Theoretical and Experimental Evaluation of Crystallite Moduli of Various Crystalline Forms of Poly(l-lactic acid)

Abstract

The crystallite modulus or ultimate Young’s modulus along the chain axis in the crystal lattice was estimated theoretically and experimentally for poly(l-lactic acid) (PLLA) α and δ (disordered α) forms and the mesophase (isolated chain model) on the basis of the refined crystal structures reported in previous papers (Macromolecules 2011, 44, 6441, 9650; Polymer, 2011, 52, 6097). The calculated modulus was 14.7 (α form), 12.9 (δ form), and 6.7 GPa (mesophase), which are in good agreement with the values obtained by the X-ray diffraction method, 13.76 ± 0.17, 12.58 ± 0.15, and 7.47 ± 0.20 GPa, respectively. (The experimental data were obtained under the assumption of homogeneous stress distribution, and so the experimentally obtained crystallite modulus should be assumed as the apparent crystallite modulus. But the observed tendency might be kept even if the true crystallite modulus is clarified in future.) The difference in Young's modulus among the three phases has been discussed in terms of the chain co...