Crystallinity changes and mechanical properties of syndiotactic 1,2-polybutadiene under plastic deformation

A. Khamidullin1, Y. Lebedev2, R. Kinzyabulatov2, D. Gunderov2
1Bashkir State University, 32 Zaki Validi Street, 450076 Ufa, Republic of Bashkortostan, Russia
2Institute of Molecule and Crystal Physics Ufa Research Center of Russian Academy of Sciences, Prospekt Oktyabrya 71, Ufa, Russia, 450054
In the present paper the influence of uniaxial tension and severe plastic deformation (SPD) on the structure and physico-mechanical properties of syndiotactic 1,2-polybutadiene (SPB), a polymer having thermoplastic properties, have been studied. Test specimens were prepared from commercial grade RB830 polymer (JSR Corp., Japan) with a weight-averaged molecular mass of 1.2∙105 g/mol, the degree of crystallinity of 29% and syndiotactic content of 85-90%. Using X-ray diffractometry and differential scanning calorimetry (DSC) it has been found that in conditions of simple uniaxial tension the crystallinity of SPB at small, less than 250%, elongations increases slightly from 32% to 37%. With further tension, the sample does not change practically the degree of crystallinity. At deformations of 600 to 650% the SPB samples lose their transparency and attain a milky-white color that presumably is due to the formation of a new structural state called «milk phase» (mph) in the polymer under deformation. This structural transition does not have any influence on further deformation modes and the resulting structure and color of the sample are maintained after the stress release. When using the technique of severe plastic deformation by means of torsion straining under high pressure on Bridgman anvils, SPB samples also attain a milky color, but become fully amorphous. They undergo a completely lose of elasticity, sharply decrease of density and become brittle. The nature of this difference when using two deformation techniques is discussed. During uniaxial tension, the change of polymer properties occurs due to the reorientation of macromolecules, while SPD apparently results in the rupture of carbon-carbon bonds.
Received: 02 December 2016   Revised: 06 January 2017   Accepted: 06 March 2017
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