Adhesive quality of lignins

Estimating the Adhesive Quality of Lignins for Internal Bond Strength... 

Adhesive quality of lignins—Continued experimental procedures, 373 GPC, 375,378/ interactive sites, 373 lignin parameters for assessing quality, 375,3791... 

The erosion resistance of the soil may be increased by raising the cohesion of the soil aggregates this may be done by treating the soil with binding substances [507]. Such substances include cellulose and its derivatives (lignin, humic acid), bitumen, peat cement, and various structure-forming substances from plant residues. The adhesive substances envelop the soil particles. The layer so formed, a few microns thick, imparts the quality of tacki-... 

There have been many attempts to replace these resins with lignin derivatives for wood composite adhesives suitable for plywood, particleboard and waferboard. Most of these studies have been empirical in nature, and few have achieved further consideration for industrial application. As wood binders, technical lignins are variable in quality and poorly reactive in comparison to conventional resin systems such as phenol-formaldehyde (PF) resins. Consequently, they are not utilized on their own. Indeed, if they were, this would adversely affect production quality and times, and necessitate equipment changes. In the wood composite industry, resins having such deleterious effects are not likely to be used even if savings could be made in terms of material costs. 

Steam-explosion lignins have received some attention as adhesives mainly because this process offers some potential for utilizing low-quality hardwoods. Like kraft lignin, these preparations also require activation [e.g., by hydroxymethy-lation (70), isocyanation (75,80)] to achieve any type of acceptable wood composite adhesive properties. 

Acidolysis lignins, organosolv, and cellulase lignins are presently laboratory curiosities due to a lack of commercialization. Whether these lignins will offer any advantages at all with respect to resin adhesives currently used remains to be established. Preliminary experiments [e.g., with acidolysis lignins (81)] have not demonstrated any superior qualities to date. 

Considerable research activity has been directed toward producing wood composite adhesives from lignin, and this has been accompanied by very little practical success in terms of commercial implementation. By themselves, and regardless of source, lignins offer no advantages in terms of chemical reactivity, product quality, or color when compared to conventional wood composite adhesives. At low replacement levels (10 to 30%), lignins can and will continue to be employed as extenders for UF and PF resins. When they are used as extenders, best results are obtained when chemically activated (e.g., by methylolation). 

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