General Description

Carboxymethyl Cellulose is a versatile cellulose derivative with unique characteristics that are crucial for various industrial applications. Its rheological properties, including viscosity, pseudoplasticity, and viscoelasticity, significantly influence its functionality, allowing for easy flow in products like food, pharmaceuticals, and cosmetics. The synthesis of Carboxymethyl Cellulose has increasingly shifted towards plant-based materials, utilizing agricultural by-products such as banana pseudo-stems and corncobs, which are abundant and cost-effective sources of cellulose. This trend not only minimizes waste but also promotes environmentally sustainable practices, enhancing the biopolymer's versatility in applications ranging from food additives to biomedical uses.

Figure 1. Carboxymethyl Cellulose

Characteristics

The answer of how Carboxymethyl Cellulose (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 Carboxymethyl Cellulose for various application purposes can be defined by the suggested three significant parameters (rheology, viscosity, and DS).¹

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, Carboxymethyl Cellulose 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.¹

Viscosity and Its Importance in Applications

The viscosity of Carboxymethyl Cellulose is a critical factor impacting its functionality in various applications. Viscosity measures a fluid's resistance to flow and is inherently linked to the concentration and degree of substitution of Carboxymethyl Cellulose. High viscosity types are extensively utilized in the production of thickening agents in food processing, while low viscosity grades serve as effective moisture binders in different formulations. The viscosity of Carboxymethyl Cellulose can also be tuned through its molecular weight and synthesis conditions, enabling its application across diverse fields, including pharmaceuticals and textiles. In addition, the relationship between the degree of substitution and viscosity means that Carboxymethyl Cellulose with higher DS values tends to offer better solubility and stability, making it ideal for use in food additives, drug delivery systems, and cosmetic products. Overall, the comprehensive understanding of the characteristics and behavior of Carboxymethyl Cellulose underscores its significance and versatility in numerous industrial applications. ¹

Synthesis from Plant-Based Materials

Role of Plant-Based Materials

From the earliest production of Carboxymethyl Cellulose, the terrestrial precursors of cellulose have been used most of the time. However, the concomitance of other compositional essences such as lignin, pectin, hemicellulose, and minerals without the expected cellulose extent demands excess energy input and costs for their removal with some excessive pre-treatment steps. Consequently, the use of conventional terrestrial cellulosic precursors is losing interest day by day in Carboxymethyl Cellulose production due to their limited availability and expensive cost-expanding pre-treatment steps. Many researchers have reported a moderate amount of cellulose percentage (i.e., 31~60%) in numerous agricultural by-products and wastes such as fruit peels, straws, corn cobs, leaves, etc. Therefore, an emerging interest has grown in recent years to utilize these materials in commercial CMC production for various applications, according to the properties of the obtained CMC. It is worth mentioning that the synthesized CMCs from different plant-based or agricultural precursors may not show similar physiochemical or morphological characteristics (e.g., DS, rheological properties, viscosity, water, and oil retaining capacity, etc.). Therefore, their targeted fields of application may vary from each other. To improve their existing properties or add new properties, the production of CMC from cotton fibers, which consist of about 95% cellulose, has been carried out.¹

Abundant and Sustainable Sources

One of the most significant advantages of utilizing plant-based materials for producing Carboxymethyl Cellulose is their wide availability and low cost. Agricultural wastes such as banana pseudo-stems and sago thwacks have been highlighted as rich sources of cellulose. Meenakshi et al. reported on the high cellulose yield from banana pseudo-stems, subsequently utilized by others to produce high-purity Carboxymethyl Cellulose. Similarly, corncobs, often discarded from maize processing, have gained attention, with significant quantities produced annually providing a substantial source for synthesis. Palm oil fronds also represent another low-cost precursor, contributing to high purity Carboxymethyl Cellulose production. Not only do these materials reduce waste from agricultural and industrial practices, but they also aid in creating more environmentally friendly production processes. Additionally, the utilization of invasive species like water hyacinth demonstrates the potential for Carboxymethyl Cellulose synthesis from underutilized or problematic plants, further enhancing the sustainability of this biopolymer's production. ^1,2