What can hydroxyethyl methylcellulose coating be used for?

1. What is hydroxyethyl methylcellulose coating?

Hydroxyethyl methyl cellulose (HEMC) coating is a water-based coating using hydroxyethyl methyl cellulose as its primary functional additive. HEMC's thickening, water-retention, and film-forming properties significantly enhance the coating's application performance and final appearance. HEMC is a semi-synthetic polymer derived from natural cellulose through etherification.

In food processing, hydroxyethyl methyl cellulose has multiple functions, including binding, emulsification, film-forming, thickening, suspension enhancement, dispersion promotion, and water retention. In the daily chemical industry, it is used as an additive in products such as toothpaste, cosmetics, and detergents. Hydroxyethyl cellulose is widely used in pharmaceutical formulations, including oral tablets, suspensions, and topical preparations.

2. The function of hydroxyethyl methylcellulose (HEMC) coating

Core Functions

Thickening and Rheology Control

Three-Dimensional Network Structure: HEMC forms a polymer network upon dissolution, significantly increasing paint viscosity (up to 150,000 mPa·s) and preventing the settling of fillers (such as titanium dioxide and calcium carbonate).

Shear-Thinning Properties: Viscosity decreases during stirring (facilitating application) and returns to high viscosity after standing (preventing sagging), making it particularly suitable for spraying on vertical surfaces.

Yield Value Adjustment: Adjustable addition level (0.2%-0.8%) allows for adaptability to different application methods (such as brushing, roller coating, or spraying).

Water Retention and Extended Open Time

Water Locking: HEMC's hydroxyethyl chains strongly bind to water molecules, achieving a 24-hour water retention rate of >95%, significantly delaying paint drying.

Cement-Based Coating Optimization: In tile adhesives and putties, it prolongs the hydration time of cement (open time up to 40 minutes), preventing cracking.

Improved Application Performance

Improved Leveling: Reduces surface tension, eliminates brush and roller marks, and creates a smoother paint film. Anti-spatter: Compared to HPMC (hydroxypropyl methylcellulose), the hydrophobic groups in HEMC reduce atomization and dispersion during spraying.

Enhanced Adhesion and Film Formation

Substrate Wetting: Improves the coating's penetration into porous substrates (such as concrete and gypsum board), enhancing adhesion (increasing pull-off strength by 20%-30%).

Film Densification: Reduces microcracks caused by drying shrinkage through uniform water evaporation.

Specific Functions in Different Coating Systems

HEMC's irreplaceable advantages

• Compared to traditional thickeners (such as CMC and HEC), HEMC offers advantages in the following applications:
• High salt tolerance: Suitable for colored mortars containing electrolytes.
• Thermal stability: Gel formation occurs only above 65°C, making it suitable for outdoor projects in summer.
• Biological stability: Hydrophobic methyl groups reduce the risk of mildew (passes ISO 22196 antibacterial testing).

3. Precautions for Using Hydroxyethyl Methyl Cellulose (HEMC) Coatings

Dissolution and Preparation

Dissolution Method

Cold Water Dispersion: First, dry-mix with powders (such as titanium dioxide and fillers) until uniformly distributed. Then, slowly add cold water (20-25°C) to avoid direct mixing, which may cause clumping.

Stirring Requirements: 800-1200 rpm for 15-20 minutes until completely dissolved (no transparent gel particles remain).

Station Activation: After dissolution, allow to stand for 30 minutes to stabilize the viscosity (pH should be adjusted to 8-10).

Dissolution Taboos

Do not use hot water (above 40°C will accelerate dissolution and cause clumping).

Avoid direct mixing with high-concentration electrolytes (such as CaCl₂) (pre-dilution is required).

Application Environment Control

Temperature and Humidity Management

Temperature Range: 5-35°C (Dissolution is slow below 5°C; add 1%-2% propylene glycol for antifreeze).

Humidity Limit: Relative Humidity <85% (In high humidity environments, reduce the HEMC dosage by 0.1%-0.2% to prevent skinning).

Substrate Treatment

Porous substrates (concrete, gypsum) must be pre-wetted (no visible water) to prevent moisture retention in the HEMC, which can lead to dehydration and cracking of the coating.

Formulation Compatibility

Compatibility with Other Additives

Defoamer: Add after HEMC is dissolved (mineral oil at 0.1%-0.3%)

Latex Emulsion: Add the HEMC solution first, then slowly add the emulsion (to prevent flocculation)

Inorganic Binder (cement/gypsum): HEMC must be mixed thoroughly while still in the dry powder stage

Prohibited Combinations

Strongly Acidic Systems (pH < 4 will degrade HEMC)

High Concentration Oxidants (e.g., ammonium persulfate)

Application Techniques

Viscosity Adjustment

Spraying: Use low-viscosity HEMC (10,000-30,000 mPa·s) or reduce the addition level (0.1%-0.3%)

Scrape Coating: Use high-viscosity HEMC (80,000+ mPa·s) at 0.5%-0.8%

Coating Interval

Apply to the next coat after surface dryness (approximately 1-2 hours). The actual drying time should be adjusted based on water retention.

Storage and Maintenance

HEMC Dry Powder Storage

Store sealed in a cool, dry place (humidity <60%). Shelf life: 2 years.

If lumps form, do not use directly; pass through an 80-mesh sieve.

Finished Paint Storage

Add a preservative (such as 0.1% BIT) to prevent mildew. Store at 5-30°C.

If the viscosity drops by more than 10%, add additional HEMC (dissolve first, then add).

Safety Precautions

Handling Precautions

Wear a dust mask (dry powder is harmful if inhaled).

Rinse immediately with water after contact with skin (may cause mild irritation).

Waste Disposal

Dispose of solidified paint as general industrial waste. Uncured paint must be diluted before disposal (COD must meet standards).

Frequently Asked Questions