Structures of cellulose in solution

Abstract

Cellulose and their derivatives only rarely form molecularly dispersed solutions. Colloidal aggregates of yet not fully explored supramolecular structure remain preserved even at the highest dilution. The present contribution is concerned with the determination of the number of aggregated chains per colloid particle. In some cases the aggregation number could be directly determined but for the non‐ionic, partial substituted cellulose‐ethers the degree of polymerization of the non‐aggregated cellulose was not sufficiently well known. A detailed analysis of the angular dependencies of scattered light revealed for the large aggregates a star‐shaped structure. The smaller ones were better described by a worm‐like structure. These observations led to the suggestion of a fringed micelle model where several chains are laterally assembled in a rigid stem leaving at both ends coronas of f/2 dangling chains. Recent SANS experiments support this model. The estimated chain length of a single strand was found with DPw = (4–20)×103 much too high and led to the conclusion that 4–20 chains must be co‐linearly (staggered) associated to form one strand. The obtained overall aggregation numbers are close to those found for cellulose in NMMNO and vary from 10 to 800. The similarity of the supramolecular structures in aggregation numbers and dimensions is interpreted as reminiscent of the semi‐crystalline structure of the parental native cellulose fibers. Much lower aggregation numbers were found for cellulose xanthogenates (viscose) in NaOH solution and for cellulose 2.5‐acetate in acetone than for cellulose in NMMNO.

Anionic surfactant aggregation with (Hydroxypropyl)cellulose in the presence of added salt

“…It is well recognized that cellulose derivatives in aqueous solutions may show the presence of clusters that originate from the aggregation of their hydrophobic groups. 41,42 Figure 7 shows the angle dependence for relaxation rate of the fast mode, Γ 1 , for different 0.5% HPC / NaCl 0.1 mol L -1 solutions with and without surfactants, calculated from a two-exponential fit to the field correlation functions. For the free HPC solution the fast mode predominates over the slow mode: at 0.5% m/m HPC shows ca.…”

On the dissolution state of cellulose in cold alkali solutions

“…It is, thus, fully possible that a vast majority of the molecules are able to move around more or less freely and that the very large clusters seen with SLS and SAXS are simply so slow that they are not seen by NMR. Another explanation is the structures suggested by Schulz et al (2000). They suggests aggregated fringed micelles, where large clusters form with a lot of free chains sticking out.…”

“…This parametrized form factor was derived by Pedersen and Schurtenberger (1996) from computer simulations (Chen et al 2006). In the present calculation we have used the experimentally determined M w ¼ 29 kg/mol corresponding to an average contour length of L h i % 82 nm, assuming a length of 0.515 nm (Schulz et al 2000) for every glucose unit, a cross sectional radius of 0.25 nm and a Kuhn length l K ¼ 2:3 nm (corresponding to approximately 4 glucose units). Here, the value of l K was adjusted to fit the experimental data at higher q.…”

Dissolution and Gelation of Cellulose in TBAF/DMSO Solutions: The Roles of Fluoride Ions and Water

“…1 Both native and processed cellulose display amorphous as well as crystalline regions, where the latter are particularly difficult to dissolve. 2 The key to get cellulose in solution is to overcome the strong intermolecular attractions between the chains.…”