Is PVA transparent ?

[Mustafa Umut Sarac]

One of my friend was talking about pva and replacement of collodion at wet plates. I know pva is carpenters glue , I know not anymore. Is there transparent pva ?

umut

 

[removed account4]

(there was a url link here which no longer exists)
(there was a url link here which no longer exists)

 

[nmp]

One of my friend was talking about pva and replacement of collodion at wet plates. I know pva is carpenters glue , I know not anymore. Is there transparent pva ?

umut

PVA, Polyvinyl acetate, in its solid film form should be transparent as it is an amorphous polymer. It is however insoluble in water. Similar to other latex based materials, the glues based on PVA are made as emulsions in water, hence the opaque whiteness (a result of scattering of light by the suspended particles.) Once applied and dried, they should become transparent or translucent though, unless there is some sort of dye or pigment to colorize it. Classic "wood" glue probably has some colorant to match the color of wood. The "white" paper glue should have none. Experiment by making a puddle on an aluminum foil and drying it completely.

If there is still some water left in the film as it might be if you are looking to use in a "wet" plate process, it will still scatter some light and not be completely transparent. It might also have other complications like what happens in the AgNo3 bath. On the other hand, perhaps you can get solid PVA (in bead or powder form) and dissolve it in one of its solvents such as acetone or methanol mixed with some water (to solubilize the salts) and apply on the plate. That would be similar to the classic Collodion process, without the problems associated with nitrocellulose that is.

 

[nmp]

Hi, new here.

This can be an odd question but I'd like to know if there is a difference between various PVA brands. I don't use PVA as a support material but as a tool for mold making. I print a shape in PVA, prepare a mold box, use transparent silicone to cover it excluding its poles then use hot water in an ultrasonic bath to dissolve the PVA. This way, I can obtain hollow silicone models shaped like objects. The problem is that the PVA that I use, manufactured by Esun, which is really easy to print is quite undissolvable. I have seen Youtube videos where PVA dissolves like it is effervescent but my PVA requires the removal of softened pieces by pliers, otherwise, it doesn't dissolve at all by itself. The problem is exacerbated by the fact that the surface area of the PVA which is in contact with the water is very small due to it being covered by silicone. My question is: Is there a difference between the solubility of different PVA brands?

I have also tried HIPS by Esun, which should dissolve by limonene, but I still have the same problem (and also the fact that Limonene is expensive doesn't make things easier)

It would be hard to say definitively what is going on unless you provide a link to the description and/or MSDS of the polymer you are using.

However, I think the problem lies in what the acronym PVA has been used/mis-used to mean. In the scientific world, PVA means polyvinyl acetate, while polyvinyl alcohol is PVOH. In the commercial world however, the same term PVA is often used interchangeably for both. The two are related but they have drastically different properties. PVA is insoluble in water. While the matter is more complicated for PVOH. The latter is made by starting from the former and hydrolyzing it, i.e. converting the acetate groups to alcohol groups. Alcohol groups have affinity towards water, so as their proportion increases, the polymer starts to increase its solubility in water. However, if you go above a certain percentage of conversion, the alcohol groups can associate to themselves and form microcrystals which inhibits water solubility. So generally water-soluble form of PVOH is partially hydrolyzed, say to about 70%, above which the polymer becomes insoluble or requires higher temperature to dissolve in water.

So the question is which PVA do you have and which PVA are the folks in the YouTube videos are using?

:Niranjan.