MOLECULAR-WEIGHT DISTRIBUTION OF (SEMI-) COMMERCIAL LIGNIN DERIVATIVES

Absolute molecular weights of several commercially and semi-commercial ly available lignins were determined by gel permeation chromatography (GPC) with a differential viscosity detector (DV). Solubility in THF w as assured by acetylation. Polystyrene molecular weight standards were used for establishing a universal calibration curve. The lignins incl uded those from hardwood, softwood, and sugar cane bagasse; and these were isolated by the kraft or orpnosolv pulping process, or by steam e xplosion/autohydrolysis. All lignins exhibited more or less uniform di stributions with weight average molecular weights (M(w)) between 3,000 and 20,000; with polydispersities (M(w)/M(n)) between 2 and 12; with Mark-Houwink-Sakurada exponential factors (alpha) between 0.17 and 0.3 5; and with intrinsic viscosities between 0.037 and 0.08 dLg-1. A sign ificant relationship between M(w)/M(n) and M(w) was discovered that ha d a correlation factor of 0.92. This relationship has the form of M(w) /M(n) = 0.45 (M(w)) 10(-3) + 0.85.