Structural changes and alkaline solubility of wood cellulose fibers after enzymatic peeling treatment

Abstract

The authors are grateful to the publisher, Elsevier, for letting the manuscript being archived in this Open Access repository. The final publication is available at http://www.sciencedirect.com/International audienceTwo dissolving sulphite wood pulps were treated by an enzymatic peeling protocol and the changes in terms of structure and alkaline solubility were analyzed. The enzymatic treatment leads to a fast and large decrease of degree of polymerization and of crystallinity, showing that the enzymes do not simply act on the fiber surface. The swelling and dissolution behaviour of the treated samples showed that the enzyme mixture used has two effects at short peeling times (i) a digestion of the primary wall which is seen by the near absence of ballooning and (ii) a destructive action on the inside of the fiber which is seen by the large decrease in the degree of polymerization. At long peeling times, the external walls are totally digested and the fiber structure is totally destroyed, as seen by the absence of birefringence. The alkaline solubility of the different treated samples was investigated in a NaOH 8%-water solution. As expected from thermodynamic considerations, there is a direct correlation between the solubility and the degree of polymerization. However, aside thermodynamics, the removal of the external walls and the macrostructural destructuration of the fibers are key factors in the improvement of the dissolution of wood cellulose fibers. At constant intrinsic viscosities of the cellulose materials, the alkaline solubility is almost two times higher when the external walls are removed. The macrostructural destructuration of fibers by enzymes allows a high degree of polymerization to be preserved while keeping a good alkaline solubility

Enzyme pretreatment of dissolving pulp as a way to improve the following dissolution in NaOH/ZnO

“…The combined treatment with xylanase, alkali and endoglucanase caused more degradation of the DP than an endoglucanase treatment alone and it has been reported that enzymes are active both in the outside and the inside of the fibers (Le Moigne et al 2010). This is in agreement with Henriksson et al (2005) who have observed that a decrease in the degree of polymerization is not the explanation behind the activating effect of the endoglucanase treatment.…”

Enzymatic hydrolysis of chemithermomechanically pretreated sugarcane bagasse and samples with reduced initial lignin content

“…These data suggest that the cellulose contained in the experimental hybrid with lower original lignin content was more susceptible to alkaline pretreatment, probably because of the decreased protection of this component against the peeling reactions. 39 This hypothesis was also evidenced by the low yield of pretreated material recovered from this sample. Figure 4 shows the data for enzymatic hydrolysis of the two samples with reduced original lignin content pretreated by the CTM process when compared with those generated from mill-processed bagasse.…”

How does the never-dried state influence the swelling and dissolution of cellulose fibres in aqueous solvent?

“…In both states, several fibres showed a large homogeneous swelling (Fig. 5a) revealing the absence of primary wall as observed by Le Moigne and Navard (2010) for wood pulps and after the enzymatic peeling of the primary wall (Le Moigne et al 2010b). As for hardwood, the parenchyma cells were not affected by this solvent system and the most intact fibres showed only slight swelling and ballooning localized in the dislocations.…”