Those price differentials may well be down to production volumes affecting prices.
PET bottles are in wide scale use for low value products, Coke bottles, mineral water etc, the equivalent HDPE bottle needed to prevent loss of pressure, gas permeability is very much thicker.
However the thicker HDPE bottles are very significantly safer to the extent that quite corrosive chemicals like concentrated acids, Nitric, Sulphuric, Hydrochloric, Fluoric and also alkalis are supplied in HDPE bottles. In fgact it's now preferred to glass.
Nothing hazarous can be sold in PET of the thickness we see in common use and it's brittle unlike HDPE.
Only at APUG could we have a coherent and useful thread about the merits of different plastics for storing chemistry. :)
The expertise here is terrific.
Yes, very interesting discussion. I use random plastic bottles from the recycling bin for most of my chemicals, I'll have to check and see what types of plastic they are.
Thanks for all the discussion. I have to admit that the PETE bottles I use don't seem as thick as the HDPE bottles, so maybe the difference in performance isn't quite as great as the raw numbers would indicate. My wife gets bottled water in PETE bottles that are so thin it's like holding a water balloon.
Just as an aside, I also looked up Saran wrap since that has been mentioned as a way to improve the cap seal on bottles for storing photo chemicals. It turns out that Saran is an exceptional oxygen barrier which is why it keeps food so fresh. Other plastic wraps use less effective polymers. Unfortunately, Saran wrap is no longer made from Saran (polyvinylidene chloride) for environmental reasons. Now they make it from ordinary LDPE.
After reading this and a few other discussions, it's safe to say that my Datatainer bottles aren't any good for long term (6-8 month) storage? I'm still a relative newbie to this. I'm still in the oooh and ahhh stage, and trying to perfect my technique.
I know somebody is going to be offended (and it is not my intention), but this all seems like we're looking for a problem where none exists. I've had T-Max developer last for years in it's container (opened and used slowly) and Xtol last for close to a year (I used it up) in those goofy old accordion bottles. I've never had Dektol go bad before it was used up. I know I've written this multiple times, but if your chemistry is going bad, you're not making enough photos! ;>)
Speaking as someone who has spec'ed out packaging, I think understand. When specing out packaging usually there are two things you usually consider.....oxygen permiability or water vapor. For developer, the gas/oxygen permeability is what you care about and oriented PET (like blow molded bottles) has about 1/50th of the O2 permeability of HDPE. The previous post that mentions a lower barrier number is probably PETG(ref. here HDPE is a lot cheaper to blow mold and has very good moisture barrier properties. The reason that the PET developer bottles suck in is that the oxygen gas in the bottle is going into the solution and oxidizing the developer. The bottle doesn't allow air into the bottle to replace the oxygen being consumed by the oxidizing developer so it sucks in. The HDPE wouldn't suck in because the air can more easily get through the bottle to replace the oxygen........bottom line is that PET is a good bet. Personally, I use glass because it is even better.
So can we conclude then that if you have the choice, reusing a PET bottle to store mixed developer in is a better option than reusing a HPDE bottle? For stop and fix, I don't think it matters. And if the PET bottle gets brittle after a few years, you just replace it with another PET bottle that was otherwise going into the recycling. My Se toner bottle is at that point and I just finished a bottle of Tonic. Lucky me. :)