During our rheological measurements, we have often solved one problem. We measure viscosity on an extrusion machine equipped with a rheological head. We need the value of density of rubber (ex. natural rubber) for the calculation of viscosity. The measurement is at an elevated temperature (ex. 110 °C).
When we measure the viscosity of plastic, it is simple, because we can measure the density on a melt flow index machine (MFI). Natural rubber is almost unmeasurable on MFI. So we tried the pycnometer, but there we can measure only to the app. 90 °C. We measure the density at four lower temperatures and we use some curve to get the density at elevated temperature. I think it is not the best technique, but we haven´t found better.
Thank you for some advice.
Drahomir Cadek
Do you mean 'calculate' or 'measure'? If you mean 'calculate' then one estimation can be from the coefficient of expansion of rubber - as the temperature increases the size/volume increases and thus the density decreases (density = mass/volume). If you mean 'measure', then you can use a gas pycnometer that allows 1100C or use an Archimedes bottle (with care!) and a fluid (e.g. silicone - not water) that allows measurement at 1100C.
Alan F Rawle
Thank you, I mean measure, sorry for that. Silicone oil is very good idea, but we have problem with bubbles, that surround the rubber sample. We try detergent, reboiled water, but the results are still very different. We will try the silicone at elevated temperature. Thank you.
Hi Drahomir Cadek
We can use the capillary rheometer to measure the density of a melted or high temperature polymer or rubber sample. You can also test the compressibility of it at different pressures or temperatures. This is a test in the Rosand capillary rheometer system. If you'd like to have this done by contract testing, please let us know.
Best regards,
Phil
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