Is it true that rubber gaskets in a dishwasher will crack if unused?

Submitted by iamaparttimemonster t3_104fy2l in askscience

I've found this claim repeated all across the Internet: that if unused for years or months (a site even says weeks!), the rubber gaskets and seals (some sources mention specifically in the motor) will "dry up and crack", leading to leaks once it's used again.

I find this a bit difficult to believe. I know UV radiation can cause cracking in rubber and plastic, but dryness? That may be the case with some kinds of sponges, but afaik rubber gaskets or seals don't need to be moist to retain elasticity. Besides, the outer side of the gasket should be dry even when the machine is used.

Is there a scientific basis for this that I'm missing, or it's a legend that people just hear and repeat?

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ttkciar t1_j35gt9s wrote

If the gaskets are made of natural latex rubber (without intensive cross-linking as seen in automobile tires), then they will grow brittle and crack if they dry out too much.

Gaskets are traditionally made from natural latex rubber, but nowadays PU and PVC are frequently used, which are not susceptible to drying out but can grow brittle eventually (several years) anyway.

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Indemnity4 t1_j3jvczh wrote

Rubber "corrosion" is similar to iron rust. More corrosion makes even more corrosion. You need to keep removing any hard or corroded segments to keep the underlying material good.

Storage environment is one of the biggest factors for lifetime of rubber seals. Some will fail via getting harder and others fail by getting softer.

Some of the types of rubber are degrading from the day they are manufactured. It can be trace amount of metal catalysts, free radicals or simply environmental oxygen, moisture, stress.

Failing soft. The way elastomers are made involves a chemical method called polymerisation. It's kind of a special type of zipper - it zips closed to make the elastomer but it can be triggered to unzip back to starting materials. That's where rubbers can fail soft.

Failing hard: A rubber when looked at under a microscope is like lots of little hairs all aligned. When it is sitting there static, some of those hairs will start to cross-link (e.g. you get a knot in your hair or some loose cables in your junk drawer form a knot). This can be residual free radicals (or oxygen induced radicals) that grab hold of the nearest neighbouring strand to make themselves stable. But similar to a relay race, that free radical never goes away, it just gets passed along the chain to the next open spot - then that crosslinks to another strand. Once you have too many knots in your hair or your Christmas lights are tangled up, it turns into a hard non-elastomeric mess.

Using the rubber gasket does involve mechanical/thermal stresses. It will be getting pushed or pulled. Any tiny hard sections will be ground away like a sacrificial layer. It keeps the majority of the seal elastomeric. Unfortunately, leave it static too long and those hard sections will get large.

Other places you see rubber degrading: knife handles getting sticky, plastic toys yellowing with age, shoe soles cracking when not worn, rubber car tyres softening in storage sheds, latex / synthetic clothing turning brittle in the back of your cupboard unworn. A gasket is no different.

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[deleted] t1_j39ix8i wrote

[deleted]

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PhiliFlyer t1_j3aelpb wrote

This is not true. Plasticizers are generally not used in elastomeric seals (nor tires as in your previous reply). Elastomers (of which natural rubber is a member) embrittle due to oxidation and thermal degradation. In the case of polyurethane elastomers, water hydrolysis can cause degradation.

Leaving a dishwasher unused will actually prolong the life of the seals since there is less exposure to water, oils, and oxygen at high temperatures.

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toxicexpectorant t1_j36ktzi wrote

Absolutely it can. Can't give you the scientific explanation but i can all but guarantee that if you let a dishwasher sit for 2 years without any use then try and run it it'll leak like a sieve. Found this to be true with taps as well. A lot of times you go to repair a dishwasher/washing machine and the tap will leak from the stem when you go to turn it off/back on. I think this may be due more to constant pressure on a single point than dryness for the taps if i had to guess though.

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