| There should be a clear relationship between the microstructure of a polymeric filament and its mechanical properties. While the tensile properties of filaments have been related to fiber microstructure in numerous studies over several decades, there have been relatively few attempts to relate shear modulus to microstructure. Most of the work on shear properties of filaments was done over twenty-years ago. Since then, there have been advances in instrumentation technology, as well as an increase in the number and types of synthetic filaments commercially available.;The objective of this study is twofold. The first objective is the construction of a fully-automated torsion test apparatus. The second is to use the device to perform a preliminary investigation of the relationship between polypropylene fiber microstructure and the shear modulus. This will lay the foundation for a definitive research program into the microstructure/shear properties inter-relationships.;The torsion test apparatus which was built is a modification of the simple torsion balance. Data acquisition and test parameters are completely controlled through a microcomputer. Raw data from digital position encoders is converted into torque-twist data, which is then entered into a statistical program which performs a least squares non-linear fit routine on the data. The parameters derived from the model fit by the statistical program are used to determine the initial shear modulus of the filament.;Torsion testing was performed on seven different polypropylene fiber samples. It was found that the shear modulus of the filaments increased with an increase in amorphous orientation, but that in a radially structurally differentiated filament, the relationship is most likely biased toward the modulus of the outer portion of the filament.;The induction of a state of shear in a filament is accomplished by torsion, or twisting, of the filament. A straight-forward apparatus known as a torsion balance is used to measure the small torques created in a filament upon twisting. The data obtained for torque relative to the amount of twist can be plotted, and converted to stress-strain data, for analysis of the torsional or shear modulus. |
