Comparative Viscosity Testing of HB-1300 Hydrophobic Fumed Silica in 107 Gum-Based Silicone Sealants

In the silicone sealant industry, fumed silica serves as the core reinforcing filler in 107 gum-based systems. Once the powder is incorporated into the compound, it boosts mechanical strength but typically drives system viscosity sharply higher, resulting in poorer processing flow and more demanding mixing conditions.

Viscosity Performance at 10%, 20%, and 30% Loadings

As shown in Figure 1, HIFULL technicians tested HB-1300 against two competing fumed silica products, measuring how system viscosity changed at loadings of 10%, 20%, and 30% in 107 gum.

The bar-chart data clearly show that viscosity rises with loading for all three powders — a universal characteristic of fumed silica.

The surface of fumed silica carries abundant silanol groups, and particles connect through hydrogen bonding to form a three-dimensional network structure. The higher the loading, the denser the network and the higher the overall compound viscosity.

Figure 1. Effect of Different Fumed Silica on the Viscosity of 107 Silicone Rubber

HB-1300 Viscosity Performance at High Loadings

At the low loading of 10%, HB-1300 and Competitor 1 exhibit similar viscosity levels, while Competitor 2 registers the lowest.

When loading increases to 20%, the gaps between the three begin to widen, with HB-1300 slightly below Competitor 1.

The differences become most pronounced at 30% — the high-loading scenario. Competitor 1 shows the steepest viscosity increase, reaching the highest value of the entire trial, while HB-1300’s system viscosity is markedly lower than Competitor 1’s and shows a more manageable increase compared to Competitor 2.

This demonstrates that HB-1300 has undergone a special hydrophobic surface modification that effectively reduces the number of silanol groups on the particle surface and weakens hydrogen bonding between particles.

While maintaining good powder dispersion, it suppresses excessive formation of the three-dimensional network — achieving a true “low-thickening effect.”

Low Thickening Without Sacrificing Reinforcement

Low thickening does not mean sacrificing reinforcement.

HB-1300 retains an appropriate specific surface area and original nanoparticle size, and when the powder is uniformly dispersed in the 107 gum matrix, the nanoparticles interact with polysiloxane molecular chains through physical entanglement and interfacial adsorption, delivering excellent reinforcement in terms of tensile strength, tear strength, and more.

With conventional hydrophobic fumed silicas, high reinforcement inevitably comes with significant thickening; pursuing low viscosity, on the other hand, compromises reinforcement performance.

Through its modification process, HB-1300 balances the two, so that even at a high loading of 30%, the compound maintains good flow, reducing the processing burden of kneading, deaeration, and extrusion, improving production efficiency, and preserving the mechanical performance of the finished sealant.

Adhesives & Sealants

Fumed Silica for Adhesives & Sealants In sealants and adhesives, fumed silica plays a major role in rheological control and viscosity strength. When fumed silica is added and dispersed in…

Read More Adhesives & Sealants

About HIFULL

HIFULL® is a Chinese high-tech enterprise dedicated to the research, development, production, and application of nanopowder materials.

With years of experience in the fumed silica field, it continuously develops customized powder products for the silicone, coatings, and composite materials industries.

HB-1300 is the company’s flagship product for the silicone sealant market, based on proprietary vapor-phase synthesis and surface modification technologies that precisely control the surface functional groups of the powder, overcoming the performance limitations of conventional fillers and giving silicone companies more flexibility in formulation design.

Guided by an application-driven approach to product development, the company conducts systematic research spanning powder microstructure and downstream formulation processes.

It provides domestic solutions that reduce costs and improve efficiency across China’s silicone materials industry chain, supporting the high-quality development of the domestic silicone new materials sector and expanding opportunities for domestic nanopowder materials to replace imports across more application scenarios.

For formulators of 107 gum-based silicone sealants, selecting an appropriate fumed silica grade requires balancing reinforcement performance against processing viscosity. Comparative viscosity testing under consistent loading conditions provides a practical starting point for evaluating candidate products and determining their suitability for a specific formulation.

Further Reading: