When we look everywhere around us, we must find plastics. They make lives easier, safer, cleaner, and even more enjoyable. They are a term commonly used to describe a wide range of synthetic or semi-synthetic materials, which are used in different applications. Plastics can be found in our houses, clothes, cars, toys, screens, medical equipment, etc.
In this reading, we’ll explore what plastics are, their applications, properties, structure, classifications, types and advantages. We’ll also explore what thermoplastic and thermosets
Let’s begin!
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What is Plastic?
The term “plastic” is derived from the Greek word “plastics”, which means “fit for molding”. This is referring to the material’s malleability, or plasticity, during manufacture, allowing it to be able to be cast, pressed, or pressed into a variety of shapes such as films, plates, fibers, bottles, boxes, and many more.
Just as mentioned earlier, plastics are a wide range of synthetic or semi-synthetic organic compounds that are malleable and can be molded into solid objects.
Plastics are organic materials, just like wood, paper, or wool, produced with raw materials that are natural products such as cellulose, coal, natural gas, salt, and crude oil.
Generally, plasticity is a property that can occur in materials that deform irreversibly without breaking. However, in the case of moldable polymers, it occurs to such a degree that their actual name derives from this specific ability.
There are various types of plastic out there with different properties and benefits. There are organic plastics, which contain carbon, and inorganic plastics which don’t. Some plastics occur in nature, like tree rubber, while some are hard and shatter-resistant. Others are soft and flexible.
Plastics occur as many things people don’t recognize as plastic, such as glues and adhesives, paints, protective coatings, linings, sealants, and insulation.
Some plastics even contain additives that make them bacteria- or fire-resistant; some additives give a rainbow of colors, make them flexible, or fill them with bubbles, making them a better insulator.
Applications of Plastics
Below are the applications and benefits of various types of plastics
Plastics aid durability, sustainability, and long-lasting design and construction in buildings, homes, and infrastructure such as bridges.
Accessories like computers, cell phones, televisions, microwaves, etc. are durable, lightweight, and even affordable as they contain plastic.
Varieties in sports are made with plastic, stuff like plastic helmets, mouth guards, goggles, protective padding, etc. in this case, plastic helps to ensure safety in sports; for example, a shock-absorbent plastic foam helps to keep feet stable and supported. Rugged plastic shells covering helmets and pads help protect heads, joints, and bones.
Plastics have improved and contributed to the performance, safety, and fuel efficiency of automobiles. In product packaging, plastic helps to protect and preserve goods and also reduces weight in transportation. Thus, it saves fuel and reduces greenhouse gas emissions.
Thermosetting plastics are heat resistant, which is why they are used in producing kettles, laptop chargers, plugs, etc. They are also used in electrical fittings, handles, adhesives, and control knobs.
Thermosetting plastics are widely used for industrial applications such as automotive, appliances, electrical, lighting, and in the energy market. This is because they have excellent chemical and thermal stability, high strength, hardness, and moldability. Thermosetting plastics are used to produce construction panels and agricultural equipment like feeding troughs and motors.
For thermoplastics, the acrylonitrile butadiene styrene (ABS) type is used to manufacture sports equipment, toys, and various automobile parts. Polycarbonates are used to make CDs and DVDs, drinking bottles, food storage containers, and eyeglass lenses. Polyethylenes are the most common and are used to make shampoo bottles, plastic grocery bags, and bulletproof vests.
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Properties, Structures and Classifications of Plastics
In industries where plastics are made, they are seen as either “commodity” resins or “specialty” resins. The term resin has been used ever since the early years of the plastics industry. Resin originally referred to naturally occurring amorphous solids such as shellac and rosin.
Commodity resins are plastics that are produced at high volume and low cost for durable goods and the most common disposable items. These types of plastics include polyethylene, polypropylene, polyvinyl chloride, and polystyrene. All these plastics will be further explained.
On the other hand, specialty resins are plastics whose properties are suitable for some applications. It is widely known as engineering plastics or engineering resins.
The plastic is produced at low volume and higher cost. Specialty plastic has the ability to compete with die-cast metals in plumbing, hardware, automotive and agricultural applications. Examples of these plastics are polyacetal, polyamide (popularly known as nylon), polytetrafluoroethylene (trademark Teflon), polycarbonate, polyphenylene sulfide, epoxy, and polyether ketone.
Thermoplastic elastomers are another member of a specialty resin. They have the elastic properties of rubber yet can be molded repeatedly upon heating.
Plastics can also be classified into two distinct categories based on their chemical composition. One of these categories is plastic which is made up of polymers containing only aliphatic (linear) carbon atoms in their backbone chains. These include polyethylene terephthalate and polyvinyl chloride, commonly referred to as PET and PVC.
There are many other types listed above, but the structure of polypropylene can serve as an example. Carbon atom contains a pendant methyl group (CH₃):
The second category of plastic is made up of heterochain polymers that contain atoms such as oxygen, nitrogen, or sulfur in their backbone chains, in addition to carbon.
Most engineering plastics are composed of heterochain polymers. A good example is a polycarbonate that contains two aromatic (benzene) rings in its molecules.
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How is Plastics Made?
Plastics are either synthetic or biobased. The synthetics are the most common plastics used today, and they are derived from crude oil, natural gas or coal. The biobased plastics are derived from renewable products like carbohydrates, starch, vegetable oils and fats bacteria and other biological substances.
The first stage in producing plastics is the extraction of raw materials, which include crude oil, coal, and natural gas. Thousands of compounds undergo a complex mixture during this process.
Refining is then performed to transform the crude oil into different petroleum products. They are converted to yield useful chemicals like monomers, which are molecules that are the basic building blocks of polymers. During the process, crude oil is heated in a furnace, which is then sent to the distillation unit.
The distillation unit is where heavy crude oil separates into lighter components called fractions. A fraction called naphtha is a crucial compound that made large amounts of plastic. Although gas can also be used.
The next step is polymerization, where light olefin gases (gasoline) like ethylene, propylene, and butylene (i.e., monomers) are converted into higher molecular weight hydrocarbons (polymers). This can be achieved when monomers are chemically bonded into chains.
The two different types of polymerization are addition and condensation polymerization. An addition polymerization reaction is when one monomer connects to the next one (dimer) and the dimer connects to the next one (trimer) and so on. This can be achieved by the introduction of a catalyst known as peroxide.
This process is known as chain growth polymerization because it adds one monomer unit at a time. Polyethylene, polystyrene, and polyvinyl chloride are the common examples of addition polymers.
On the other hand, condensation polymerization includes joining two or more different monomers. This is achieved by the removal of small molecules like water and it requires a catalyst for the reaction to occur between adjacent monomers.
This is also called step growth because an existing chain can be added to another chain. Nylon and polyester are good examples of condensation polymers.
Final stage of making plastic is compounding or processing which involves melting and mixing various blends of material. This is done to make various formulations for plastics. Extruder is used during this process as the mixture is pelletized.
Some sort of molding process or extrusion is performed to transform the pellets into finished or semi-finished products. The compounding process often occurs on a twin-screw extruder, where the pellets are processed into plastic objects of different designs, sizes, shapes, and colors.
They are processed with accurate properties according to the predetermined conditions set in the machine.
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Types of Plastics
Just as mentioned earlier, plastics are categorized into two: commodity plastics or standard plastics and engineering plastics. The following are the various types of plastics we can see around us.
1. Commodity Plastics:
Below are the various types of commodity plastics:
Polyamides (PA) or nylons – it is used as fibers, toothbrush bristles, tubing, fishing line, and low-strength machine parts like engine parts or gun frames.
Polycarbonate (PC) – polycarbonate is used to produce compact discs, riot shields, traffic lights, eyeglasses, security windows, lenses, etc.
Polyester (PES) – it’s widely used in fashion and textiles as fibers and textiles.
Polyethylene (PE) – these are inexpensive types of plastics used for making supermarket bags and plastic bottles. It’s of three types:
- High-density polyethylene (HDPE) – milk jugs, molded plastic cases, and detergent bottles are made with this type.
- Low-density polyethylene (LDPE) – it’s used for making outdoor furniture, siding, floor tiles, shower curtains, clamshell packaging, etc.
- Polyethylene terephthalate (PET) – is used in carbonated drinks bottles, peanut butter jars, microwavable packaging, plastic film, etc.
Polypropylene (PP) – it’s used in bottle caps, yogurt containers, drinking straws, appliances, plastic pressure pipe systems, car bumpers, etc.
Polystyrene (PS) – it is widely used for producing food containers, foam peanuts, disposable cups, plastic tableware, plates, cutlery, compact-disc, cassette boxes, etc.
- High-impact polystyrene (HIPS) – is used in food packaging and vending cups.
Polyurethane (PU) – these types of plastics are used to produce thermal insulation forms, surface coatings, printing rollers, cushioning foams, etc.
Polyvinyl chloride (PVC) – is used as electrical wire/cable insulation, plumbing pipes, guttering, window frames, shower curtains, flooring, etc.
Polyvinylidene chloride (PVDC) – these plastic types are widely used for food packaging.
Acrylonitrile butadiene styrene (ABS) – it’s used in cases of electronic equipment like computer monitors, keyboards, printers, etc., and drainage pipes.
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2. Specialist Plastics or Engineering Plastics
Below are the various types of engineering plastics, which can also be called high-performance plastics.
Polyepoxide – also known as epoxy used as an adhesive and potting agent for electrical parts. It is also used as a matrix for a composite material with hardeners including amine, amide, and boron trifluoride.
Polymethyl methacrylate (PMMA) – also known as acrylic.
Polytetrafluoroethylene (PTFE) – also known as Teflon. Has good heat resistance and low-friction coatings. It’s used in plumber’s tape and water slides and non-stick surfaces for frying pans.
Phenolics or phenol-formaldehyde (PF) – these types of polymers are relatively heat resistant, high modulus, and good fire resistant. This is why they are often used for insulating parts in an electrical joint. it is also used in paper-laminated products like Formica and thermal insulation foams.
Some other types of specialist plastics include:
Melamine Formaldehyde (MF) – these types of plastic are one of the aminoplasts, used as a multi-colorable alternative to phenolics like moldings. It breaks resistance alternatives to ceramic cups plates and bowls for children.
Thermoplastic, biocompatibility is one of the most expensive commercial polymers. It allows use in medical implant applications like aerospace moldings.
Maleimide/bismaleimide – these types of plastics are used in high-temperature composite materials.
Furan – it’s a resin based on furfuryl alcohol used in foundry sands and biologically derived composites.
Silicone poly – a diketoenamine heat-resistant resin used mainly as a sealant but also used for high-temperature cooking utensils. It’s also used as a base resin for industrial paints.
Polyetherimide (PEI) – it’s also known as Ultem. A high-temperature, chemically stable polymer that does not crystallize.
Polyimide – is also a high-temperature specialized plastic type used in materials like Kapton tape.
Plutarch material – this is a biodegradable and heat-resistant thermoplastic that contains a modified cornstarch.
Polylactic acid (PLA) – it’s also a biodegradable thermoplastic that can be converted into a variety of aliphatic polyesters gotten from lactic acid. This in turn can be made by fermentation of various agricultural products like cornstarch when made from dairy products.
Urea-formaldehyde (UF) – it’s also one of the aminoplasts, used as a multi-colorable alternative to phenolics. It’s used as a wood adhesive for plywood, hardboard, and chipboard. It is also used as an electrical switch housing.
Polysulfone – these types of plastics are high-temperature melt-processable resins used in membranes, filtration media, water heater dip tubes, and other high-temperature applications.
Polydiketoenamine (PDK) – it’s a new type of plastic that can be dunked in acid and change shape endlessly.
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What are Thermoplastic and Thermosetting Plastic?
Thermoplastics, which are also known as thermosets or thermosetting polymers, are types of plastics that irreversibly become rigid when heated. They are initially liquid or soft solid but heat offers energy for chemical reactions that increase the cross-linking between the polymer chains and cure the plastic.
On the other hand, a thermoplastic, which is also known as thermo-softening plastic, is a plastic polymer material. They are moldable and pliable at some certain temperature and solidify when cooled.
Thermosetting plastics are generally stronger than thermoplastics because of their three-dimensional network of bonds, which is also called cross-linking. This is why they are suitable for high-temperature applications, as they keep their shape as strong covalent bonds between polymer chains that cannot be easily broken.
Thermoplastics are materials that become softer when heated and hard when cooled. They can be heated and cooled on several occasions without changing their chemical and mechanical properties.
Thermoplastics have a high molecular weight; their polymer chains associate with intermolecular forces. This weakens rapidly with increased temperature, resulting in a viscous liquid. In this state, thermoplastics can be reshaped and can be used to produce various parts.
Polymer processing techniques used include compression molding, calendering, injection molding, and extrusion.
Furthermore, thermosetting plastics are made up of long chains of molecules that are cross-linked. This is to say they have a very rigid structure. Also, they can be molded, shaped, and pressed when heated. However, they cannot be reheated because they are permanently set.
The heat degradation and chemical attack can be determined by the level of the crosslink density and aromatic content of a thermoset polymer. This is to say the higher the crosslink density and aromatic content, the higher the resistance to heat degradation and chemical attack.
The mechanical strength and hardness can also improve with crosslink density. This is at the expense of the brittleness as they normally decompose before melting. Examples of thermosetting plastics are epoxy resin, phenolic (bakelite), Vinyl Ester resin, cyanate ester, polyester, silicone, polyurethane, and phenolic.
On the other hand, examples of thermoplastic materials are polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamides, polyesters, and polyurethanes. High-temperature thermoplastics include polyether ether ketones, liquid crystalline polymers, polysulfones, and polyphenylene sulfide.
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Advantages and Disadvantages of Plastics
Advantages:
Thermoplastics offer numerous advantages, including their high strength, low processing costs, high recyclable nature, excellent impact resistance, corrosion resistance, and remolded properties.
They also offer flexibility, electrical insulation, and aesthetic finishes.
On the other hand, thermosetting plastics offer a variety of color and surface finishes, resistance to corrosion, molded-in tolerances, high mechanical properties, and low thermal conductivity.
They also offer outstanding dielectric strength, lower tooling and setup costs, cost-effectiveness, excellent dimensional stability, and reduced production costs compared to metal fabrication.
Disadvantages:
Thermosetting plastic has several disadvantages, including the inability to be recycled, low tensile strength, ductility, and remolding; poor thermal conductivity; difficulty in surface finishing; and potential product failure in high-vibration applications.
Additionally, thermoplastics degrade more easily in direct sunlight or UV exposure, not all resist hydrocarbons, organic solvents, and polar solvents, experience creep under long-term loading, and can fracture rather than deform under high stress.
Conclusion
Plastics are a diverse group of synthetic materials made from polymers that offer a wide range of properties such as lightweight, corrosion resistance, electrical insulation, and flexibility. They are widely used in the packaging, automotive, construction, electronics, and medical industries.
Plastics are typically categorized into thermoplastics (which can be remelted and reshaped) and thermosetting plastics (which permanently set after molding). With growing concerns over environmental impact, recycling and biodegradable plastics are gaining increased attention in both industry and research.
FAQs on Plastics
What are plastics made of?
Plastics are made from polymers, which are long chains of molecules derived from petroleum-based chemicals or renewable sources like cornstarch.
What is the difference between thermoplastics and thermosets?
- Thermoplastics can be reheated and reshaped multiple times.
- Thermosetting plastics harden permanently after heating and cannot be remelted.
What are common types of thermoplastics?
- Polyethylene (PE)
- Polypropylene (PP)
- Polyvinyl chloride (PVC)
- Polystyrene (PS)
- Acrylonitrile Butadiene Styrene (ABS)
What are examples of thermosetting plastics?
- Epoxy
- Phenolic
- Melamine
- Bakelite
- Urea-formaldehyde
What are the advantages of plastics?
- Lightweight
- Corrosion-resistant
- Good electrical insulators
- Easy to mold
- Cost-effective
What are the disadvantages of plastics?
- Non-biodegradable (for most types)
- Can degrade under UV exposure
- Potential environmental pollution
- Lower mechanical strength compared to metals in some cases
Can plastics be recycled?
Yes, many thermoplastics are recyclable, though the process depends on the plastic type and local recycling infrastructure. Thermosets are generally not recyclable.
What is the future of plastics?
The future focuses on bioplastics, recyclable materials, and sustainable production to reduce environmental impact.