The Chemistry of Lego
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Lego is one of the most popular and instantly recognisable childhood toys out there. Have you ever wondered what those bricks are made of, or how they’re made? Or, for that matter, why it hurts so much if you tread on one? This graphic takes a look!

Lego bricks have always been made of plastic, but it’s not always been the same kind of plastic. From 1949 until 1963, cellulose acetate was the polymer used. This is the same substance that was once used in the movie industry for films. It’s also used in the plastic frames of some eyeglasses to this day.
In 1963, Lego changed the plastic their bricks were made from to another polymer, acrylonitrile butadiene styrene (ABS for short). ABS has several advantages over cellulose acetate: it’s stronger, warps less over time, and is more resistant to colour fading. The only downside was that, unlike cellulose acetate, ABS is opaque, so transparent Lego parts can’t be made from it. In these cases, a polycarbonate plastic is now used instead. To get the various colours of Lego pieces, Macrolex dyes are added to the ABS.
The Lego manufacturing process starts with tiny granules of ABS, brought by the lorry-load to factories. Here, they’re dumped into giant metal silos, then fed into molding machines where they’re heated to 230˚C (450˚F). This melts the granules, producing a plastic goo which is automatically fed into Lego part molds. The molding machine applies pressure to ensure that the Lego parts are perfectly formed, then they’re cooled and ejected. After this, any necessary decorations are added, and parts that need to be put together, such as mini figures, are assembled.
In 2014, Lego manufactured an astonishing 60 billion parts. Of these parts, at least 318 million are miniature tyres for Lego vehicles – making Lego the biggest tyre manufacturer in the world! These tyres are made from a slightly different polymer to ABS, styrene butadiene styrene (SBS).
When it comes to the pain experienced when you tread on a piece of Lego, ABS is to blame. Lego test pieces during the manufacturing process as part of Lego’s quality control measures. Tests include compression between discs with a force of 15 kilograms, and dropping objects on bricks to ensure they don’t break on impact. One test even simulates a 50-kilogram child stepping on a Lego piece to ensure it inflicts maximum pain doesn’t break or splinter. The average force a 2×2 Lego piece can withstand is 4,240 Newtons – equivalent to being stood on by someone weighing around 430 kilograms. In short, Lego bricks are essentially designed to be painful to tread on.
Lego has other risks as well as being a stepping-hazard. Older Lego bricks from the 1970s and 80s contained cadmium to help the colouring of red and yellow bricks. Those with some chemistry knowledge will know that cadmium and its compounds are poisonous and can have toxic effects. Research has shown that cadmium levels in these older bricks are above the current EU limits. It’s important to put this in context of the amounts, which are at microgram levels. Handling these old bricks poses a minimal exposure risk, but you might want to refrain from putting them in your mouth! Lego phased out cadmium as its toxic nature became apparent, and newer Lego bricks do not contain it.
There’s one other issue with all Lego pieces: they’re made from oil-derived plastics. Oil is a finite resource, and making Lego from oil has a significant environmental impact. In 2012, the Lego group set itself a target of finding and using more sustainable raw materials for its products by 2030. They took a small step towards this goal earlier this year, announcing that from this year onwards the green leaves, bushes, and trees in their products will be made from polyethene derived from sustainable sugar cane sources. This polyethene is nowhere near strong or durable enough to replace ABS, however, so the search for its replacement continues.
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