Low cellulose concentration (1%), low temperature (below 12 °C) and short centrifugation time (5 min) prevent gelation of the solutions during centrifugation (Roy et al. 2003). The carbohydrate composition of the non-recovered fraction (Snr) was subtracted from the composition of the insoluble and recovered fractions (I1, I2, I3, I and Sr). These fragments are the result of fiber breakage, flat rings and their large fragments.
Steam exploded (SE) wood pulps: influence of mixing on the shapes of insoluble parts. Wood pulps: Observations of the insoluble fraction I for PH Kraft pulp and bleached sulphite pulp. In the case of the PH Kraft pulp solution, most of the fibers are only slightly swollen.
The molecular weight distributions of the insoluble fractions (I1, I2, I3, I) have higher average molar masses than the average molar masses of the original samples (Figure 10). The molecular weight distributions of the insoluble fractions and recovered fractions (Sr) of Avicel PH 101 are similar. However, some hemicelluloses (10% of xylans and 28% of mannans) remain aggregated with cellulose in both the insoluble and recovered fractions (Sr).
In the case of the recovered fractions (Sr), the presence of hemicellulose should come from their capture during the regeneration in distilled water.
Discussion
The destructuring of the layer structure by steam explosion, acid hydrolysis or stirring aids the dissolution. Our results show that the steam explosion of the SE DP 360 and SE DP 403 samples acts as a destructuring treatment that facilitates the disassembly and fragmentation of the fibers in the NaOH 8% - water mixture and finally reduces the amount of insoluble material towards 42 % for the bleached sulphite mass). It shows that the dissolution capacity of cellulose chains, in addition to thermodynamic considerations, is highly dependent on their localization in the cell wall structure.
The higher concentration of hemicelluloses, especially mannans, in the insoluble fractions suggests that the variations in the dissolving power of cellulose chains may be related to the localization of the cellulose chains in the cellulose/hemicellulose complex, i.e. the reasons leading to the specific “flat” rings” geometry needs to be more detailed. To what extent is cutting into flat rings due to the original structure of.
In the highly swollen fibers, we have previously shown that the primary wall is not present due to the absence of ballooning. Numerous tears across the fiber axis (white lines) can be observed along highly swollen fibers and sections. Given the high radial swelling (230 to 560%), the outer S1 wall must be torn because its microfibrils are nearly perpendicular to the fiber axis.
The frequent repetition of this tear every 10 µm remains to be explained, but it must be related to the deposition and the cohesion of the cellulose microfibrils in the S1 wall. This mechanism requires that the S2 wall be cut transversely while its microfibrils are nearly parallel (0-30°) to the fiber axis. The loss of mechanical properties of the S2 wall can be explained by the fact that the original compact cellulose structure is not preserved as the S2 wall is highly swollen and partially dissolved.
It should be noted that cutting the highly swollen fibers into rings and not slices shows that the wood fibers were not fully mature or that the inner tertiary wall and wart layer had been removed by the pretreatments or were easily soluble in the NaOH. 8% - water solution. 1990a) assumed that the alkaline solubility of cellulose samples can be improved up to 100% when the DPw value falls below 400 after steam explosion. NaOH and 1 wt% urea at -5°C were shown to dissolve bacterial cellulose as long as its DPw is lower than 560 (aszkiewicz 1998), highlighting the detrimental influence of cell wall structure and composition on dissolution capacity.
Conclusions
All these experiments show that wood fibers can be decomposed into flat rings when placed in NaOH 8% - water, regardless of their initial cooking (steam explosion pretreatment, sulfite or sulfate processes). Puls from vTI- Institute of Wood Science and Wood Biology for discussions and providing the kraft sample and Institute of Molecular and Cellular Pharmacology (IPMC) for help with centrifugation. Brändström J, Bardage SL, Daniel G, Nilsson T (2003) Structural organization of the S1 cell wall layer of Norway spruce tracheids.
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Effect of cellulose sources on changes in morphology, degree of polymerization, solubility and solid structure. Yamashiki T, Matsui T, Saitoh M, Okajima K, Kamide K, Sawada T (1990b) Characterization of pulp treated by steam explosion method. 6 Optical microscopic images of highly swollen fibers, sections and flat rings. a) direct transmission of light; (b) between a cross polarizer.
10 Molecular weight distributions of original samples, insoluble fractions (I1, I2, I3 and I) and recovered fractions (Sr) for SE DP 360, SE DP 403 wood pulp and Avicel PH 101.