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rmazzullo
01-10-2009, 05:11 PM
Hello PE,

Can you please discuss the action of plasticizers, and how they would best be used on the scale being discussed here? What are the best plasticizers to use?

Thanks,

Bob M.

Photo Engineer
01-10-2009, 05:53 PM
Humectants and plasticizers fall somewhat into the same category.

This includes things like Sorbitol (H) and PVA or Poly Vinly Alcohol (P). Others are PVP or Poly Vinly Pyrrolidone and some others that I don't have OTOMH. They are not significant in our work for home coating for the most part.

PE

AgX
01-11-2009, 12:11 PM
Bob,

About the action of plasticizers:

I assume the action of humectants is obvious. Their mechanical effect thus is indirect.
The rest of the plasticizers act due to their own mechanical property. By blending the gelatin with them the mechanical property of the emulsion changes.

Hardeners are always related to the mechanical properties of the wet gelatin. But I assume, due to them linking the protein chains, they will have an effect on the dry gelatin too. (Though I am not sure about the extent of such effect.) From this perspective, when used as emulsion addenda, they could be seen as opponents to plasticizers.

The use of plasticzers is not only aimed at keeping the emulsion flexible, which would be a mere mechanical issue. They also, by keeping the gelatin flexible, reduce sheer forces on the halide which otherwise would result in a change of sensitivity.

rmazzullo
01-11-2009, 03:32 PM
Thanks PE and AgX....

This is very useful information. It looks like you need to balance the proper use and amount of plasticizer, hardening agent, wetting agent, anti foaming agent, etc, etc., properly. I am sure this has been covered in different threads here....just need to dig it out.

Bob M.

Photo Engineer
01-11-2009, 03:53 PM
I have not covered Plasticizers and Humectants at all. Jim Browning's formula uses Sorbital (H) in his coatings.

Some surfactants are Humectants and Plasticizers. I forgot to mention that before.

PE

rmazzullo
01-12-2009, 09:12 AM
PE,

Is there a preferred ratio of hardener to plasticizer per unit of emulsion that can be used as a starting point? I imagine this might depend on which hardeners and plasticizers are used, but could you use the most appropriate compounds as an example?

Thanks,

Bob M.

Photo Engineer
01-12-2009, 09:21 AM
Bob;

The hardener is based on aim swell and gelatin, not plasticizer. Their ratios are also based on rate of hardening, coating speed and coatability. These are non-problems for the most part in our home coating applications and represent somewhat of a red herring in our context. If your coating cracks, add a tad of Sorbital, and that will probably be the end of your problems.

So, unless you intend coating mutiple layers at speeds of 100+ ft/min, this is a very very minor side issue unless you live (and coat) in the Sahara Desert. :D

PE

Kirk Keyes
01-12-2009, 11:18 AM
Bob - The title of the thread is "plasticizers for flexible support" - are you also asking about plasticizer in the acetate base or in the emulsion?

rmazzullo
01-12-2009, 11:35 AM
Hello Kirk....

I was asking about adding plasticizers to the emulsion.

Thanks,

Bob

rmazzullo
01-12-2009, 11:43 AM
....unless you live (and coat) in the Sahara Desert. :D

PE

Well....we have Sahara-like temperatures in the NYC subways in mid-August, and the humidity above ground of course makes it worse. But since it's going to be 6 degrees later on this week without the wind chill factor (so they say), that visual doesn't seem so bad right now. ;)

Bob