Nonvolatile gelatin hardener

I've tried bisepoxide compounds to harden gelatin. As I anticipated
from molecular structures and chemical properties of epoxides, they
react much more slowly than glutaraldehyde (glut). My preferred
compound for this purpose was diglycidyl ether of glycerol
(epox). There are several other diglycidyl or polyglycidyl ethers of
glycols and similar substrates, which can be useful. A 2 to 10% of dry
gelatin weight is a good starting point for the hardener dose.

Example

In a 1000 ml of water at 25C, 30g of ossein gelatin of 230 Bloom
strength was soaked with slow agitation until fully swollen. The
mixture was heated to 40C with continuous agitation. The temperature
and agitation were maintained until the gelatin was completely
"dissolved" with water to form a single phase. A 0.06 ml of a
surfactant (a blend of secondary alcohol ethoxylates) and 0.1g of
sodium salt of 2-phenylphenol (bactericide and fungicide) were added
thereto, and the mixture was set aside until use.

A 100ml portion of the premade sizing solution was taken, heated to
40C and 0.1ml epox was mixed thereto, followed by a vigorous agitation
until the epox was completely mixed into the aquaous gelatin
phase. The mixture was maintained between 35 and 40C while applied to
the surface of Strathmore Bristol 300 series smooth vellum (260gsm)
with a brush twice, without drying, with diagonal strokes.

Comparison mixture was made with same gelatin solution except glut was
used instead of epox.

Glut can smell if the ventilation of the room is inadequate. Epox
doesn't smell.

Epox hardened solution is a bit easier to coat with brush because it
is significantly less viscous. (Viscosity of epox hardened gelatin
solution is almost unchanged from plain gelatin solution.) Epox
hardened solution is virtually free of foaming because epox serves as
a defoaming agent as well. If too much epox is added, the excess epox
simply won't get blended with the water phase and it makes a separate
phase.

Gelatin hardened with glut is easier to gel when cooled. Gelation of
epox hardened solution is probably about the same as the original
(unhardened) gelatin solution.

Glut hardened paper is usable when the paper is completely dry. On the
other hand, epox hardened paper is still almost unhardened by that
time. By day 2, gelatin is significantly hardened but it is not
hardened enough to use for silver gelatin emulsion (coated warm). By
day 3, the gel is hardened enough, but the best result is obtained a
week after sizing the paper.

Hardening property of epox can be increased by increasing gelatin
concentration, epox concentration, or both. Unless impractically large
amounts of them are used, they do not cause immediate hardening to
make stiff solid that doesn't dissolve again. (With glut, it's easy to
cause the gelatin to solidify like that to ruin the brush if excessive
amount of glut is used.)

Hardening property of epox decreased when gelatin of smaller molecular
weight was used. Users of food gelatin might want to use a bit higher
amount of gelatin, epox, or probably both (e.g. 4% gelatin, 0.3% epox
in water). But more stronger paper surface can be obtained with high
quality ossein gelatin of large avg molecular weight.

Advantage:

1. it gives off little or no fume (and no smell)
2. it does not ruin the brush when too much hardener is added
3. it also serves as a defoaming agent in aquaous solution of gelatin
4. it does not immediately increase the viscosity of gelatin solution
5. it does not immediately lower the gelling temperature of gelatin
6. gelatin hardened with it swells just as much as glut-hardened gel
7. it hardens gelatin as well as many nongelatin polymers having
   reactive carboxyl or amino groups (yes this reacts with both these
   and probably more)

Disadvantage:

1. it hardens gelatin very slowly (gel isn't hardened when just dried)
2. it is more expensive than glut (so what?)
3. it is harder to buy than glut (but it is commercially available)

MSDS and other info indicates that this compound is not terribly
dangerous, and safety devices recommended in MSDS are totally within
the reach of this community. But I strongly recommend to review MSDS
before using any new chemical.

Finally, please don't ask me where you can buy this chemical. It is
commercially produced at least by a couple of chemical companies in
Japan, and it is found in the catalogues of chemical dealers. I think
companies like B&S and Photographer's Formulary should be carrying
this chemical, and you should call them to show that there is market
interest. A small bottle (say 50ml) can go a very long way as you see
above.

PS. This Strathmore Bristol vellum paper is quite absorbent and takes
wet processing well, but this paper doesn't dry very flat, at least
after silver gelatin emulsion is coated on the sized paper, processed,
and dried. This vellum is cheap but I like Artistico Extra White
better for anything of value.
Received on Fri Aug 5 12:20:13 2005