All You Need to Know About Thermoplastics
Thermoplastics are formed by additional polymerization and are soft and less brittle. They are soluble in organic solvents. On heating the thermoplastics, it gets softer and hence are amenable for molding into any shape in the hot condition, on cooling the reason becomes hard and rigid and retains the molded shape. They can be reheated and molded into any other shape reversibly, any number of times without any change in the chemical nature.
It is the most common term used in polymer chemistry. In this article, we will cover all the important topics such as thermoplastic meaning, thermoplastic uses, characteristics of thermoplastic, and thermoplastic examples.
Characteristics of Thermoplastic
Thermoplastics are generally high molecular weight polymers.
The chains in the polymer are associated with the intermolecular forces.
The intermolecular force acting between the chains becomes weak on increasing temperature and yields a liquid with high viscosity.
These polymers can be reshaped.
These polymers are different from thermosetting polymers because thermosetting polymers do not get melted when heated.
Thermoplastics are recyclable.
These are lightweight and high strength polymers.
They act as flame retardants.
Thermoplastic Examples
Few thermoplastic examples are polyvinyl chloride, polystyrene, polypropylene, and polyethylene.
Polypropylene:
It is made up of monomer propene. It is produced by the chain growth polymerisation reaction mechanism. It belongs to the polyolefins group. It is a non-polar compound and partially crystalline.
Effect of Additives on the Properties of Polypropylene Thermoplastic Polymer
Since polypropylene has a low UV tolerance, additives such as hindered amines stabilize the light and prolong the service life when compared to unmodified polypropylene. Clarifiers, flame retardants, glass fibers, minerals, conductive fillers, lubricants, pigments, and a variety of other polymer additives can enhance the physical and/or mechanical properties of PolyPropylene.
Polypropylene can be divided into two types:
Homo polypropylene
Co polypropylene
Difference Between Homo Polypropylene and Co Polypropylene
Types of Polypropylene Films
Cast Polypropylene Film-
CPP stands for cast polypropylene and is well-known for its versatility. Polypropylene of this form is highly resistant to tears and puncture. They have higher heat tolerance and transparency at high temperatures.
Biaxially Oriented Polypropylene Film-
BOPP is a biaxially oriented polypropylene film that is extended in both the transverse and longitudinal directions, resulting in molecular chain orientation in both directions. This improves the tensile strength and stiffness of the material.
Polyvinyl Chloride-
It is made up of monomer vinyl chloride. It is a high strength material. Its abbreviation is PVC. It is a white-brittle and lightweight solid material.
Polystyrene
It is a polymer made up of a styrene monomer. It contains an aromatic group. It exists in either solid or foamed form. It is hard, clear, and brittle in nature. Its molecular formula is (C8H8)n.
Thermoplastic Uses
Thermoplastic material used in making sports equipment.
It is also used in making toys.
It is used in automobile parts.
It is used in making CDs and DVDs.
Containers like shampoo bottles, drinking bottles, and food storage containers are made up of thermoplastic polymer.
Some of the thermoplastics (polyurethane) are used as a sealant, adhesives, and coating material.
Disadvantages of Some Thermoplastic Polymers are:
The UV, effects, and scratch resistance is low for thermoplastic polymers.
Under -20°C, thermoplastic polymer embrittles
90 - 120°C is a low upper service temperature for thermoplastic polymers.
Thermoplastic polymer shows Paint adhesion problems
These types of polymers swell quickly in chlorinated solvents and aromatics when attacked by strongly oxidizing acids.
Action with metals has a negative impact on heat-aging stability.
Dimensional changes after molding due to crystallinity effects are observed in these polymers.
Did You Know?
Polyvinyl chloride is the world's third most widely produced synthetic plastic polymer.
Some of the thermoplastic can melt in direct sunlight.
Most thermoplastics show higher fatigue properties than metals. Therefore, it can tolerate higher deflections than metal.
FAQs on Thermoplastic Polymers
1. What is a thermoplastic polymer?
A thermoplastic polymer is a type of plastic that becomes soft and mouldable when heated and solidifies upon cooling. This process is reversible, meaning they can be reheated and reshaped multiple times without significant chemical degradation. This property is due to their molecular structure, which consists of long, linear chains with weak intermolecular forces (like van der Waals forces) holding them together.
2. What are the key characteristics of thermoplastics?
Thermoplastics exhibit several distinct characteristics that make them useful for various applications:
- Reusability and Recyclability: They can be melted and reshaped, making them easily recyclable.
- Solubility: They are generally soluble in specific organic solvents.
- Mechanical Properties: They possess high strength and are lightweight, though they can become brittle at very low temperatures.
- Chemical Resistance: They show good resistance to many chemicals but can be attacked by strong oxidising acids and certain organic solvents.
- Formation: They are typically formed through addition polymerisation.
3. What are some common examples of thermoplastic polymers?
Several thermoplastic polymers are widely used in daily life. Some common examples include:
- Polyethylene (PE): Used for plastic bags, bottles, and packaging films.
- Polypropylene (PP): Used in automotive parts, containers, and textiles.
- Polyvinyl Chloride (PVC): Used for pipes, window frames, and electrical wire insulation.
- Polystyrene (PS): Used in disposable cups, insulation, and packaging material.
- Polyethylene terephthalate (PET): Used for making beverage bottles and polyester fibres.
4. How do thermoplastic polymers differ from thermosetting polymers?
The primary difference lies in their behaviour when heated, which stems from their molecular structure. Thermoplastics have linear or lightly branched polymer chains held by weak intermolecular forces that break upon heating, allowing the plastic to melt and be remoulded. In contrast, thermosetting polymers have a three-dimensional network structure with strong covalent cross-links. When heated for the first time, these cross-links form, and the polymer sets permanently. It will not melt upon reheating; instead, it will char and decompose.
5. What happens at a molecular level when a thermoplastic is heated and cooled?
When a thermoplastic is heated, the thermal energy supplied overcomes the weak intermolecular forces that hold the long polymer chains together. This allows the chains to slide past one another, causing the material to soften and melt into a viscous liquid. When it is cooled, the chains slow down, and the intermolecular forces re-establish themselves, locking the chains back into a rigid solid state. This physical change, not a chemical one, is why the process is reversible.
6. What are some common real-world uses of thermoplastic materials?
Thermoplastics are used across numerous industries due to their versatility. Common applications include:
- Packaging: Food containers, shampoo bottles, and plastic wrap.
- Automotive: Bumpers, dashboards, and other interior parts.
- Consumer Goods: Toys, sports equipment, chairs, and electronic casings.
- Construction: Pipes, window frames, flooring, and insulation for wires and cables.
- Medical: Syringes, tubing, and implantable devices.
7. Why are thermoplastics considered recyclable?
Thermoplastics are considered recyclable because of their fundamental property of being able to melt and resolidify without undergoing chemical change. The recycling process involves collecting, sorting, shredding, and cleaning the plastic waste. It is then melted down and reformed into pellets, which can be used as raw material to manufacture new products. This ability to reverse the solid-to-liquid state transition is not possible with thermosetting plastics, which cannot be re-melted.
8. What are the main disadvantages of thermoplastic polymers?
Despite their advantages, thermoplastics have certain limitations. They generally have a lower upper service temperature compared to thermosetting plastics and metals, meaning they can soften or deform in high-heat environments. They can also exhibit poor resistance to UV radiation, which can make them brittle over time if not treated with stabilisers. Additionally, many thermoplastics are susceptible to swelling or dissolving when exposed to certain chlorinated solvents and aromatic compounds.
