Methylcellulose Samples Research Articles

Analysis of the substituent distribution along the chain of water-soluble methyl cellulose by combination of enzymatic and chemical methods

Abstract Four methyl cellulose samples in the degree of substitution range from 0.5 to 2.0 were characterised by combination of different analytical methods. Samples were analysed regarding their partial degree of substitution by hydrolysis and anion exchange chromatography with pulsed amperometric detection. For calibration of the chromatographic system, standard substances were isolated by preparative HPLC and their structure was confirmed by 13C-NMR spectroscopy. For two methyl cellulose samples per-acetylation and 13C-NMR with inverse gated decoupling was carried out for comparison with the chromatographic analysis. Endoglucanase fragmentation of methyl celluloses was performed and water-soluble and insoluble fractions were analysed separately. A preparative size exclusion chromatography system for enzymatic-degraded water-soluble methyl cellulose was developed and the molar masses of the individual fractions were examined by analytical size exclusion chromatography. By combination of endoglucanase fragmentation, preparative chromatography, hydrolysis and anion exchange chromatography an approach for the analysis of the substitutent distribution along the polymeric chain of water-soluble methyl cellulose could be established.

Temperature effect on the moisture sorption isotherms for methylcellulose and ethylcellulose films

Moisture sorption isotherms were obtained at 9°C, 15°C, 20°C, 25°C and 35°C for methylcellulose (MC) and ethylcellulose (EC) films following the normalized microclime method. Cast MC and EC film samples were equilibrated to 0.22, 0.44, 0.57, 0.75, and 0.90 a w values. MC films had an equilibrium moisture content about five times higher than the EC films. The Guggenheim–Anderson–deBöer (GAB) and Brunauer–Emmett–Teller (BET) equations were fitted to the experimental data using nonlinear regression. The regression coefficient ( R 2) used to evaluate model fit showed a best fit for the GAB model. The monolayer moisture content ( x m) decreased with temperature and correlated better with values calculated using the BET equation.

Influence of Substituent Distribution Along a Cellulose Chain on Enzymatic Degradation of Methylcellulose.

A commercially available methylcellulose (DS 1.9) was treated with cellulase, and the reaction mixture was subjected to gel-filtration. The eluate was divided into four fractions, and each fraction was subjected to a sugar analysis to see compositions of partially methylated sugars and its degree of substitution. Methylcellulose synthesized with methyl iodide in a nonaqueous cellulose solvent (DS 1.6) was also subjected to the same analysis. As a result of the sugar analysis, a higher molecular weight fraction gave a higher DS value, indicating that higher DS regions in methylcellulose are less degraded by cellulase than lower DS regions. Comparison of these two methylcellulose samples revealed that the substituent distribution along a cellulose chain of synthesized methylcellulose is more heterogeneous than that of commercial methylcellulose.

Physical and Sensory Properties of Sweetpotato Puree Texturized with Cellulose Derivatives

ABSTRACTWe evaluated the physical and sensory characteristics of restructured sweetpotato puree texturized with methylcellulose (MC) or methylhy‐droxypropylcellulose (MHPC). Samples were studied by instrumental texture profile (TPA), dynamic rheometric and sensory analyses, and scanning electron microscopy. Gelation of the gum‐puree mixtures gave maximal values of the storage modulus (G') at 60‐70°C. The TPA curves measured at 60°C for the 0.50%MC or MHPC sample were similar to those of baked sweet potatoes (control). A texture profile panel rated the 60°C samples of the 0.25‐0.50%MC or MHPC product as nearly equal to baked roots for several texture notes. An untrained acceptability panel scored the 0.25%MC and MHPC samples significantly higher in flavor and overall acceptability than baked roots.

Preparation, characterization, and mesophase formation of esters of ethylcellulose and methylcellulose

AbstractA range of mixed ether‐esters of cellulose was prepared from partially substituted ethylcellulose and methylcellulose. The 13C‐NMR analysis of ethylcellulose with a DS of 2.5 indicated that the hydroxyl groups at carbon six of anhydroglucose units were completely substituted. Acetylation of the ethylcellulose under different conditions yielded (acetyl) (ethyl) cellulose (AEC) samples with acetyl degree of substitution ranging from 0 to 0.5. Fully substituted (propionyl) (ethyl) cellulose (PEC) and (acetyl) (methyl) cellulose (AMC) were also prepared. Chiral nematic liquid crystals were formed in these mixed ester/ethers of cellulose in concentrated solutions of acidic solvents. The critical concentration for the phase separation of the cellulosic solutions depended on the nature of the substituent, the degree of substitution, and the solvent at a given temperature. Methylcellulose solutions in trifluoroacetic acid and dichloroacetic acid form chiral nematic liquid crystals with a left‐handed helicoidal structure. The acetylated methyl cellulose samples did not show the reversal of handedness with increasing acetyl content that was previously observed for the corresponding ethylcellulose samples. © 1994 John Wiley & Sons, Inc.

Effects of concentration and degree of polymerization on the rheological properties of methylcellulose aqueous solution.

Rheological studies were carried out on aqueous solutions of five methylcellulose (MC) preparations, with degrees of polymerization (DP) between 330 and 1020. Comparison of the intrinsic viscosity of MC with that of sodium carboxymethylcellulose (CMC) of similar DP indicated that MC molecules were relatively compact coils when they were present as isolated coils in dilute solution. However, the Huggins constants (k'1) of MC samples were higher than those of CMC samples, suggesting that intermolecular interaction of MC was larger than that of CMC at low concentration. The second virial coefficients of MC samples in dilute solution, determined by ultracentrifugation analysis, were divided at about DP 500 int two groups, low and high DP samples. A similar tendency was observed in the rheological properties of concentrated MC solution. It is suggested that the increase in DP was accompanied with an increase not only in molecular size but also in intermolecular interaction of MCs in solution. Interesting rheological characteristics were observed in high DP samples, particularly at concentrations higher than a critical concentration. The dynamic viscoelastic behavior of these samples depended significantly on both DP and concentration.

Melting temperatures of thermally reversible gels IV. Methyl cellulose-water gels

The gel/sol transition temperatures (T ) were measured by cooling of thermally reversible methyl cellulose (MC)-water gels using the ten MC samples. A linear relationship between 1/T and the logarithm ofv 2 x was found for each MC gel, wherev 2 is the volume fraction of MC andx the degree of polymerization. The X-ray diffraction patterns of both MC films and gels revealed that the network junction points of the MC gels are crystalline and consist of trimethyl glucose units. The heat of fusion of trimethyl cellulose was estimated as 2.6 × 103 J/mol, and entropy of dilution parameter = −1.6 andΘ = 320 K were also evaluated. Using these values, the gel/sol transition temperature was analysed according to our previous theory. It is concluded that the network junction points of MC gels are between 4 and 8 units long and also that the length is in good agreement with the sequence length estimated from the methoxy content of MC.

Electric birefringence of aqueous solutions of methyl cellulose

Electric birefringence studies have been conducted on six samples of methyl cellulose in the molecular weight range 3 × 10 4 to 1.5 × 10 5. Using pulsed electric fields, both the amplitudes and rates of the transient birefringence induced in these solutions have been analysed. For molecular weights below 2 × 10 3, the molecules are represented by rigid rods. Above this value increasing flexibility is evident. This can conveniently be seen through reduced electrical parameters, defined herein, which are obtained from a combination of the electrical and geometrical properties of the molecules. These parameters are apparently very sensitive to flexibility in the near-rod regime. It demonstrates the utility of electro-optic experiments in which both the electrical and geometrical data are obtained simultaneously. The persistence length concept does not appear to be adequate when rotary relaxation times are interpreted through it using current equations.