Rheometics Dynamic Mechanical Analyzer

The viscoelastic properties such as storage modulus, loss modulus, and tan 8 are measured using a dynamic mechanical analyzer (DMA) and/or a rheometer. 

Small deformation rheometry refers to testing procedures that do not cause structural damage to the sample. Constant stress rheometers, such as dynamic mechanical analyzers or oscillatory constant stress rheometers, are often used. 

FIGURE20.3 Illustration of how forces are applied to samples in a rota tional rheometer and a dynamic mechanical analyzer. 

Rheometers are used in a much larger frequency range than DMA, for a large variety of materials, from liquids to soft solids. Their configurations are plate-plate and cone-plate, whereas torsion and tension attachments are optional. Dynamic mechanical analyzers perform only oscillatory experiments on load-bearing samples (i.e., those that have a shape with well-defined dimensions, such as films, fibers, or bars). The samples can be fixed in specific attachments, such as tension, bending, shear, or compression. A new attachment has been developed for DMA that is intended for non-self-supporting samples—a material pocket (Pinheiro and Mano 2009). The material pocket behaves elastically over the studied temperature... 

This chapter covers some of the methods and instruments used to determine the mechanical properties of polymers. Examples of instrument designs and typical data generated in these measurements will be introduced. In particular, automated axial tensiometers (to find elastic modulus, yield stress, and ultimate stress), dynamic mechanical analyzers (to determine storage and loss moduli), and rheometers (to measure flow viscosity) will be introduced. This chapter considers the principles behind the devices used to establish and measure the properties of viscometric flows. One of the common techniques used to determine viscous flow properties, PoisueiUe (laminar) flow in cylindrical tubes, is also important in technical applications, as polymer melts and solutions are often transported and processed in this manner. The time-temperature superposition principle is also covered as a way to predict polymer behavior over long timescales by testing materials across a range of temperatures. 

Two types of shrink testing were conducted on these films, and these methods are as follows (1) fixed length shrink force testing, and (2) free shrink testing. A TA Instruments ARES-LS rheometer and a TA Instruments Q800 Dynamic Mechanical Analyzer (DMA) were employed, respectively, to perform these two shrink tests. The rotational rheometer (ARES-LS) was used to conduct the fixed length shrink force test. In this test, the length of the film was fixed and the normal force was... 

This study looked used a series of polyethylene samples to determine alternate methods to measure their Melt Index values. These methods used a controlled rate capillary rheometer and a Dynamic Mechanical Analyzer. Both methods showed reasonable estimates of around 1 gram/10 minutes for most of the samples tested. The DMA was able to improve its estimate of the Melt Index by doing a multiple regression with both complex viscosity and the Tan5 value. 

Blends of vulcanized rubber particles may be analyzed using dynamic mechanical rheological techniques if the particle size is less than 1/10 of the gap between the plates of the rheometer. If the average particle size approaches the width of the gap, anomalous results may be obtained. More research is needed to establish the optimum conditions for analyzing crumb rubber mixtures. 

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