X-Ray Powder Diffraction Analyses of Kraft Lignin-Based Thermoplastic Polymer Blends

Plasticization of methylated kraft lignin-based polymeric materials by miscible low glass transition temperature (T_g) aliphatic polyesters affects the x-ray powder diffraction pattern in a counterintuitive manner. The d-spacing at the point of maximum intensity in the characteristic amorphous halo is displaced towards smaller values. A reduction in molecular weight of the kraft lignin components alone engenders a similar trend. These effects can be understood by describing the diffuse scattering from methylated kraft lignin preparations as a sum of two overlapping Lorentzian component peaks centered at d = ~4.1 Å and d = ~5.1 Å. Comparison with the crystal structures of selected di- and trilignols indicates that these two peaks encompass d-spacings between aromatic rings which are, respectively, in roughly parallel-but-offset and edge-on orientations relative to one another. As would be expected, the latter peak is broadened much more than the former when a miscible low-Tg polymer is blended into a methylated kraft lignin-based material.