Torsional braid analyzer method

Free- Vibration Methods. Free-vibration instruments subject a specimen to a displacement and allow it to vibrate freely. The oscillations are monitored for frequency and damping characteristics as they disappear. The displacement is repeated again and again as the specimen is heated or cooled. The results are used to calculate storage and loss modulus data. The torsional pendulum and torsional braid analyzer (TBA) are examples of free-vibration instruments. 

Free vibration and forced vibration methods have been employed to determine the respective data. Free vibration was common earlier in polymer blend studies, but forced vibration data is much more common today due to the availability of more sophisticated testing equipment. Free vibration methods include the torsion pendulum, the vibrating reed and the torsional braid analyzer. The torsion pendulum is comprised of an inertial source (disk or rod), which can freely vibrate and is attached to a specimen, which is rigidly fixed at one end. Upon angular deformation of the inertial source and releasing, a damped sinusoidal curve depicts the resultant deformation of the sample [18,19]. Tan S can be calculated from... 

Dynamic mechanical analysis is quite useful to observe the result of chemical reactions of polymer chains (e.g., transesterification) as evidenced by Figs. 3.12 and 3.13 [26]. The DMA method can be applied isothermally to determine crystallization kinetics (modulus versus time measurements) [13, 27] and reaction rate of thermosetting materials (e.g., epoxy) [28]. For reaction rate determination of liquid systems, the torsional braid analyzer is most appropriate as the braid can be saturated with the prepolymer liquid. A cellulose blotter could be used for the torsion pendulum, and a section of nylon hosiery could be used for forced vibration studies (both supports saturated with liquid prepolymer). 

The curve of tan8 vs. o) is very useful, since it peaks at characteristic polymer transitions. Certain methods of dynamic analysis, such as the torsional braid method, yield loss tangents readily, but are difficult to analyze separately for the storage and loss moduli. (See also Chapter 5 by Chu.)... 

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