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Plastic remains one of our most serious environmental pollutants. Small plastics such as bottle caps, medicine containers and bread clips are found in thousands of consumer products. Bottle tops come in a range of different sizes and colours and are often embossed with a company logo or some other design. Bottle caps are manufactured by high speed injection moulding. 

The main constituents used in the manufacture of bottle caps include:

PET – polyethylene terephthalate – lightweight and strong and used in soft drink and water bottles. 

HDPE – high density polyethylene – tough, stiff and lightweight.

LDPE – low density polyethylene – flexible and good impact strength.

PP – polypropylene – a hard and rugged plastic used in many bottle caps. 

What is polyethylene?

Polyethylene is the most common type of plastic found in most packaging products including plastic bags. Over 100 million tons of polyethylene plastic is produced annually and accounts for over 34% of all plastic produced. Polyethylene is made from hydrocarbons (the main constituents of petroleum and gas) and various chemical additives to give the plastic certain strengths and characteristics. 

There are two main types – low density polyethylene is extruded using high pressure and high temperatures whilst high density polyethylene is extruded using low pressure and low temperatures. 

Polyethylene plastics are not biodegradable but can be collected and recycled. However, some bacteria can feed on polyethylene plastic under certain conditions and can slowly break down the plastics. Daniel Burd, in May 2008, won the Canada-Wide Science Fair after discovering that a bacteria Pseudomonas fluorescens together with Sphingomonas can degrade up to 40% the weight of plastic bags within six weeks. A Chinese researcher also discovered by accident that the Indian mealmoth Plodia interpunctella is also capable of ingesting plastic and has bacteria in the gut able to break down the plastic particles. Research into this field is ongoing. 

The European Union has set down recent legislation pertaining to single-use plastics under Directive (EU) 2019/904. This Directive aims to ensure manufacturers produce plastics subject to product requirements and standardized for recycling purposes. There will also be a requirement for separate collection of plastic bottles and their lids. 

Home recycling

I tend to remove all caps and small plastic tags and store them separately in a large empty water container. This way these small plastics don’t make their way into a landfill site. As an added precaution, I cut all plastic rings as these are commonly found entangled in a range of wildlife including birds. It is important to note that recently, some soft-drink manufacturers have written instructions on the bottle cap for it to be replaced. This is to prevent it from being discarded. However, if responsibly removed and stored with other small plastics, then these, together with the other plastics, can be dropped off at a recycling collection point. In future articles we will investigate this aspect further. 

It is not only bottle caps and rings that fall into this category of small plastics, but also a range of other small plastic items. These include plastic bread clips, vitamin and medicine containers, contact lens containers, milk bottle caps (including those of aluminium sealed cardboard cartons) and many other types. 

Most bottle caps and small plastics are manufactured from high density polyethylene which can be recycled.

Some softdrink bottle caps come with the instruction to replace the cap after use so that it is not discarded into the environment.
The inside of a bottle cap showing the plastic constituent HDPE and recycling symbol.
Safely contained. A variety of small plastic clips and bottle caps are kept from filtering into the environment.

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