Pipes & Plastics in the Sun

[Spinny]

Now the daylight is stronger and longer, does anyone know what the position is with pipes and plastics left outside and UV degradation ?

 

I currently have the following uncovered:

MDPE ends coiled outside where they come up out of the ground.

Some spare end of coil MDPE barrier pipe lying about

Multiple lengths of 110 underground drainage pipe lying outside.

Some black and other plastic type sheeting

Some black pipe fittings/silt trap

Some black sheathed network cable exposed

Some lengths of black covered armoured cable exposed

 

(I long ago covered over all tail ends of plastic membrane like radon membrane etc that stick out, until they get cut off at the right length.)

 

 

Edited April 20 by Spinny

[JohnMo]

Mdpe is fine, just look in most farmers field, mdpe pipe been there for decades.

 

Underground plastic drain pipe will turn white and may go brittle.

 

Armour cables generally UV stable.

[SteamyTea]

How timely, from this weeks comic.

 

Why do plastic clothes pegs fade and get brittle in the sun?

One reader draws on his chemistry days to explain why some types of plastic become fragile after exposure to ultraviolet light

 

16 April 2025

Caroline Burrows/Alamy

 

Last Word is New Scientist’s long-running series in which readers give scientific answers to each other’s questions, ranging from the minutiae of everyday life to absurd astronomical hypotheticals. To answer a question or ask a new one, email lastword@newscientist.com

I recently bought plastic multi-coloured clothes pegs, which have slowly disintegrated in the sun except for the yellow ones. Why?

Peter Holness

Hertford, Hertfordshire, UK

The phenomenon that destroyed the non-yellow clothes pegs is called “unzipping”. Many years ago, a chemistry colleague told me about it. His explanation was that the sun emits high-energy photons capable of breaking chemical bonds. This explains things like sunburn and curtains faded by sunlight.

Most plastics are polymers, which are made from smaller units called monomers that link together through chemical bonds. Polyvinyl chloride (PVC), for example, consists of repeating vinyl chloride subunits. In turn, the subunits consist of carbon, hydrogen and chlorine atoms. Sunlight has been known to unzip PVC by dislodging hydrogen and chlorine atoms, creating hydrochloric acid and causing further erosion of plastic subunits. Unzipping potentially affects other plastics, too. It can be slowed or prevented by introducing certain chemical additives to the material. So, one possible explanation for the survival of the reader’s yellow pegs is stabilising additions of this sort.

Another explanation for the disintegrating pegs involves both light absorption and heat. The colour of the plastic affects the amount of light reflected or absorbed, and hence heat, with darker colours absorbing more than lighter shades, such as yellow. But without chemical and spectroscopic analysis, it is impossible to know whether the reader’s yellow pegs were protected by their colour or additives, or perhaps a combination of both.