Structures of Biopolymers in the Pulp and Paper Industry

                   

Principal Investigator

Lawrie Dunn

School of Chemistry

University of Tasmania

Co-Investigator

Karen Stack

School of Chemistry

University of Tasmania

Project

g53-PC

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.
 
             

   
             
                   

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

b-0-4 aryl-ether linkages are the dominant structural features incorporated into the lignin biopolymer during plant cell wall biogenesis in each of the hardwood, softwood and grass botanical families. Gaussian-94 ab initio molecular orbital techniques are being used to calculate optimised molecular energies, polarities and geometries for the syringyl - syringyl dimers in the lignin present in hardwoods, for the guaiacyl - guaiacyl dimers in the lignin present in softwoods and for the p-hydroxyphenyl - p-hydroxyphenyl dimers in the lignin present in grasses. Solvation effects in aqueous solution for each of these dimer species have also been investigated to generate theoretical results which simulate the properties of lignin in the aqueous environment associated with paper-making processes.

Present and future work includes calculation of energies, polarities and 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. For these mixed dimer species, the first named monomer includes the Cb-ring while the second includes 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.

                   
Appendix B -

                   

       

What computational techniques are used ?

The Gaussian-94 computational modelling package is presently being used. Preliminary ab initio gas phase calculations have been carried out at the RHF/3-21G level. These have been followed by geometry optimisations and frequency calculations in an aqueous environment at both the RHF/6-31G and the RHF/6-31G(d) levels. Outputs from these for the syringyl monomer and the syringyl-syringyl dimer in hardwoods have been carried out at the MP2/6-31g(d) level.

Publications

Dunn, L.A., Electronic and Steric Effects in Lignin in an Aqueous Environment. Some theoretical insights into Sinapyl Alcohol homo-dimers as models for the b-0-4 linkage of the lignin biopolymer in hardwoods. Paper accepted for oral presentation at the 10th International Symposium on Wood and Pulping Chemistry in Yokohama, JAPAN, June 7-10, 1999.

       
- Appendix B