Rheology Testing

Polyhedron Laboratories performs rheological testing according to ASTM standards, such as Dynamic Mechanical Properties of Plastics in Tension (from –100 to 200 Degrees Centigrade) (ASTM D5026) and Capillary Rheometry (ASTM D3835). Polyhedron also provides other rheological testing, including flow stability, log viscosity versus log shear rate, die swell, Brookfield viscosity and fan viscosity. All ASTM standard descriptions below are paraphrased from the ASTM website (www.astem.org). Due to copyright restrictions, Polyhedron Laboratories cannot make available copies of standards. Standards can be found and are available at www.astm.org.

ASTM D5026-01 - Standard Test Method for Plastics: Dynamic Mechanical Properties: In Tension - This test procedure deals with the use of dynamic mechanical instrumentation for reporting and gathering the viscoelastic properties of thermosetting and thermoplastic resins and composite systems in the form of rectangular samples molded directly or cut from molded shapes, plates or sheets. This test routine provides the means for determining the modulus as a function of temperature of a wide variety of plastics materials using nonresonant forced-vibration techniques. Plots of the loss (viscous); elastic (storage); and complex moduli and tan delta as a function of temperature, time, or frequency are indicative of notable transitions in the thermomechanical performance of the polymeric material system. This test procedure is valid for a wide range of frequencies from 0.01 to 100 Hz.

ASTM D3835-02 - Standard Test Method for Determination of Properties of Polymeric Materials by Means of a Capillary Rheometer - This test procedure outlines the measurement of the rheological properties of polymeric materials at various shear rates and temperatures common to processing equipment. This test routine covers measurement of sensitivity, melt viscosity, or stability of melt viscosity with respect to polymer dwell time and temperature in the rheometer, die swell ratio (polymer memory), and shear sensitivity when extruding under constant rate or stress. The methods described permit the characterization of materials that exhibit both unstable and stable melt viscosity properties. Log Viscosity versus Log Shear Rate is determined by this method. This test procedure is useful for quality control tests on both unreinforced and reinforced thermoplastics, cure cycles of thermosetting materials, and other polymeric materials with a broad range of melt viscosities.

Die swell is a memory effect in which the polymer tries to return to its original shape. As the polymer is forced through the nozzle, it assumes the shape of the nozzle. Once the polymer exits the nozzle, it "recalls" that it wasn’t this shape originally. When the polymer tries to regain or re-form to its former (original) dimensions, distortion and warping occurs.