Carboxymethyl cellulose (CMC)

Characteristics of CMC

The answer of how CMC responds when it is used for a variety of conditions or applications is the central pivotal point to define the character of CMC. This section highlights the properties or parameters that directly impact CMC applications or behavior of the final products of CMC, such as rheology, viscosity, and DS. In contrast, rheology defines the physical properties and the flow and fracture behavior of the CMC’s final products (under different pressures). However, the rheological properties (stress-strain flow behavior, pseudoplasticity, viscoelasticity, and thixotropy) are primarily controlled by the viscosity. Likewise, viscosity is interrelated to the DS of CMC. Thus, the overall characteristics of CMC for various application purposes can be defined by the suggested three significant parameters (rheology, viscosity, and DS).

Rheological Properties

In between the discussion of the characterization of matter, rheology plays a vital role in connecting the study of the flowing behavior of matter and its deformation under the force of application. Moreover, the rheological study of materials gives an overall idea about the flow system like thixotropy, pseudoplastic, viscoelastic, and stress-strain flow behavior. After all, this behavior or properties of rheology are closely interrelated to the structure of polymer systems such as structure, particle size, concentration, shape or surface characterization, etc. According to the study of structure, CMC shows some complex and interesting flow behaviors under stress-strain action that directly impact the various application purposes of CMC such as food packaging, film fabrication, or coating of materials, etc. CMC’s thixotropy, pseudoplastic, or viscoelastic behavior is directly attached to suspension injection, paint, adhesive, food processing, cosmetics, etc. Here, the rheological characterization of CMC is discussed under the following subtopics.

Stress-Strain Flow Behavior

For the application of CMC for various purposes, how or how fast CMC-based materials deform under applied force or various conditions are general questions that must be answered. Deformation study of materials is defined as the amount of strain under applied stress. The stress-strain relationship of materials to determine its flow behavior also helps to prescribe the CMC, whether it is suitable for a specified condition or not. As a polymeric derivative, CMC often behaves like a non-Newtonian fluid. CMC sometimes follows the property of Newtonian fluid or viscous flow behavior in low concentrations. Therefore, according to the Ghannam and Esmail (1997) investigation , CMC covers the Newtonian character at 1% and non-Newtonian above 1% (or 2–5%). The investigation followsthe shear stress-shear rate curves, which mainly were linear for all concentrations (1–5%), as shown in the Supplementary Materials (Figure S1a). Still, the viscosity-shear rate curves were nearly horizontal type (below or at 1%) or decreasing linear type (above 1% or up to 5%), as shown in the Supplementary Materials (Figure S1b). The horizontal curve indicates the flow is viscous or has a Newtonian character. Gradually decreasing curves define the shear thinning behavior (STB) or non-Newtonian character, indicating sharp and highest flow behavior. Other CMC properties like thixotropy, pseudoplastic, and viscoelastic behavior are fully interconnected to STB. Above all, STB plays an important role during the various applications of CMC, which control the film fabrication, packaging, injection molding, or melt strength property of CMC .