The effect of lignin content and lignin modification on Norway spruce wood properties and decay resistance

Abstract

This thesis describes studies with three different Norway spruce cutting clones in three growing environments differing in soil and climatic conditions within the boreal zone. The main aim was to follow variation in the radial growth rate, wood properties and lignin content and to modify wood lignin with a natural monolignol, coniferyl alcohol, by making use of inherent wood peroxidases. In addition, the incorporation of chlorinated anilines into lignin was studied with synthetic model compounds and synthetic lignin preparations to show whether unnatural compounds originating from pesticides could be bound in the lignin polymer. Annual ring width, latewood proportion and wood properties such as weight density, modulus of rupture (MOR) and modulus of elasticity (MOE) were determined. Fourier transform infrared (FTIR) spectroscopy was applied to the quantitative estimation of lignin in heartwood, sapwood and earlywood samples by using a principal component regression (PCR) technique. Wood blocks were treated with coniferyl alcohol by using a vacuum impregnation method. The effect of impregnation was assessed by FTIR and by a fungal decay test. Trees from a fertile site showed the highest growth rate and sapwood lignin content and the lowest latewood proportion, weight density and MOR. Trees from a medium fertile site had the lowest growth rate and the highest latewood proportion, weight density, MOE and MOR. The most rapidly growing clone showed the lowest latewood proportion, weight density, MOE and MOR. The slowest growing clone had the lowest sapwood lignin content and the highest latewood proportion, weight density, MOE and MOR. Fairly large variation was found between the individual trees and between the growing seasons but much less variation between the sites and between the clones. The coniferyl alcohol impregnation increased the content of different lignin-type phenolic compounds in the wood as well as wood decay resistance against a white-rot fungus, Coriolus versicolor. Also the incorporation of chlorinated anilines into lignin was shown to be possible and the intermediate quinone methide was seen to be trapped by 3,4-dichloroaniline during the dehydrogenative polymerization of coniferyl alcohol, which resulted in a dimer of coniferyl alcohol with a β-O-4 structure and with dichloroaniline bound by a benzylamine bond. In conclusion, in this thesis it was shown that the different Norway spruce cutting clones maintained clone-dependent wood properties in the different growing sites although variation between tree individuals was high and climatic factors affected growth. It was also shown that the natural monolignol, coniferyl alcohol, and chlorinated anilines could be incorporated into the lignin polymer in vivo and in vitro, respectively. The coniferyl alcohol impregnation experiment resulted in the improved resistance of the wood blocks to fungal decay, while chlorinated anilines were covalently bound into the lignin polymer and they could not be released by mild acid hydrolysis.