Carboxymethyl cellulose (CMC) is an essential additive in ceramic production, used for green body reinforcement, glaze suspension, and bonding. However, improper selection or incorrect use of CMC can lead to production defects that affect product quality and yield. This article summarizes the five most common CMC-related problems in ceramics and offers practical solutions to help manufacturers optimize their processes.
1. Incomplete CMC Dissolution
Symptoms: Undissolved CMC appears as white spots or lumps in the green body, causing surface defects or uneven strength after firing.
Causes:
CMC is added too quickly, creating "fish-eye" clumps.
Water temperature is too low, or mixing time is insufficient.
CMC has poor dispersibility or excessively high molecular weight.
Solutions:
Slowly add CMC while stirring to ensure full dispersion.
Use water at 40–50 °C and stir for at least 20–30 minutes.
Choose a high-purity, easy-dissolving CMC designed for ceramics.
2. Viscosity Instability or Sedimentation in Glaze
Symptoms: The glaze slurry stratifies or loses viscosity after standing, leading to uneven glazing.
Causes:
Poor compatibility between CMC and glaze electrolytes.
Inappropriate degree of substitution (DS), reducing colloid stability.
pH is too acidic or alkaline, degrading CMC performance.
Solutions:
Select CMC with DS ≥ 0.8 for better salt tolerance.
Maintain glaze slurry pH between 6 and 8.
Combine CMC with other suspending agents such as xanthan gum if necessary.
3. Cracking or Low Green Body Strength
Symptoms: Cracks appear during drying, or the green body breaks easily, increasing scrap rate.
Causes:
CMC addition is too low, providing insufficient bonding.
CMC molecular weight is too low to form a strong network.
Drying speed is too fast, causing uneven shrinkage.
Solutions:
Adjust CMC dosage to 0.3–0.8% depending on clay properties.
Use CMC with medium-to-high viscosity (2000–5000 mPa·s).
Adopt staged drying to balance moisture loss.
4. Black Core or Internal Pores After Firing
Symptoms: Fired products show black impurities or internal pores.
Causes:
Excessive organic impurities in CMC cause incomplete carbon burnout.
The kiln heating curve does not match CMC decomposition.
Solutions:
Use low-ash CMC (≤ 0.5%) with high purity.
Optimize the firing curve, allowing enough time at 300–500 °C for CMC burnout.
5. Pinholes or Orange Peel on Glaze
Symptoms: The glaze surface is rough, with pinholes or orange-peel texture.
Causes:
Air bubbles from incomplete CMC dissolution.
CMC viscosity too high, reducing glaze leveling.
Solutions:
Let glaze slurry stand to release bubbles or add defoamer.
Use low-viscosity CMC (500–1500 mPa·s) to improve leveling.
Control drying speed to avoid overly rapid film formation.
Conclusion
By selecting the right Ceramic CMC grade and optimizing dissolution, dosage, and process parameters, ceramic manufacturers can reduce defects, improve yield, and enhance product appearance. Regular technical communication with CMC suppliers and small-scale pilot tests are recommended to ensure consistent quality and process stability.
