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Author Topic: Why do only my clean, dry bath towels get hot when I dry off with them?  (Read 10690 times)

Offline John Burnap

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This has bugged me for years. I have noticed that only my clean bath towels seem to get hot when I dry off with them. Is there an exothermic reaction going on? Perhaps the clothes dryer (endothermic) has something to do with it?


 

Offline Geezer

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You must be creating a lot of friction by rubbing them too hard on your skin :)
 

Offline John Burnap

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Only towels that have gone through the dryer do it. And yes, they have cooled off before I use them.

So, it seems that somehow the towel is storing the heat from the dryer, and the heat is released when the towel gets wet.

In some heating pads, Sodium Acetate crystals can be heated and become a supersaturated liquid. When cooled it will remain a liquid until a catalytic reaction takes place to crystallize it and it subsequently gives off heat. Maybe the towel, fabric softener or something is storing the heat of the dryer and the water is the catalyst to trigger an exothermic reaction.

I know what I feel and its not friction. The towel has a marked increase in temperature when it gets wet.

Thank you!
« Last Edit: 25/07/2012 06:36:15 by John Burnap »
 

Offline John Burnap

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I just found this pertinent information:

Plaster of Paris is created when gypsum is heated to 150˚ C. At this temperature, the mineral partially dehydrates, with 75% of the water content escaping as water vapor. This is an endothermic reaction. When water is re-added to plaster of Paris, it resets itself as a gypsum crystal lattice and undergoes an exothermic reaction, which creates heat.

Interesting don't you think?
 

Offline peppercorn

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Perhaps a towel from the dryer is actually quite a bit drier than an air-dried towel, so the heat of friction goes to actually heating the towel to the touch rather than warming and evaporating a portion of the wetness as experienced with the used towel.
Water has a very good heat capacity and good heat transfer also, so a small residual amount of moisture could make a noticeable difference.
 

Offline RD

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Maybe the the fibers are stiffer after heating , like memory metal, the stiffer fibers creating more friction and more heat.

https://en.wikipedia.org/wiki/Shape-memory_polymer

« Last Edit: 25/07/2012 19:20:15 by RD »
 

Offline Geezer

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Perhaps it's just because the clean towels absorb more heat from you via the water on your skin.

After you have used a towel for a bit, it acquires oil from your skin that acts as a sort of waterproofing agent.
 

Offline John Burnap

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Thank you for the responses. I would like to point out that I need only wrap the towel around me with no movement (friction) to feel this heat. It may sound odd to you, but I know what I am feeling. I am a very perceptive scientific person and I would not bring this to the forum if I felt that it was due to friction.

Thank you Geezer, but if the towel were absorbing heat from my skin, it would have a cooling sensation.

The fabric softener is the suspect here. Please think about my plaster of paris reference above. I am certain there is an endothermic reaction in the dryer, yet I do not know what chemicals in the fabric softener would cause this.

Kitchen Science!! I do not have a thermometer suitable for such an experiment, but I am considering dehydrating some fabric softener with heat, letting it cool, and then re-hydrating it to investigate a temperature change. Perhaps I will be able to feel a change with my hand or something.

I am most interested in an investigation of the fabric softener, because I have noticed that when we don't use it, I don't notice the warming.

This is a list of the chemicals commonly found in fabric softener:
Benzyl acetate, Benzyl Alcohol, Ethanol, Limonene, A-Terpineol, Ethyl Acetate, Camphor, Chloroform, Linalool and Pentane.

Does anyone know if hydrolysis of any of these is an exothermic reaction?

Thank you! 

John
« Last Edit: 25/07/2012 22:05:53 by John Burnap »
 

Offline Geezer

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Wouldn't it be best to try to quantify the effect with some objective and repeatable experiment first?
 

Offline John Burnap

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Thanks Geezer! I am not sure how to approach the experiment. I can't very well measure the temperature of a towel. I thought of a washcloth in a bowl of water, but I have no thermometer. Perhaps I could do something with the fabric softener sheets. What do you think I should try?

Just a note, I don't think I like fabric softener much anymore.

Thanks!

John
 

Offline Geezer

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Maybe something like this:
 
Heat a surface to a uniform temperature.
 
Apply an even mist of water droplets.
 
Place a newly laundered towel on part of the surface and not so new towel on another part and measure the temperatures of the surface under the towels.
 
 

Offline RD

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The polymer the fabric is made of could release heat when it is deformed by altering its structure,
[ a bit like the heat generated when bending a piece of plastic ]
this process could be reversed (recharged) by re-heating the polymer, (heating the towel in the clothes dryer), enabling it to release heat when it is deformed again.

« Last Edit: 26/07/2012 09:35:10 by RD »
 

Offline John Burnap

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Thank you RD!

I do not have a proper thermometer, but I do have cotton, and poly-blend towels. This I can try! I will dry the towels, let them cool, hop in the shower and give them a go!

Now that I think about it, I can also try a batch of towels free of fabric softener. 

Bathroom Science! I suppose that doesn't sound too good...

I will report my findings after work tomorrow.

Thanks!

John
 

Offline RD

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Possible experiment: does the heating effect still occur with towels which have been washed at a cool temperature and dried outdoors, (i.e. not exposed to hot water and high-temperature tumble drier).

[ a "blind trial" is best ... https://en.wikipedia.org/wiki/Randomized_controlled_trial#Blinding ]
« Last Edit: 26/07/2012 09:39:08 by RD »
 

Offline John Burnap

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I will try it. My wife can help with the blind part.

It has been very hot outside... do you think I should put them in the shade? Maybe one in the shade, one in the sun.

We are establishing quite a few permutations! By the end of this experiment I will be as clean as a whistle!

Thanks!

John
 

Offline John Burnap

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Greetings!

I realized today I am truly a naked scientist!  :P

I decided to try the cotton vs. poly blend test with hot wash and hot dry without fabric softener. I thought I would go with the hot because it would definitely lead to an endothermic reaction.

RESULTS: Neither towel had the hot sensation and there was no difference between the two.

This leads me to to speculate that the fabric softener is the likely culprit. The next trial will be both cotton and poly blend, hot wash and hot dry with extra fabric softener.

We shall see in about 24 hours if one or more of the many chemicals in fabric softener is capable of an exothermic reaction in hydrolysis.

Thank you for being patient on this naked bathroom science!!

John
« Last Edit: 27/07/2012 16:20:10 by John Burnap »
 

Offline RD

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It does appear that fabric softener produces smoother fibres ...


Liquid Detergents  By Kuo-Yann Lai

so should have less heating via friction. 

... This leads me to to speculate that the fabric softener is the likely culprit ...

Just a thought, what about the fabric softener being an irritant / allergen ?,
 that could cause a warm sensation on contact with your skin,
( if so it could also cause redness / rash / dry-skin ).
« Last Edit: 27/07/2012 17:38:06 by RD »
 

Offline chris

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Interesting discussion; but as this isn't an official QotW we'll need to move it; the Chemistry section would be more appropriate, so I'll put it there in a day or two.

Chris
 

Offline John Burnap

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Greetings!

Thank you Chris, I apologize for the misplacement. I am a bit of a newbie here.

I have tried my final experiment. I washed and dried the towels on hot, and I added 4 fabric softener sheets to the dryer.

RESULTS: Both the poly and cotton towels had the warming sensation when I used them. So either the chems in the fabric softener are exothermic in hydrolysis, or I am allergic to the fabric softener.

I do not have a proper thermometer, so I guess the experiment will end here. I am a bit disappointed that it seems most of you have a hard time believing it could be an exothermic reaction. I guess it doesn't really matter, because I am no longer going to use fabric softener.

Thank you for your time, I enjoyed the discussion very much.

John
« Last Edit: 29/07/2012 17:12:12 by John Burnap »
 

Online Bored chemist

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I think it's something to do with the energy released when the water molecules absorb onto the hydroxyl groups of the cellulose: a dipole- dipole interaction.

It is fairly similar to the case of plaster of Paris, but in the case of bath towels no simple compound is formed- just an amorphous hydrate.
Silica gel might be a better model than plaster.
 

Offline Lab Rat

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It could be that the fabric softener affects the pile on the towel, making it stand up more.  This would hold more heat in the towel.  Also, you could buy an infrared thermometer to test the temperature-just point it at the towel to get a reading.
 

Offline pacpac

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I have noticed this effect even when I do not use any softener.

And this is not due to body oil either, because I heat dried a used towel without washing, and the effect is there too.
 

Offline jccc

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Reading this thread making me hot too, strange?
 

Offline Colin2B

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I have tried my final experiment. I washed and dried the towels on hot, and I added 4 fabric softener sheets to the dryer.

John
Will try some experiments here.
Did you try drying cold tumble? Sorry if I missed that and am repeating stuff. Tumbled towels are certainly fluffier than air dried, hence feel warmer.
 

Offline itsjustben

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I would think it's more likely that the softener is depositing a thin layer on the towel that is reflecting heat rather than some other heat generating reaction. Not to mention, if I remember correctly, towels with softener absorb less water than towels without.
 

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