Getting rid of stains? Rinsing — not detergent — is key, UH study finds

(Image: Hawaii News Now)
(Image: Hawaii News Now)

MANOA, OAHU (HawaiiNewsNow) - It's a chore we do without thinking much about how it works: Dirty laundry goes into a washing machine and comes out clean.

Ian Rutka does a lot of laundry at Kapahulu Xpress Laundromat.

He thinks the quality of the washing machine and detergent are the most important things in the laundry process.

"I was always under the impression that it was beginning with all the soap and detergent," he said.

Gloria Lewis, of Makiki, agrees.

"The laundry soap or laundry detergent," she said.

Well, not quite.

University of Hawaii mechanical engineering professor Sangwoo Shin actually studied how dirty clothes get clean and published the results in a new study that's getting a lot of attention.

Turns out, detergent isn't the key to clean clothes.

"A general understanding is that particles are removed from fabric during the washing process, but what we have found out is it's the rinsing process that is responsible for cleaning your fabric," he said.

Shin worked eight months on an experiment. He used soiled pieces of cloth, soapy water and an agitator filled with fresh water to replicate the laundry cycle. He learned detergents don't wash away dirt and stains.

"Detergent is only responsible for loosening the particles from your fabric," he said.

His study showed that soiled fabric is completely cleaned only after it goes through the rinse cycle.

Shin's discovery is actually a pretty big deal. It could be used to develop more efficient detergents.

Princeton University and detergent maker Unilever partnered on the experiment.

Shin thinks his discovery is useful beyond laundry to the skin care and petroleum industries. He's on to the next phase of his research.

"The next step would be to think about what would be the optimal laundry process that could further enhance your cleaning," he said.

Shin's findings were just published in the scientific journal Physical Review Applied.

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