Miscible blends of kraft lignin derivatives with low-T _g polymers

Alkylated and acylated kraft lignins are predominantly composed of well-defined supramacromolecular complexes assembled from thousands of individual components. The integrity of these very high molecular weight species can be compromised as kraft lignin derivatives (which alone are quite brittle) are plasticized when blended with miscible low-T _g polymers. The complexes tend to be dismantled when the intermolecular interactions between the lignin components and low-T _g polymer molecules are strong; this engenders a counterproductive increase in the proportion of polymeric plasticizer required to reach the plasticization threshold. X-ray powder diffraction analyses of the kraft lignin-based materials reveal two broad distributions of separation distances between the aromatic moieties; these are attributable to relative orientations of rings that are more or less edge-on and cofacially offset. Plasticization broadens the former significantly but has less impact on the latter. A similar effect is observed as the kraft lignin components themselves are reduced in molecular weight to the point where their mere presence enhances the plastic deformation that can be withstood before tensile fracture.