Role Of Formalin In Non Gelatin Elulsion

[wildbillbugman]

Hello P.E.,
Please pardon my bringing up a topic I remember you writing about years ago. A search did not find it. I remember you saying that Formalin can cause an action which can be mistaken for cross linking in a gelatin silver/ halide emulsion. Instead there is another,non-cross linking action that can be mistaken for cross linking. The reason that I ask is because I have long used Formalin as an anti-fogging agent in my silane-functional PVA/halide emulsions. It really dose work. I have tested it many times. Besides cross linking, what can formalin do in a gelatin emulsion?
Thanks,
Bill

 

[Photo Engineer]

I'm afraid that with the passage of time, I think what you have said above is a very very rough misquote of what I did say.

Formalin is very reactive. If you inhale the gas it can react with proteins in your lungs for example, and that is why it is good to avoid smelling Formalin. It will react with any active Nitrogen group or Methylene group. So, R-NH2 in gelatin reacts with CH2O to give R-NH-CH2-NH-R. An active methylene is hard to show here but it is basically a reactive -CO-CH2-CO- such as found on couplers and so too much formalin can deactivate couplers in color film. We had to use mixed hardeners there.

Anyhow, any reactive group can react with Formalin, but the reaction may not need to cause hardening. You see, you must have two proteins linked together to harden. If a protein reacts with itself, it does not harden, it denatures or unwinds.

Now, all of this is true for polymers as well. I worked for a few years on hardenable polymers as a way to improve films and use less gelatin. We used Formalin and other hardening agents and they worked just fine. So, if your silane has active enough groups it could crosslink and end up harder. As far as antifogging goes, I have no idea. Usually, Formalin causes fog if used under the right conditions because it is a reducing agent.

PE

 

[wildbillbugman]

Thanks P.E.,
Once I have earned my PhD. in Photochemistry, I may know what is going on here. I expect that will happen around the year 2050. As far as breathing formalin,I have smoked unfiltered cigarettes for 50 years. About as long as I have worked with toxic chemicals It would be hard to blame formalin in my case. But all of my breathing test come out "normal". Go figure.
Bill