Sciencemadness Discussion Board

Sulfuric Acid and LDPE issue

Ax165Xj - 16-8-2013 at 17:11

According to a couple of chemical compatibility charts I checked, LDPE was fairly resistant to 98% sulfuric acid. I ordered a LDPE dropper bottle from china and filled it with sulfuric in order to test it. I came back 24 hours later to a green/grey solution. Does anyone know what happened? I'd like to use this bottle but I don't want it to break on me. I can dilute the sulfuric a little but ideally not too much.

Pyro - 16-8-2013 at 17:26

you should be able to buy HDPE containers in a local paint shop. you can also use glass bottles such as the ones used to hold vinegar, olive oil, even some booze bottles will do. the cap should just be plastic lined, then it will be OK as H2SO4 doesn't fume a whole lot.

don't dilute it, you can always dilute it as you need but concentrating it is a lot harder and many applications require 98%

blogfast25 - 17-8-2013 at 04:41

Quote: Originally posted by Ax165Xj  
I came back 24 hours later to a green/grey solution.


What precisely do you mean? The bottle had dissolved? The sulphuric acid inside the bottle had acquired a green colour?

LDPE should be very resistant to conc. H2SO4. Are you sure the bottle was effectively made of LDPE?

Protium1 - 17-8-2013 at 04:49

LDPE and other plastics have curing agents and UV protective agents and who knows what other chemicals from some proprietary process used in there manufacture, not to mention the innumerable post-production contaminants possible on even the inside surfaces of a sealed container.
Try a thorough washing of the container with distilled water or another high-grade, LDPE compatible solvent.
After washing, I would rinse the inside a few times with the H2SO4 that will be stored in it.
This does not though preclude contaminants from inside the plastic itself from leeching into the H2SO4 over time.

Ax165Xj - 17-8-2013 at 08:07

Thanks for the suggestions. I'll definitely try washing it out. And to be more specific about what I found: the sulfuric acid was green/grey. The bottle itself didn't seem to be any different.

And as to whether or not I am sure it is LDPE, the answer is no. The eBay supplier from china said it was LDPE but there is no mark on the bottom of it so I can't be completely sure.

[Edited on 17-8-2013 by Ax165Xj]

blogfast25 - 17-8-2013 at 08:26

Quote: Originally posted by Protium1  
LDPE and other plastics have curing agents and UV protective agents and who knows what other chemicals from some proprietary process used in there manufacture, not to mention the innumerable post-production contaminants possible on even the inside surfaces of a sealed container.
Try a thorough washing of the container with distilled water or another high-grade, LDPE compatible solvent.


LDPE for packaging and bottles isn't generally cured (neither is HDPE), although cross-linked PE for demanding applications is commercialised. Using cured PE for that application significantly increases cost that is usually not warranted by the specification of the material/artefact.

It does contain some other chemicals in very small amounts, including usually the catalyst needed for the polymerisation of ethylene to polyethylene, anti-UV and antioxidant and possibly some mould-release agent.

Personally I use HDPE bottles for commercial packaging of various solutions (but not concentrated H2SO4) without problems.

'innumerable' sounds like a rather vague over-statement.



[Edited on 17-8-2013 by blogfast25]

Fantasma4500 - 17-8-2013 at 10:29

of what i know HDPE is suitable for 98% H2SO4
however, at the local ''car store'' or well where you buy stuff for cars and what else not, they sell 37% 'battery acid'
1L, it comes in a LDPE bottle
the point: H2SO4 needs a good container, and i have heard hardcore cleaning brands (using 96% H2SO4) sold in the usa leaking, as the H2SO4 very slowly dissolves the plastic, i suppose it must be LDPE used in USA also, in my town they had bottles leaking a few times, considerable mess, and thats only 37%, 1.27M IIRC, where 98% is +18M

HDPE or PET should work, perhaps turn a regular PET bottle into a dropper bottle? im quite sure PET is more than plentiful resistant to H2SO4, tho i could be wrong

blogfast25 - 17-8-2013 at 11:49

@antiswat:

Leaks in bottles may also be caused by mechanical causes: cracks developed during dropping, very heavy-handed handling or incorrect stacking. Bottle caps and threads are particularly vulnerable to mechanical failure.

If by PET you mean polyethylene terephtalate, that is an (poly) ester and thus likely to be prone to acid hydrolysis, over time.



[Edited on 17-8-2013 by blogfast25]

Fantasma4500 - 18-8-2013 at 06:31

i dont believe it could be entirely mechanically caused, as they would very seldomly cause small enough cracks to not see them immediately, probably a mixup

anyhow, of what i understand pretty much all plastics are poly esters (correct me if im wrong) so wouldnt that make all plastics prone to acidic hydrolysis anyways? (ofcourse some more and some less resistant)

plante1999 - 18-8-2013 at 06:34

Not all plastic are ploy ester at all, most of them are not in fact.

blogfast25 - 18-8-2013 at 07:38

Quote: Originally posted by Antiswat  
i dont believe it could be entirely mechanically caused, as they would very seldomly cause small enough cracks to not see them immediately, probably a mixup

anyhow, of what i understand pretty much all plastics are poly esters (correct me if im wrong) so wouldnt that make all plastics prone to acidic hydrolysis anyways? (ofcourse some more and some less resistant)


You don't believe it but I have seen it first hand.

Polyesters are a particular class of polymers with often very specific uses. For packaging/bottling PET is the only polyester in use, as far as I know. And the predominant use of PET bottles is for carbonised (thus pressurised) drinks, presumably because of the higher tensile strength of PET compared to other contenders.

The highest volume plastics worldwide are polyethylene, polypropylene and PVC. None of these are polyesters. Polyester use is usually in the higher price/higher performance bracket of the so called 'engineering plastics'.

[Edited on 18-8-2013 by blogfast25]

Fantasma4500 - 28-8-2013 at 10:07

hah just thought for a second i knew what polyesters were.. (:

anyhow, about pressure and plastic types, of what i know the normal PVC bottles which are thicker and cheaper can stand up to 16 PSI, where the regular coca cola PET bottles can stand only 6 or 8
also PET slowly disintegrates giving a smell of rotten fruit or well, just hard to describe tho its among PPM amount of material giving the smell
this can be tested out by taking a regular PET bottle
putting it somewhere decently hot on a shelf with water in and then open it a few weeks later

i would believe the LDPE would be more flexible, but it probably have strange properties if it really does crack mechanically and not chemically, i did check my bottle, it says ''PE''
and its not really hard.. so i take it for being LDPE

i did see a show where a professor was using PE LD and HD when referring to polyesters, he showed the differences using plastic bags, how it stretches and becomes HD from LD, and how there are negative / positive words
i mean you would feel much more safe if something was build of polyesters rather than plastics, not knowing there isnt really that much difference

plante1999 - 28-8-2013 at 10:25

Polyester is a plastic type, anyhow, PET bottle here easily withstand 100 PSI.

Zephyr - 31-8-2013 at 10:45

i had a similar problem a PET bottle (resulting in sulfuric acid all over my bench). if you dont have access to a glass or high quality acid resistant plastic bottle, why not simply store it in its original container?

if on the other hand you are producing your own sulfuric acid then wouldnt it be 70% and relatively easier to store?

blogfast25 - 31-8-2013 at 13:02

Quote: Originally posted by Antiswat  
anyhow, about pressure and plastic types, of what i know the normal PVC bottles which are thicker and cheaper can stand up to 16 PSI, where the regular coca cola PET bottles can stand only 6 or 8
also PET slowly disintegrates giving a smell of rotten fruit or well, just hard to describe tho its among PPM amount of material giving the smell


As far as I know, both statements are false.

PET is the material of choice for carbonated (pressurised) drinks and NOT PVC, which does however find a lot of use in bottling other products, often were better chemical resistance is required.

Re the slow degradation of PET, it also doesn't ring true to me. PET is recycled on a very large scale with often considerable lapses between collection (as 'waste') and actual reprocessing and that doesn't seem very compatible with a material that degrades. I guess it depends on what you call 'slowly', though... If you do have evidence of the slow degradation of PET I'd be interested to learn about it.