Polymer melt rheology is a complex subject that requires careful experiment design in order to obtain the information needed to meet an investigator’s requirements. AAPPI’s Rheology Laboratory is well-equipped to satisfy the rheological testing needs of research and development. Among the instruments present in the lab are a TA Instruments ARES-LS strain-controlled rheometer, a TA Instruments AR 2000 stress-controlled rheometer, a Malvern RH10 Advanced Capillary Rheometer, a Brabender torque rheometer, and a 100-ton, 18" x 18" Wabash-MPI compression molding press.
These instruments provide the necessary support for sample preparation, and linear and non-linear shear rheological analyses of fluids ranging from aqueous solutions to highly viscous polymer melts. Extensional viscosity measurements can be provided using the TA Instruments ARES-LS in conjunction with the planetary gear extensional viscometer fixture.
Rotational Rheometers
These instruments normally require a small specimen of the material to be
tested in the form of disk, typically 25mm diameter and 1mm thick. The
sample is placed between a pair of parallel plates or upper cone and lower
plate whose temperature can be maintained by an oven.
Rotational rheometers use a number of test types to characterize a material
over a range of temperatures and flow rates. Examples of the types of the
types of tests available are:
• Flow curves
• Creep tests
• Stress relaxation tests
• Small amplitude sinusoidal oscillatory testing
Capillary Rheometers
Capillary rheometers are comprised of a temperature-controlled barrel incorporating one or more precision bores fitted with capillary dies at the exit. Pressure transducers are mounted immediately above the dies to record the pressure drop as the material being tested is extruded through the dies at a set volumetric flow rates.
Capillary rheometry is a technique whereby a sample is extruded through a die of defined dimensions and the shear pressure drop across the die recorded at set volumetric flow rates.
What materials can be tested using a capillary rheometer?
Polymer and rubber testing are historically the main areas for capillary rheometry use. However, applications for capillary rheometers cover a wide range of industries:
Ceramics – to determine the flow and moulding properties
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Paints and inks – to characterize materials used in spraying and
printing
processes
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Foods – to determine mould filling, cooling and setting properties
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Personal care products – to assess container filling, spraying and
pumping
properties -
Why Do We Have Different types of Rheometers?
Rotational rheometers are the preferred choice when the requirement is to obtain information concerning the molecular structure (e.g., the average molecular weight and molecular weight distribution) and how this affects processing characteristics. The capillary rheometer extends the shear rate range attainable in the laboratory beyond that available in a rotational instrument and allows the flow properties to be measured under typical processing conditions. The ability to readily determine both the shear and extensional properties under real life conditions provide the researcher and polymer processor with information that is vital to the successful use of a polymer melt.
Malvern
RH10
