Single crystals of cellulose IV_II: Influence of the cellulose molecular weight

Abstract

The influence of the degree of polymerization (DP) of cellulose was evaluated in the preparation of micron‐sized cellulose IVII lamellar crystals in order to ascertain whether a regular chain‐folded morphology could develop during their growth. For this purpose, sharp fractions of cellulose acetate were collected by preparative gel permeation chromatography. Aliquots of these fractions were deacetylated and crystallized in dilute solutions containing water, methylamine, and DMSO, and held at 150°C under pressure. Well‐developed cellulose IVII lamellar crystals were obtained with fractions of DP 22–24 whereas higher‐DP material gave polycrystalline aggregates. This behavior indicates that large lamellar crystals of cellulose IVII can be obtained only with unfolded short cellulose chains. The occurrence of chain‐folded crystals with high–DP cellulose samples cannot be demonstrated.

Tailoring the Structure and Morphology of Low-Molecular-Weight Cellulose Produced during Supercritical Water Hydrolysis

“…However, at a slightly lower precipitation temperature of 120 °C, hybrid cellulose II–cellulose IV II crystals were formed. Moreover, increasing the DPn of cellulose from 22 to 40 resulted in badly formed lamellar crystals …”

“…Moreover, increasing the DPn of cellulose from 22 to 40 resulted in badly formed lamellar crystals. 38 At the end of the reaction, the contact between the dissolved low-molecular-weight cellulose chains and water under ambient conditions triggered the precipitation of the former due to a solubility differential. In addition, the higher the cellulose concentration, the more cellulose−cellulose interaction related to cellulose−solvent interactions, and the faster the precipitation occurred.…”

Solvent-Assisted Fractionation of Oligomeric Cellulose and Reversible Transformation of Cellulose II and IV

“…Narrow molecular weight distribution has also been found to affect the crystal morphology such that DP24 at Đ = 1.11 producing more perfect crystals . In another study, enzymatically synthesized oligocellulose with an average DP of 9 forms highly ordered cellulose II .…”

“…Narrow molecular weight distribution has also been found to affect the crystal morphology, such that DP24 at PDI = 1.11 producing more perfect crystals. 28 In another study, enzymatically synthesized oligocellulose with an average DP of 9 form highly ordered cellulose II. 29 Comparing to previous findings, this study demonstrates new pathways of interconversion between cellulose IV and II by simple solvent environment in an oligocellulose fraction with a lower DP at 7.70 and narrower polydispersity at 1.01.…”

Polymorphic and Morphological Aspects of Recrystallized Cellulose as a Function of Molecular Weight

“…On the other hand, with high molecular weight, the cellulose II crystals are fibrillar in nature as they are elongated along the cellulose chain axis. Such changes in morphology, associated with a change in molecular weight, is remarkable and must certainly be connected with the impossibility for cellulose to crystallize as regular chain folded crystals (20). In an earlier study on cellulose II crystals (14), it was shown that the growth habit for low DP cellulose crystals was is the form of long flat ribbons when the crystallization conditions were optimized.…”