Freeze-Thaw Stability of Polyvinyl Acetate

Manufacturer: We are manufacturing and supplying coating compounds based on polyvinyl acetate emulsion. While this works well in South East Asia, it fails in temperate countries due to instability of the latex (i.e. emulsion) during winters. Please explain what could have happened, what tests we need to do and how to overcome the problem.

John Woon (Senior Latex Consultant): I believe your products have poor Freeze-Thaw stability. I suggest you test the Freeze-Thaw stability using the following method:

1) Fill up a glass bottle (of capacity of about 250 gram) with the latex to three-quarter full.

2) Subject the bottle to 10 cycles of 18 hours freezing at - 20°C followed by 6 hours thawing at room temperature.

3) Examine the sample for signs of gelling and precipitation (coagulation).

If the test confirms that the product has poor resistance to freeze/thaw, proceed to do the following:

1) Add ethylene glycol at 1 to 2% into a fresh sample of adhesive and stir gently
for 1 hour.

2) Repeat the freeze-thaw test.

Solidification and Gelling Issue of Plastisol Under Infrared Heater

Manufacturer: We observed something strange when trying to solidify and gel two different PVC plastisol compounds using oven with infrared heater. We thought they would both solidify within 20 minutes but we observed that while one gelled and solidified the other remained fluid.

However both plastisol compounds gelled and solidified satisfactorily when heated in an oven which is using electric heater. Can you explain why?

John Woon (Senior Latex Consultant): Unlike your electrical oven, infrared heaters depend on not only the wavelength it emits but also the substrate type i.e. the absorption characteristics of the substrate, e.g.
PVC plastisol.

Different IR heaters have different wavelengths. For instance, some IR heaters can't heat up water efficiently because the wavelength dose not match the absorption spectrum for water.

Apparently, the two PVC plastisol compounds have different absorption characteristics.