Polymers are everywhere in our daily lives! From the clothes we wear to the pens we use, they are super important. But do you ever wonder what happens to them when we're done with them?

Well, we have a few options for getting rid of polymers. It depends on whether they're biodegradable or not. Biodegradable means that they can break down naturally over time. This article is all about biodegradability in chemistry. We'll start by explaining what it means. Then, we'll talk about how some chemical polymers can biodegrade, while others can't. Finally, we'll look at different ways to dispose of polymers and weigh their pros and cons. So, let's dive in and learn about biodegradability!

Biodegradable meaning

When we're done using a polymer, we want to make sure we don't waste anything. A polymer is made up of small parts called monomers, and we want to reclaim as many of these as possible. To do this, we need to break the bonds holding them in place. This is where biodegradation comes in.

Biodegradation is when living organisms called decomposers break down a substance into smaller pieces. If a substance can be broken down in this way, it's biodegradable. Some polymers are biodegradable, while others are not. Let's focus on biodegradable polymers and how they can be broken down naturally.

Biodegradable polymers

In chemistry, there are two main types of polymers: addition polymers and condensation polymers. Addition polymers are not biodegradable, but condensation polymers are.

Condensation polymers are formed when monomers with two different functional groups undergo a condensation reaction. This creates a long polymer chain and releases a small molecule, like water. If we want to break down a condensation polymer, we can use hydrolysis. Hydrolysis involves adding water to the polymer, but it's a slow reaction. However, if we use a catalyst like an acid or alkali, the reaction happens faster. Some living organisms have these catalysts and can biodegrade condensation polymers. There are two main groups of condensation polymers: polyesters and polyamides. Nylon is an example of a biodegradable polyamide, and we'll look at it in more detail later. But first, let's learn more about polyesters and their biodegradability.

Biodegradability of polyamides

Polyamides are a type of condensation polymer made in a condensation reaction between an amine and a carboxylic acid. This reaction releases water. The resulting polymer contains the amide functional group, -NHCO-. The polymer can be broken back down into its monomers in a hydrolysis reaction like the one we described above, using an acid or an alkali as a catalyst.

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Nylon is a polyamide. It is made industrially from 1,6-diaminohexane and hexane-1,6-dicarboxylic acid (also known as hexanedioic acid). Like all polyamides, it is biodegradable and breaks down in a hydrolysis reaction. The reaction is slow, but is dramatically sped up using an acid catalyst.

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Biodegradability of polyesters

Polyesters are another type of condensation polymer made in a condensation reaction between an alcohol and a carboxylic acid. They contain the ester functional group, -COO-. Once again, the condensation reaction releases water. The polymer can be broken down in a hydrolysis reaction with an acid or alkali catalyst.

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It's interesting to note that polyesters and polyamides can also degrade under the influence of light, a process known as photodegradation. UV radiation from the sun interacts with the bonds in the polymer, creating highly reactive free radicals that react with oxygen in the atmosphere. This weakens the polymer and makes it more brittle, eventually breaking it down into smaller pieces. However, the biodegradation process of polyamides and polyesters isn't quick or easy. It requires specific conditions such as light, water, oxygen, and temperature levels for the living organisms responsible for biodegradation by hydrolysis to work effectively. Even photodegradation is a slow process, so throwing a piece of nylon fabric on the ground outside and leaving it for a couple of months may not lead to complete biodegradation.

Non-biodegradable polymers

It's important to note that addition polymers are not biodegradable, unlike condensation polymers. These polymers are made up of many identical monomers, which join together in a long chain with a C-C backbone. The C-C bond is strong and non-polar, making it difficult for any living organism to break it down - even with a catalyst. This resistance to biodegradation is what makes addition polymers non-biodegradable. As a result, they can accumulate in the environment and pose a threat to wildlife and ecosystems if not properly disposed of.

Polyalkenes

Polyalkenes are a type of addition polymer. They're made from alkene monomers and are based on many strong C-C and C-H bonds. Because of this, they can't be broken down easily and don't biodegrade.

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Disposal of polymers

Learning about polyalkenes and their resistance to biodegradation brings up one big question: how else can we dispose of polymers? Getting rid of them can be done in one of three main ways. Disposal in landfill site sIncineration Cracking Recycling, Unfortunately, none of these methods are ideal, and they each have their pros and cons. Let's start with landfill sites.

Disposal in landfill sites

It's alarming to hear that in 2016, 24 percent of the UK's waste was sent to landfill sites. These sites are essentially areas of land where rubbish is dumped, either in large piles or holes in the ground. While they do keep waste together in one location, they have significant drawbacks. For instance, polyesters and polyamides slowly biodegrade in landfill sites due to the anaerobic conditions, which release a lot of methane into the atmosphere. Additionally, these sites are unsightly, emit unpleasant odors, and take up a lot of land. Worse still, toxic chemicals present in the waste polymers can seep into the environment, contaminating the soil, water, and air in the surrounding area. It's clear that we need to find more sustainable and eco-friendly solutions for managing waste.

Incineration

Another way of getting rid of waste is by burning it: incineration. Incineration is quick, saves on space, and even releases useful energy, but has its drawbacks as well. For example, burning polyalkenes releases carbon dioxide, a greenhouse gas, whilst burning other polymers can release toxic chemicals such as styrene vapour or hydrochloric acid.

Cracking

In the article "Cracking (Chemistry)," we learn how long-chain alkanes can be broken down into shorter, more useful alkanes and alkenes through a process called cracking. Interestingly, this process can also be used for polyalkenes since they are essentially very long alkane chains. One of the benefits of cracking is that it's more energy-efficient than incineration. Unlike recycling, it can also be used for mixtures of dirty or impure polymers, making it a more versatile option. By breaking down these long-chain polymers into shorter, more useful ones, we can reduce waste and create new materials for various industries. However, it's essential to find sustainable and eco-friendly methods for these processes to minimize their impact on the environment.

Recycling

Recycling is a popular method for managing waste, especially when it comes to plastics. This process involves melting and remoulding polymers to create new products. One of the primary benefits of recycling is that it helps us save raw materials by reducing the need to produce more polymers, which typically come from the finite resource, crude oil. Additionally, recycling releases less carbon dioxide into the atmosphere than incineration, making it a more eco-friendly option. However, it's worth noting that most polymers can only be recycled a handful of times since their polymer chains break down with each subsequent melting and remoulding. Moreover, sorting and processing waste for recycling is a costly and time-consuming process that requires significant infrastructure and resources. As such, we need to explore more sustainable and efficient ways of recycling to reduce waste and create a more circular economy.

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Biodegradability - Key takeaways

Biodegradable substances are becoming increasingly popular due to their eco-friendliness, and they can be broken down naturally by living organisms. Among the biodegradable polymers are condensation polymers such as polyamides and polyesters. These can be broken down through a hydrolysis reaction, which is a slow process, but it can be accelerated by adding an acid or alkali catalyst. However, addition polymers such as polyalkenes are not biodegradable because of their strong, non-polar C-C bonds. When it comes to disposing of non-biodegradable polymers, alternative methods include burying them in landfill sites, incineration, cracking, and recycling. Each of these methods has its benefits and drawbacks, and it's essential to consider the environmental impact of each method to make the most sustainable decisions.

Biodegradability

What are biodegradable materials?

Biodegradable materials are materials that can be naturally broken down due to their chemical structures, which allow their bonds to be easily broken. Examples include food refuse and condensation polymers.

Is nylon biodegradable?

Nylon is biodegradable because it is a condensation polymer that has polar bonds which can be attacked by nucleophiles. 

Is polyethylene biodegradable?

Polyethylene is not biodegradable. The covalent bonds that hold it together are non-polar, and are therefore very stable and unreactive.

What does biodegradable mean?

Biodegradable means that a compound can be broken down through natural processes such as decay by microorganisms.

What is an example of a biodegradable product?

An example of a biodegradable product is food refuse. This can be broken down by microorganisms.

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