Lignin Quantification
Gravimetric analysis based on the complete hydrolytic dissolution of wood polysaccharides by concentrated sulfuric acid isolates and measures acid-insoluble lignin content in plant biomass and unbleached pulps. Executing klason lignin determination provides the baseline reference measurement for total structural lignin within woody raw materials and chemical pulps. The analytical procedure treats extractive-free wood meal or pulp with 72 percent sulfuric acid at room temperature to hydrolyze cellulose and hemicellulose polymers.
The mixture is then diluted with water to a three percent acid concentration and boiled under reflux for several hours. The insoluble residual lignin precipitates completely and is collected, dried and weighed gravimetrically.
Laboratory Procedure
Standard protocols established under TAPPI T 222 or ISO 21436 govern every operational step of the analytical digestion and filtration sequence. Prior to klason lignin determination, sample materials undergo rigorous solvent extraction using acetone, ethanol or toluene-ethanol mixtures to remove waxes, fats, resins and tannins. Hydrolysis with concentrated acid requires precise temperature control between 15 and 20 degrees Celsius to prevent premature charring or carbohydrate condensation artifacts.
Following secondary boiling, the brown insoluble residue is separated using filtering crucibles and washed thoroughly with hot distilled water to remove all traces of acid. The dried residue mass is corrected for inorganic ash content through high-temperature muffle furnace combustion.
Furnish Evaluation
Pulp and paper researchers, chemical recovery engineers and fiber procurement managers rely on insoluble lignin measurements to evaluate raw material delignification efficiency. Conducting klason lignin determination reveals the chemical yield ceiling and pulping resistance of virgin softwood and hardwood species. Highly bleached chemical pulps cannot be evaluated through this gravimetric method alone, as acid-soluble lignin fractions remain dissolved in the acidic filtrate and require supplementary UV spectrophotometry.
Unbleached kraft linerboard and semi-chemical corrugating medium production rely on insoluble lignin values to predict refining energy requirements and final sheet stiffness. Accurate gravimetric lignin profiling ensures continuous optimization of chemical recovery boilers and digester cooking parameters.
