Finally, a comparison between biobleached treated sulfite pulp Chapter 6 and bleached commercial treated dissolving pulp Chapter 7 in terms of Fock solubility and carbohydrate composition, provided more information about the mechanism of action of endoglucanase and cold caustic extraction treatments.
Concerning Fock solubility results, the application of B or F endoglucanase resulted more positive on biobleached dissolving pulp rather than bleached commercial dissolving pulp, even when a cold caustic extraction was previously applied. By its side, a cold caustic extraction (CCE) treatment had different effect on respective studied pulps. A much higher Fock solubility loss was found for bleached commercial dissolving sample (-26%) in comparison to biobleached sample (-9%). Actually, commercial dissolving pulp had lower content of hemicelluloses than biobleached sulfite pulp, but lower hemicellulose removal was achieved. Specifically, CCE treatment decreased hemicelluloses by 12% for Com_CCE and about 40% for L_CCE samples, with respect to each original pulp. The action of CCE treatment was limited to the accessibility of residual hemicelluloses. Therefore, from these results two effects were suggested by CCE treatment: on the one hand, CCE helped to reduce mainly galactan fraction and then mannan and xylan fractions of biobleached sulfite pulp, and on the other hand, was responsible for the formation of cellulose II in commercial dissolving pulp leading to lower Fock solubility.
Moreover, the presence of cellulose II polymorph detected by NMR and the low Fock solubility value of Com_CCE sample were in agreement with the proposed explanation. Regarding to the combined treatments (CCE + endoglucanases) different Fock solubility improvements were found:
commercial dissolving samples (CCE_B120 and CCE_F12) exhibited a 39% of gain, while L_CCE_B120 and L_CCE_F12 biobleached samples only provided a 2% and 18%, with respect to CCE treatment. Once more, the different improvement can be explained by the different effect of CCE treatment:
conversion of cellulose I to cellulose II or hemicellulose removal, respectively.
7-153 To conclude, same enzymatic treatment conditions, biobleached sulfite up-graded pulp presented higher Fock solubility value than bleached commercial treated dissolving pulp.
Concerning carbohydrate composition B and F endoglucanases performed the same mechanism of action on biobleached sulfite pulp and commercial dissolving pulp. Specifically, both enzymes reduced galactan and mannan fractions by about 50% and 15%, respectively, of commercial dissolving pulp. By contrast, both endoglucanase attacked mainly xylan, followed by galactan and mannan fractions of biobleached sulfite pulp. Interestingly, xylan removal was more effective with B endoglucanase (79%) in comparison with F (54%), but similar percentage of reduction was found for galactan and mannan.
7.4 Conclusions
Two different cellulases, named as B and F, were used to increase the reactivity according to Fock method of dried bleached commercial dissolving pulp with the intention to bring a satisfactory advantage to the viscose process.
Working at high enzyme dose, F60 treatment, provided a reactivity increase of 42%, which belongs to a 96% Fock solubility. In terms of fiber morphology, the amount of fines increased significantly after F60 treatment, which is in connection with somewhat viscosity loss. The F12 treatment provided a 13%
Fock solubility improvement. Interestingly, applying a cold caustic extraction (CCE) treatment before the hydrolytic treatment (CCE_F12) resulted in further increased Fock solubility than an enzymatic hydrolysis alone (F12), although the relative value was much lower. In terms of WRV, this property was also improved with the combination of a cold caustic extraction and hydrolytic treatment (CCE_F12). The NMR results revealed that the starting pulp had already an important proportion of cellulose II, but after the CCE_F12 treatment this amount of cellulose II became higher. The B enzyme did not cause viscosity loss, although the Fock solubility was improved by 17% with respect to commercial pulp, which corresponds to a 79% of Fock solubility.
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