Strain-Induced Molecular Ordering in Polylactide upon Uniaxial Stretching

TLDR: In this paper, the tensile drawing behavior of polylactide material containing 4% of d-stereoisomer units, in the amorphous state, was studied.

Abstract: This study deals with the tensile drawing behavior of a polylactide material containing 4% of d-stereoisomer units, in the amorphous state. The draw temperature domain spanned from the glass transition to the onset of thermal crystallization, namely 70−100 °C. The stress−strain curves exhibit a strain-hardening strongly sensitive to the draw temperature regarding both the onset and the slope of the phenomenon. A detailed structural investigation reveals that various strain-induced phase changes take place depending on the draw temperature. For Td = 70 °C, a mesomorphic form develops from the strain-oriented amorphous chains, starting at a strain level e ≈ 130%. In the case Td = 90 °C, a well-defined crystalline phase grows beyond the strain e ≈ 250%. In the midtemperature range, i.e. Td = 80 °C, both the mesomorphic and the crystalline phases are generated in parallel. In all cases, the final weight content of ordered phases at rupture was roughly 30%, irrespective of their form. The observed evolution wi...