Mechanical Properties of Poly(L-Lactide) Films Controlled by Blending with Polyesters of Lignin-Derived Stable Metabolic Intermediate, 2-Pyrone-4,6-Dicarboxylic Acid (PDC)

Two kinds of polyesters containing 2-pyrone-4,6-dicarboxylic acid (PDC) moieties in poly(L-lactic acid) (PLLA) and poly(butylene succinate) (PBS) main chains were for the first time employed as an additive to PLLA for improvement of the mechanical properties. Solution casting of a mixture of PLLA and PDC polyesters provided the blend films, which were comprehensively characterized by thermal analyses, tensile measurements, and crystallinity evaluation. Differential scanning calorimetry measurements revealed that PDC incorporation into polymer main chain dramatically improves the miscibility with PLLA. PDC-incorporated PBS showed better miscibility than PDC-incorporated PLLA. Optical microscopy measurements also suggested the superior orientation of PDC-incorporated PBS over PDC-incorporated PLLA in the blend films. The fracture strain of the blend films could be linearly increased by a draw ratio in the region of low PDC polyester content. On the contrary, the fracture strain decreased at high PDC polyester content due to the restricted strain caused by the strong dipolar interactions between PDC moieties. Elongation at break was significantly varied as a function of PDC polyester content, whereas tensile modulus was almost independent of the additive content and draw ratios. It is concluded that the blend films containing < 10 wt % of PDC-incorporated PBS as an additive show the best tensile property.