Investigation of the deformation and recovery behavior of nylon-6/rubber thermoplastic vulcanizates on the molecular level by infrared-strain recovery measurements

Thermoplastic vulcanizates (TPVs) prepared by dynamic vulcanization are blends in which cross-linked rubber particles are finely dispersed in a thermoplastic matrix. These blend materials, which are in our case based on nylon-6 and EPDM rubber, show excellent strain recovery behavior, even though the matrix consists of a semicrystalline polymer which should deform plastically. To understand the elastic behavior, infrared spectroscopy in combination with tensile stress-strain measurements have been used. With this method it was possible to follow the orientation behavior of the different phases during stretching. It could be shown that for blends with a high content of rubber (greater than or equal to60 wt %) the degree of orientation of the crystalline and amorphous phase in the nylon matrix is much smaller compared to that of pure nylon during deformation, while the EPDM rubber phase is almost completely stretched. This fact can only be accounted for by a model that assumes a very inhomogeneous phase deformation of the nylon matrix and a good adhesion between the matrix and the dispersed rubber particles. The plastic deformation will be initiated and concentrated in zones where the matrix ligaments are thinnest, whereas the thicker nylon ligaments remain unyielded.