High Molecular Weight Carboxymethylcellulose Research Articles

Applicability of Modified Cox-Merz Rule to Concentrated Suspensions

The present work studied the rheological properties of concentrated non-colloidal aqueous suspensions of graphite particles together with carboxymethyl cellulose (CMC) having various molecular weights, especially focusing on the applicability of the modified Cox-Merz rule. These suspensions were investigated as model slurries to produce anode electrodes of lithium ion batteries. In the case of suspensions containing high molecular weight CMC, the complex viscosity resulting from the measurements of frequency dependence of the viscoelastic moduli at high strain values was in good agreement with the steady state viscosity. That is, the data conformed to the modified Cox-Merz rule. However, the data obtained from suspensions containing low molecular weight CMC did not agree with the modified Cox-Merz rule. The difference in the applicability of this model is considered to be attributed to variations in the ability of the suspensions to recover to a stable state during the application of cyclic strain.

Understanding the Role of Polymeric Binders in Water Based Lithium Ion Electrodes

Polymers find application in Lithium ion Batteries (LiB) as binders, providing cohesion in the dry electrode layer as well as adhesion to the current collector. They may also be added as a thickener to control the flow and hence the processing behavior of the paste. Furthermore, polymeric binders can act as dispersing agents for active material or carbon black particles, thus strongly determining the component distribution in dry electrodes. Despite the vast amount of research activities in the field of LiB, the contribution of the binder to the cell performance still remains elusive. Therefore, the adsorption of carboxymethylcellulose (CMC) on LiFePO4 and graphite particles as active material was investigated. The flow behavior of the electrode pastes as well as the electrical conductivity, mechanical properties and microstructure of corresponding dry electrodes were thoroughly characterized. Rheological measurements were carried out to study paste flow behavior as a function of CMC and solid particle concentration. The electrical conductivity of thin electrode layers was measured using the four point resistivity test. The adhesion force between electrode layer and current collector was determined via 90°-peel test. Thick electrode layers were prepared to investigate the cohesion in the electrode employing compression, bending and shear tests. Finally, the microstructure of the dry electrodes was characterize by means of scanning electron microscopy (SEM). Yield stress and viscosity exhibit a pronounced minimum with increasing CMC concentration for both the cathode and anode pastes, indicating that CMC acts as dispersing agent at low concentrations and as a thickener at higher concentration when the equilibrium adsorption concentration is exceeded. Furthermore, the degree of substitution of CMC have no significant influence on the slurry viscosity, whereas higher molecular weights and CMC concentrations lead to significantly higher viscosities. Electrical conductivity of thin electrode layers increases with increasing CMC concentration and yields a pronounced maximum when the equilibrium adsorption concentration is covered, suggesting a critical polymer concentration at which electrode components ideally distribute. In addition, mechanical tests show no clear dependence of the adhesion strength on CMC concentration, irrespective of the degree of substitution or molecular weight, i.e. it does not contribute to the adhesive strength. In contrast, the cohesive strength of the electrode layers increases with higher polymer concentration and molecular weight, but decreases with increasing degree of substitution. Micrographs of the electrode layers show an alignment of the particles for electrodes based on high molecular weight CMC. Preliminary measurements exhibit higher adhesion strength when adding styrene butadiene rubber (SBR), whereas cohesion strength and electrical conductivity significantly decreases. This demonstrates that the optimum CMC concentration has to be chosen according to the required specifications with respect to cohesion and electrical performance.

Influence of CMC Molecular Weight and Degree of Substitution on Clay Swelling Inhibition in Water‐Based Drilling Fluids

SummaryIn this paper, the clay hydration inhibitive properties of carboxymethylcellulose (CMC) in drilling fluids systems were studied. The clay swelling degree was evaluated as a function of time in presence of different aqueous solutions containing sodium chloride, potassium chloride, CMC A (9 × 104 g/mol − DS 0.7), CMC B (2.5 × 105 g/mol − DS 0.7), CMC C (2.5 × 105 g/mol − DS 1.2) and a commercial clay inhibitor based in quaternary amine, that was used as reference pattern. According to results obtained, the low molecular weight CMC showed slightly lower clay swelling degree compared to the high molecular weight along 180 minutes. In parallel, it was confirmed the higher efficiency of quaternary amine‐based commercial inhibitor (QABCI) to control the clay swelling mechanism. Basically, this inhibition effect was attributed to the ability of cationic quaternary ammonium groups to form electrostatic interactions with negatively charged surfaces of the clay, enhancing associative interaction between their particles. Besides, it was visualized by microscopy that the highest molecular weight of CMC provided a reduction in formation and pores size compared to CMC of lower molecular weight after 1,000 minutes in aqueous medium. This behavior could be attributed to the dynamic of interactions between clay and high molecular weight CMC along the time, which is a result of strong contribution of electrostatic interactions between carboxylate groups located along the polymer backbone and positively charged clay layers edges as well as hydrogen bonds.

Ethylene vinyl acetate blends with cellulosic fillers and reinforcements

Polymeric blends based on ethylene vinyl acetate (EVA) rubbers filled with high molecular weight carboxymethyl cellulose were investigated in view of possible employment as biodegradable materials. The effect of vinyl acetate (VA) content and of addition of transesterification agent to increase interaction between EVA and cellulosic components was considered. Blends reinforced with cellulose microfibers in different amounts were also characterized in their mechanical, rheological, and thermal behavior. POLYM. COMPOS., 36:980–986, 2015. © 2015 Society of Plastics Engineers

Synergy of CMC and modified chitosan on strength properties of cellulosic fiber network

Previously, the application of modified chitosan (MCN) and carboxymethyl cellulose (CMC) in a dual polymer system showed promising results in increasing the strength of fiber networks. This work evaluates the influence of CMC molecular weight (MW) and of CMC/MCN ratio on the characteristics of formed CMC/MCN complexes in polymer solutions and on the properties of cellulosic fiber networks. The results showed that the application of MCN and the high MW CMC (HCMC) (1:1 charge ratio) enhanced the tensile, burst, and tear indices, but reduced the light scattering coefficient of the fiber network more significantly than that of MCN and the low MW CMC (LCMC). Increasing the ratio of HCMC/MCN marginally affected the tensile index, the burst index, and the light scattering coefficient of the fiber network, even though the ratio significantly affected the characteristics of the CMC/MCN complexes in polymer solutions. The tear index and brightness were improved by increasing the HCMC/MCN ratio. These results were explained based on the retention of HCMC/MCN complexes and the layer-by-layer assembly of HCMC and MCN on the fiber surface.

Topochemical modification of cotton fibres with carboxymethyl cellulose

Adsorption of carboxymethyl cellulose (CMC) as a method to introduce charged (ionizable) groups onto cellulose cotton fibre surfaces was investigated. The method was based on application of a previously published method used for wood fibres. The amount of adsorbed ionizable groups was determined indirectly by analysis of CMC in solution by the phenol–sulphuric acid method and directly by conductometric titration of the fibres. Results from the two methods correlated well. The molecular weight and purity of the CMC had an influence on its adsorption onto cotton; high molecular weight CMC was preferentially adsorbed. The adsorbed charge correlated linearly with the amount of CMC adsorbed. The total charge of the cotton fibres could be increased by more than 50% by adsorption of CMC. It is expected that this modification procedure can be used in a wide spectrum of practical applications.

Untypical rheological behaviour of the lignite–carboxymethylcellulose–water dispersion system

Suspensions of lignite in a solution of a high molecular weight carboxymethylcellulose show peculiar rheological behaviour. Unless the lignite concentration is sufficiently high, apparent viscosity and viscoelastic moduli of the suspension are lower than those of the pure solution. This effect is not suppressed by changing pH and seems to be common for low-concentrated suspensions in solutions of high molecular weight (bio)polymer. It is explained by specific structuring of the suspensions. Lignite particles at lower concentration separate long cellulose chains and facilitate their movement under shear flow. The particles loosen inter-chain contacts, disturb and release elastic gel-like structure formed by the long cellulose chains, which results in the low strain oscillatory deformation, the decrease in the moduli and the increase in the loss angle. If the amount of lignite particles is sufficiently high, suspension stiffening occurs as usual. No such effect was observed for suspensions prepared from the low molecular weight derivative.