The concentration of the methylcellulose solution, whether it’s dissolved in water or organic solvents, is a crucial factor that should be determined based on the specific application and the type of product chosen. For low viscosity products (15~100mPa·s), a concentration of 10% and 15% is recommended, while high viscosity products (400 75000mPa ·s) should not exceed a concentration of 2%~3%. This careful determination of concentration is key to ensuring the solution’s effectiveness and preventing any potential issues.
Whether it is a methylcellulose powder product with or without surface treatment, there are different requirements for the preparation process of the prepared solution. Preparing gel-free methylcellulose solutions usually requires three basic steps: dispersion, where each particle of methylcellulose must be moistened; agitation, which maintains dispersion; and dissolution, which is the hydration process (which creates viscosity). Before dissolving, it is essential to disperse the solid particles or powder nicely. Good dispersion can effectively prevent the formation of gel clusters. Products with different physical forms require different processes.
Surface treated powder
Surface-treated powder products can be added directly to the water system. This powder product disperses well with regular agitation and dissolves in alkaline conditions. It provides users with flexible operating space and a controllable dissolution rate, is readily wetted by cold water, and can be evenly dispersed without clumping with a bit of stirring.
Ordinary tap water can be used to prepare an aqueous slurry with a concentration of up to 10% with slight stirring for surface-treated powder. Beyond this concentration, the holding time will be reduced, and the system will quickly become too sticky to pour and difficult to pump.
After 45 minutes, the aqueous slurry can still be used. The slurry can be quickly and completely dissolved in an alkaline environment. The optional methods are as follows.
(1) Add enough ammonium hydroxide to the solution system to obtain an environment with a pH of 8.5 to 9.0, promoting a rapid increase in viscosity and forming a smooth and gel-free solution. Surface-treated products can be thoroughly and quickly dissolved only if the pH is adjusted to a specific alkalinity (pH 8.5 to 9.0). Attempting to adjust the pH of a highly concentrated slurry will result in a viscosity that is so high that the slurry cannot be pumped or poured. pH adjustment can only be used after the slurry has been diluted with water.
(2) Dry alkaline ground color or filler dispersion can be added to the slurry, or the alkaline color latex component can be added to dissolve it to form a uniform viscosity quickly.
(3) Dry alkaline colorants or fillers can be added to the slurry, and high-speed or variable-speed mixing equipment can quickly dissolve the slurry and form a solution with a specific viscosity. Surface-treated products are used in latex coatings and can be added at various points in preparation. The powder can be added directly, or it can be mixed into a stock solution and then added. For example:
(1) As a dispersible powder, it can be added directly to the ground color before adding the pigment. It does not need to be added at the end of the high-solid composition preparation or when the original neutral or acidic composition has not been adjusted to alkaline.
(2) After adding the ground color, ethylene glycol slurry or water slurry is added as a stock solution.
(3) After the latex is formed, glycol or water slurry is added to the coating as a stock solution.
Methylcellulose
Methyl cellulose (MC) is an early variety in the industrial production of cellulose ethers. It was successfully trial-produced in 1905. At that time, it was prepared with dimethyl sulfate. Based on the various properties of MC, it has been used in multiple industrial sectors for a long time. The United Kingdom and Germany were successfully developed and produced in 1923-1924, respectively, and the United States put it into production in 1938 at Dow Chemical Company. MC can prepare high-viscosity solutions. Since its surface tension is more minor than water and its excellent wettability and dispersion, it can be used as a thickener, suspending agent, dispersant, and wetting agent in polymer polymerization (such as polychloride). Ethylene), coatings, textiles, printing and dyeing, medicine, and food are widely used. MC has good film-forming properties, and the film formed has excellent toughness, flexibility, and transparency to be used as a film-forming agent and adhesive. MC is impermeable to animal, vegetable, and mineral oils and can be used as an ideal surface treatment for grease-resistant materials; MC is also a USDA-approved edible cellulose derivative. Due to its multi-faceted uses, it has been used in many related departments, and its application fields are still expanding.
Like most ethers, MC will be degraded by microorganisms and oxidation. The more evenly distributed the substituents, the higher the DS and the less susceptible MC is to mold damage.
As a non-ionic water-soluble polymer, MC is the most common and essential non-ionic ether in industry, along with ethyl cellulose and hydroxypropyl methylcellulose. One of the most crucial properties of MC is its ability to form gels in aqueous solutions. MC does not dissolve in water to form a gel when heated but melts when cooled. This phenomenon is entirely reversible. Many properties of MC rely on this gelling ability. Other applications depend on the thickening ability of MC in aqueous solutions.