Lignin-based adhesives

Forss, K., and Fuhrmann, A. (1976). KARATEX—the lignin-based adhesive for plywood, particle board and fibre board. Pap. Puu 58, 817-824. 

The objective of this research was to gain a better understanding of the oxidative-cleavage pathway. If this mechanism could be comprehended, it is possible that a relatively low-cost and environmentally safe process could be developed for producing a durable, commercially acceptable, lignin-based adhesive. 

Many examples of lignin-based wood adhesives have been presented in the scientific literature in the last few decades (i). While undoubtedly many interesting adhesive formulations and uses have been devised, the lignin-based adhesives that have been proposed or even industrially used for limited periods of time have always suffered from some serious drawbacks, sometimes technical, sometimes economical. 

Though the contact area between adhesive and wood is much larger in particleboards than in wood laminates, only 75% of the tensile strength was obtained when the lignin-based adhesive was applied as thermosetting system in particleboards (Table II). The following reasons may be applicable ... 

Recently, adhesives that include lignin in their formulation have shown several properties similar to phenol-formaldehyde resins [11, 12] and are extensively utilized in the plywood, particleboard, fiberboard and laminated wood industries. The chemistry of the lignin-based adhesives has been studied from an empirical point of view [13] however, the molecular mechanism and the interactions of the structural cross-linked 4-hydroxyphenylpropanoids of lignin that drive the adhesion phenomenon remain unclear. 

Nimz, H.H., Lignin-based wood adhesives. In Pizzi, A. (Eds.), Wood Adhesives Chemistry and Technology, Ch. 5. Marcel Dekker Inc., New York, pp. 247-288, 1983. 

When a new method is reported for synthesis of polymers, in a short time it is also tried on lignins. New lignin-based raw materials are also constantly appearing the use of steam exploded hardwood lignin for making plywood adhesives has recently been explored by Gardner and Sellers (64) and found promising in this intensively competitive area. 

Adhesive Formulation. Adhesives for testing consisted of 100 parts resin, 10 parts wheat flour as extender, 4 parts commercial additive, and 2 parts water. This formulation is recommended by Japanese board manufacturers. Adhesives without wheat flour were also formulated to examine the bond strength of the neat lignin based resins. 

Cure Rate of the Phenolated SEL Resins. 13C NMR spectra of the phenolated SEL formaldehyde-treated resins revealed the formation of methylol groups. A similar cure reaction to resole type phenolic resins is expected to occur with the phenolated lignin-based resins. Since cure rate normally determines production capacity of a board mill, it is important that new types of adhesives have at least the same cure rate as the conventional phenolic adhesives. Cure analysis of resins has usually been examined by... 

This lignin-based bio-adhesive can be applied under conventional pressing conditions. The resulting particle boards meet German performance standards without emission of harmful vapors. An added advantage is the total utilization of lignin from spent pulp liquor. 

Progress toward producing industrially acceptable lignin adhesives can be broken down into two main categories as either 1) lignin-based binders (by themselves as such or in chemically modified form), or 2) as copolymers (with other reactant adhesives). 

Nimz, H. Lignin-Based Wood Adhesives In Wood Adhes. Chem. Technol., Pizzi, A., Ed. Dekker, New York, 1983 Chapter 5, 247-88. 

Hydroxyalkyl lignin derivatives were crosslinked with diisocyanates or with melamine in both solvent and aqueous emulsion-based adhesive formulations for wood products (51) (Figure 7). Adhesive performance was found to be related to component solubility and compatibility (51), The use of kraft lignin in aqueous alkali and that of lignin sulfonates in water has been explored in combination with emulsifiable diisocyanates (52) in wood adhesives. Satisfactory strength properties were reported. 

In this chapter, the development of a thermosetting adhesive from soda bagasse lignin is described. The research has concentrated on the development of interior-grade adhesives for particleboard. The local market for exterior boards is smaller than that for the interior panels, and adhesives for exterior boards are already covered by an excellent range of tannin-based adhesives. 

Lignin-based cold-setting adhesives evaluated on beech strips (74% lignin 26% resorcinol). 

Van der Klashorst, G. H Cameron, F. A Pizzi, A. Lignin Based Cold-Setting Wood Adhesives Structural Fingerjoints and Glulam. Holz als Roh- und Werkstoff 1985, 43, 472-481. 

Progress in the use of condensed tannins in adhesive formulations might be expected to be more rapid than is the case for lignins because of the impetus provided by the commercialization of wattle tannin-based adhesives and because of the extraordinarily high reactivity of tannins in reactions with formaldehyde. This reactivity offers an opportunity to substitute tannin for resorcinol (currently priced at about 1.80/lb) instead of phenol (about 0.40/lb). Now that wattle tannins have been successfully introduced, their application can be expected to continue to expand. The situation remains difficult, on the other hand, for use of conifer bark tannins in adhesives. Herb Hergert is certainly... 

H. H. Nims, in Lignin-Based Wood Adhesives (A. Pizzi, ed.), Marcel Dekker, New York, 1983. 

A wood-based composite can be defined as a composite material mainly composed of wood elements. These wood elements are usually bonded together by a thermosetting adhesive (wood truss products could also be regarded as wood-based composites, but connected by metal connectors). The commonly used adhesives include urea-based adhesive (such as urea formaldehyde resin), phenolic-based adhesive (including phenol resorcinol adhesives), isocyanate-based adhesive, and adhesives from renewable resources (like soybean, lignin etc). The wood elements in wood composites can be in many different forms such as ... 

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