木素及其应用

Lignin And Its Utilization

木素是由苯基丙烷单体脱氢聚合而成的无定型天然高聚物,广泛存在于种了植物中,其具体结构尚有待揭露,文章在论述木素的物理和化节性能的基础上,介绍了商品木素的性质及其应用。目前,世界商品木素的总生产量约为138.5万吨/年,主要为木素磺酸盐。

Lignin, one of the major constituents in vascular plants, plays an important role in the internal transport of water, nutrients and metabolites in the plants.lt also serves to provide rigidity to the plant by binding the individual fibers together. Maximum concentration of lignin is found in the inter-fiber zones, whereas more uniform but lower concentrations are observed in the bulk of the cell walls.Due to heterogeneity and polydispcrity, no definite structure has thus far been claimed for lignin.Howcver, it is generally acknowledged that lignins are dchydrogcnative polymerization products of three phcnylpropanoid monomers, namely p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol, and that they are predominately linked through arylglycerol-β-aryl ether bondings and also some carbon-to-carbon linkages.The chemical and physical properties of milled wood lignin and industrial lignins arc briefly reviewed.And important chemical reactions relating to pulping and bleaching are described.The utilization of commercial lignins (lignosulfonate and kraft lignin) is reported.Annual consumption of lignin in the Western world amounts to 500,000 tons in 1985,with steady growth in recent years,mainly as surfactants, dispersants, binders etc.Even though lignosulfonatcs have been used in China for quite some years, the market is still awaiting further and better exploitation. Most of the lignin products sold in China are in the non-modified forms, and as liquids of 25-35% solids.A sulfonatcd kraft lignin product, the first one of the kind in the country,has recently emerged on the market. Vanillin from a sulphite mill in the South has been exported abroad for many a year.Howcver, most of the lignin-containing black liquors and ammonium-based spent sulfite liquors from medium and small sized enterprises are currently being discharged directly into the water-way pausing hazardous pollution to the cnvironment.It is imperative,therefore,that efforts be made to develop useful lignin products for various industrial needs.