In ceramic manufacturing, binders are used to increase the mechanical and cohesive strength of pre-fired, "green" ceramics. The increase in strength provided by the binder in a ceramic system allows formed ceramic parts to pass through the production process and make it to the firing step without breaking or falling apart. Ceramic binders come in many varieties but in order to be effective they must have the following characteristics:
Increase mechanical strength of formed ceramic parts
Does not cause the ceramic paste to stick to processing equipment
Burns out with low ash content upon firing
Doesn't interfere with glazing
Ceramic Binder Types
While there are dozens of different binders used commercially for ceramic production, most fall in one of two categories: Inorganic and Organic.
Binders that fall into the inorganic category are mineral based materials. These types of binders are often based on silicate chemistry and provide increases in mechanical strength at incredibly high temperatures. While inorganic binders like sodium silicate and bentonite are relatively inexpensive, they often require a higher usage rate than organic binders which can cause issues with viscosity that lead to ceramic defects.
Organic binders cover all polymeric based materials used in ceramics that are not mineral based. This type of binder performs by forming hydrogen bonds with ceramic particles during drying. Organic binders are typically more expensive than inorganic binders but they can often be used at a lower rate and offer some additional benefits to ceramic processing that inorganic cannot.
METHOCEL™ - The Ideal Ceramic Binder
METHOCEL™ is a line of methylcellulose and hydroxypropyl methylcellulose polymers that are excellent organic binders and processing aids for the production of high performance ceramics. These water-soluble polymers are unique in that unlike other organic binders, METHOCEL™ solutions form a three dimensional gel structure at elevated temperatures that provides extra stability to green ceramic bodies during drying and early stage firing. This thermal gelation feature also prevents binder migration and reduces the potential for stress cracks and blisters during firing.
The Effect of Thermal Gelation on Green Strength
When ceramic mixes containing METHOCEL™ are held above the thermal gelation temperature the result is a sharp increase in green strength and cohesiveness. The graph above illustrates this increase in green strength using a torque rheometer to measure the viscosity of an aluminum oxide ceramic mixture containing METHOCEL™ A4M.
Improving Ceramic Processes with METHOCEL™
As shown above, METHOCEL™ is exceptional at improving the mechanical strength of green ceramic bodies. Perhaps equally impressive is how METHOCEL™ can simplify ceramic manufacturing processes and improve efficiency. The same thermal gelation characteristic previously discussed changes ceramic mixes from adhesive to cohesive at the gelation temperature. This is demonstrated in the images below.
Ceramic Mix in a Torque Rheometer
A ceramic mix containing METHOCEL™ was observed in a torque rheometer below the thermal gelation point and above the thermal gelation point. As you can see, above the thermal gelation point, the ceramic mix does not stick and separates cleanly from metal surfaces. This is an incredibly valuable characteristic in the extrusion and injection molding of intricate ceramics.
Preventing Binder Migration
Many organic binders will migrate to the surface of drying ceramic bodies along with the evaporating liquid. This can cause a "skin" of binder to form at the surface that will inhibit drying. Upon firing, the uneven binder distribution can lead to stress cracks, surface blisters, and other surface defects. METHOCEL™ binders remain fixed in the three dimensional network formed during thermal gelation and will not migrate to the surface. Ceramic bodies that contain METHOCEL™ as a binder are more consistent and are far less likely to show surface defects.
Gelation Variation of METHOCEL™ Binders
Thermal gelation temperature, gel firmness, and the dynamic viscosity of a ceramic mix containing METHOCEL™ varies on the type and concentration of METHOCEL™ in the system. Thermal gelation causes a significant increase in the apparent viscosity of ceramic mixes at varying concentration and temperature based on grade. This makes it easy to obtain the right balance of properties for particular ceramic applications.
Selection of the appropriate METHOCEL™ grade for a ceramic application is dependent on your particular formulation and processing requirements. The grades listed in the table below are starting point recommendations based on application.
Depending on your particular requirements other METHOCEL™ grades and concentrations may be recommended. Our METHOCEL™ specialists are standing by and would be happy to assist you in finding the right grade and getting you a sample.