Spent sulfite liquor adhesives

The application of lignin as an adhesive is possible in principle. The first attempt needed very long press times due to the low reactivity (Pedersen process) [161]. This process was based on lignin polycondensation under strong acidic conditions, which led to considerable corrosion problems in the plant [161]. The particles had been sprayed with spent sulfite liquor (pH = 3-4) and pressed at 180°C. After this step, the boards were tempered in an autoclave under pressure at 170-200°C, whereby the sulfite liquor became insoluble after splitting off water and SO2. 

Chen (29) found that the amount of sulfuric acid directly determines the hardening time in the acid condensation of spent sulfite liquors used in plywood and veneers. However, in general the adhesives based purely on acid condensed lignins have often been found to be an uneconomic and qualitatively inferior alternative to adhesives based on synthetic polymers and phenol or lignin-formaldehyde resins. 

Milled wood lignin was mixed with the crude enzyme solution of Tram-ties versicolor extracellular phenoloxidases produced on spent sulfite liquor in a ratio of approximately 2 1. This comprised the main part of the two-component bio-adhesive. Industrial particles were bonded with 15% bioadhesive under conventional pressing conditions to have 19 mm particle boards (40 x 50 cm) of the properties described in Table IV. The bonding reaction (crosslinking) took place in aqueous solution at room temperature. If conventional pressing technology is applied, the temperature should be elevated in order to maintain water evaporation within a reasonable press time. 

Nimz, H. H. Hitze, G. The application of spent sulfite liquors as an adhesive for particleboards. Cell. Chem. TechnoL 1980, 14, 371-38. 

Shen, K. C. Calve, L. Ammonium-Based Spent Sulfite Liquor for Waferboard Binder. Reprinted Adhesive Age, August 1980. 

A cooperation agreement was made in 1973 between DDS-RO and the Finnish Pulp and Paper Research Institute with the aim to develop products and processes on the basis of membrane filtration of effluents from the pulp and paper Industry. The cooperation with Dr. Kaj Forss section at FPPRI has been very successful. For instance, through an extensive development program UF has been found to be a feasible tool for the preparation of lignin for the Karatex ( ) plywood binder. This adhesive, which is made from ultrafiltered spent sulfite liquor (SSL) or kraft black liquor (KBL), can be used for partial replacement of the much more expensive petroleum based phenol-formaldehyde resin in plywood and other wooden boards. 

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