Wood adhesives based on lignin wastes: Influence of the carbohydrates in the polymerization of spent sulfite liquor

The influence of carbohydrates on the thermosetting properties of ammonium-spent sulfite liquor (NH4SSL) was studied using various fractions of the liquor obtained by ultrafiltration. While a low molecular weight carbohydrate-rich fraction thermoset readily, a higher molecular weight sugar-free fraction failed to thermoset. Optimum results in the use of NH4SSL as a binder for wood particles were obtained by adjusting the carbohydrate to lignin ratio through addition of carbohydrates to the liquor. Similarly, several sugars used alone as binders without addition of lignin gave satisfactory results at slightly higher press temperatures. A study of various sugars and similar molecules in the binding of wood particles suggested that a combination of ene-aldehyde or ketoalcohol functionalities was likely to produce good results. Condensations involving sugars were affected by such variables as carbohydrate chain length, moisture content, acid catalysis, and press temperature.