Anionic stilbenes optical brighteners can be added to certain photographic elements, reacting with a hydrophilic ligand, preferably gelatin. Some technological implications of optical brighteners addition in gelatin systems have been investigated:
a) the effect on viscosity as a consequence of ionic strength influence;
b) the impact on the kinetics of the hardening process, quantifying the size of the rate constant for the cross-linking reaction of gelatin with a slow acting hardener (pseudo first order reaction), by measuring the reduction of swelling for the coated layers.
Variations of the rate constant are given in relation to:
-optical brighteners' concentration
-optical brighteners' type (disulphoaminostilbene or dichloraminostilbene)
-gelatin type (limed bone or acid bone)
The experimental results have confirmed the structure-breaking action of optical brighteners in the gelatin network.
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