How to adjust the plasticity of cellulose ether in the formation of honeycomb ceramic bodies?

cellulose etherIn the forming of honeycomb ceramic bodies (such as extrusion forming), the plasticity is mainly adjusted by improving the rheological properties, moisture retention ability, and interparticle bonding force of the body material, making it easier to form a honeycomb structure with a regular structure (without cracking or deformation). Its mechanism of action and regulatory mechanism are as follows:

1、 Enhancing the plasticity of materials through moisture regulation

The plasticity of honeycomb ceramic bodies depends on the water film on the particle surface (which lubricates the particles and generates capillary attraction), and cellulose ether optimizes the water distribution through the following methods:

Water retention effect: The hydroxyl groups (- OH) on the cellulose ether molecular chain form hydrogen bonds with water molecules, significantly reducing the water evaporation rate of the raw material (the water retention rate can be increased by 30% -50%). This ensures that a stable water film is maintained on the surface of the material particles during the molding process (especially during extrusion), avoiding increased friction between particles and decreased plasticity due to rapid loss of local moisture (such as "billet breakage" and "surface roughness" during extrusion).

Uniform distribution of moisture: Cellulose ether dissolves in water to form a viscous solution that can encapsulate ceramic particles (such as cordierite and silicon carbide), allowing moisture to be evenly adsorbed on the surface of the particles, avoiding local over drying or over wetting (over drying can cause the body to collapse, while over drying can result in insufficient plasticity). For example, in green bodies with a high proportion of poor plasticity materials such as quartz and feldspar,cellulose etherBy evenly distributing moisture, the plasticity index (a measure of plasticity) of the material can be increased from 1-2 to 3-5 (the higher the plasticity index, the easier it is to form).

2、 Enhancing the binding force between particles through molecular chain entanglement

The long-chain molecular structure of cellulose ether can form a "three-dimensional network" in the body, enhancing the bonding strength between particles and thus increasing plasticity:

Bridging effect: Cellulose ether molecular chains are adsorbed onto the surface of ceramic particles through van der Waals forces, bridging dispersed particles together to form flexible bonds (different from rigid binders). This combination allows particles to slide relative to each other under force (such as when pushed by an extruder screw), but is not easily broken, giving the blank good ductility (the core characteristic of plasticity).

Thickening effect: The dissolution of cellulose ether significantly increases the viscosity of the raw material slurry (viscosity can be increased by 10-100 times at low shear rates), inhibits particle settling and delamination, ensures that the raw material maintains a stable shape during the forming process (such as when extruding honeycomb channels), and avoids channel deformation and uneven wall thickness caused by material "scattering".

3、 Adapt molding process by adjusting rheological properties

Honeycomb ceramics are commonly extruded and require the raw material to have * * "pseudo plasticity" * * (viscosity decreases and flows easily under stress, and viscosity returns to maintain shape after unloading). Cellulose ether adjusts its rheological properties through the following methods:

Shear thinning characteristics: Under the high shear action of the extruder, the molecular chains of cellulose ether are stretched and oriented, and the viscosity of the slurry temporarily decreases, allowing the material to pass smoothly through the honeycomb channels of the mold (reducing resistance and avoiding channel blockage); After the material leaves the mold, the shear force disappears, the molecular chains re entangle, the viscosity quickly recovers, and the blank immediately maintains its shape (without collapse or deformation).

Control yield value: The amount of cellulose ether added (usually 0.2% -1.0%) can adjust the yield value of the green body. The yield value is too low, and the billet is prone to deformation under its own weight; If it is too high, the extrusion resistance will be high, which can easily lead to mold wear or billet cracking. By accurately controlling the amount of addition, the yield value can be matched with the forming requirements of the honeycomb structure (such as a slightly lower yield value for thin-walled honeycomb blanks and a higher yield value for thick walled ones).

4、 Synergistic optimization of plasticity with other components

Cellulose ether needs to work synergistically with other components in the body, such as clay and plasticizers, to avoid the limitations of a single component

Coordination with clay: Clay provides basic plasticity, but has poor water retention. The water retention effect of cellulose ether can compensate for the water loss of clay during drying and prevent early cracking of the body;

Cooperate with lubricants (such as stearic acid): Lubricants reduce friction between particles, while cellulose ether enhances particle adhesion. The combination of the two gives the green body both good flowability (easy to extrude) and sufficient strength (maintaining shape);

Avoid conflicts with strong electrolytes: If the green body contains high concentrations of electrolytes (such as certain mineralizers), it may damage the water solubility of cellulose ether. It is necessary to choose cellulose ether with strong salt resistance (such as hydroxypropyl methyl cellulose HPMC) to ensure its uniform dispersion in the green body and play a regulating role.

summary

cellulose etherThe plasticity of honeycomb ceramic bodies is regulated from the three dimensions of "moisture particle flow" through three core functions: water retention and thickening (maintaining moisture film), bridging particles (enhancing adhesion), and regulating rheology (adapting extrusion process). In practical applications, it is necessary to adjust the type (such as HPMC, CMC) and amount of cellulose ether added according to the raw materials of the billet (such as the proportion of barren materials) and the parameters of the honeycomb structure (pore density, wall thickness), in order to achieve the goal of "easy molding, no cracking, and stable shape" of the billet.