Plastic is defined as a material that contains an organic substance of greater molecular weight as an important ingredient. It is also characterized as polymers with long chains of carbon. All plastics are said to be polymers. There are two different types of plastic-
Thermoplastic
Thermosetting
In this article, we will study different types of plastic and their uses in detail.
Thermoplastic and Thermosetting Plastic
Thermoplastic:
Plastics that are easy to bend when heated. Thermoplastics include linear polymers and a mixture of linear and cross-linked polymers. For instance, PVC, nylon, polythene, etc.
Types of Plastic Materials
There are 7 types of plastic. They are as follows-
1. Polyethylene Terephthalate
PET is often known as a fabric that is wrinkle-free. It's different from the plastic bag we usually see at the grocery store. Due to its good ability to avoid oxygen from getting in and spoiling the substance inside, PET is often used for food and drink packaging purposes. It also helps keep carbon dioxide from getting out of carbonated drinks.
2. Polyvinyl Chloride
A synthetic polymer whose monomer is vinyl chloride (a chemical compound with the formula CH₂=CHCl or C₂H₃Cl) is polyvinyl chloride (often abbreviated to PVC). More than 40 million tons of this plastic are manufactured around the globe every year. Rigid PVC (or RPVC) and flexible PVC are the two basic types of PVC. Rigid PVC is mainly used for plumbing, windows, and doors in the building industry. In the development of bank cards, packaging, bottles, and food-covering sheets, this type of PVC is often used. It is understood that flexible PVC has applications in electrical cable insulation, flooring, plumbing, and imitation leather. The melting point ranges from 100 to 200 degrees celsius.
3. Polyethylene
Polyethylene is a very popular plastic, or simply polythene, whose monomer is ethylene (a chemical compound with the formula C₂H₄). You can write the generalized chemical formula of this plastic as (C₂H₄)n. Polyethylene density can vary between 0.88 grams per cubic centimetre and 0.96 grams per cubic centimetre. This plastic has a relatively low melting point, ranging from 115 degrees Celsius to 135 degrees Celsius. There are four different polyethylene densities-
Low-density polyethylene - It is used for the production of plastic bags, shopping bags, and disposable products.
Medium-density polyethylene- It is used in gas pipes, carrier bags, etc.
High-density polyethylene- As they are more rigid than the above two they are used in plastic bottles, snowboards
Ultra-high molecular weight polyethylene- They are highly resistant. Used in is in military body armour, hydraulic seals and bearings, biomaterial for hip, knee, and spine implants, and artificial ice skating rinks.
4. Polypropylene
Polypropylene is a non-polar, partly crystalline polymer whose monomer is propylene (sometimes referred to as polypropene and abbreviated to PP) a chemical compound with the formula C₃H₆. The generalized polypropylene chemical formula may be written as (C3H6)n. It is important to note that when heated to certain temperatures, polypropylene becomes moldable so it is a thermoplastic polymer. The melting point usually ranges from 130 degrees Celsius to 171 degrees Celsius. It is estimated that the density of amorphous polypropylene is 0.855 grams per cubic centimetre, whereas that of the crystalline variant is approximately 0.95 grams per cubic centimetre.
To make laboratory equipment, vehicle parts, medical devices, and food containers, polypropylene sheets are used.
5. Polystyrene
Acrylonitrile butadiene styrene (often abbreviated to ABS) is a thermoplastic synthetic polymer that is made up of three different monomers.
Acrylonitrile - they are represented by the formula
Styrene- It is a derivative of benzene with the chemical formula C8h8
1,3 butadiene- organic compound with the formula c4h6
The density typically varies from 1.06 to 1.08 grams per cubic centimetre of this engineering plastic. In drain-waste-vent pipe systems or DWV pipe systems, one of the most important applications of ABS is In certain musical instruments, inhalers, automobile bumper bars, and the heads of golf clubs, this plastic is often used.
6. Nylon
Nylon 6 - they have very high tensile strength and, to some degree, are also lustrous and elastic. It is known that nylon 6 fibres are highly resistant to chemical products (such as alkalis and acids). They are immune to abrasion or wrinkling, too. In addition, nylon 6 is proven to be wrinkle-proof. Nylon 6 plastic is commonly used in many sectors, such as the aircraft industry, the automobile industry, the electronics industry, and the textile industry, because of its many attractive properties.
7. Others
Others refer to all plastics other than those referred to in numbers 1-6 and also to plastics that may be layered or mixed with other plastics, such as bioplastics. The most popular plastic in this group is polycarbonate (PC), which has not been used as much in recent years because of its association with bisphenol A. (BPA). PCs are known by different names as well: Lexan, Makrolon, and Makroclear. Ironically, for baby bottles, sippy cups, water bottles, water gallons, metal food can liners, ketchup containers, and dental sealants, PC is usually used. Owing to its toxicity, the use of PCs for baby bottles and infant formula packaging has been banned in many countries.
Thermosetting:
Plastics that, once molded, can not be softened again by heating. Heavily cross-linked polymers fall into the thermosetting plastics group. There are primary bonds between molecular chains in thermosetting plastics and strong cross-links hold them together. Bakelite, melamine, etc. Example: Bakelite is used to make electrical switches, while floor tiles use melamine.
Types of Plastic Materials
Melamine formaldehyde- Heat-resistant plastic. Hardest of all the plastics.
Bakelite- Used in bottle caps, plastic automobile parts, etc.
Polyesters- Used for reinforced plastics
Epoxies - Used as adhesives
Did You Know?
Plastic recycling is very significant. If they are not recycled at the right time, they are mixed with other chemicals or products, making them harder to recycle and a source of pollution. They are non-biodegradable, and the microbial effect does not decompose them. It is important to use biopolymers or biodegradable polymers to prevent this.
FAQs on Types of Plastic
1. What are the two main types of plastic based on their thermal properties?
The two main types are thermoplastics and thermosetting plastics. Thermoplastics can be repeatedly softened by heating and hardened by cooling, which allows them to be remoulded. Thermosetting plastics, once shaped and cured, undergo a chemical change and cannot be remelted or reshaped.
2. What are the 7 common types of plastic identified by recycling codes?
The 7 common types of plastic, often identified by their recycling codes, are:
- PET (Polyethylene Terephthalate) - Code 1
- HDPE (High-Density Polyethylene) - Code 2
- PVC (Polyvinyl Chloride) - Code 3
- LDPE (Low-Density Polyethylene) - Code 4
- PP (Polypropylene) - Code 5
- PS (Polystyrene) - Code 6
- Other (including Polycarbonate, ABS, and bioplastics) - Code 7
3. What is PVC, and what makes its rigid and flexible forms useful for different applications?
PVC, or Polyvinyl Chloride, is a synthetic polymer of the monomer vinyl chloride. Its versatility comes from its two main forms. Rigid PVC (RPVC) is strong and durable, making it ideal for construction applications like pipes, windows, and doors. When plasticisers are added, it becomes Flexible PVC, which is used for electrical cable insulation, flooring, and imitation leather.
4. What is HDPE, and how do its properties make it suitable for items like plastic bottles and pipes?
HDPE stands for High-Density Polyethylene. It is a type of polyethylene plastic with a higher density, which makes it more rigid, stronger, and more chemically resistant than LDPE. These robust properties make it an excellent choice for products that require structural strength and durability, such as milk jugs, detergent bottles, gas pipes, and plastic lumber.
5. How does the molecular structure of thermoplastics differ from thermosetting plastics, and why can only one be reshaped?
The key difference is in their chemical bonds. In thermoplastics, the polymer chains are linear or slightly branched and held by weak intermolecular forces. Heating overcomes these forces, allowing the chains to slide past each other so the plastic can be remoulded. In thermosetting plastics, strong covalent bonds called cross-links form between the polymer chains during curing, creating a rigid 3D network. These strong links cannot be broken by heat without degrading the polymer, which is why thermosets cannot be reshaped after their initial moulding.
6. Why is Polycarbonate (PC), a Type 7 plastic, often avoided for food containers despite its durability?
Polycarbonate (PC) is often avoided for food and drink containers, especially for baby products, because of its association with Bisphenol A (BPA). BPA is a chemical used to make PC and can leach from the plastic into food and beverages, particularly when heated. Since BPA is a known endocrine disruptor, its potential health risks have led many countries to ban its use in products like baby bottles and sippy cups to ensure consumer safety.
7. What is the practical difference between a polymer like Polyethylene and a co-polymer like ABS?
The main difference is their monomer composition, which affects their properties. A polymer like Polyethylene is a homopolymer, meaning it's made from a single type of monomer (ethylene), resulting in uniform properties. In contrast, a co-polymer like Acrylonitrile Butadiene Styrene (ABS) is made from three different monomers. This allows manufacturers to combine the best qualities of each:
- Acrylonitrile provides chemical resistance and hardness.
- Butadiene offers toughness and impact strength.
- Styrene gives it a glossy finish and rigidity. This combination makes ABS a highly versatile and strong engineering plastic.
8. What are the main environmental disadvantages of conventional plastics?
The primary environmental disadvantages of conventional plastics include:
- Non-biodegradability: Most plastics persist in the environment for hundreds or thousands of years, leading to long-term pollution on land and in water.
- Harm to Wildlife: Animals can ingest or become entangled in plastic waste, causing injury, starvation, and death.
- Waterway Pollution: Plastic debris clogs rivers, lakes, and oceans, harming marine ecosystems and infrastructure.
- Resource Depletion: Most plastics are derived from non-renewable fossil fuels like petroleum and natural gas.
