Plastics are organic polymers that are in solid state under normal conditions, and may be shaped or molded by mechanical methods using pressure and heat.
Plastics fall under one of two general categories: Thermoplastics and thermosets.
Thermoplastics retain their plastic properties under heat and pressure, and may be reshaped many times with the use of heat and pressure. This is similar to melting a wax candle and molding it into a different shape. The lifespan of thermoplastics depends on the fatigue of the material, and they usually degrade under their own weight in temperatures between 54°C and 120°C, with some retaining their properties in temperatures of 260 to 270°C depending on their structure. Therefore, heat must be precisely controlled during processing. Thermoplastics are shortly known as plastics, and are one of the end-products in the vast range of the petrochemical industry. Thermoplastics are classified as engineering plastics and general purpose plastics depending on their usage. Engineering plastics like Polycarbonate (PC), Acrylonitrile Butadiene Styrene (ABS) and Polyphenyl Oxide (PPO), which are not produced in Turkey, can replace metals thanks to their mechanical and heat properties.
Thermosets are plastics that cannot be reshaped once formed under heat and pressure. They are one-way plastics because chemical changes during processing alter the material into a network structure, causing it to lose its plastic properties and become a tough material. This can then be processed in turning or milling machines. There are a variety of thermosets in the market; however, due to their unique properties, thermosets cannot be used on their own and must be blended with additives such as thermoplastics. Thermosets may remain stable between temperatures of 60°C to 150°C, and some thermosets are stable up to 230°C, after which they begin to degrade.
Plastics are used in large quantities in many industries like machinery, aviation, electrics and electronics due to low weight, ease of processing, corrosion resistance, and good electrical and heat insulation. However, plastics have different properties compared to metallic and other engineering materials. The physical and chemical properties of plastics are influenced by the molecular weight, structure and cross-binding levels of the constituent polymers, and the functional groups contained in the structure.