Entanglement properties of cellulose and amylose in an ionic liquid

Abstract

Concentrated solutions of cellulose and amylose were prepared with an ionic liquid 1‐butyl‐3‐methylimidazolium chloride (BmimCl), which was chosen as a good solvent for these polysaccharides. Dynamic viscoelasticity of the concentrated solutions was examined to obtain the molecular weight between entanglements, Me. The value of Me in the molten state (Me,melt), a material constant that reflecting the entanglement properties, was determined for cellulose and amylose by extrapolating Me to the “melt.” A marked difference in Me,melt was found: 3.2 × 103 for cellulose and 2.5 × 104 for amylose. The value of Me,melt for cellulose, which is composed of β‐(1,4) bonding of D‐glucose units, is very close to those for polysaccharides with a random‐coil conformation such as agarose and gellan in BmimCl. The much larger Me,melt for amylose can be attributed to the helical nature of the amylose chain, α‐(1,4)‐linked D‐glucose units. The effect of concentration on the zero‐shear viscosity for the solutions of cellulose and amylose was also examined. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Entanglement network of agarose in various solvents

“…Here, the plateau modulus G N 0 can be defined as the G¢ value at oa T where the loss tangent (tand¼G 00 /G¢) curve attains a minimum [7][8][9]15 and is related to the molecular weight between entanglements (M e ) by…”

“…The ionic liquid BmimCl (Aldrich) was the same as that described in the previous studies. 7,8 Agarose solutions were prepared as follows: agarose was added to each solvent (for BmimCl, the solvent was preheated to convert it into the liquid state) in a dry glass vessel, and the mixture was quickly stirred with a stainless spatula on a hot plate at B80 1C. Then, the vessel was sealed and left on the hot plate for complete melting.…”

“…The concentration of agarose (c) was 1.0Â10 2 or 2.0Â10 2 kg m À3 , that is, ca 10 or 20 wt %. In the calculation of c, 1.0Â10 3 kg m À3 was assumed for the density of agarose, and 1.14Â10 3 , 1.00Â10 3 and 1.08Â10 3 kg m À3 were used for the densities of FA, 14 MFA 14 and BmimCl, 7,8 respectively. To minimize the effect of moisture absorption, a fresh bottle of solvent was used every time agarose samples were prepared, and the rheological measurements were made just after finishing the sample preparation.…”

“…We prepared concentrated solutions of several kinds of polysaccharides in an ionic liquid 1-butyl-3-methylimidazolium chloride (BmimCl) and carried out rheological measurements for the solutions to determine M e,melt for the polysaccharides. [7][8][9] The experiments yielded rather small values of M e,melt for the polysaccharides; for example, 8 M e,melt was 2.3Â10 3 for agarose, which is composed of (1,3)-b-D-galactopyranose and (1,4)-3,6-anhydro-a-L-galactopyranose. 10 This value appears to be much smaller than expected for a stiff polymer and is actually comparable to the M e,melt for the simplest flexible polymer polyethylene (M e,melt ¼1.3Â10 3 ), 3 although no reported value of C N for agarose is available.…”

“…The M e,melt for amylose was also determined and was much larger than that for cellulose. 7 To explain the M e,melt values, it is necessary to examine whether the use of an ionic liquid as a solvent affects the estimation of M e,melt . It has been proposed that ionic liquids form three-dimensional structures even in the liquid state because of cation-anion hydrogen bonding and cation-cation ring stacking.…”