聚木糖酶对纸浆中LCC的辅助去除作用

The mechanism of degrading LCC with xylanase aid-bleaching of pulp

在造纸用植物原料中，木素与半纤维素之间存在着化学连接，形成木素与碳水化合物复合体（LCC）。在制浆过程中，当蒸煮进行到一定时间后，尤其是在蒸煮的后期，蒸煮液中药液的浓度下降，而聚木糖浓度较高，溶出的聚木糖有一部分又重新回吸到纤维上，而另一部分半纤维素与残余木素形成新的化学结合，形成LCC。聚木糖的回吸对纸浆中残余本素的进一步去除起到了屏蔽作用。聚木糖酶处理纸浆主要是当用内切聚木糖酶降解、溶出回吸到纸浆纤维上的聚木糖，提高了纤维表面的通透性，使漂白处理时漂白剂容易与残余木素作用，有利于残余木素的溶出。同时，由于聚木糖酶分解LCC中的部分聚木糖，使LCC的分子量降低，易于溶出，进而也促进了残余木素的去除，改善了纸浆的可漂性，降低了漂白剂用量和漂白废水中的AOX含量以及有害物质的排放量。但是，聚木糖酶处理需要与纸浆洗涤和化学漂白处理相结合，还不能完全替代纸浆的化学漂白处理。

Lignin is partically covalently linked to the poysacchchdes to form lignin - carbohy-drate complexes (LCC) in the Papermaking materials. On the other hand, during the PtilPmakingprocess, as the alkali concentration is high, xylan is pwhy dissoved in cooking liqUor, whi1e tllecook pmceeds, the alkali concentration decrease below a critical POint, de^ed, chorter cllain- xyan Precipitates in a more or less crytalline on the aniface of ndallril. The hendCellulooe^ning in th pu1p are closely associated with and even chemically bound to the residual lignin.The pnd of xyan initally dissoved in the cooking liquor can be reabsorbed or redeposited on theschce of pulp fibres. The redeposited xylan may physically shield the residual lignin frombleaching chendcds. As xylanase hydrolyzes the part of redeposided xylan, the bleaching chemicals are easily allowed better access to degrade and extrat the residual lignin from pulp fibres.Another explanation for xyanase action in bleaching is that the degradatin and solubilizatin of the xyan by xyanase aooears ti reduce the molecular mass of LCC, and facilitates easier removalof solubilized lighin in bleaching process. The mechanism of xylanase pretreatment shows that the empe betment based largely on the action of endoxyanase removes some of the reprecipted xylan, increasing the Permeability of the fibres and thus the extraction of lignin from them. Xyhaase heatmnt improves pulp bleachability, resulting in a sugniticant reduchon in chemdcals -consumphon. Another imporiant role chows that xyanase beatment reduces the AOX in bleachingdeuents. The xylanase treatlnnt as one stage is cowhined with the other bleaching stages whichinclude washing stage and chemical beatment stage. The paper showed that the replacement ofchlorine - based chendcals can' t be achieved by xyanase beatmnt aline.