The Christmas-iest molecule – PVC?

Boom Advent #2 – Molecular Madness

Christmas is a festival of the senses. There are the sights of Christmas decorations hanging in our house and the lights sparkling through the cold, dark nights, and who can forget the Christmas tree? There are the wonderful smells and tastes of a fabulous selection of food and drink from mulled wine to turkey and mince pies to chocolate. All around us we hear the sounds of people singing carols, the ringing of bells and the bang of Christmas crackers. We can also touch Christmas, the feel of wrapping paper as we tear it off presents, the bristles of pine on a spruce fir and the cold, mush of snow. There are so many ways to experience the festival season. Let’s take a look at a molecule that makes Christmas – our first one is PVC!

This is molecular madness!

Tinsel Claus

A popular decoration used around the house is tinsel. We put around the Christmas tree, around picture frames or hang it across the ceiling. There are so many colours as well: silver, gold, red, blue, green, purple, yellow, white, and that’s before we include multi-coloured ones! Tinsel is meant to look like ice – at least that was the original idea.

Tinsel is much older than you might think. Modern tinsel was first used in the German city of Nuremberg in the 1600s. They were originally made of silver and the shiny metal really did help to make it look like ice. Unfortunately, silver can become dull over time and is also very expensive. However, tinsel remained popular and by the start of the 1900s, tinsel was being made of aluminium and used everywhere at Christmas.  There was even a period where lead foil was used! Luckily, this is no longer the case. You can read more about the history of tinsel here.

All I see is PVC

Modern day tinsel is made of substance called polyvinyl chloride (PVC). PVC is a plastic and one of the most widely produced plastics. However, to give tinsel a more shiny appearance, it is often coated to make it look shiny and metal like.

Plastics are a type of polymers. Polymers are very large molecules made up of repeating units. For example, I could connect a lot of As together to form a chain of them.

A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A

You can see that we have formed a very large molecule, made up of lots of As joined together. Polymers can be natural. Natural polymers include silk, wool and even DNA. However, it is the man-made polymers that we use every day. These include nylon and many, many, plastics.

Polyvinyl chloride is a plastic polymer made up of lots of molecules joined together. We call the individual molecule a monomer. We can often determine the monomer by removing the “poly” from its name. So the monomer of polyvinyl chloride is simply called vinyl chloride. The more modern name is chloroethene. 

Double Trouble

The structure of chloroethene is shown below. It is a very simple molecule containing two carbon atoms connected by a double bond. The double bond is very important for creating the polymer. One carbon is also bonded to two hydrogen atoms. The other carbon is bonded to one hydrogen atom and one chlorine atom.

Lots of these vinyl chloride molecules can be reacted together. This process is known as polymerization. In simple terms, the reaction causes the carbon double bond to break. This allows each carbon atom to bond to the carbon atom of another molecule. This reaction repeats and repeats forming longer and longer chains. We can see this process below.

We’ve looked at some polymers before – whether it’s proteins found in spider silk or the rapid polymerisation that makes superglue set – so have a look at those articles too!

Who’s a pretty polly-mer?

There are many different ways to perform this reaction. There are also many different ways to start the process off. Simply having a container of chloroethene is not enough. We often require another molecule or some condition to start to process. However, the exact process involved is complicated.

In its pure form, PVC is white and rather brittle. This is certainly very different to the soft and bendy behaviour of tinsel. What’s going on? How do we take this PVC molecule to Tinseltown for Christmas? Well, in order to change the properties of PVC other substances are often added. These are known as additives.

Add a little bit of this

An important additive is plasticizers. Don’t worry about the name, the most important to know is that these additives help to make the PVC softer and more bendy. Tinsel made from PVC would not be very good if you were unable to bend it. Worse still, imagine if every time you tried to bend it, it just snapped!

Heat stabilizers are often added to PVC as well. These help to reduce the amount the plastic wears away when it gets hot. At high temperatures, PVC can start to lose molecules of hydrogen chloride (HCl).

PVC is a good electrical insulator and also resistant to most other chemicals. These properties make it ideal for other uses such as pipes and electrical cables. PVC is also water resistant, and so is used for water- resistant clothing.

Plastics are for life (and beyond)

Like so many plastics, there is a real concern about how to dispose of PVC. A plastic PVC molecule is for life, not just for Christmas! The effect of plastics on the environment is a major concern.

There are a lot of recycling symbols and it can be really difficult to tell whether or not we can do our bit to be green! Especially at Christmas when there is so much packaging flying around. Even some wrapping paper can’t be recycled…

Recycle plastic and a PVC molecule or two this Christmas!

So which of these symbols could apply to our Christmas molecule PVC?

Well the top left one with the three ‘chasing arrows’ in a triangle with a ‘3’ in the middle is specific to PVC so if you said that one well done! The chasing arrows mean that the material can be recycled and the 3 refers to PVC itself. The black and white symbol in a circle means the company producing the product funds recycling schemes but this product is not recyclable itself. The one with ‘alu’ in the middle is a total red herring – it means the product is alumnium which is almost infinitely recyclable. The other two symbols – the green circular arrow and the green triangle ‘chasing arrows’ both mean that a product can be recycled.

 Plastics are all around us. Nearly every part of our lives involves plastics in some way. But if that isn’t enough, even more plastics come out at Christmas. So many decorations, presents, wire cables and other items are made of plastic. Tinsel is no exception.

However, while plastics are wonderful substances there are also massive concerns about them. Enjoy the festive season, marvel at the decorations and the wonder of plastics, but just be mindful of how much plastic you are using, wasting and how we can cut back.