Structures of Biopolymers in the Pulp and Paper Industry

                 

Principal Investigator

Lawrie Dunn

School of Chemistry,

University of Tasmania.

Abundance of the native lignin biopolymer in various wood species together with the complexity of
chemical changes induced in this biopolymer during pulping, bleaching and paper discoloration processes are of immense economic significance to the pulp and paper industry. Electronic and steric effects in lignin from such botanical sources as hardwoods (Eucalyptus species), softwoods (Pinus species) and grasses(Bambusa species) are of interest in this project.
 

Co-Investigators

     

Karen Stack

School of Chemistry,

University of Tasmania

     
             

   

Projects

g53 - PC

           
                 

What are the results to date and the future of this work?

For the homo-dimeric syringyl - syringyl lignin [C22H26O8] in hardwoods, the homo-dimeric guaiacyl - guaiacyl lignin [C20H22O6] in softwoods and the homo-dimeric p-hydroxyphenyl - p-hydroxyphenyl lignin [C18H18O4] in grasses, each dimer with the b-0-4 aryl-ether linkage, Gaussian-94 ab initio molecular orbital techniques have been used to calculate optimised molecular energies, polarities and geometries. Solvation effects in aqueous solution have also been investigated to generate theoretical results which simulate the properties of these lignin dimer species in the aqueous environment associated with paper-making processes.

Present and future work includes studies of the conformations of mixed lignin dimer species such as p-hydroxyphenyl-guaiacyl, p-hydroxyphenyl-syringyl, guaiacyl-p-hydroxyphenyl, guaiacyl-syringyl, syringyl-p-hydroxyphenyl and syringyl-guaiacyl. In these mixed dimer species, the first named monomer is the Cb-ring and the second is the O4-ring of the b-O-4 aryl-ether linkage. These mixed lignin dimer structures are the first step towards further theoretical calculations on some new fundamental structures in the lignin biopolymer, which involve dihydroconiferyl alcohol, ferulates and p-coumarate g-esters.

What computational techniques are used?

Currently, the ab initio Gaussian 94 computational modelling package is being used. Preliminary gas phase calculations are being done at the RHF/3-21G level. These are then followed by frequency analysis and initial geometry optimisation in an aqueous environment at the RHF/6-31G(d) level. Outputs from these are presently being prepared for final geometry optimisations at the MP2/6-31g(d) level.

                 
Appendix B -

                 

       

Publications

L. A. Dunn, Electronic and Steric Effects in Lignin in an Aqueous Environment. I : Sinapyl alcohol [4-(3-hydroxy-1-propenyl)-2,6-dimethoxy-phenol], the lignin monomer in hardwoods. J. Wood Chem. Technol., Submitted for publication, 1997.

L. A. Dunn, Electronic and Steric Effects in Lignin in an Aqueous Environment. II : Sinapyl alcohol homo-dimers as models for the b-0-4 linkage of the lignin biopolymer in hardwoods. Chemistry of Pulp and Paper Makin, Report to Australian Newsprint Mills, February, 1998.

       
- Appendix B