PVOH looks simple but there is a lot of polymer chemistry going on in there. Extent of hydrolysis and molecular weight both determine the viscosity and solubility behavior of the product.
PVOH-borax interaction is the principle behind the well known
"slime" making that kids are very familiar with. Some time ago I was trying to see if it could be used make a sizing that is both insoluble and hydrophilic unlike say, PVAc based sizes which when set become plastic-like hydrophobic surfaces. The idea is to coat the paper with soluble PVOH, like the
Elmer's Washable Clear Glue (which by the way is super convenient source of soluble PVOH.) Then treat it with dilute solution of borax which will form an insoluble film. For example, I added some India ink to EWCG and painted it on a strip of paper, dried. Then dunked half of it in 1% borax for a couple of minutes. Then washed it for several minutes. As can be seen below, the portion that was treated with borax remains untouched and the untreated side cleared out completely, save for a little stain.
View attachment 348559
So my thinking was since the developer is generally alkaline, small amount of borax wouldn't hurt it but could harden the binder. Alternatively, the paper can be pre-treated with borax solution before putting it in the developer. I don't know what happens in the stop bath - does it undo borax? Need to experiment as with all great ideas and alternative processes.
:Niranjan.
