Molecular Interactions Between Wood Pitch and Wood Pitch Fixatives

Significant Achievements, Anticipated Outcomes and Future Work

During 2005 the interactions between components in wood extractives and various model polymeric fixatives was investigated by reoptimising the geometry of the molecules using a higher level of theory (HF/STO-3G) than previously used and then recalculating the stabilization energy of the complexes at HF/STO-3G and B3LYP/6-31G(d). Of the 43 molecules being investigated, calculations for 36 molecules could be undertaken. It is proposed to complete the rest of the calculations on triolein in 2006.
The problem encountered in 2004 with negative binding energies was found to be overcome by optimizing the geometry at HF/STO-3G. Some differences in the calculations between HF/STO-3G and B3LYP are apparent. HF/STO-3G calculates that abietic acid forms more stable complexes than oleic acid while B3LYP indicates that they have similar stability. Both methods indicate that the stability of the complex increases with charge as expected. Earlier results using MM3 to optimize the geometry did not show this. Some differences between the different chemical structures for the fixatives are also apparent. Primary amines appear to form more stable complexes than the secondary and tertiary amines. Steric affects appear to be contributing to this. A copolymer was found to form a more stable complex than other single polymers. It appears that the spacing between the charged groups in the copolymer are positioned to allow for “better fit” of the charged end of the wood extractive component Calculations of the free energy of solvation show a substantial decrease in the stabilization energy due to strong solvent-solute interactions between the individual components and water.
Further calculations are required in order to determine if optimization of geometries at B3LYP is needed or if optimization at HF/STO-3G is sufficient. Further work is also required to see if differences in the interaction between dehydroabieitc acid and abietic acid as well as stearic acid and oleic acid can be calculated with the different fixatives. Laboratory work has shown that differences in deposition behaviour occurs and experimental work in 2006 will be undertaken to study the deposition behaviour of these other wood pitch components in the presence of fixatives and wood fibres. One of the aims of 2006 is to complete the calculations and compare the results to experimental deposition results and to interaction coefficients determined by capillary electrophoresis. The other aim is to propose new fixatives that are copolymers and the synthesis and trial these new fixatives in the laboratory.

Computational Techniques Used

The Guassian 03 program was used to optimise geometry, calculate Heat of Formation in the gas phase and also free energy of solvation of complexes formed between abietic acid, oleic acid and triolein with 10 model oligmers which represent common fixatives used in the paper industry (cationic polyacrylamide (CPAM), polyethelyenimine (PEI), poly diallyl-dimethyl ammonium chloride (poly DADMAC) and co-polymers of PAM and DADMAC) of varying charge density. The complexes formed ranged in size from 350-450 atoms. Optimisation of the geometry was carried out at HF/STO-3G.
The heat of formation (Hf) for each single component and complex was obtained using Hartree Fock and density functional theory. The minimum basis set STO-3G as well as the split-valence basis set 6-31G(d) which added a set of d polarisation functions to each heavy atom were used. From the heats of formation the stabilisation energy of the complex formed was determined.
SE = (Hf A + Hf B)- Hf complex
Solvation Free Energy (Gsol) for the individual molecules and also complexes were determined using the polarisable continuum model with both HF and DFT levels of theory using Gaussian 03 program on the APAC super computer. This was then used to determine the effect of solvation on the formation of the complex.

Publications, Awards and External Funding

External Funding and Awards

ARC Linkage grant Project ID LP0453774. ARC contribution is $179,987 over 3 years. Industry contribution is $99,000 in cash over 3 years and $99,000 in kind over 3 years.
Winner of 2005 Jasper Mardon prize for conference paper making the most significant scientific and technical contribution to papermaking awarded at 59th Appita Annual Conference Rotorua New Zealand for paper “A study of the interactions leading to wood pitch deposition”., Vercoe, D, Stack K, Blackman A, Richardson D.

Publications

K. Stack, D. Vercoe, L. Maher L, B. Yates, The use of molecular modeling to study pitch deposition and interactions with fixatives, First Applied Pulp and Paper Molecular Modelling Symposium, Montreal August 24-26, 2005, 135-153.
D. Vercoe, K. Stack, A. Blackman and D. Richardson, Gaining an insight into the interactions leading to wood pitch deposition through correlation between theoretical and experimental results, First Applied Pulp and Paper Molecular Modelling Symposium, Montreal August 24-26, 2005, 195-214.
D.Vercoe, K. Stack, A. Blackman, D. Richardson, A study of the interactions leading to wood pitch deposition, 59th Annual Appita Conference proceedings, 2005, 123-130.
L. Mayer, K. Stack, D. McLean and D. Richardson, Adsorption behaviour of cationic fixatives and their effect on pitch deposition, 59th Annual Appita Conference proceedings, 2005, 115-122.
D. McLean, M. Breadmore, K. Stack, D. Richardson, P. Haddad, Wood pitch fixative selection by capillary electrophoresis, 59th Annual Appita Conference proceedings, 2005, 137-142.
D. Vercoe, K. Stack, A. Blackman, D. Richardson, A multi component insight into the interactions leading to wood pitch deposition, Appita Journal, 58(3), 2005, 208-213.