Hi All, Does anyone have a source for zip-top Polypropylene bags? Preferably a coin related / trusted source. I want to store my 20pocket coin pages in these bags for moisture protection, all I can find are the small size bags. Would need ~ 10in x 12in min size. Thanks in advance..
I'm not sure there is such a thing as archival polypropylene or polyethylene. These polymers are already flexible and do not require plasticizers to make them so. The same is true for polyester (polyethylene terphthalate, PET, etc.), but polyvinyl chloride (PVC) is a brittle plastic that requires an "inert" material to be added to make the polymer molecules "slide" over each other and make it soft and flexible. All of these WILL transmit gases.
I been keeping my gold in Ziplock bags for years now. They aren’t 100% air tight, but living in a high humidity part of the country, I do believe it has offered me an inexpensive layer of insurance…….. And don’t hold me to this but I do believe there was conversation here a while back about the Ziplock bags and the determination was that food quality equates to safe for storing your coins.
I am in a high humidity environment as well which is why the thread. According to this below that was posted on this site a while ago, PET isn't the best for moisture barrier, polypropylene is better. Hence the search for the bags. LDPE (Ziplocs) can work till I find better I guess. "I'm not sure there is such a thing as archival polypropylene or polyethylene." - I guess what I mean is the polypropylene used for coin pages like this. Something I can trust has no additives.
In a high humidity location, your best way of keeping your coins in a dry environment is to use a desiccant that is replaced or regenerated when necessary … and don’t worry about the container composition … PP, LDPE, HDPE, acrylic, polycarbonate, glass, etc. Diffusion through these will be insignificant compared to what comes in at the seams or openings … including you periodically opening or closing the container. Note that 10 to the 10th multiplier for moisture permeability in Table 2. That means the actual value is the value stated multiplied by 0.0000000001! That means for even the most permeable plastic in the table, which happens to be acrylic, it takes a long, long time for moisture to get through any reasonable thickness. If you put a liter of water in a well-sealed container made of the above substances and put it in a near zero humidity environment, it would take many years for it to decrease in weight by even 0.01%. Avoid plasticized vinyl, but otherwise, don’t be concerned about the plastic you choose to protect your coins from moisture. Cal
