The full name of the well-known PVC is polyvinyl chloride (PVC). It was actually the first plastic ever discovered, however, the importance of this discovery was not yet maturely recognized until around 1835. As a thermoplastic polymer, PVC is produced by a chain reaction typical of plastics production (Injection Molding), in which one monomer automatically combines with the next to form a polymer.
Researcher Charles discovered vinyl chloride while studying chlorine gas. When he left it in the sun for a while, the heat was enough to trigger it and start the chain polymerization into PVC. however, it took another 90 to 100 years before the substance was actually rediscovered and started to triumph all over the world. The rather toxic gas vinyl chloride was used as a coolant for a while, but after that, it was mainly used to produce polyvinyl chloride.
History of Polyvinyl Chloride
In fact, polyvinyl chloride has rather brittle properties that make it useless in many applications. However, as early as around 1935, it was discovered that it was possible to change the properties of plastics with so-called additives. As early as 1945, the I.G. Farben Company developed the first plasticized PVC with which the plasticity of PVC could be consistently increased. Now, nothing prevents mass production, and new application possibilities excite industry and customers alike. As an extremely inexpensive plastic, PVC was very successful, and its many properties made it the most widely produced plastic in the postwar world.
Floor coverings, components, pipes, shoe soles, and even all records were eventually made from this material, even though it was called vinyl. With the right additives, even artificial leather is made from PVC and is virtually indistinguishable from natural leather, except for the smell. In addition, polyvinyl chloride is a flame retardant due to its high chlorine content. The low production cost is mainly due to the sodium hydroxide solution. Caustic soda is indispensable as a basic substance in many soaps and detergents. Chlorine is produced during manufacture and processing, which can then be used to produce PVC inexpensively. polyvinyl chloride without additives is called PVC-U (for unplasticized), while modified polyvinyl chloride is called PVC-P.
Polyvinyl Chloride As an Ideal Plastic – with Its Limitations
PVC-U is actually a versatile material, especially for use in the construction industry. It is resistant to acids and bases and can be easily processed with metal cutting techniques. However, it retains its good properties only at a temperature of about 140 °F (60 °C). After that, its instability increases, and with it its tendency to corrode. At temperatures below 23 °F (-5 °C), PVC-U tends to become brittle, which increases the risk of breakage. To prevent this, additives come into play to improve weatherability and temperature resistance, elasticity, and toughness. However, some plasticizers in PVC-P have come under scrutiny.
These so-called phthalates change the properties of PVC but are not separated from it. For example, they evaporate and are thus released, especially when combined with fat or during long-term storage. For some time, some of these phthalates have been suspected of causing cancer and other diseases. Therefore, in the recent past, special additives with different behavior have been developed. At the same time, there are many forms of PVC on the market, whose groups are classified by different letters. In addition to the top PVC-U and PVC-P, there are PVC-C (highly chlorinated PVC), mixtures with other plastics such as PVC + PE-C or PVC + NBR. PVC-E, PVC-M, PVC-HI, and PVC-S are also well known and all have different characteristics.
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PVC Treatment and Recycling
However, as a plastic, this material still has some problems. Its stability and durability allow it to be used for a long time, but these plastics are expensive to dispose of. On the one hand, it requires a lot of space to be stored in landfills, and on the other hand, it cannot be excluded that the components will not leak and contaminate the soil after many years. When these plastics are incinerated, energy can be generated from them, but toxic gases such as hydrogen chloride are produced. The industry now operates a recycling system where pure thermoplastics are recycled and simple components can still be produced by melting and re-molding.
Injection Molded Photovoltaic Products
This long preamble is in some ways necessary to explain why PVC injection molding is not practiced by all companies in the injection molding industry today. It is true that PVC as a thermoplastic can be injection molded and extruded at temperatures below 392 °F (200 °C). Extrusion is mainly used for PVC pipes. During injection molding, the PVC passes through a specially hardened screw into the mold, where it cools and can then be removed. Otherwise, the PVC leaves a residue that sticks to the surface of the screw. Molding PVC at temperatures of around 302 °F (150 °C) is problematic because, in this region, stretching is greatly reduced. Therefore, PVC shows non-linear properties in different temperature ranges. In addition, there are strong differences related to the use of many different additives. The further processing of materials for composite or other modified injection molded parts is complicated because depending on the conditions, cutting, machining, plastic welding, and even special adhesives must be used. Therefore, only a few companies have the ability to injection mold injection molded parts made of different types of hard and soft PVC. Today, injection molding with PVC is a frequently used technology for the production of accessories and similar parts. However, hollow bodies and various similar products are more often produced by extrusion than by injection molding.
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