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Classification of Plastics
Plastics can be classified into different categories based on their properties, chemical composition, and intended use. The classification of plastics helps in understanding their characteristics, recycling capabilities, and appropriate applications. Here are some common classifications of plastics:
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Thermoplastics: Thermoplastics are plastics that can be melted and re-molded multiple times without undergoing significant chemical changes. They can be heated and cooled repeatedly without losing their original properties. Examples of thermoplastics include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and polyethylene terephthalate (PET). Thermoplastics are widely used in packaging, consumer products, automotive parts, and construction materials.
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Thermosetting Plastics: Thermosetting plastics are plastics that undergo a chemical reaction during curing, resulting in a hard and rigid structure that cannot be melted or reshaped once cured. They have high heat resistance and dimensional stability. Examples of thermosetting plastics include epoxy, phenolic resins, and melamine. They are commonly used in electrical insulation, adhesives, composites, and molded components.
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Elastomers: Elastomers, also known as rubber-like plastics, exhibit elastic properties, allowing them to stretch and return to their original shape. They have excellent flexibility, resilience, and impact resistance. Examples of elastomers include natural rubber, synthetic rubbers (such as styrene-butadiene rubber or SBR), and thermoplastic elastomers (TPE). Elastomers are used in applications that require elasticity, such as gaskets, seals, tires, and footwear.
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Engineering Plastics: Engineering plastics are high-performance plastics that exhibit superior mechanical, thermal, and chemical properties compared to standard plastics. They have excellent strength, toughness, heat resistance, and dimensional stability. Examples of engineering plastics include polyamide (nylon), polycarbonate (PC), polyoxymethylene (POM), and polyetheretherketone (PEEK). Engineering plastics find applications in automotive components, electronics, industrial machinery, and aerospace.
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Biodegradable Plastics: Biodegradable plastics are designed to break down naturally through biological processes, reducing their environmental impact. They can be derived from renewable sources like corn starch or synthesized from petrochemicals with additives that enhance biodegradability. Biodegradable plastics can include both thermoplastics and biopolymers. They are used in applications such as packaging, disposable cutlery, and agricultural films.
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Composites: Composites are materials made by combining two or more different types of plastics or plastics with other reinforcing materials, such as fibers or fillers. The combination results in enhanced mechanical, thermal, or electrical properties. Composite materials find applications in aerospace, automotive, construction, and sporting goods industries.
Plastic can also be classified according to their composition
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- Homogeneous Plastics:These variety of plastic are composed of carbon atoms only and they exhibit homogeneous structure.
- Heterogeneous Plastics:These variety of plastic are composed of the chain containing carbon and oxygen, the nitrogen and other elements and they exhibit heterogeneous structure.
Plastics can also be classified according to their physical and mechanical properties.According to this classification, plastics are divided into four groups.
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- Rigid Plastics: These plastics have high modulus of elasticity and they retain their shape under exterior stresses applied at normal or moderately increased temperatures.
- Semi- rigid Plastics: These plastics have a medium modulus of elasticity and their elongation under pressure completely disappears when pressure is removed.
- Soft plastics: These plastics have a low modulus of elasticity and the elongation under disappears slowly when pressure is removed.
- Elastomers : These plastics are soft and elastic materials with a low modulous of elasticity. They deform considerably under load at room temperature and return to their original shape when the load is released. The extension can range up to ten times their original dimensions.
It’s important to note that within each classification, there can be various subcategories and specific types of plastics, each with its own unique properties and applications.