No abstract

No abstract

In recent years, significant amounts of various lignins became commercially available. Their technical utilization for thermosets such as phenol formaldehyde resins is widely discussed as an added value. However, the comparably low number of reactive sites is still limiting utilization in higher proportions. To overcome this obstacle, lignins can be activated by phenolation prior to resin synthesis. In this study, the applicability and outcome of phenolation was studied for a set of organosolv lignins from hardwood, softwood, and annual plants and was compared to their counterparts from commercial processes, i.e., kraft, sulfite, soda, and hydrolysis lignin. Thus, structural properties of various raw lignins could be linked to the increase of reactive sites upon phenolation. Large differences were found and could mainly be attributed to the number of aliphatic hydroxyl groups in the raw lignins. Highest activation was achieved for hardwood organosolv and softwood sulfite lignins. With ion-exchanged sulfite lignin in H+ form the phenolation could even be performed autocatalyzed to a high extent. In contrast, soda grass and softwood kraft lignin showed weak potential for activation. Additionally, the influence of ash and sulfur content, and the changes in molecular weight were elucidated.

An efficient, nontoxic, and solvent-free oxyalkylation of European beech wood organosolv lignin (OL) has been developed. Two approaches were studied: a direct reaction of lignin with propylene carbonate (PC) and a two-step reaction of lignin with maleic anhydride (MA) followed by oxyalkylation with PC. The structural analysis of lignin polyols was performed by 1 H NMR, 13 C NMR, 31 P NMR, and FTIR spectroscopy. It was demonstrated that PC was able to almost completely oxypropylate aliphatic and phenolic OH groups. Moreover, the carboxylic acid groups of maleated OL were fully oxypropylated by PC. This modification strongly facilitates the generation of a uniform lignin polyol applicable as a biobased component in polyurethanes and polyesters based on cyclic organic carbonates.

No abstract

No abstract

Spent sulfite liquors (SSLs) were fractionated by two common separation techniques: amine extraction and ultrafiltration. The lignin fractions obtained were characterized with respect to their elemental composition, functional groups and molecular weight distribution. The results of size exclusion chromatography indicate a broad molecular weight distribution of the lignosulfonates (LS). Irrespective of the separation technique used, a small LS fraction with high molecular mass and low degree of sulfonation was obtained, while most of the lignosulfonates have much lower molar masses and a much higher degree of sulfonation. Both separation methods offer the opportunity to extract high-purity LS fractions; however, compared to amine extraction, ultrafiltration provides additional information about the molecular weight distribution of the SSL components without application of other analytical techniques.

The article contains sections titled: 1. Occurrence and Functions 2. Structure and Biosynthesis 3. Physical Properties 4. Chemical Properties 4.1. Kraft Pulping 4.2. Sulfite Pulping 4.3. Other Pulping Processes 4.4. Pulp Bleaching 4.5. Yellowing Reactions 5. Commercial Lignins 6. Analysis 6.1. Detection and Quantification 6.2. Isolation 6.3. Spectroscopic Methods 6.4. Degradation Methods 6.5. Molar Mass Determination 7. Uses 8. Toxicology