# Identifying the solubility of Polyvinyl Alcohol (PVA) in water versus temperature

Background:

Poly Vinyl Alchohol (PVA) is a plastic used for a sacrificial support material for 3D printing and sewing. This material is used specifically because it is water soluble, and can be dissolved by placing the PVA in water. As dissolving the PVA is basically a processing step, I'm interested in optimizing this step. For me, optimizing this process consists of:

• Minimizing the amount of time that the process takes
• Minimizing the cost of processing (e.g. water, heating)
• Minimizing the waste material (e.g. saturated water)

From my limited experimentation, I know that increasing the temperature of the water increases the speed that the PVA dissolves. I also know that increasing the water volume (either through water changes or just a larger processing tub) also reduces processing time. From my limited understanding, this isn't really that surprising - many chemicals have increased solubility with temperature, and increasing the volume of solvent decreases the concentration of the PVA.

Question: What is the solubility of PVA in water vs. temperature? Is there a source for a graph that ties the speed of dissolving PVA vs. temperature and PVA concentration? (How could I find this information, if that's better to answer)

(Some) Limits of my knowledge:

1. I don't know if all PVA is created equal.
2. I don't really know any organic chemistry.

According to Tager et al.[1]:

All the material described here is thus evidence of the complexity of the PVA-water system, and of the fact that the temperature coefficient of PVA solubility in water depends on the studied temperature and concentration ranges. [...] At medium concen- trations and fairly low temperatures, heating will improve the PVA solubility in water, but it will become poorer again at higher temperatures.

For more information, you can refer to the commentary they made on their Figure 4. Beware though, I read the article quickly and it seems that what they termed "solubility" is not the actual solubility $$-$$ in $$g.L^{-1}$$ for instance $$-$$ but is more like the thermodynamic affinity of the two compounds (water and PVA). I may have misinterpreted something though...

For a clearer view, you may also have a look at Finch[2]:

As you can see, the solubility strongly depends on the degree of polymerization of the PVA. Thus, depending on this parameter in your particular PVA, it may or may not be necessary to heat the water to have a better solubility...

Anyway, in your view of optimizing the process, the final decision should essentially depends on which factor(s) is(are) crucial for you: energy (for heating), water, or time.

Indeed, although the overall solubility ($$g.L^{-1}$$) of PVA in water can decrease with temperature in certain cases, if the kinetic of the reactions if favoured by an elevated temperature, you may want to heat your water anyway. Please note that solubility $$-$$ i.e. the amount of substance that you can dissolve in a given volume of solvent (in $$g.L^{-1}$$ or $$mol.L^{-1}$$) $$-$$ and rate of dissolution $$-$$ i.e. the speed at which a given compound dissolves (in $$g.s^{-1}$$ or $$mol.s^{-1}$$) $$-$$ are two different and possibly unrelated things!

Let say time is crucial for you, you would want to use a lot of heated water and replace it often, so as to "flush" your PVA with hot, 0%PVA water. The dissolution will probably be extremely quick but you will waste much water and energy.

At the opposite, if you are short on water and energy but have plenty of time. You may want to keep the amount of cold water minimal so that at the end of the dissolution, the water is just below the its saturation point with respect to PVA concentration.

1. Tager et al. The effect of temperature on the water solubility of polyvinyl alcohol, Polymer Science U.S.S.R. Volume 13, Issue 3 pp751-758, 1971, DOI: 10.1016/0032-3950(71)90042-6
2. C. A. Finch, Some Properties of Polyvinyl Alcohol and their Possible Applications, Chemistry and Technology of Water-Soluble Polymers pp 287-306, 1983, DOI: 10.1007/978-1-4757-9661-2_17
• This is tremendously useful foothold into the subject matter. I couldn't get a copy of [1], but I am reading through [2]. I think you may be right that I'm also interested in the rate of diffusion of PVA.
– W5VO
Sep 27 '21 at 15:32
• @W5VO I apologize for I mistakenly wrote "rate of diffusion" instead of "rate of dissolution" (corrected in my answer): en.wikipedia.org/wiki/Solubility#Rate_of_dissolution As for [1], I am afraid that the community is against circumventing paywals, so I can absolutely not put you a direct link to Sci-Hub, nor can I strongly advise you to use it so as to quickly find research items using their DOI : chemistry.meta.stackexchange.com/questions/3634/… Sep 28 '21 at 9:56
• @mrnvick: Very good answer: +1. Sep 28 '21 at 14:43
• @W5VO: If you contact the manufacturer of the PVAl (rather than PVAc), you may be able to get a brochure listing all their products: mw variations, % hydrolyzed variations, and various solubility and mixture effects. This may not give you the exact optimal procedure, but may be a helpful reference and elucidate the molecular interactions going on. It could also lead you to a better PVAl. (BTW, I've also seen PVOH as an abbreviation, to distinguish from PVA = polyvinyl acetate.) Sep 28 '21 at 14:43
• @JamesGaidis Part of the problem is that I'm purchasing the PVAl as water soluble "fabric" or "filament", and I don't have information about the PVAl source, molecular weight or percent hydrolyzed (wouldn't surprise me if it's a trade secret). Looking for materials information from manufacturers of PVAl is a good tip, I'll see if that turns anything up.
– W5VO
Sep 28 '21 at 14:59