A brief history of lignin-containing polymeric materials culminating in X-ray powder diffraction analyses of kraft lignin-based thermoplastic polymer blends

The past 30-year history of lignin-containing polymeric materials has been fashioned by changing perceptions of macromolecular lignin structure. The first formulations originated in a view of lignins as "three-dimensionally branched network" polymers. Whether incorporated covalently or noncovalently into polymeric materials, lignin preparations were, with few exceptions, limited to maximum contents of 30-45% (w/w). However, once the significance of noncovalent interactions between the constituent molecular components had been recognized, it was possible to generate promising polymeric materials composed exclusively of ethylated and methylated kraft lignin, and other equally simple lignin derivatives. Plasticization of these materials can be achieved in a predictable way by blending with miscible low-T _g polymers. X-ray powder diffraction analyses have helped to identify characteristic variations in the separation distances between aromatic rings that accompany such plasticization effects.