The need for renewable alternatives to conventional petroleum based polymers has been the motivation for work on biobased composites, blends and materials whose foundations are carbon neutral feedstocks. Lignin, an abundant plant derived feedstock, and waste byproduct of the cellulosic ethanol and pulp and paper industry, qualifies as a renewable material. Despite the fact that it is often difficult to blend lignin with other polymers due to its complex structure and reactivity, published research over the past decade, has focused on issues such as lignin miscibility with other polymers, the thermal and mechanical strength behavior of its copolymers and its fractions as well as efforts of tuning its thermal properties via chemical modifications and other means. As such this effort now attempts to offer a comprehensive overview that largely discusses the importance of these processes with the aim toward effective, cost efficient and environmentally friendly means that may allow the utilization of this important and largely ignored biopolymer.

This work focused on providing a molecular understanding of the way the polymeric properties of kraft lignin and its derivatives are affected by various thermal treatments. This information was then correlated with the polymeric properties of the materials (glass transition temperature (T g ), molecular weight characteristics, and thermal stability) for a series of selectively and progressively derivatized softwood kraft lignin samples. Softwood kraft lignin was highly susceptible to thermally induced reactions that caused its molecular characteristics to be severely altered with the concomitant formation of irreversible cross-linking. However, by fully methylating the phenolic OH groups from within the structure of softwood kraft lignin, the thermal stability of these materials was dramatically enhanced and their T g reduced. While optimum thermal stability and melt re-cycling was observed with the fully methylated derivatives, fully oxypropylated phenolic substitution did not offer the same possibilities. The accumulated data is aimed at providing the foundations for a rational design of single component, lignin-based thermoplastic materials with reproducible polymeric properties when thermally processed in a number of manufacturing cycles.

During cellulose dissolution in non-derivatizing solvents, the inter-and intramolecular hydrogen bonds of the polymer are deconstructed. This occurs either by hydrogen bond formation between one or more components of the solvent systems and the hydroxyl groups of the cellulose or by coordination bond formation between the metal ion present in the medium and the hydroxyl group of cellulose molecules. None of the polymer molecules are actually chemically modified during dissolution. In the first part of this review, we examine the literature pertaining to the different interaction mechanisms between cellulose and non-derivatizing solvent systems with emphasis on the inorganic molten salt hydrates. In the second part of this effort, we further review inorganic molten salt hydrates from the point of view of the changes they impart to the physical properties of the cellulose and the various chemical reactions that can be performed in it.

Methylation of lignin is essential for inducing thermal stability when a multitude of thermoplastic applications are envisaged.