If a problem in a molded product occurs, is it possible to correlate the (rotational) rheological data of that specific sample with the data obtained from the virgin granules of the materials?
If a defect occurs in an injection molded product, it is most likely to come from either the improper properties of the selected raw material or the incorrect flow properties during the processing of the raw material. If it is a processing issue, then studying the flow properties through a capillary rheometer or using a rotational rheometer at high shear rates under identical conditions to those used for the injection molding will help in developing a correlation between the rheological properties and the defects. On the other hand, if the issue is with the properties of the selected raw material then gathering rheological data in the low shear rate range with a rotational rheometer will aid in seeing the correlation between the raw material properties and the molded product defect. A better understanding can be got through the following books:
In case, fillers or reinforcing fibers have been added to the raw material then the following book may help in showing how the rheology is affected by their presence.
3. Aroon V. Shenoy, Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Netherlands (1999).
In your case I suggest that rheological data should be obtained as a function of temperature. If you expect problems above the melting temperature you may define a temperature range between Tm and an upper temperature limit. I would expect that rheological behaviour between solid (granules) and molten (liquid) thermoplast will be too different to draw any conclusions.
Kind regards
Peter
If a defect occurs in an injection molded product, it is most likely to come from either the improper properties of the selected raw material or the incorrect flow properties during the processing of the raw material. If it is a processing issue, then studying the flow properties through a capillary rheometer or using a rotational rheometer at high shear rates under identical conditions to those used for the injection molding will help in developing a correlation between the rheological properties and the defects. On the other hand, if the issue is with the properties of the selected raw material then gathering rheological data in the low shear rate range with a rotational rheometer will aid in seeing the correlation between the raw material properties and the molded product defect. A better understanding can be got through the following books:
In case, fillers or reinforcing fibers have been added to the raw material then the following book may help in showing how the rheology is affected by their presence.
3. Aroon V. Shenoy, Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Netherlands (1999).
It is best to use the combination of methods. I think we can use DSC, XRD, and oscillatory rheometer for identification of defects.
If the feedstock is a random co-polymer (single Tg, multiple Tms), perform DSC of annealed material at various temperatures above apparant Tm and cool them down to below Tc. Comparing results will tell you if melt memory effect (or liquid-liquid phase separation) occured.
Use small amplitude oscillatory shear (SAOS) experiment and build master curves and determine the plateau modulus and molecular weight between entanhlements. Moreover, this will give you a very good understanding about the relaxation behaviour of your sample at a given frequency. Note that you can easily convert the rotational speed of the screw in extruder to angular frequncy of the rheometer and vice versa (needs very basic mathmatics). Just be advised that if your polymer feedstock is the blend of thermoplastics, time-temperature superposition of the moduli may not result in a smooth curve, and therefore, you may not be able to build master curve.
Lastly, if you are dealing with a block co-polymer, phase segragstion is very likely to happen and long-ranged forces due to degrees of imcompatibility between blocks will leave their measurable footprint in terminal region of the viscoelastic properties. As the conclusive remark, I should ask you to provide greater depth of detail about molecular characteristics of your polymer and explain more about the nature of defect.
Not only you can but it is actually recommended for comparing the viscoelastic properties that you can get only with when you graps the low shear rate range.
Capillary rheometer could be useful to get the onset of some defects but shear stresses are much less different and discrimatory at high shear rate.
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