Enzymatic hydrolase-, or oxidoreduc- tase- based approaches for yellowing inhibition of high yield pulps and pulp delignification

摘要

Some new approaches comprising enzymes will be presented useful for photostabilizing of high yield mechanical pulps preventing their photoyellowing and for delignification/bleaching of chemical pulps. The enzyme systems used contain in the case of photostabilizing e.g. peroxidases/ H_2O_2 or hydrolases like lipases etc., some grafting and/or coupling facilitating substances and selected UV-absorbing and/or radical scavenging compounds. An other possibility for initiating coupling is the in situ generation of bis-epoxides with the aid of special lipases. In the case of delignification/ bleaching of chemical pulps the system consist of peroxidases/ H_2O_2 or other oxidoreductases such as laccases etc.. In the presence of enhancing compounds such as thiocyanates, isothiocyanates or their corresponding dimeric compounds sulfur- based radicals as oxidizing, grafting or coupling agents can be generated depending on reaction conditions etc. Based on these new oxidation or coating/coupling concept significant delignification/ bleaching results (up to 40 % delignification) at good strength properties can be obtained. Furthermore good yellowing inhibition effects can be achieved by coupling of special photostabilizing additives like UV-absorbing substances and/or radical scavengers on the fibre surface or by blocking of relevant groups like phenolic and aliphatic hydroxyl groups within the fibres. A further possibility is the combination of both strategies. Some selected results will be presented. The main advantages of these optimised approaches ( grafting, coupling and delignification applications) are their low dosage/ low cost properties, faster reaction and a very high strength preserving behaviour in comparison to chemical methods.