LIGNIN DERIVATIVES .2. FUNCTIONAL ETHERS

Two hardwood (kraft and organosolv) lignins were reacted with propylene oxide, ethylene oxide, and chloroacetic acid. The primary lignin derivatives, hydroxypropyl kraft lignin, hydroxyethyl organosolv lignin, and carboxymethyl kraft lignin were converted into secondary derivatives by acetylation. The synthesis of the hydroxy and carboxy-functional.ether derivatives involves the generation of oxyanions, the concentration of which determines the eventual degree of derivatization. Whereas the pH of the alkaline (aqueous) reaction medium rises during the reaction with the oxirane species, this declines during the reaction with chloroacetic acid. Careful pH control during the synthesis is needed for controlling the eventual extent of modification. Because of the volatility and reactivity of ethylene oxide, hydroxyethylations are best performed in anhydrous isopropanol under pressure. Because of their surfactant characteristics, functional lignin ethers are difficult to isolate from aqueous solution. However, ether derivatives with as much as 80% lignin content have properties that are dramatically different from their parent polymers in terms of solubility, color, molecular weight distribution, and glass transition temperature. The latter is between 40 and 80-degrees-C lower than the corresponding underivatized lignin. The secondary acetate derivatives are easier to isolate than the primary ones.