Re: What effect does long term vacuum have on materials.

Hi Charles, thanks for the question. 

The reason materials are kept in airtight containers is to reduce the 
amount of oxidation that occurs to the materials. Oxidation is a chemical 
reaction between oxygen (from the air) and the material in question. The 
oxidation can result in a number of changes depending on the composition 
of the particular material. 

Coins tarnish as a result of oxidation and paper can turn yellow. Often 
the mechanical properties also change and the material gets more brittle. 

By placing the collectible material in a container and then applying a 
vacuum to the container much of the oxygen is removed from container, 
which reduces the chances that the oxygen will react with the collectible. 
If there is less oxygen around the material there will be less oxidation 
occurring. Chemical reactions occur faster at higher temperatures so 
keeping the temperature lower will also slow the oxidation reactions. 

Light can also initiate similar chemical reactions that will result in 
changes of the color or physical properties of a material. Because of 
this, important documents are often stored in folders that block light 
from the documents to reduce the aging effects of the light. This is also 
a primary reason some companies have started making milk jugs out of 
colored plastic rather than clear plastic, to block the light. 

The specific chemical reactions can become quite complex so I won’t 
present that here. If you are interested, let me know and I can expand on 
the reactions associated with the aging of paper.