Analytical methods for lignin characterization - Differential scanning calorimetry

Results of a round robin on lignin thermal analyses are reported. Six laboratories have conducted thermal analyses of four lignin types to determine their c(p) values and softening points, and to study the thermal behaviour, materials endo- and exotherms included. The lignin types examined were wood Kraft lignin, steam explosion lignin, bagasse lignin, and lignosulfonates. Thermal analyses were carried out over the 20900 degrees C temperature range, at a heating rate of 10 degrees C/min, under both inert (nitrogen) and oxidative (air/oxygen) atmosphere. Six different types of thermal analyzers (DSC and TG equipment) were tested. A lignin chemical reactivity test was also considered. Several laboratories identified similar lignin softening temperatures for some of the samples, yet, generally, the results attained are characterised by a high variability of the lignin types and analytical protocols applied in the six laboratories. The different results have been mainly attributed to the "history" of the material, e.g., whether the samples were completely dried before the experiments.