Chemistry (including Biochemistry)/packing/storage method to preserve odor
QUESTION: Dear Dr. Raymond
I had a consultation with a textile chemist and she said Materials Chemistry or Polymer Chemistry are two chemistry specialties that would be able to provide additional information.
I need to pack away and store ladies fashion accessories(used footwear) for long term. Preserving the original odor of each object for as long as possible is the most important element.
A Conservator answered firstly, odor is caused by volatile chemicals, and therefore by definition will diminish over time as the chemicals evaporate. It's a little outside my range of expertise, but I suspect that eventually, whatever you do, the odor would disappear. I am not familiar with the chemical composition of human sweat, so I cannot say whether those off gassed chemicals will cause further deterioration of the shoe materials. It is possible.
I am not convinced that freezing or vacuum sealing would help in the long term. Freezing would certainly retard degradation of the chemicals present, but you would be risking damage to the footwear every time you thawed and re-froze it. Vacuum sealing would tend to extract the very volatile chemicals you wish to preserve. As I say, I can't be completely sure, but I suspect you may have to accept that there is no long term way to preserve the odor.
A Non Conservator answered this is indeed a dilemma! I cannot think of any ideal scenario that suites both your needs of long term storage while maintaining the odors. If the items can't breathe then they will be locked into a micro climate and the off gassing will accelerate deterioration.
Anoxic storage may be what you are looking for but I have no idea if the odors will persist and survive. Also, freezing may be an option worth looking into. (Frost free freezer and vapor proof packaging but access will need advanced planning.
A lady from customer service responded all of the wraps that we do have are still going to allow for some breathability. We also do not have any impermeable cases. The other issue with having something impermeable is that you might create a micro environment inside the case with condensation. The best bet is to store it in an archival wrap inside of an archival box and keep it stored in a climate controlled environment.
In a later email she responded all of our wraps are archival. Tissues are probably not the way to go. Either Nomex, or Tyvek Softwrap should work.
I will need a packing and storage procedure for regular access to the collection about 10 to 15% and a packing and storage procedure for occasional access to the larger collection about 85 to 90%.
You may suggest the packing method for regular access to the collection to be an easier method than for occasional access.
Which top packing and storage procedure do you recommend for each while trying to preserve the original odor of each object for as long as possible?
ANSWER: I disagree with one of the comments of the conservator. I think that vacuum sealing is exactly what you want and here is why:
1. Food grade vacuum sealing plastics are quite impermeable.
2. The volatiles (odor molecules) you use when first packing the system will be a small part of the total system. The reason things (that are not degrading) smell over time is the slow desorption of molecules. So the vacuuming will only grab a fraction of the odor (whatever is in the air at the moment and a small amount pulled from the system).
3. Organic molecules break down over time due to heat (avoid changing temperature), light (store away from light) and collisions with molecules - this last one is a big deal. When you break down a chemical, you typically need something to react with. In a vacuum/low air environment, this means you can reduce those collisions a lot.
4. It's easy to test... because vacuum food prep systems are cheap and readily available.
Feel free to follow up with me as I'd be happy to explain the specifics (eg odor related molecule degradation, plastic/polymer/materials degradation etc.).
---------- FOLLOW-UP ----------
QUESTION: Dr Raymond I will need to learn about odor related molecule degradation, plastic/polymer/materials degradation.
Another textile chemist responded the shoes could be stored in sealed polyethylene bags. Polyethylene has some permeability. If sealed completely in an air tight package volatile compounds from degradation products could damage the shoes. It is a balance between trying to retain the smell for as long as possible and the best practices for the long term preservation of the objects. If the objects start to deteriorate due to volatile compounds, moisture and light then the smell of the objects becomes a moot point (as well the deterioration of the shoes will lead to other odors being released from the shoes, thus overtaking the original odor). Remember that the environment in which your shoes are stored is key to their preservation and the preservation of the smell.
Is it possible with a safe packing and storage procedure for long term the original odor will never change to a new odor molecule that is different from the wearers feet, only fade the original odor or fade completely with the original odor never changing to a different odor?
Or what I am smelling is considered off gassing and no matter which packing and storage procedure I follow the shoe materials are already deteriorating else it wouldn't smell and the original odor will change over time to a new odor that is different from the day the footwear was purchased?
I wish for the original odor of the footwear over time to never change to a new odor that is different than the day the shoes were purchased. Maybe this can't be avoided.
I will need you to explain how the original odor evolves over time once the footwear is packed away and in storage for long term.
Sorry for the delay:
Ultimately you won't be able to do the high cost, high end sealing that occurs in places like the microelectronics industry. However, the PE bags is a solid idea. The degradation products will have a minimal effect on things... the real concern is always microbes. If your environment does not let the bacterial or fungal materials grow, then any degradation product effect will be minimal.
So: my recommended 'pilot' test would be for you to seal your shoes in clear PE using a regular food vacuum sealer, then store in a dark (no light) tub in an environment with low humidity. You can get this effect by putting some dry saw dust in the bottom of the tub. You also would want a constant temp if possible, specifically a cooler temp if available. If this project is for a forensic effort, I would suggest a large freezer. If not, a room that doesn't see drastic environmental changes.
With regards to your questions:
Q1: I think that this solution will give you this effect.
Q2: Simply - no. More in depth - many of the odor molecules are already there, just stuck to the surface. They release at a rate that is dependent on temperature, but it should be noted that in a sealed environment they will eventually settle back on the shoe (since the shoe has WAY more surface area than the plastic you seal it in).
Last request: Ultimately you want to look around online and look for the following terms - desorption, the process by which molecules 'pop' off a surface, and adsorption, the process by which molecules 'stick' to a surface. A lot of these will be a bit mathy, but the diagrams of these processes should be straight forward.