What is a Polymer?

Every material or substance is made up of molecules. Molecules can be micro molecules or macromolecules. Micro molecules are smaller molecules or the individual molecules that make up the material. When micro molecules are combined, a macromolecule is formed.

Polymers are substances that are formed by repeated combinations of macromolecules. A strong covalent bond forms between the individual molecules of the polymers. The most common example of polymers is plastic. Other examples include polyethylene and packaging wraps.

Products made out of plastics are harmful to the environment, as they require hundreds of years to decompose. Hence, there is a need for recycling plastics and plastic waste in order to reduce the damages caused to the environment.

Types and Properties of plastics

Plastics are materials that may be synthetic or non-synthetic, but polymers are the primary constituent of macro-molecular chains found in them. Plastics are difficult for the environment to decompose because it takes almost two hundred years for a single plastic material to decompose into the soil. Moreover, plastics are affected strongly by the sunlight and release harmful chemical substances. Also, the fumes released during burning plastics are composed of toxic chemicals that are dangerous for living beings. Hence, to destroy plastics, burning them is not a good choice. The only effective means available is to recycle plastics products and plastic wastes.

There are various kinds of plastics based on the chemical composition and the nature of polymer linkages. Some of the classifications include acrylonitrile-butadiene-styrene (ABS), polylactic acid (PLA), polyethylene, polyurethane, ethylene terephthalate, transparent packaging wrappers, silicones, polyesters, and so on. According to the chemical processes used for plastics manufacturing, plastics can be classified as condensation, polyaddition, and cross-linked plastics. Plastics are also classified based on their mechanical properties. Some of the mechanical properties include hardness, tensile strength, and glass transition temperatures. There are other mechanical properties as well based on the polymer types, relevant polymerization, and depolymerization. Apart from these, polymer plastics can be biodegradable and non-biodegradable.

A cross-linked polymer
CC0 1.0 | Image Credits: https://commons.wikimedia.org | Roland. Chem

Plastic recycling

The general meaning of the term 'plastic recycling' is to reprocess or recycle an existing plastic product into useful and meaningful products. Generally, the recycling of plastic waste is considered a major concern. Recycling plastic waste has an added advantage because it reduces the usage of landfills, which are regarded as the areas where used plastics and other polymer-based waste products are dumped. This leads to increased environmental pollution.

There are various ways of plastic recycling, two of the most common ways to recycle plastic wastes are

  1. Traditional recycling
  2. Advanced recycling

Traditional recycling

In the traditional recycling way to recycle plastics, mostly the thermoplastics such as high-density and low-density polyethylene are used. A different name for the traditional way of recycling is mechanical recycling. In this method to recycle plastic, the plastic waste is melted and made into pellets, which are processed further to make new and meaningful components through the injection molding process in the plastics industry.

Advanced recycling

In the advanced recycling technique to recycle plastic, it is broken down into its constituent compositions, known as downcycling. They are broadly divided into three categories. They are pyrolysis, recycling through chemical means, and the gasification recycling process. In the pyrolysis technique, the waste is converted to crude oils through relevant chemical processes. The chemical process causes the end-of-life of the polymer associated with the plastic waste. The polymers are turned into monomers in the process. In the gasification process, the post-industrial plastic waste is turned into a gaseous phase, which is used to produce energy.

Plastics are composed of polymers, where these polymers are unstable in nature. The stability of the polymer chains can be enhanced by adding foreign substances. This process is known as the compatibility of polymers. This aids in polymer chains stability and enhances the mechanical properties.

Recycled plastic products

Some of the plastic products that are created after recycling plastics are:

  • Packaging wraps: Packaging wraps are thin transparent plastic substances that are used in every industry for packaging and sealing purposes.
  • Plastic containers: These are created from recycled plastic pellets. These pellets are fed to the injection molding machine, the pellets are melted and injected into a die that has the shape of the required product.
  • Mobile phone cases.
  • Decorative interior items.
  • Water bottles.
  • Kitchen wares.
  • Garbage bags and drums, and so on.

Context and Applications

The topic is extensively taught in undergraduate courses of bachelor of science, primarily in the chemistry, physics, and material science domain. The related concepts of the topic are majorly used in the plastic industries that make plastics products and practice plastic recycling.

  • Bachelors in Technology (Mechanical)
  • Masters in Technology (Mechanical)
  • Bachelors in Science in Chemistry
  • Masters in Science in Chemistry

Practice Problems

1. Which of the following processes turns the plastic waste into a gaseous phase that can be used to produce energy?

  1. Mechanical process
  2. Pyrolysis
  3. Gasification
  4. Injection molding

Correct option- c

Explanation: The by-products from the plastic industry are converted to gas, which is then burned to produce energy. This process is known as gasification.

2. Which of the following processes uses plastic pellets to produce useful products?

  1. Pyrolysis
  2. Chemical process
  3. Polymerization
  4. Injection molding

Correct option- d

Explanation: In the injection molding process, the pellets made from melting waste plastics are fed into a hopper of an injection molding machine, where it is re-melted and forced inside a die. The die has the shape of the required product. Upon cooling, the plastic acquires the shape of the die.

3. Which of the following is true for downcycling?

  1. It is a chemical process.
  2. It is used for recycling plastics.
  3. The process breaks down the plastic into its constituent substances.
  4. All of these

Correct option- d

Explanation: Downcycling is a chemical process that breaks down plastic into its constituent substances.

4. Which of the following is true for polymers?

  1. They are long chains of macromolecules.
  2. They are composed of micro molecule chains.
  3. They are made up of short hydrocarbon chains.
  4. None of these

Correct option- a

Explanation: Polymers are long chains of macromolecules.

5. Which of the following is an example of plastic?

  1. Acrylics
  2. Polyurethane
  3. Polyethylene
  4. All of these

Correct option- d

Explanation: Polyurethane, polyethylene, and acrylics are all examples of plastics.

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