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Dual Blade Cutter

Extensional Rheology

The miniature SER fixture can be easily attached to the rotational rheometer host station and configured to operate with the existing control software. By controlling the motor rotation and operating temperature of the host station, the SER can be used to characterize extensional melt flow. As illustrated by the data, the SER is a robust yet sensitive instrument capable of characterizing the flow properties of ultra high viscosity elastomers and low viscosity polymer melts in either a controlled rate or controlled stress mode of operation.

Stress Growth and Relaxation

As has been described, a constant Hencky strain rate deformation is achieved by applying a constant drum rotational speed with the SER. By collecting the time and torque for a given temperature and rate, the data can be easily converted to produce tensile stress growth curves.

Extensional Rheology   Melt Rheology

LLDPE and LDPE   Branched Polymer

Because of the high degree of molecular orientation and polymer chain stretch that can be achieved in simple extension, differences between linear and branched polymer architectures are clearly evident from the melt tensile stress growth data. Note the broad span of Hencky strain rates and how the low strain portions of the tensile stress growth curves superpose with the linear viscoelastic envelope defined by the plot of 3 times the shear stress growth curves taken from cone & plate measurements.

Natural Rubber   Low Density Polyethylene

Even subtle differences in polymer architecture that are often difficult to detect from shear rheology data are clearly evident from extensional rheology data - a feature that makes the SER also well-suited for even the most challenging of polymer quality control applications. Regardless of the host platform being used, whether of controlled rate or controlled stress/rate design, the SER provides accurate and consistent results over a very broad range of extensional rates and melt viscosities.

Stress Relaxation   Cessation

Although historically difficult to perform, the tensile stress relaxation modulus of polymer melts can be easily and directly determined from step extension experiments. Cessation of extension experiments are useful in determining the strain dependence of relaxation behavior and in studying the onset of elastic melt instabilities.

Creep

Because the cross-sectional area of a sample undergoing uniaxial extension decreases exponentially with deformation, the application of a constant tensile creep stress requires the exponential decrease of applied force as a function of deformation. A feature unique to certain controlled stress/strain rotational rheometers allows for the exponential decay of applied torque with spindle rotation, enabling the SER to be used for extensional creep flow measurements as well as tensile stress growth measurements with polymer melts.

Tensile Creep   Viscosity

As illustrated by the data above, the SER is a robust yet sensitive instrument capable of characterizing the flow properties of ultra high viscosity elastomers and even low viscosity polymer melts in both tensile stress growth and tensile creep modes of operation.

The SER Advantage

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