Attività

Rheometers: How and What do they Measure?

To measure the rheological properties of your sample with a rotational and oscillatory rheometer requires the determination of the torque and deflection angle of the measuring bob. Your sample provides resistance or a reset torque to the setting. The resulting deflection angle is then measured by the rheometer encoder. The speed is calculated from the deflection angle and the time.

However, as the user, you are usually more interested in the rheological parameters. How do you get these? Rheological parameters are calculated from the measured values torque, deflection angle, and speed using conversion factors. All further parameters, such as viscosity, are not measured but calculated.

There is a new grading system for color concentrates and additive masterbatches. It is the European test of melt dispersability known as FPV or Filter Pressure Value. It is reportedly more stringent than the ASTM dispersion test and a more objective indicator of both dispersion quality in a concentrate and how well it will disperse in a polymer matrix. Above all, it is a single number that shows how a concentrate compares with other products.

What is an FPV?

The basic principle is that you run compounded material through a screen mesh, which gradually blocks up with trapped particles. The time it takes to block and the degree of pressure build-up are a good indication of how well dispersed the masterbatch was.