 1954. The diver wears a neoprene wetsuit and the body can't keep dry, so it is best not to wear any other clothing in the wetsuit. Nowadays, diving suits are also like this. Water will soak in wetsuits. This is not accidental, but the purpose that the design wants to achieve. Through the movement of the human limbs, the circulation of heat exchange with the surrounding environment is generated to keep the body. temperature. But this is not to say that there is a warm diving experience only in places with high water temperatures such as the Red Sea or the Indian Ocean. Professional divers wear a special diving suit, which is higher when they dive in colder waters. Temperature water is introduced into the wetsuit to help the diver maintain body temperature. More practical is a semi-dry suit, which is even suitable for diving in icy waters. The semi-dry suit in the cold water is water-sealed to prevent cold water from passing through the wetsuit, but The warm waters become wet wetsuits.
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