Chapter 26
Modification of Dissolving Pulp by Hydrolysis with Cellulase Enzymes 1
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L . Rahkamo , M . Vehviläinen , L . Viikari , P. Nousiainen , and J. Buchert 1
V T T Biotechnology and Food Research, P.O. Box 1501, 02044 VTT, Finland Tampere University of Technology, Fiber, Textile and Clothing Science, Box 589, 33101 Tampere, Finland
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The environmental risks caused by the use of carbon disulfide in the viscose process have lead to the search for new types of processes for fiber production from cellulose. As a novel approach, cellulose degrading enzymes have been investigated in the manufacture of a directly soluble cellulose. In this paper, the potential of monocomponent cellulases from Trichoderma reesei in the transformation of dissolving pulp into directly alkaline soluble cellulose is discussed.
Cellulose can be processed to textile fibers by the viscose process. The use of carbon disulfide in the viscose process causes several environmental problems. Carbon disulfide is the main reactant in converting cellulose into alkaline soluble cellulose xanthate. The problems associated with carbon disulfide have lead to the search for more environmentally friendly techniques. These alternative processes for fiber production from cellulose include direct dissolution of cellulose pulp in organic solvents (7), or the use of cellulose derivatives such as cellulose carbamate (2,3,4). Also, cellulose degrading enzymes, cellulases, have been investigated in the manufacture of directly alkaline soluble cellulose (5,6). Cellulases are produced by many fungi. Due to the complex structure of cellulose, several different enzymes are required for its complete degradation. The enzymes involved in cellulose degradation typically include several endoglucanases (EG), two or more cellobiohydrolases (CBH) and at least one β-glucosidase (7,8). Cellulases act in synergy in the hydrolysis of crystalline cellulose. Endoglucanases randomly attack the amorphous regions in native cellulosic substrates, resulting in a rapid decrease in cellulose chain length (9). Cellobiohydrolases cleave cellobiose units either from the reducing or non-reducing ends of cellulose chains and they have been shown to hydrolyze crystalline cellulose without the aid of endoglucanases (10). Vehvilâinen et al. (5) have studied the activation of cellulose with mixtures of
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©1998 American Chemical Society
In Enzyme Applications in Fiber Processing; Eriksson, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
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cellulases produced by Trichoderma reesei and Aspergillus niger. They concluded that cellulose can be converted into directly alkaline soluble form by the use of cellulase enzymes. Films and fibers can be spun from this cellulose solution. In order to optimize the composition of the cellulase mixture it is necessary to understand the effects of individual cellulase enzymes. In our studies we have used purified Trichoderma reesei cellulases to investigate their individual effects in the activation of cellulose into alkaline soluble form. In our studies we have found that of the purified Trichoderma reesei cellulases investigated, endoglucanase Π was most effective in reducing the viscosity and improving the alkaline solubility of hardwood dissolving pulp (6). The effect of E G Π was not clearly improved by the action of hemicellulases or other cellulases (unpublished data). Also, a two-step solubilization of hardwood dissolving pulp has been investigated. Thé readily alkaline soluble fraction was first solubilized in alkali and the resulting insoluble residue was treated with cellulases. Materials and Methods Dissolving Pulps. Dissolving pulps were obtained from Saiccor (SA) and Borregaard. The Saiccor pulp was hardwood dissolving pulp (eucalyptus and acacia with a ratio of 3:1) and the Borregaard pulp was softwood dissolving pulp. The characteristics of the pulps are presented in Table 1. Prior to the enzymatic treatments the pulps were disintegrated in an L & W SE 003 apparatus at 1.5 % concentration and with 30 000 revolutions.
Table I. Characteristics of Saiccor and Borregaard Pulps Borregaard Saiccor Softwood Hardwood Origin 510 555 Viscosity (dm /kg) Carbohydrate composition (%) 96.0 97.9 glucose 2.0 2.1 xylose 2.0
