# Best plastics for containing lye solution?



## mikvahnrose (Sep 27, 2016)

Okay, so i have a pyrex mixing glass i have been using (i know people will be like NOO don't use that! It will shatter!) But it has hold up really well even when putting the lye solution in a ice bath. I have used a plastic pitcher twice and both times it left an odd residue floating in the lye solution unlike the glass.

But i'm looking for a sturdy and reliable plastic container to hold my lye solution so i don't have to worry about the glass. I am curious whats the best one out there and how they differ.

One thing i have wondered due to my experience, does anyone know if BPA's are leeched into the solution? Because the odd floaters make me think it was plastic bits that melted in. Water in hot temperatures can leech these chemicals, so why not lye?


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## penelopejane (Sep 27, 2016)

Use a plastic with a 2 or a 5 in the triangle on the bottom.


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## Susie (Sep 27, 2016)

The odd floaters are called lye lint and have nothing to do with the plastic or BPA.  They are completely harmless, and I don't even sieve them out before making soap.  They have something to do with the lye reacting with the air, but I forget what they exactly are.


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## shunt2011 (Sep 27, 2016)

I get the same thing but I don't strain it either and have never had an issue.   I use containers with #5 in the triangle on the bottom of the container.


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## DeeAnna (Sep 27, 2016)

Here's a discussion we had recently on this topic: http://www.soapmakingforum.com/showthread.php?t=60822

The consensus is most people prefer containers made from high density polyethylene, HDPE, #2 recycling code, or polypropylene, PP, #5 code. Containers with these codes are resistant to lye and usually thick and sturdy enough to withstand the heat of the hot lye and the weight of the solution itself.

Other plastics will work fine as far as _lye resistance_. Low density polyethylene, LDPE, #4 code, is an example. But that's not the only thing to consider. Most containers made from these plastics are often _more flimsy and not as heat resistant_ as HDPE or PP containers.

Absolutely do not use polyethylene terephthalate, PET or PETG or PETE, code #1. This is the clear plastic often used for soft drink bottles. It is not lye safe, no matter how thick and sturdy it may seem. I did a test awhile back to prove it to myself. The plastic turns progressively cloudy and eventually cracks and leaks. This is seriously NOT safe!


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## earlene (Sep 27, 2016)

Are you talking about long term storage of the lye solution as in masterbatching?  Or are you talking about mixing the lye solution?

If mixing, you can use stainless steel (not mixed with other metals) or
PP#5 (polypropylene) 
HDPE #2 (high density polyehtylene) 

For storing masterbatch solution after it has cooled sufficiently, I use HDPE #2.

These letters and numbers are standard in the US.  I don't know if they are standard in all countries.

Edit to remove erroneous temperature quotes.


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## cmzaha (Sep 27, 2016)

earlene said:


> Are you talking about long term storage of the lye solution as in masterbatching?  Or are you talking about mixing the lye solution?
> 
> If mixing, you can use stainless steel (not mixed with other metals) or
> PP#5 (polypropylene) melting point 266°F, or
> ...


I would not use stainless for mixing lye. There are many that will still pit over time


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## DeeAnna (Sep 27, 2016)

_"...Are you talking about long term storage of the lye solution as in masterbatching?  Or are you talking about mixing the lye solution?...."_

My advice applies to both. You could arguably use stainless steel for mixing and storage, but as Carolyn points out, there's stainless steel and there's stainless steel. Her caution is especially true when using consumer grade stainless steel containers, rather than lab/industrial equipment.

_"...HDPE #2 (high density polyehtylene) melting point 190°F..."_

None of the plastics we're talking about will melt below the boiling point of water (100 C or 212 F). Nikos and you have both mentioned this number -- 190 F melt point for HDPE -- but it's not correct. If you replace degrees Fahrenheit with degrees Celsius, then you're closer to the truth -- 

"...For common commercial grades of medium- and *high-density polyethylene the melting point is typically in the range 120 to 180 °C (248 to 356 °F)*. The melting point for average, commercial, low-density polyethylene is typically 105 to 115 °C (221 to 239 °F)...." Source: https://en.wikipedia.org/wiki/Polyethylene

Also these quotes from a distributor of laboratory chemicals: 

"...LDPE is unreactive at room temperatures except by strong oxidizing agents. It can withstand temperatures of 80 °C [175 F] continuously and 95 °C [203 F] for a short time...." *

And

"...HDPE bottles offer stronger tensile strength than LDPE containers, are harder and more opaque, and can withstand somewhat higher temperatures: 120°C (248°F) for short periods, 110°C (230°F) for longer periods...." *

Source: http://www.calpaclab.com


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## earlene (Sep 27, 2016)

DeeAnna said:


> _"...Are you talking about long term storage of the lye solution as in masterbatching?  Or are you talking about mixing the lye solution?...."_
> 
> My advice applies to both. You could arguably use stainless steel for mixing and storage, but as Carolyn points out, there's stainless steel and there's stainless steel. Her caution is especially true when using consumer grade stainless steel containers, rather than lab/industrial equipment.
> 
> ...



Okay, I stand corrected.  

I am sure I read it here on SMF the 190°F but maybe I mismembered that.  In looking back, I see here it is mentioned but not as a melting point, only as a safe maximum usage temperature.  My mistake using melting point in that sentence.

I got the 266°F here and here (maybe Wikipedia is not totally trustworthy.)

Regarding stainless steel, then would you recommend against purchasing this 18/0 stainless steel pitcher from Brambleberry?

ETA: Bagels are made with lye in stainless steel pots.  So I suspect restaurant quality stainless steel pots should be safe for mixing lye solution.  Granted it is at a lower concentration than we use in soap making, but that is the quality of stainless steel I have in my house, although I suppose you aren't talking about that grade of SS.  I had never given any thought to lower grade stainless steel, though.


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## DeeAnna (Sep 27, 2016)

Safe temperatures for USE are entirely different than the MELT temps for a given type of plastic. In the general literature, a range of temps is normally given for the melting point of a given plastic resin. For example, each brand of polyethylene will have its own characteristic melt temp depending on formulation and molecular weight. If you want to nail it down, you have to look at the manufacturer's literature for that specific brand of resin.

"...I got the 266°F here and here (maybe Wikipedia is not totally trustworthy.)..."

Wikipedia is often a decent resource especially if a person wants to get an overview on chemistry and other science topics. If you need precise info about the numbers, then I'd suggest a search of manufacturers' websites for their product literature. But Wikipedia is generally fine for a quick source of info.

The two links you gave both link back to the same article on Wikipedia about poly*pro*pylene. And the 266 F melt temp in that article refers to the MINIMUM melt temp, not the ONLY melt temp. 

I was talking about poly*eth*ylene in response to your very clear statement: "...HDPE #2 (high density polyehtylene) melting point 190°F..." Entirely different critter.


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## earlene (Sep 27, 2016)

Again, my error.  I guess Google auto-corrected my spelling when I did  the search and I did not notice.  It happens and unfortunately I don't  always notice.

And as I admitted above ("My mistake using melting  point in that sentence"), I made the error of misremembering what  IrishLass said about 190.  I do understand that safe use temps and  melting temps are two different things.


Again, I stand corrected.   I will go back and correct my errors in my previous post so as not to mis-lead anyone.


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## DeeAnna (Sep 27, 2016)

Hi, Earlene -- The point is to learn more about our craft and to pass on good information so others learn too. You're doing fine! --D


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## topofmurrayhill (Sep 27, 2016)

earlene said:


> Regarding stainless steel, then would you recommend against purchasing this 18/0 stainless steel pitcher from Brambleberry?



Just BTW, bagels are not authentically made with lye but pretzels are.

I would not buy the 18/0 pitcher. It might be okay for light use, but it's not the type of steel you ideally want for lye, and better alternatives aren't hard to find. The problem is the second number being zero. A magnet will probably stick to that pitcher because it has no nickel content. It wouldn't have as much corrosion resistance as you would want.

For soaping use, it would be better to use austenitic steel labeled something like 18/8, 18/10 or 300-series (304, etc.). It's pretty common. Although not impervious to lye, the vulnerability is based on concentration and temperature. Maybe avoid using it if you're mixing up 50% lye solutions, but under typical conditions it should be very resistant to lye. Personally would use plastic for storage.


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## earlene (Sep 28, 2016)

topofmurrayhill said:


> Just BTW, bagels are not authentically made with lye but pretzels are.
> 
> I would not buy the 18/0 pitcher. It might be okay for light use, but it's not the type of steel you ideally want for lye, and better alternatives aren't hard to find. The problem is the second number being zero. A magnet will probably stick to that pitcher because it has no nickel content. It wouldn't have as much corrosion resistance as you would want.
> 
> For soaping use, it would be better to use austenitic steel labeled something like 18/8, 18/10 or 300-series (304, etc.). It's pretty common. Although not impervious to lye, the vulnerability is based on concentration and temperature. Maybe avoid using it if you're mixing up 50% lye solutions, but under typical conditions it should be very resistant to lye. Personally would use plastic for storage.




Thank you, TOMH.  I actually don't use steel for mixing lye, but do for cooking soap sometimes (not often as I prefer the crockpot).  However I have considered buying a SS pitcher sometime in the future at the local Restaurant Supply house we used to use when we had a restaurant.  One reason I have not done so is the added weight factor, and another is that I don't go near there very often anymore.


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## Arimara (Sep 28, 2016)

topofmurrayhill said:


> Just BTW, bagels are not authentically made with lye but pretzels are.
> 
> I would not buy the 18/0 pitcher. It might be okay for light use, but it's not the type of steel you ideally want for lye, and better alternatives aren't hard to find. The problem is the second number being zero. A magnet will probably stick to that pitcher because it has no nickel content. It wouldn't have as much corrosion resistance as you would want.
> 
> For soaping use, it would be better to use austenitic steel labeled something like 18/8, 18/10 or 300-series (304, etc.). It's pretty common. Although not impervious to lye, the vulnerability is based on concentration and temperature. Maybe avoid using it if you're mixing up 50% lye solutions, but under typical conditions it should be very resistant to lye. Personally would use plastic for storage.



Good to know, even though I'm still not mixing lye in a stainless steel pitcher. And as for the bagel info, does it really matter? NYC still has the best bagels there are, even within the state (upstate NY tried and FAILED )


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## topofmurrayhill (Sep 28, 2016)

Arimara said:


> And as for the bagel info, does it really matter? NYC still has the best bagels there are, even within the state (upstate NY tried and FAILED )



They are indeed the best, and it matters if you want to make them. I did a lot of research into that and initially was frustrated by conflicting information about how bagels are made. However, there used to be a union of bagel makers here, and while some details may vary between bakeries, certain basic principles apply to the authentic NYC product. And it's not the water.


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## Arimara (Sep 28, 2016)

topofmurrayhill said:


> They are indeed the best, and it matters if you want to make them. I did a lot of research into that and initially was frustrated by conflicting information about how bagels are made. However, there used to be a union of bagel makers here, and while some details may vary between bakeries, certain basic principles apply to the authentic NYC product. And it's not the water.



Good to know. :mrgreen:


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