Glass pendulum analysis

Torsional pendulum analysis exhibits discrete relaxations at the glass transition temperatures of PVDF and PA-6 at -45°C and 50°C, respectively. This also indicates incompatibility of the blend components in the amorphous phase after solidification. 

Glass-transition temperatures are commonly determined by differential scanning calorimetry or dynamic mechanical analysis. Many reported values have been measured by dilatometric methods however, methods based on the torsional pendulum, strain gauge, and refractivity also give results which are ia good agreement. Vicat temperature and britde poiat yield only approximate transition temperature values but are useful because of the simplicity of measurement. The reported T values for a large number of polymers may be found ia References 5, 6, 12, and 13. 

It should be noted that a TL, l would not be expected in this polystyrene) braid sample because of its high molecular weight (approximately 100,000) (46). Also, this analysis of the composite structure of the braid supports Nielsen s (47) suggestion that rL, L arises solely from the residual elasticity of the glass. The torsional pendulum, braid, and TL, l will be discussed in more detail elsewhere (16,17). 

A variation of the torsion pendulum, torsional braid analysis (TBA), utilizes a supported specimen so that the dynamic mechanical properties of a sample can be monitored in the liquid as well as the solid states (1, 2). An inert multifilamented glass braid is impregnated with the sample (usually in its liquid state or in solution). The observed dynamic mechanical properties are relative due to the composite nature and complex geometry of the specimen. 

In torsional braid analysis,a flexible, braided fiber, usually glass, is impregnated with the material to be studied. The impregnated fiber then becomes the torsion member in the pendulum. This type of device is useful for following the cure of a material that starts out as a liquid and cures to a solid (e.g., an epoxy). In analyzing the data from such a device, care must be exercised in separating interactions between the sample and supporting fiber. 

In torsional braid analysis (TBA) the sample is impregnated into a multistranded glass braid which acts as support. The method allows analysis of mechanically weak materials, and also materials which are available in very small amounts. Since the specimen is a composite the properties determined are only relative. The main use of TBA is in locating the temperatures of transitions and relaxations. The temperature range available is similar to that given above for conventional torsion pendulums. Manufacturers include Plastics Analysis Instruments Inc., Princeton, NJ, USA. 

---