The previous section introduced the general physical properties of methylcellulose. Other performance indicators include methoxy content, viscosity, moisture, ash (in terms of sulfate), chloride (in terms of NaCl), alkalinity (in terms of NaOH), iron content, heavy metal (in terms of lead) acid esters, and relative density.
The initial application of MC hinges on its water solubility, a crucial property. The methoxy content of alkali-soluble MC (DS=0.1 0.9) ranges from 2% to 16%; for water-soluble MC (DS=1.3 2.0), the methoxy content is 26% to 32%; and for organic solvent-soluble MC (DS=2.1 or above), the methoxy content exceeds 36%. These methoxy content variations play a significant role in the diverse applications of MC.
In addition, MC aqueous solution forms gel when heated and liquefies after cooling, turning into a transparent solution. Many uses of MC are based on this ability. MC can be used as a film former, adhesive, dispersant, wetting agent, thickener, and emulsifier stabilizer. It is widely used in building materials, cosmetics and medicine, detergents, polymers, and other fields.
1. Building materials industry
Methyl cellulose, a versatile compound, finds extensive use as a binder in the building materials and ceramic industries. Its unique properties enhance the cohesiveness of slurry, reduce flocculation, and improve viscosity and shrinkage. In ceramic glazes, MC acts as a suspending agent and binder, ensuring even dispersion of pigments and allowing for thick application. Its addition to refractory materials reduces water demand, enhances product uniformity and dimensional stability, and minimizes scrap. MC also serves as a curing agent in the mortar of bricks and tiles, enhancing bonding force and controlling structural cement’s setting time and initial strength.
MC, like HPMC, has a moisture-retaining effect in the cement slurry, which can significantly reduce moisture loss on the concrete surface. For example, using MC to prepare cement for dry wall structure bonding can avoid cracks on the edges and improve adhesion, cohesion, and construction performance. Pasting bricks and tiles on rough surfaces can increase mortar bonding, and bricks and tiles do not need to be pre-soaked. It can also be used to prepare water-resistant and temperature-resistant (-15-60℃) mortar for bonding bricks and tiles; mortar for bonding silica fire bricks that are resistant to high temperatures (1500℃); adding 4000mPa·s MC and a small amount of urea or sodium thiocyanate to cement mortar can be used for construction at high temperatures, and cement mortar for bonding load-resistant ceramic tiles can be prepared. Adding MC and vinyl acetate-maleic anhydride copolymer to the cement mortar for bonding bricks and tiles can increase the adhesion strength of bricks and tiles on the cement surface from 0.277MPa (without additives) to 0.78MPa.
By adding a small amount of MC and a cement coagulation accelerator (such as calcium formate) to the cement mortar used for the internal and external walls of buildings, its coagulation and construction performance can be significantly improved. For example, the addition of MC and polyvinyl acetate to cement mortar enables thin layer construction on bricks and tiles. MC also enhances the performance of water-dilutable spray powder brush materials, increasing adhesion, reducing cracks and water consumption, improving wear resistance, and facilitating construction.
Adding MC, dispersant, and synthetic fiber to cement and quartz sand mortar can be used as heat-insulating plaster and for repairing and replacing gypsum plaster. Adding MC to white cement slurry can be used as a wear-resistant, acid-resistant, and well-adhesive concrete surface coating and waterproof layer.
If glass fiber, steel wire, or nylon fiber is dipped in MC (molecular weight 18000-200000) solution and added to plaster or concrete, it can become a fiber-reinforced cement building material. Lightweight mortar slurry that can be extruded and constructed, prepared by MC (0.1%~2%), fiber, and foaming agent, can be used as a high-strength, porous building material. Lightweight cement material prepared by a mixture of MC, surfactant (such as sodium alkylbenzene sulfonate), and sodium bicarbonate can make cement coagulate quickly and prevent cracking. Due to different proportions, the density can be adjusted in the 573.4~1103.4kg/m³ range.
MC, along with other polymers, can significantly enhance the properties of cement paste in building elements. For instance, the addition of high-viscosity MC (10,000-15,000 mPa·s) to cement, sand, or lime paste can improve its bonding strength and ease of mixing. The resulting cement products are not only hard but also resist excessive shrinkage. Moreover, MC can also be used to protect the surface of molded cement element structures, further demonstrating its value in construction.
Adding MC can control the setting time of cement slurry, improve the bending and compression strength, and reduce shrinkage. For example, by adding a mixture of 0.1% MC and retarder sodium tartrate into cement slurry, the setting time of the original cement slurry of 2h22min (initial) and 3h18min (final) can be delayed to 4h11min (initial) and 5h21min (final), and its flexural strength and compressive strength are increased from the original (without additives) 6.64MPa and 39.2MPa to 7.24MPa and 42.4MPa; for example, by adding binder MC, expansion agent (such as calcium aluminate sulfate), pore former [calcium silicide (CaSi) or aluminum nitride (AlN)], dispersant (such as lignin sulfate), promoter (such as ZnCl₂, AlCl₃) into cement slurry, the setting time of the original cement slurry can be delayed to 4h11min (initial) and 5h21min (final). Its flexural and compressive strength are increased from the original (without additives) 6.64MPa and 39.2MPa to 7.24MPa and 42.4MPa. , CaCl₂ or other halides) can prevent weathering and improve early strength, especially when fixing bridge foundations. Its flexural strength and expansion coefficient after 7 days are 3333.15MPa and +0.32%, respectively, while those without these additives are 309.46MPa and -0.47%, respectively; for example, adding 0.1%~0.5% MC and a small amount of sodium pentachlorophenol (5%~30% of the MC addition) to cement slurry can retain moisture and improve plasticity, improve adhesion to the surface, reduce gel shrinkage and water requirement, reduce shrinkage and no cracks, and improve flexural strength. After 28 days, the flexural strength increased by 276% compared with that without additives.
2. Application in coatings
Methylcellulose, a versatile compound, is extensively used in various coating components such as latex and water-soluble resins. It serves as a film former, thickener, emulsifier, and stabilizer, among other roles. This multifunctionality contributes to the coating’s wear resistance, fluidity, leveling, storage stability, pH stability, and tolerance to heavy metal pigments, providing a comprehensive understanding of its applications in the industry.
MC’s role in paper processing is equally significant. It acts as a light primer component in wax paper, reducing paraffin penetration during waxing and preventing ink or varnish penetration. This enhances the luster and brightness of printed paper products. MC also improves the printing performance of white thin paper and strengthens the strength of kraft paper. Its versatility extends to recording paper and photosensitive copy paper, where it plays a role in the coating emulsion of pressure-sensitive transfer carbon paper. It demonstrates good adhesion to pigments in paper coating components and serves as a dispersant for pigments used in color paper coatings, underscoring its practical value in the industry.
In the 1950s, MC was used in paint strippers. It can be mixed with paraffin in a mixed solution of water/alcohol/dichloromethane, which can block the volatilization of solvents and make the paint strippers suitable for surface paint removal. It can be mixed with low-level fatty alcohols (such as ethylene glycol, ethylene glycol monoethyl ether, or butyl ether) to give paint strippers thixotropy. In the paint stripper components, MC is mainly mixed with paraffin, dichloromethane, low-level fatty alcohols, ammonium salts, soda, and water, which can remove air-dried paint or dry synthetic enamel (such as urea-formaldehyde, melamine formaldehyde resin) coatings. It softens or melts the old paint, which is easy to scrape off or wash with water; there are also cases where the paint stripper is used to treat the old paint on bronze objects and then wash it off with solvents. Representative quick paint strippers are made of MC, dichloromethane, methanol, methyl benzyl alcohol, ethylbenzene, thiourea, paraffin, and water. For a thick layer of alkyd/melamine resin coating on the epoxy primer, the paint stripper can be dissolved after 7 minutes of application and removed by flushing with strong water flow.
