Lignin characterization/analyses

Lignin is a complex polyaromatic macromolecule that has the potential to be used in the production of a variety of sustainable materials and chemicals. The chemical structure of lignin is extremely complicated, consisting primarily of three different kinds of methoxylated phenylpropane units. The phenylpropane units randomly polymerize with each other, resulting in a three-dimensional cross-linked amorphous structure. The structure and polymeric properties vary depending on origin i.e. plant species, industrial processing as well as isolation and purification procedure.  

Technical lignin is lignin extracted from diverse biomasses using technical procedures such as wood pulping. The most common technical lignins are lignosulphonates (separated from sulphite pulping), kraft lignins (separated from kraft pulping black liquor), organosolv lignins (separated from organosolv pulping), soda lignins (separated from soda pulping), and lignin residue following enzymatic treatment of biomass. 

Lignin can be characterized by its purity, molecular structure, and thermal characteristics.  

• Dry matter content – Moisture and non-volatile part of lignin (gravimetric analysis) 
• Lignin content- the total amount of acid insoluble (acid hydrolysis) and acid soluble content (UV spectroscopy) 
• Carbohydrate content- Glucose, xylose, arabinose, galactose, and mannose (ionic chromatography) 
• Ash content- inorganic residue (gravimetrically determined at defined temperatures) 
• Metals/elemental content- Al, Ca, Mg, Mn, K, P, Na, Ba, Fe, S (ICP-OES) 
• Extractive contents- Fatty acids, resin acids, fatty alcohols, sterols glycerides and styryl esters (Soxtec apparatus and GC-MS). 
• Hydroxyl groups- aliphatic, phenolic, carboxylic groups (31PNMR) 
• Structural elements-Pyrolysis (GC-MS) and NMR 
• Molar mass distribution-weight average molar mass (Mw) and number average molar mass (Mn) (SEC) 
• Thermal properties-Thermal decomposition (TGA) and glass transition temperature (DSC)