| Hysteresis properties of polyester and polyether based polyurethanes were studied by varying the chemical backbone structure, polyblending, and the addition of fillers. Their effects on the transition temperature and the loss factor were investigated dynamic mechanically. These systems were evaluated then for their damping performance as coating materials on steel plates in the extensional and constrained layer configurations.;Variation of hard and soft segments in polyether (poly(ethylene oxide)) based polyurethanes resulted in a range of morphological structures and properties. Two tan (delta) peaks were observed for samples with long soft segments indicating phase separation. With intermediate soft segment lengths, partial phase separation was inferred from the appearance of two transition regions close together with an intermediate region of high tan (delta) values. More complete phase mixing occurred for poly(propylene oxide)diol based polyurethanes and when the symmetry of the hard segment structure was reduced. Higher tan (delta) values were found generally for morphologically heterogeneous structures.;Blending of polyurethane and epoxy resin resulted in a pseudo-interpenetrating polymer network structure with increased modulus and loss factor at temperatures between the two glass transition temperatures of the homopolymers.;Above the glass transition temperature of the matrix, tan (delta) values were increased by the addition of mica and calcium carbonate. Analysis of the relaxation spectrum showed that the fillers affected the average relaxation time of polymer molecules near the filler surface and caused widening of the transition regions.;For the polyester based polyurethanes, it was found that the transition region was broadened by the presence of bulky groups in a relatively long soft segment. Tan (delta) values were also increased. The introduction of heterogeneity would account for these effects.;The damping performance of the systems in the extensional configuration showed that the loss modulus of the coating layer was the most important variable, Mica filled polymers were very effective coatings as the planar fillers increased the flexural modulus greatly and behaved similarly to constraining layers. In the constrained layer configuration, the composite damping factor depended on the loss factor of the viscoelastic layer and the bending stiffness of the constraining layer. The temperature dispersion curve of the composite damping factor resembled the tan (delta) - temperature dispersion curve of the viscoelastic layer closely. Theoretical treatment showed that the damping performance followed Oberst's theory in the extensional mode and Kerwin's theory in the constrained mode. |
