Liquid Castile soap creating a vacuum. How?

[Karen jw]

This week I made my first liquid soap. I only used pure extra virgin olive oil (later found out extra Virgin is not the best choice if you want a clear soap but that's not important just now). It diluted nicely to a good thick liquid and I put it into a lemonade bottle. It was room temperature when I bottled it.
It seems to be creating a vacuum as the bottle is getting sucked inwards.
I equalised the pressure yesterday and it's done the same again today.
Can anyone explain what's causing this as I'm intrigued.

 

[Zany_in_CO]

Weird. I'm intrigued too! I hope one of the science gurus drops in to explain what's going on.

 

[Karen jw]

Weird. I'm intrigued too! I hope one of the science gurus drops in to explain what's going on.
View attachment 40484

Haha yes I'll post a pic in the morning as it's 2:30 am here in the UK and I don't want to disturb the family

 

[Mobjack Bay]

Very interesting. Is the bottle totally filled with liquid soap, or is there an air space?

 

[Karen jw]

Very interesting. Is the bottle totally filled with liquid soap, or is there an air space?

It's about two thirds full so a fair bit of air space.

 

[Mobjack Bay]

I am by no measure a chemist, but I’m still willing to throw out some hypotheses! It’s a puzzler for sure! Based on what you’ve described, it doesn’t seem like a change in soap temperature, room temperature or ambient air pressure can explain what happened. You need a volume change inside the bottle due to some other process. One thought I had is that the soap is pulling something out of the airspace that is “fitting” into the liquid soap without changing the volume of the soap fraction while the volume of the air decreases. Alternatively, perhaps the volume of the liquid soap can decrease (density would increase) due to the molecules “packing” together with time.

 

[HaniS]

This week I made my first liquid soap. I only used pure extra virgin olive oil (later found out extra Virgin is not the best choice if you want a clear soap but that's not important just now). It diluted nicely to a good thick liquid and I put it into a lemonade bottle. It was room temperature when I bottled it.
It seems to be creating a vacuum as the bottle is getting sucked inwards.
I equalised the pressure yesterday and it's done the same again today.
Can anyone explain what's causing this as I'm intrigued.

Carbon dioxide. The reaction still needs Oxygen and it's trying to absorb it from the outside.

 

[Karen jw]

I am by no measure a chemist, but I’m still willing to throw out some hypotheses! ........ that the soap is pulling something out of the airspace that is “fitting” into the liquid soap without changing the volume of the soap fraction while the volume of the air decreases. Alternatively, perhaps the volume of the liquid soap can decrease (density would increase) due to the molecules “packing” together with time.

Yes I agree it does seem to be some sort of reaction so I am hoping someone can confirm the chemical process going on

 

[Karen jw]

Carbon dioxide. The reaction still needs Oxygen and it's trying to absorb it from the outside.

This would make sense. I thought the process with liquid soap is finished by this point though. Is this a known phenomena?

 

[Karen jw]

Pictures.
This is after equalising the pressure once. It was worse the first time around.

 

[HaniS]

I can think of the reason why the bottle is collapsing in this sense: The breakdown of the triglyceride inside of the bottle emits carbon dioxide. The Carbon dioxide that becomes dissolved in the liquid (water) produces carbonic acid. Carbonic acid neutralizes the potassium (or sodium) hydroxide in the solution. This result in the conversion of gaseous carbon dioxide to an aqueous solution of sodium carbonate (soda ash). As the amount of carbon dioxide decreases, the pressure inside the bottle decreases while the atmospheric pressure on the outside remains the same, leading to a collapsing the bottle.

From another point of view, the reaction of KOH, water and the triglyceride (olive oil) might still be active and emitting heat. The heat causes moisture vapor to migrate and pass throughout the bottle’s cap. And as a result, the volume of the contents is reduced and the bottle wall sucks in to compensate for that loss. This is because Oxygen is not absorbed back to balance the pressure between the inside and the outside.

I can think of Mobjack Bay’s point of view also. The molecules “packing” together in order to prevent or compensate the loss or the need for oxygen, and creating an (inward stress) to compensate and acquire oxygen by creating an absorption force.

Did you bottle the liquid soap soon after you finished the reaction? And how much water did you use or add? Also how much KOH did you use?

note: if it's KOH that is being used then it potassium carbonate not soda ash (sodium carbonate)

 

[Karen jw]

I can think of the reason why the bottle is collapsing in this sense: The breakdown of the triglyceride inside of the bottle emits carbon dioxide. The Carbon dioxide that becomes dissolved in the liquid (water) produces carbonic acid. Carbonic acid neutralizes the potassium (or sodium) hydroxide in the solution. This result in the conversion of gaseous carbon dioxide to an aqueous solution of sodium carbonate (soda ash). As the amount of carbon dioxide decreases, the pressure inside the bottle decreases while the atmospheric pressure on the outside remains the same, leading to a collapsing the bottle.

From another point of view, the reaction of KOH, water and the triglyceride (olive oil) might still be active and emitting heat. The heat causes moisture vapor to migrate and pass throughout the bottle’s cap. And as a result, the volume of the contents is reduced and the bottle wall sucks in to compensate for that loss. This is because Oxygen is not absorbed back to balance the pressure between the inside and the outside.

I can think of Mobjack Bay’s point of view also. The molecules “packing” together in order to prevent or compensate the loss or the need for oxygen, and creating an (inward stress) to compensate and acquire oxygen by creating an absorption force.

Did you bottle the liquid soap soon after you finished the reaction? And how much water did you use or add? Also how much KOH did you use?

note: if it's KOH that is being used then it potassium carbonate not soda ash (sodium carbonate)

I can think of the reason why the bottle is collapsing in this sense: The breakdown of the triglyceride inside of the bottle emits carbon dioxide. The Carbon dioxide that becomes dissolved in the liquid (water) produces carbonic acid. Carbonic acid neutralizes the potassium (or sodium) hydroxide in the solution. This result in the conversion of gaseous carbon dioxide to an aqueous solution of sodium carbonate (soda ash). As the amount of carbon dioxide decreases, the pressure inside the bottle decreases while the atmospheric pressure on the outside remains the same, leading to a collapsing the bottle.

From another point of view, the reaction of KOH, water and the triglyceride (olive oil) might still be active and emitting heat. The heat causes moisture vapor to migrate and pass throughout the bottle’s cap. And as a result, the volume of the contents is reduced and the bottle wall sucks in to compensate for that loss. This is because Oxygen is not absorbed back to balance the pressure between the inside and the outside.

I can think of Mobjack Bay’s point of view also. The molecules “packing” together in order to prevent or compensate the loss or the need for oxygen, and creating an (inward stress) to compensate and acquire oxygen by creating an absorption force.

Did you bottle the liquid soap soon after you finished the reaction? And how much water did you use or add? Also how much KOH did you use?

note: if it's KOH that is being used then it potassium carbonate not soda ash (sodium carbonate)

This is the recipe I used.
I didn't measure the amount of water I added altogether as it was over the course of a day or two. I didn't want to make it too thin by throwing in too much water at once.
It was bottled about 2 days after processing.

 

[HaniS]

KOH seems to be almost right, slightly increased though. To the best of my knowledge, the water used is being incorporated over two stages. The first time is when KOH is dissolved in it to produce the water/lye and react the oil with it. By looking at the recipe I can see that first amount of water. After few days of settling the liquid soap, without covering it yet, more water is being added - usually at least another 100 grams to this recipe. I used to add more, about 200 grams relative to this recipe. But as you said, this is up to you if you want to make it more concentrated. But again as far as I know, the second amount of water is added without further heating, and the mixture is left to cure for at least couple of weeks or more to neutralize. I'll try and look it up again, and find a resource to confirm this. The last time I made olive oil liquid soap was probably 15 years ago!

Also by looking at the picture, the top fatty layer indicates that the soap still hasn't fully reacted, there's free fat on top. So it seems like it needs more heating. I checked one site, and found that adding more water is there. But the (maker) added the water soon after she finished cooking the soap. From a chemical/ reaction point of view, the liquid soap should be allowed more time to cure gradually. I'd use a prolonged (or repeated) hot water bath to speed up neutralizing..

 

[Karen jw]

KOH seems to be almost right, slightly increased though. To the best of my knowledge, the water used is being incorporated over two stages. The first time is when KOH is dissolved in it to produce the water/lye and react the oil with it. By looking at the recipe I can see that first amount of water. After few days of settling the liquid soap, without covering it yet, more water is being added - usually at least another 100 grams to this recipe. I used to add more, about 200 grams relative to this recipe. But as you said, this is up to you if you want to make it more concentrated. But again as far as I know, the second amount of water is added without further heating, and the mixture is left to cure for at least couple of weeks or more to neutralize. I'll try and look it up again, and find a resource to confirm this. The last time I made olive oil liquid soap was probably 15 years ago!

Also by looking at the picture, the top fatty layer indicates that the soap still hasn't fully reacted, there's free fat on top. So it seems like it needs more heating. I checked one site, and found that adding more water is there. But the (maker) added the water soon after she finished cooking the soap. From a chemical/ reaction point of view, the liquid soap should be allowed more time to cure gradually. I'd use a prolonged (or repeated) hot water bath to speed up neutralizing..

Thank you that's interesting and most helpful. I'll try that and look forward to confirmation of the process and curing timing.
I was quite surprised to see free fat appear as I used a 0% superfat to avoid that and had cooked it for longer than instructed and there was no zap on testing.

 

[HaniS]

It looks like a great start anyways! Liquid Olive Oil Soap is so special as far as I remember when I used it, it has a unique effect especially to the hair.. What I think happened, is that you might have exceeded the amount of water that is required to achieve the reaction during the initial stage, which resulted in low concentration of KOH. Never the less this can be corrected by heating the soap again. KOH reacts slowly with oil. This is why a relatively small amount of water should be used to achieve the first saponification. Usually the soap turns into a paste not liquid yet after finishing the first stage. It's left to cure to advance the reaction and allow further neutralization. After few days the additional amount of water is added and the soap is not stirred yet. It's left to emulsify with the water. Then it's stirred every few days slowly, as it starts to become more clear and stable.

I'm sure that you will find a way to work it out and have a great all-natural liquid olive oil soap..

 

[Karen jw]

It looks like a great start anyways! Liquid Olive Oil Soap is so special as far as I remember when I used it, it has a unique effect especially to the hair.. What I think happened, is that you might have exceeded the amount of water that is required to achieve the reaction during the initial stage, which resulted in low concentration of KOH. Never the less this can be corrected by heating the soap again. KOH reacts slowly with oil. This is why a relatively small amount of water should be used to achieve the first saponification. Usually the soap turns into a paste not liquid yet after finishing the first stage. It's left to cure to advance the reaction and allow further neutralization. After few days the additional amount of water is added and the soap is not stirred yet. It's left to emulsify with the water. Then it's stirred every few days slowly, as it starts to become more clear and stable.

I'm sure that you will find a way to work it out and have a great all-natural liquid olive oil soap..

That makes sense. I'll try some again soon and follow your tips and hopefully have a less problematic experience. I'll let you know how I get on fixing this soap and if I have any other problems I'll no doubt be back for some more expert advice. Thank you most kindly

 

[Saranac]

www.oberk.com/packaging-crash-course/plastic-bottle-paneling-5-causes-and-the-cures

I'm leaning towards Causes #2 and #3 in the above article. I've had full bottles of LS do this, so I ruled out #2 when it occured to me. Temperature fluctuations, pressure changes, and the gas permiability of your bottle all seem at play.

 

[DeeAnna]

...Temperature fluctuations, pressure changes, and the gas permiability of your bottle all seem at play.

Yep, my thinking too. A thin walled bottle will buckle simply from ambient temperature and pressure changes, especially if there is a lot of headspace (air) in the bottle to expand and contract due to environmental changes. A tall, narrow cylinder shape doesn't have much rigidity simply due to its geometry, so that will also contribute even more to a lack of stability.

 

[Karen jw]

www.oberk.com/packaging-crash-course/plastic-bottle-paneling-5-causes-and-the-cures

I'm leaning towards Causes #2 and #3 in the above article. I've had full bottles of LS do this, so I ruled out #2 when it occured to me. Temperature fluctuations, pressure changes, and the gas permiability of your bottle all seem at play.

Yes I'm thinking 2 or 3 and if it happened to you with a full bottle then 2 is likely not the cause here either. Also the ambient temperature has been increasing drastically here over the last few days so if temperature alone were responsible I'd be seeing pressure build as well as drop but it's only been dropping.
It's a very flimsy bottle being from cheap generic cola so I think reason 3 could be the most likely.
Very interesting indeed

 

[Mobjack Bay]

Yes I'm thinking 2 or 3 and if it happened to you with a full bottle then 2 is likely not the cause here either. Also the ambient temperature has been increasing drastically here over the last few days so if temperature alone were responsible I'd be seeing pressure build as well as drop but it's only been dropping.
It's a very flimsy bottle being from cheap generic cola so I think reason 3 could be the most likely.
Very interesting indeed

If there was no gas buildup in the headspace for the other poster, then #3 is not likely. The gas would be much more likely to collect in the bottle and cause the sides to bulge compared with escaping out through the container walls. I ruled out ambient changes in pressure and temperature because it happened twice. That suggested to me that the soap itself was actively changing.