Applications of CMC and HEC in Daily Chemical Products
Cellulose ethers are widely used polymer polymer fine chemical materials made from natural polymer celluloses by chemical treatment. Since cellulose nitrate and cellulose acetate were made in the 19th century, chemists have developed many series of cellulose ether derivatives and continually discovered new application areas, involving many industrial sectors. Cellulose ether products such as sodium carboxymethyl cellulose (CMC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), methyl hydroxyethyl cellulose (MHEC), and hydroxypropyl methyl propyl cellulose (MHPC) are known as “Industrial MSG (mono sodium glutamate)”, and have been widely used in oil drilling, construction, paints, food, medicine and daily chemicals, etc. Now, CMC and HEC are used as the water-soluble rheological additives for toothpaste, shampoo, hand sanitizer, shoe polish and other household chemical products, playing a role in thickening and preventing the sedimentation of insoluble matter.
Properties of Solution
3.1 Dissolution in Water
CMC and HEC are easily dissolved in hot water and cold water. Generally speaking, the products of low viscosity are more easily dissolved. The production process of CMC and HEC is: dispersing by stirring—swelling—dissolving by hydration. During swelling, the phenomenon of agglomeration often occurs, and the time required for dissolution is controlled by the degree of agglomeration. Suitable methods of dispersing and dissolving CMC and HEC are as belows: ①At the water temperature of 30℃ ～50℃, slowly add CMC or HEC in the constantly stirring water flow center, and the adding speed should be enough to make it fully dispersed and swollen in water; ②Wet CMC or HEC with alcohol or ethyl cellosolve, and then slowly stir by adding hot water; ③Mixing and stirring of dry powder can make the mixture not produce agglomeration when added into water; ④In the slight alkaline (pH = 7-9), the hydration time gets shortened, so CMC or HEC accelerates dissolution, and the viscosity of solution rapidly increases to the maximum value.
CMC and HEC are both dissolved very quickly in hot and cold water to form a solution; they are substantially not dissolved in organic solvents, and partially dissolved in those water miscible solvents (such as ethylene glycol, propylene glycol and glycerol).
3.3 Moisture Absorption
CMC and HEC can easily absorb water, and for long-term storage, their moisture will reach an equilibrium value of water and will change with the ambient temperature. At the temperature of 23℃ and the humidity of 50%, the equilibrium moisture content is 6%, while at the humidity of 84%, the equilibrium moisture content is 29%, so there is need to compensate for changes in moisture when weighing in advance.
The solutions of both CMC and HEC are non-Newtonian fluids. Their viscosities will change with the shear rate, independent of time. The viscosity of solution will be rapidly increased with increasing concentrations, and increasing the shear rate can significantly lower the viscosity. When only in the presence of gravity and surface tension, the viscosity seems very high. This liquidity is called pseudoplastic property, and the higher the viscosity of model is, the stronger its pseudoplastic property will be.
3.4.2 Effects of Mixed Solution On the Viscosity
Considering the viscosity of the solvent itself, CMC and HEC have more thickening properties in the mixed solvent system and in water. If the consistency of solvent is 10 times that of water, then their viscosity in this solvent has to be thickened 10 times that in the pure water solution.
3.4.3 Effects of Temperature on the Viscosity
The viscosity of CMC and HEC solution will decrease with the increase of temperature. Contrary to some cellulose ethers, no precipitate and gel will occur when heating their solution.
3.4.4 Effects of pH Value on the Viscosity
The viscosity of CMC and HEC is very small within the pH range of 2-12. In the pH range of .5-8.0, the solution has excellent viscosity stability. When pH<3, due to acid hydration, the viscosity will slightly decreased, which is the normal phenomenon of soluble polysaccharide polymer, and high temperatures can exacerbate this effect. In high alkaline conditions, CMC and HEC are prone to some oxidative degradation, and heating and seeing light can even exacerbate its occurrence, reducing the viscosity.
3.5 Compatibility with Other Substances
CMC is compatible with with most water-soluble nonionic, anionic polymers and gum in solution. Its compatibility with the salt depend on the valency of metal ions. HEC can be mixed and used with many kinds of water-soluble or water dispersible substances. On the performance of compatible dissolution, HEC is higher than most water-soluble polymers. HEC can also be added to other substances in the form of dry powder, ensuring that HEC is completely dissolved by stirring with the mid shear rate.
3.5.1 With Inorganic Salt Solution
As a general rule, CMC can form the soluble salts of carboxymethyl cellulose with the monovalent cations, have the edge line with divalent cations, and form insoluble salts with trivalent cations. CMC with high degree of substitution (DS of 0.9-1.2) has greater tolerance to most of the salts. The tolerance of salt can also get improved adding salt before dispersing CMC. Adding dry CMC can into the salt solution or dispersing salt and gum at the same time will reduce the compatibility. Due to the solubility and nonionic property of HEC, it is soluble in many other water-soluble polymers and insoluble salt solutions.
3.5.2 With Water-Soluble Celluloses
CMC and HEC are compatible with other water-soluble celluloses in a wide concentration range, and low viscosity models are compatible in a wider range than high viscosity models. When the anionic CMC solution is mixed with non-ionic HEC solution or HPC solution, a synergistic effect of viscosity can be observed and a soluble high viscosity solution can be formed.
3.5.3 With Natural Gums
CMC and HEC are compatible with such natural gums as sodium alginate and arabic gum, with no unusual or unexpected results.
3.5.4 With Active Agents
HEC is compatible with 4 kinds of synthetic surfactants: anionic, cationic, amphoteric and nonionic.
4. Application Examples
CMC and HEC have been widely used in the daily chemical products that need thickening to form a stable emulsion system such as toothpaste, shower gel, hand sanitizer, skin care cream, shampoos, glycerin lotions, shoe polish and detergent.
CMC has been one of the important raw materials in the production of toothpaste. Its role is to uniformly mix the liquid and solid raw materials of toothpaste and give toothpaste the shaping flow, proper viscosity and a certain brightness and delicateness. For the common type toothpaste with no additive formulations of special effects, CMC can be used as the binder. But the anionic CMC is more sensitive to the ions of high concentrations and can reduce the adhesion properties of CMC, so CMC has been limited in the toothpaste of high quality and special effects. With the nonionic HEC as the binder, the resistance of HEC to high concentration ions has been enhanced; the storage stability of paste has been greatly improved; and the storage time of toothpaste has been extended. Toothpaste manufacturers can use the compound of CMC and HEC in high-salt toothpaste, causing little change in the product cost. CMC applied in toothpaste is DS = 0.9 ~ 1.0, the viscosity specification of 6500mPa·s; the viscosity specification of HEC is 6000mPa·s (2% aqueous solution, 25 ℃, Brookfield viscometer).
|Toothpaste Formulations of Calcium Carbonate Type|
|Toothpaste Formulations of Calcium Hydrogen Phosphate Type|
|Calcium Hydrogen Phosphate||35～50|
4.2 Shower Gel
The shower gel with soap base as the active ingredient has no creamy feel of general surfactants after using, is easy to clean and can protect the natural luster of skin. HEC has has excellent solvent resistance to electrolytes. Its solution contains a high concentration of salts and then keeps stable and unchanged. Using HEC as the thickener of soap-based shower gel is the best choice. The viscosity specification for HEC of such a kind is 30000mPa·s (2% aqueous solution, 25 ℃, Brookfield viscometer).
|Formulations of Soap-Based Shower Gel|