General considerations on hysteresis and Mullins effect

Hysteresis, which is characteristic of most polyurethanes, has been attributed to a number of factors including nonafline deformation, plastic deformation of the hard 

Numerous studies have been reported on the investigation of the PUs and other elastomeric materials hysteresis behaviour [284-293]. As shown, the hysteresis and the associated mechanical loss processes can be partly attributed to the breakdown and reformation of the mesophase morphology during mechanical cycling [284], 

The mechanical hysteresis of poly ether PUs investigated by Gorge et al was studied as a function of temperature, percent strain, and deformation energy. Hysteresis values remained small at low temperatures when the extent of the sample deformation did not disrupt the glassy matrix. This was readily evident at temperatures below the glass transition temperature Tg) of the polymer where the material did not formally yield. At temperatures above the Tg of the polymer, hysteresis remained small even at substantial strains levels and demonstrated the capabilities of the HS domains to act as physical crosslinks. At high emperatures, the percent hysteresis increased as the hydrogen-bonded HS domains weakened. 

Nallicheri examined the influence of hard domain cohesion on the hysteresis behaviour. The hard domains of these materials were selectively crosslinked in the solid state by polymerizing the diacetylene groups contained within their HS. For materials with weakly associated HS, it oberved that low levels of crosslinking 

As revelead by Godovski, irrespective of temperature, the extension of PBU based materials curves for the first cycles differ from those of subsequent deformations. Similar conclusions were drawn by us for other polyester of polyether PUs derived from MDI, DBDI or mixturews of them [135]. 

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