Utilization, lignin

The aromatic ring of a phenoxy anion is the site of electrophilic addition, eg, in methylolation with formaldehyde (qv). The phenoxy anion is highly reactive to many oxidants such as oxygen, hydrogen peroxide, ozone, and peroxyacetic acid. Many of the chemical modification reactions of lignin utilizing its aromatic and phenoHc nature have been reviewed elsewhere (53). 

Eds. "Pollution Abatement by More Effective Lignin Utilization. Grafting to Lignin and Lignin-Containing Pulps" North Carolina State University, Raleigh, New York, 1970. 

Hagglund and Enkvist (6) developed a laboratory scale method for manufacturing methyl sulfide from kraft black liquor by pressure heating after addition of sodium sulfide. This process was later taken over by Crown-Zellerbach in the United States and developed in pilot plant and full scale. However, the yield is only about 7% of the initial lignin utilized in the process. 

Lignin utilization studies have been conducted in several fields. However, no practical, commercial process has yet emerged for the manufacture of lignin-based polymeric materials. This is undoubtedly related to such factors as product inhomogeneity, reactivity differences, and also with lack of familiarity with this type of raw material. It should be also stressed that lignins are only by-products from pulp manufacture. However, the utilization of lignins in polymeric materials seems to be possible. 

For many years wood chemists have tried to find applications for lignins other than their use as fuel. The amount of proposed products and applications is considerable. For instance, a recent literature survey on lignin utilization includes more than 3700 references, mostly patents (10). In spite of this massive amount of work on products, processes and applications, less than 2% of lignin available in spent liquors from conventional pulping processes are recovered and marketed for non-fuel applications in the U.S. 

Olivares M, Guzman JA, Natho A, Saavedra A (1988) Kraft lignin utilization in adhesives Wood Sci Technol 22 157-165... 

Hill M, Fricke A (1984) Ultrafiltration studies on a kraft black liquor. Tappi J 67(6) 100-103 Klinkowski PR (1978) An emerging unit operation. Chem Eng 8 165-173 Lin SY, Detroit WJ 1981 Heterogeneity of technical lignins - its significance in lignin utilization. Proc 1981 Int Symp Wood Pulp Chem. Ekman-Days 1981 (Stockholm). SPCI Rep 38,4 44-52... 

Lin, S. Y. Lignin Utilization Potential and Challenge In Progress in Biomass Conversion, Academic Press, Inc. Orlando, 1983 Vol. 4, 31-78. 

In summary, progress on the use of lignins in wood adhesives has been made, but the level of effort directed to lignin utilization in general has been small in comparison with the enormity of the problem, possibly because of the limited advances that have been made in this field in the past. Unless high petroleum prices return, we can expect to see slow continual improvement in opportunities to use lignins as a basis for adhesives. 

---