The production of carbon fibers based on lignin reduces the cost and the environmental impact associated with carbon fiber manufacturing. However, the melt processing of lignin as a carbon fiber precursor is challenging due to its brittleness and limited thermoplastic behavior. For this reason we produce biopolymer blends based on Alcell organosolv hardwood lignin, hydroxypropyl modified Kraft hardwood, and a thermoplastic elastomer polyurethane (TPU). Samples with TPU content greater than 30% showed excellent melt processability and carbonization yield (35% carbon yield for the samples containing 30% of TPU). The thermal properties were analyzed by differential scanning calorimetry, rheology and thermogravimetric analysis. Fourier infrared measurements were utilized to explain the lignin/TPU interactions which governed the thermal and rheological behavior of the blends. SEM analysis showed that the blends produce a homogeneous structure which was void free after carbonization. These structurally complementary biopolymeric blends should open up new avenues for lignin valorization and bring closer the realization of the production of carbon fibers from biosources.

Under mild conditions, PPO-PEO-PPO ("reverse Pluronics") and PBO-PEO-PBO copolyether were generated by way of N-heterocyclic olefin-based organocatalysis. Reverse Pluronics with molar masses > 20 000 g mol could be synthesized with excellent control (Đ ≤ 1.03) and were converted into (ordered) mesoporous carbons via organic self-assembly to showcase the need for tailor-made copolymer as structure-directing agent.

The synthesis of isocyanurate-free, linear poly­(oxazolidin-2-one)­s starting from diepoxides and aromatic as well as aliphatic diisocyanates is reported. N-Heterocyclic carbenes (NHCs), liberated in situ from thermally labile CO2 adducts, in combination with Lewis acids of the simplest kind (metal halides such as LiCl and MgCl2) were employed in a cooperative manner to prepare linear polymers with molecular weights (M n) ranging from 6 to 50 kg/mol. Crucially, it is demonstrated that action of either NHC (Lewis base) or metal halide (Lewis acid) alone entails the formation of significant amounts of trimerized isocyanates (isocyanurate) and concomitant gelling of the thus cross-linked material, highlighting the advantages of a cooperative, dual catalytic approach. Reactions were conducted at 200 °C with low NHC loadings (0.5 mol %) to deliver isolated yields of 60–90% within 3–8 h polymerization time. Investigations regarding regioselectivity revealed that exclusively 5-substituted oxazolidin-2-one was formed. Notably, these transformations can be catalyzed by a combination of 1,3-dimethyl­imidazolium-2-carboxylate, a readily accessible and robust NHC-precursor tolerant toward atmospheric conditions, and well-available LiCl. A mechanism is proposed whereby the high molecular weights and the selectivity for oxazolidinone formation over side reactions are attributed to the high nucleophilicity of the NHC, cooperative monomer activation by the metal halide, and specifically chosen reaction conditions.

The molar masses of acetylated kraft lignin and organosolv lignin are determined using both dynamic light scattering and size-exclusion chromatography (SEC). Preparative gel fractionation of both lignins is allowed for the further analysis of low-polydispersity lignin fractions. Fundamental information about the aggregation behavior of different molecular weight lignins in different solvent systems is provided. Two different solvent systems are used for SEC. Universal calibration is used for analysis. Applying the Flory-Fox theory, the obtained molecular weights are allowed for determining the maximum glass transition temperature at theoretical infi nite molecular weight, T g ∞ , of both acetylated lignins. from synthetic polymers. First, lignin is structurally quite inhomogeneous. Both the structure and molecular mass depend on the wood species used, and the pulping and subsequent isolation process. In course of its biogenesis, lignin is built up via radical enzymatic coupling reactions out of three monomeric subunits, i.e., cumaryl, coniferyl, and sinapyl alcohol. The coupling of these monomers leads to p -hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units. [ 2 ] On the basis of these subunits, lignin can be divided into three different types which are softwood lignins containing mainly G units, hardwood lignins containing both the G and S units, and lignin from annual plants primarily consisting of H units. [ 2 ] The relative ratio of these subunits determines the degree of branching in lignin. Softwood lignins are more prone to branching due to a lower number of methoxy groups. Vice versa, hardwood lignins have a lower degree of branching and as a consequence a more linear molecular structure.One crucial step that infl uences the properties of lignin and its molecular weight is the pulping process. The main industrial pulping processes are the kraft process, the sulfi te process, and the soda-anthraquinone process. [ 3 ]

Novel, melt processible PAN-based CF precursors prepared via the copolymerization of acrylonitrile with N,N′-substituted acryloamidines and their transformation into carbon fibers is presented.