Ozonized lignin

Ozonization of lignin forms derivatives of muconic acid that have the unique chemical structure of conjugated double bonds with two carboxyl groups. These derivatives have great potential for chemical modification. The ozonized lignin of white birch was soluble in epoxy resin at 120°C, and the free carboxyl groups were found to react with epoxide. This paper discusses developmental work on the preparation of pre-reacted ozonized lignin/epoxy resins the dynamic mechanical properties of cured resins and preliminary results of the application of these resins as wood adhesives. 

Ozone has recently become industrially available at low cost. From the point of view of the development of complete wood utilization, the pretreatment of wood with ozone enhances the yield of glucose by enzymatic saccharification. Ozonized lignin is thereby obtained as a by-product. 

The lignin isolated from white birch after steaming was ozonized. The ozonized lignin was soluble in epoxy resins at 120°C. It was also found that free carboxyl groups (introduced by ozonization) react with epoxide only by heating. Previous developmental work on the blending of lignin with epoxy resin has been reported by Ball and his co-workers (3). They synthesized... 

Gel Permeation Chromatography. Each ozonized lignin was analyzed by liquid chromatograph (ALC/GPC 201 with R-401 Differential Refractome-ter Water-Associates). Columns and solvent conditions were as follows p-Styragel 1,000, 500, 500,100A in series and tetrahydrofuran at 2.0 ml/min. Molecular weight was estimated by use of polystyrene standards. 

Preparation of Ozonized Lignin/Epoxy Resins. Each ozonized lignin (1.0 g) was mixed with DGEBA and heated at 120°C with stirring as described in the previous section. After heating for 30 min, the mixture was cooled to room temperature. The solidified reactants were dissolved in acetone (2 ml) and the curing reagents, diethylenetriamine (DETA) or hexamethylenedi-amine (HMDA), were added at 90% of the stoichiometric amount to epoxy equivalent. 

The ozonization was performed at the three levels of molar equivalents to phenylpropane unit shown in Table I. The highest yield of over 100% in sample No. 1 was caused by the addition of ozone to lignin. On the other hand, the yield decrease in samples No. 2 and No. 3 was considered to be the result of removal of a considerable amount of ozonized lignin by... 

Figure 3. Process scheme for the preparation of ozonized lignin.

Figure 4. Gel permeation chromatograms of lignin isolated from birch and its ozonized lignins. Sample 0 untreated lignin 1 ozonized lignin No. 1 2 ozonized lignin No. 2 3 ozonized lignin No. 3.

Figure 5. Temperature dependence of viscoelastic property of ozonized lignin/epoxy resins cured with hexamethylenediamine. Ozonized lignin content in DGEBA (1) 0 PHR (2) 20 PHR (3) 40 PHR (4) 80 PHR.

Table III. Tensile Shear Adhesive Strength of Ozonized Lignin/Epoxy Resins. (Normal Test)...

Yoshida et al. [197] developed thermostable materials based on ozonized lignin. Hence, the authors ozonized lignin to prepare muconic acid or its hemi-ester, as shown in Scheme 46. 

Tomita B, Kurozumi K, Takemura A, Hosoya S (1989) Ozonized lignin-epoxy resins, synthesis and use In Glasser WG, Sarkanen S (eds) Lignin, properties and materials American Chemical Society, Washington, DC, 496-505... 

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