- Do you know that flexible materials are prone to absorb more water than the rigid ones?
- Do you know that 25-27 m2 of PVB might absorb to 1 liter of water?
- Do you know that NovoGlass®SF, being also a soft polymer, absorbs 25% less water that PVB?
Depending on the level of water retention, they are classified as hygroscopic or hydrophobic materials. Almost all of them are hygroscopic, in a higher or lower level. Hydrophobic materials are wear. If we analyze the capacity to absorb water of one material, there are several important factors to take into account. Between all of them the most important is their specific chemical composition. Other important factors are also their type of their own surface, its mechanical structure and the environmental conditions.
If we focus our attention on polymeric materials (the plastic ones) we can group them, according their mechanical structure, in two types: rigid and soft. Mainly the rigidity depends on the density and hardness and both parameters are dependent on their chemical structure.
Focusing on Films (pieces of thicknesses between 20 to 1,000 microns), it is normally seen that the rigid Films, like the polycarbonate, PC, tend to absorb less water than the soft ones, like the PolyVinylButyral, PVB. That is a true fact. This is because regardless of their chemical tendency to link with water, the soft films have more surface available to contact with water. Moreover, due to their lower density, the soft ones have internal channels and voids that can physically trap water molecules on them. So we might figure out the soft polymers like “sponges” , where part of the water gets stick to the their surface and part gets physically trap into the voids.
To compare the different capacities to absorb water between the PC (a rigid polymer) and the PVB (a flexible one) we have measured their water content at 25ºC and 50% degree of humidity.
The following graph presents the losses of water of film samples when both samples were heated at 80ºC during 90 minutes. The losses represent the water absorbed %. PVB absorbed a 1,61%, while the PC a 0,23%.
The same study shows that around 25 m2 of PVB might absorb up to 1 liter of water, while the same quantity of water might be absorbed by around 260 m2 of PC. In other words PVB absorbs 10 times more water than PC.
If we compare two soft products like the PVB and the NovoGlass® SF, then we might see some differences, depending on their chemical composition. In that case the NovoGlass® SF absorbs 25% less water than PVB.
If you are interested to get the details of how this analytical study has been performed and the detailed data, please just let us know. You will be able to reproduce our results!, and the best of all, you will add a new analytical procedure to your Analytical toolbox.
If you want to know more about soft materials performance differences (PVB vs NovoGlass® SF), please click at this link