Alexei Volkov
Plastic is a polymeric material that can be moulded or shaped, with properties such as low density, low electrical conductivity, transparency, and toughness. Plastics are polymers made of carbon and hydrogen, with additives such as fillers, reinforcements, anti-degradants, stabilizers, flame retardants, and plasticizers. The polymer chains are formed through a process called polymerization, which results in a three-dimensional network of long chains consisting of smaller repeated units. The fundamental differences in the properties of these polymers are due to the varying functional groups within their molecular structure. The chemical structure of plastic determines its degradation process, with photo-oxidation being the most significant.
| Characteristics | Values |
|---|---|
| Chemical composition | Polymers made of carbon and hydrogen, often mixed with additives for different properties. |
| Additives | Colorants, plasticizers, stabilizers, fillers, and reinforcements. |
| Polymerization | The process of bonding monomer molecules together through a chemical reaction, resulting in a three-dimensional network of long individual polymer chains. |
| Polymer types | Commodity resins, specialty resins, thermosetting polymers (thermosets), and thermoplastics. |
| Degradation | Plastics degrade over time, with photo-oxidation being the most significant process. Marine degradation takes longer due to the saline environment and cooling effect of the sea. |
| Durability | Plastics are durable and resistant to many natural degradation processes due to their chemical structure. |
| Toxicity | Many plastic additives are toxic and can leach into the environment. Examples include phthalates and BPA. |
| Environmental impact | Plastic waste persists for centuries and contributes to pollution and health issues in humans and animals. |
| Applications | Packaging, siding, piping, automobile interiors, compact discs, plumbing, hardware, and more. |
Explore related products
What You'll Learn
Polymers
Plastics are a range of synthetic or semisynthetic materials composed primarily of polymers. Polymers are macromolecules based on a structure built up, chiefly or completely, from a large number of similar structural units bonded together. They are formed through a process known as polymerization, in which monomer molecules are bonded together through a chemical reaction that results in a three-dimensional network of long individual polymer chains consisting of smaller repeated units.
Polymerization reactions can be broadly categorized into two types: addition and condensation. Addition polymerization is the formation of polymers from monomers containing a carbon-carbon double bond through an exothermic addition reaction. The polymer chains formed through this process are of unequal length, resulting in polydispersity. The variation in chain length contributes to the differences in material properties, such as ductility, impact resistance, strength, and stiffness.
The inherent viscoelastic nature of polymeric materials allows for movement within the polymer chains when subjected to stress. Consequently, plastic materials exhibit time-dependent behaviour, with their properties, such as strength and ductility, decreasing over time. This phenomenon often leads to creep and stress relaxation within plastic products.
Plastics can be broadly categorized into two types based on their molecular structure: semicrystalline and amorphous. Crystalline plastics, such as high-density polyethylene (HDPE) and polyether ether ketone (PEEK), exhibit a regular pattern of atom spacing. In contrast, amorphous plastics have a less ordered structure, resulting in both a melting point and glass transitions. Semi-crystalline plastics, including polyethylene and polypropylene, possess characteristics of both crystalline and amorphous structures.
The versatility of plastics stems from their customizable properties. By modifying the chemical structure of the polymer backbone and side chains, plastics can be tailored to suit specific applications. For instance, the addition of different molecular groups as side chains influences the characteristics of the polymer, leading to the development of acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Furthermore, additives such as fillers, reinforcements, anti-degradants, stabilizers, and plasticizers can be incorporated to enhance specific properties.
Molding Plastic on Fabric: A Step-by-Step Guide
You may want to see also
Explore related products
![Sem Paints SEM-39757 Dual-mix[tm] Structural Impact Resistant Adhesive](https://m.media-amazon.com/images/I/31K+0YVqOJL._AC_UL320_.jpg)
Additives
Plastic additives are compounds added during the moulding process of polymers (synthetic resins) to improve their processing performance or to enhance the properties of the resin itself. Additives make up 32% of plastic waste. Without additives, plastics would not work, but with them, they can be made safer, cleaner, tougher, and more colourful. Additives also reduce production costs and make products last longer, helping to conserve the world's raw material reserves.
Optical brighteners absorb ultraviolet and violet light and then re-emit this energy at a higher wavelength, usually as a blue glow. Antioxidants help prevent thermal oxidation reactions when plastics are processed at high temperatures and light-assisted oxidation when plastics are exposed to UV light.
To improve processability, additives such as lubricants, release agents, stabilizers, and plasticizers are used. To enhance mechanical properties, plasticizers, toughening agents, and impact modifiers are added. Finally, to enhance optical properties, nucleating agents and optical brighteners are used.
How Bleach Removes Mold from Plastic Surfaces
You may want to see also
Explore related products
Plastic types
Plastic is a polymeric material that can be moulded or shaped. Its chemical composition can be categorised into two types: plastics made up of polymers having only aliphatic (linear) carbon atoms in their backbone chains, and heterochain polymers, which contain atoms such as oxygen, nitrogen, or sulphur in their backbone chains, in addition to carbon.
Plastics can also be categorised according to their recycling codes. The following paragraphs will discuss some of the most common types of plastics.
Polyethylene Terephthalate (PET)
PET is a form of polyester that is lightweight, strong, and typically transparent. It is commonly used in plastic bags, plastic trays, and beverage bottles, such as water bottles, cooking oil bottles, and soda bottles. It is also used in food packaging and fabrics.
Polyvinyl Chloride (PVC)
PVC is a hard and rigid plastic that is resistant to chemicals and weathering. It is commonly used in building and construction applications and high-tech applications such as wires and cables due to its inability to conduct electricity. PVC is also widely used in medical applications, such as medical bags and tubing, as it is easily disinfected and impermeable to germs.
Polypropylene
Polypropylene is a hard and sturdy plastic that can withstand high temperatures. It is used in a variety of products, including Tupperware, car parts, thermal vests, yogurt containers, and disposable diapers. It is also used for living hinges due to its resistance to fatigue.
Polystyrene
Polystyrene can be solid or foamed and is a very inexpensive resin with a low unit weight. It is easy to create and can be found in beverage cups, insulation, packing materials, egg cartons, and disposable dinnerware. It is highly flammable and can release harmful chemicals when heated, making it dangerous. The commercial name for polystyrene is Styrofoam.
Polycarbonate
Polycarbonate is used to create strong and tough products, such as lenses for eye protection in sunglasses, sports goggles, and safety goggles, mobile phones, and compact discs. However, polycarbonate has been controversial due to its leaching of bisphenol A (BPA), which is a potential environmental hazard.
Other Types of Plastics
Other types of plastics include acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Acrylic (Polymethyl methacrylate or PMMA) is often used as a replacement for glass due to its transparency. Polylactic acid (PLA) is a bioplastic made from fermented plant starch, used for plastic bottles, bags, and film. Acrylonitrile Butadiene Styrene (ABS) is a tough and impact-resistant plastic used in automotive parts, toys, and other consumer products. Polyamide, commonly known as nylon, is a thermoplastic with low density, high thermal stability, and decent chemical resistance.
Plastic Fabrication: A Profitable Business Venture?
You may want to see also
Explore related products
Degradation
Plastics are a polymeric material that can be moulded or shaped. They are composed of long chains of carbon atoms, with or without oxygen, nitrogen, or sulfur atoms attached. The chemical structure of most plastics makes them durable and resistant to many natural degradation processes. However, plastic pollution has caused significant ecological problems and raised concerns about its potential adverse effects on human health.
The degradation of plastics is a critical aspect of addressing plastic pollution. Degradation refers to the reduction in the physical properties of a polymer, such as strength, caused by changes in its chemical composition. Plastics are subject to degradation throughout their product life cycle, including during processing, use, environmental disposal, and recycling. The rate of degradation varies, with biodegradation taking decades, while some industrial processes can decompose polymers in hours.
There are two main types of degradation mechanisms: physical and chemical. Physical degradation refers to changes in the bulk structure, such as cracking, embrittlement, and flaking. On the other hand, chemical degradation involves changes at the molecular level, including bond cleavage and the oxidation of long polymer chains, resulting in shorter chain lengths.
One of the most significant degradation processes for plastics is photo-oxidation, which is more common in ambient conditions. Plastics in the ocean, for example, are exposed to sunlight, rain, and other environmental conditions, causing them to decompose and release toxic chemicals like bisphenol A. However, due to the increased volume of plastics in the ocean, decomposition has slowed down. The Marine Conservancy estimates that a foam plastic cup will take 50 years to degrade, while a disposable diaper will take 450 years.
Biodegradation of plastics is also influenced by additives and plasticizers in their composition. These additives can have harmful impacts, and their degradation by microorganisms can cause a significant reduction in toxic plastic pollution. Pretreatments to enhance biodegradation efficiency have been explored, and various bacterial strains show potential for efficient plastic degradation, improving human health and safety.
Additionally, mechanical degradation, such as the cracking and erosion of plastic pipes, can be reduced by adding lubricants or processing aids that lower friction between polymer chains. Polymer stabilizers are also used to inhibit degradation, ensure desired properties, and extend the lifespan of plastic items. Conversely, biodegradable additives can be added to accelerate degradation by improving the biodegradability of plastic waste.
Are Rite-Cell Plastic Frames Safe for Food Contact?
You may want to see also
Explore related products
Molecular weight
Plastics are polymeric materials that can be moulded or shaped. Polymers are macromolecules that are based on a structure built up, chiefly or completely, from a large number of similar structural units bonded together. These structural units are often called chains and consist of repeating units, similar to links. The chains are entangled within each other.
The molecular weight of a molecule is the sum of the atomic weights of the atoms comprising it. For example, the molecular weight of polyethylene can be calculated by multiplying the molecular weight of the repeating ethylene functional group times the number of units comprising the chain. Thus, for polyethylene, where the repeating unit contains two carbon atoms and four hydrogen atoms, the molecular weight is 28n, where n represents the number of repeating segments. Most commercial polymers have an average molecular weight between 10,000 and 500,000.
Higher molecular weights are associated with longer molecular chains, resulting in a greater level of entanglement. This has important implications as higher-molecular-weight grades of plastics will have superior mechanical, thermal and chemical resistance properties compared with lower-molecular-weight grades of the same material. This is because the lack of covalent intermolecular bonds facilitates polymer chain mobility, resulting in viscoelasticity.
However, unlike molecular weight, the relationship between molecular weight distribution and end properties is not uniform. For example, in comparing two similar materials with different molecular weight distributions, the material with a wider distribution will generally exhibit better ductility and impact resistance but will demonstrate reduced strength and stiffness.
Plastic Spoons: Convenience or Environmental Threat?
You may want to see also
Frequently asked questions
Plastic is any synthetic or semisynthetic organic polymer. In other words, while other elements might be present, plastics always include carbon and hydrogen.
Polymers are macromolecules that are based on a structure built up, chiefly or completely, from a large number of similar structural units bonded together. Often called chains, the polymer consists of repeating units, similar to links.
Plastics can be divided into two distinct categories based on their chemical composition: polymers having only aliphatic (linear) carbon atoms in their backbone chains, and heterochain polymers, which contain atoms such as oxygen, nitrogen, or sulfur in their backbone chains, in addition to carbon.
Polymers are formed through a process known as polymerization, in which monomer molecules are bonded together through a chemical reaction that results in a three-dimensional network of long individual polymer chains consisting of smaller repeated units.
