Raman line-mapping of cell walls of four hardwood genotypes and a softwood genotype: Influence of acid bi-sulphite pulping

摘要

To provide a better understanding of the delignification process during acid bi-sulphite pulping the ultrastructural distribution of lignin within wood cell walls and the topochemical distribution of lignin in the cell wall layers of four hardwoods (E. grandis x urophylla, E. grandis x camaldulensis, E. dunnii, E. nitens genotypes) and a softwood (Pinus patula genotype) were investigated using confocal Raman spectroscopy. For the purposes of this study the Raman line scans for the wood samples were analysed in terms of the middle lamella, secondary wall (S2), and lumen regions. Changes in lignin intensity were recorded across these cell wall regions by tracking a lignin Raman band centred on 1600 cm~(-1). Acid insoluble (klason) lignin and acid soluble lignin measurements were determined by gravimetric analysis and Ultraviolet (UV) spectrometry respectively The distribution of lignin within the wood cell walls (i.e. middle lamella and S2 regions of the cell wall) provided by confocal Raman spectroscopy is invaluable from a pulping perspective since the efficiency of delignification depends not only on the amount and type of lignin (i.e. acid insoluble (klason) lignin and acid soluble lignin) present in the wood but more importantly its location within the cell wall.