Uniaxial stretching of polylactide with different initial crystalline morphologies and temperature effect

• Sample with nucleators owns larger elongation and higher crystal orientation.
• The newly formed fibrillar crystals are less perfect than the original lamellae.
• The original lamellar thickness governs the crystalline evolution under strain.
• Higher draw temperature benefits the chain unfolding in the original lamellae.

The investigation about the uniaxial stretching behavior of two crystallized poly(L-lactide)s (PLLA) with the same degree of crystallinity but different crystalline morphologies was carried out by two dimensional Wide Angle X-ray Scattering (2D-WAXS) and Differential Scanning Calorimetry (DSC). The original lamellar blocks and the orientation induced fibrillar crystals coexist during stretching for both samples, and a mesophase is detected when the material is drawn at 65 °C. Larger elongation and hence higher crystal orientation can be obtained for the sample with nucleating agent which owns the thinner average lamellar thickness, whereas the lower melting point indicates the fibrillar crystals in this stretched sample are less perfect. Besides, higher draw temperature benefits the unfolding of chains in the original lamellae but can also decrease the chain orientation due to the enhanced chain relaxation. The original lamellar thickness is supposed to be the governing factor which determines the different crystalline structures under strain.

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