This new thread is in response to the "Rubbemaid No" thread posted by Hex (http://www.homebrewtalk.com/f11/rubbermaid-says-no-203227/
. I thought it made sense to start a new thread in case anyone is interesed in this info and didn't plan on returning to the old thread.
So last night after my "chemistry lesson" on plastics, everyone still had some questions regarding the materials making the mash tun. Is it HDPE, LDPE, PP, LLDPE or MDPE? Turns out it's none of them!!!!
My mash tun sacrificed some small shavings from itself in the name of science to identify it's composition. I took the samples into the lab for chemical analysis. My cooler is a Rubbermaid 1655, 7 gallon, manufactured September 2007. Here are the results:
>Orange plastic on outside: HDPE
>White plastic on inside: Modified polypropylene copolymer (i.e. Dow Engage 8450, 8540 or similar resin). The melting point is somewhere between 100 and 110 deg C, which would make it fine for mashing, just don't pour boiling water (100C) in it or it may deform. This type of material is often used in car panels or bumpers where you need a rigid plastic but also need it to "give" some so that it does not shatter when banged into, especially at low temperatures.
Wait, there's a "7" on the bottom of the cooler! It can't be HDPE!
Yes it can. There's a "7" on the bottom because the cooler istelf is composed of at least three layers of different polymers - the HDPE orange part, the PP copolymer and the insulating layer inside (urethane? foamed styrene? not sure since I don't feel like destroying the cooler to find out). The recycling number "7" is applied when the finished good has multiple layers and/or multiple blends of different polymers in it's composition. When discarded, the entire cooler is considered for recycling, not each of its individual parts. Number 7's are often thrown out at the recycling center since they are not "pure" materials.
Warning: Science below!
This is concerning the white portion only. It would have been ideal situation to determine melting points and glass transition temperatures to get a better ID, but a differential scanning calorimeter is required for that, and mine happens to be broken. So I just used infrared spectroscopy to ID the plastic. I needed to get the plastic into a thin film for analysis, so that required melting it and pressing it out. I started at 100C, and it softened but did not melt all the way. Mission accomplished at 110C. If this were PP, it would have melted at 160C (or perhaps 130C if it were syndiotactic). So I knew it wasn't PP. Then I actually took the sample to the spectrometer, and the results showed a infrared spectrum matching PP. But wait, there was also the indication of some PE present. I then realized that this had to be a PE modified PP copolymer. This makes sense since the PE portion lowers the crystallinity of the PP giving better low temperature properties (this is supposed to be a cooler after all). HDPE would not be ideal at below freezing temps, and LDPE is too elastomeric. A modified PP copolymer gives a rigid material with better low temp properties.
I have the FTIR data saved as a picture, but have no way of posting it. Can someone give me a hand with it?
The lid and orange parts were easily ID'd by the same methods. There is the indication that there may be some UV stabilizers in the orange portion.
I would have like to have done more, but I only had an extremely small sample size (only a few milligrams) and didn't want to kill my mash tun completely.