Familiar to most homeowners are the DIY (do-it-yourself) or OTC (over-the-counter) silicones used to seal bathtubs and showers. They represent the lower end of the performance spectrum among silicone sealants, which collectively account for one of the highest production volumes among these sealants. Higher-performance versions are used in commercial construction for joint sealing, field and factory glazing, fire stopping, and insulating glass windows. The major automotive uses are original equipment manufacturers (OEM) and aftermarket foamed-in-place gaskets. Silicone sealants also play a role in the manufacture of appliances, airplanes, subway cars, buses, and boats.
Silicone sealants use polysiloxane polymers, which are based on room temperature vulcanized (RTV) silicone rubber. For single-component formulations, the silane is blocked and released when exposed to moisture. A catalyst such as dibutyltin dilaurate speeds up the cure. In two-component formulations, the catalyst is placed into a separate package from the polysiloxane and the crosslinker, often ethyl orthosilicate. An internal desiccant is usually added to reduce pre-curing in the package.
High Performance Silicone Sealants with SMI Precipitated Calcium Carbonates
Precipitated calcium carbonates (PCCs) provide rheological control in silicone sealants but their use is usually restricted to the higher-performance types. In addition to building viscosity and yield value, PCCs produce excellent control of slump and sag, good extrusion rates, and added reinforcement.
Several of Specialty Minerals Inc.’s (SMI’s) PCCs are suggested for silicone sealants, some for single components and some for two component products. These include:
- Thixo-Carb® 500 PCC – is the most hydrophobic PCC. This PCC has the lowest moisture level and maintains good package stability. It is especially recommended for one-part silicone sealants. It provides low modulus and high flexibility and the best cure properties, specifically the longest skin-over time and shortest tack-free time of U.S.-made PCCs. It is a 0.15 micron PCC with a proprietary coating and is manufactured in SMI’s Adams, Massachusetts plant.
- Calofort® SV PCC – is a high efficiency PCC. It is a true nano PCC with a particle size of 70 nanometers (0.07 micron) and a stearic acid coating. It can be used in one- and two-part products and is manufactured in SMI’s Birmingham, U.K., plant.
- Ultra-Pflex® PCC – is a high-efficiency, 70 nanometer, stearic-acid coated PCC. It is manufactured in SMI’s Adams, plant.
- Calofort® SM PCC – is recommended for two-part systems. It allows higher loadings because it provides slower viscosity build. It is a 0.07 micron, stearic-acid coated PCC manufactured in the U.K.
- Thixo-Carb® 300 PCC – is used primarily in two-component systems where high modulus and high elongation are needed. However, it can also be formulated into single component products. It is a 0.15 micron PCC with a proprietary coating and is manufactured in Adams.
Click on a product’s name to download the technical data sheet for the product.
The rheological, cure, and mechanical performance of several of the U.S.-manufactured SMI PCCs were evaluated in a two-part silicone sealant. To view the results, click here.
Click here for information on how PCCs function in sealants as well as on the range of SMI PCCs for sealant applications and then click here for information on how factors such as particle size, hydrophobicity, and other pigment properties influence the choice of the right PCC for your application. A PCC selector chart for various polymer systems can be seen by clicking here.
SMI Ground Calcium Carbonates and Dolomites in Silicone Sealants
Increasing non-thixotropic viscosity and reducing cost by filling and extending the polymer are two reasons why manufacturers use ground limestones (calcium carbonates) and ground dolomites (calcium magnesium carbonates) in silicone sealants. By adjusting the ratio of ground calcium carbonates (GCCs) to the rheology-controlling PCCs, sealant manufacturers can control the overall rheological response, especially the extrusion rate. Increasing the proportion of PCC will increase the high-shear viscosity, thus increasing the extrusion time. Increasing the proportion of GCC will reduce the high-shear viscosity, reducing the extrusion time.
GCCs, which are coated with stearic acid to make them more hydrophobic and have lower moisture levels, are often used in moisture-curing sealants such as silicones to help package stability and reduce pre-cure. Other effects of coating are reduction in oil absorption, which permits higher filler loadings, and an improvement in the dispersibility of the GCC in the polymer.
Coated GCCs from SMI useful in silicone sealants include:
- Hi-Pflex® 100 - East and Hi-Pflex® 100 - West GCCs – are 3.5 micron ground limestones coated with stearic acid. They are produced in Adams, Massachusetts and Lucerne Valley, California.
- Pfinyl® 402 GCC – is a 5.5 micron stearic acid coated GCC produced in Adams. The larger particle size allows higher filler loading.
Click on the product’s name to download the technical data sheet for the product.
Uncoated SMI GCCs for filling silicone sealants are the Vicron® and Marblewhite® ground limestones made in Adams and Lucerne Valley.
Use the links below to learn more about the SMI ground carbonates for adhesives and sealants.
- SMI minerals for adhesives and sealants
- SMI products used in construction sealants
- SMI products used in automotive sealants
- What is an Adhesive? What is a Sealant? What is the difference?
- SMI precipitated calcium carbonates (PCCs) for adhesives and sealants
- Choosing the right PCC for a sealant application
- SMI precipitated calcium carbonates (PCC) – sealant application selector chart
- SMI ground calcium carbonates (GCCs) for adhesives and sealants
- SMI minerals in automotive uses - See the parts of your car that may contain a Specialty Minerals product.
- SMI minerals in housing and construction - See the products used to build your home or in your home that may contain a Specialty Minerals product.
- Download a product’s technical data sheet or MSDS
- Request a sample
- What is Dolomite? A mineral introductory webpage.
- What is Ground Calcium Carbonate (GCC) / Limestone? A mineral introductory webpage.
- What is Precipitated Calcium Carbonate (PCC)? A mineral introductory webpage.
- What is Nano Precipitated Calcium Carbonate (PCC)? A mineral introductory webpage.
- About Specialty Minerals Inc.
- Specialty Minerals plant profiles: Adams, Birmingham, Canaan and Lucerne Valley
- Quality and ISO at Specialty Minerals