The reinforcement effect

They are often overlooked. They only cost a few cents. But if they do not work properly, your house can be ruined! Rubber seals in your water pipes are a small but good example to show how we count on rubber in our daily lives. But what exactly is rubber?

Natural rubber comes from the milky sap of the rubber tree that is processed and vulcanized. But natural rubber would be far too weak for technical applications. That’s why during processing several ingredients are added to the rubber “dough”. One of them is a reinforcing filler called silica.

Silica fillers raise the mechanical stability of rubbers. Which leads to rubber products that can deal with mechanical stress like tensile or compression strengths better. And it leads to rubber products that can stand abrasion better. The silica particles build “bridges” between all the ingredients of the rubber dough. These bridges are stronger than the weak physical forces between the rubber polymer chains, so a more resilient rubber is the result. At the same time, the bridges remain very flexible so that the rubber becomes strong, but never stiff.

However, some rubbers are hydrophobic so that they do not mix very well with hydrophilic silica. In that case you add another ingredient to the rubber dough called “silane”. Silanes are a kind of “superglue” for molecules. They link the rubber polymer chains and silica aggregates together to get the advantages described above.

How does this affect the quality of rubber products? Let us give you an example: When you add synthetic amorphous silica and silanes as coupling agent to the rubber recipe of tire treads, it raises the performance and prolongs the product’s life.

• The rolling resistance will be reduced which lowers the energy consumption of your car significantly.
• The grip will be improved which lowers the braking distance greatly, especially on wet roads.
• The abrasion resistance will be improved which means that you can rely on the safety of your tires for a sustained time.

To make a long story short: Silica is an enhancer for rubber. Now you have learned that, you could learn something about foils too. Find out how silica also facilitates the production and use of plastic films in our next effects profile.  

Rubber accompanies us through our lives: our first pacifier, our first football, the rubber mounts of our first car’s suspension, the medical silicone in our joint replacement when we suffer from rheumatoid arthritis. The rubber products change throughout our lives, but the silica technology within them stays the same. Let’s take a magnifying glass to take a closer look at the silica effect in silicone rubbers …

The goal of silicon dioxide (SiO₂) as an active filler is to enhance the mechanical stability of silicone rubbers by absorbing and transferring the various forces that act upon it. But how does it do that? The secret lies in the geometrical shape of silica particles: They are porous like a miniature sponge. The rubber will fill the void spaces within that sponge so that there is a good deal of contact points between the huge surface of the filler and the polymer chains. Each contact point establishes a physical bond between silica and rubber. And all bonds together build a three-dimensional network which is much stronger than the bond between rubber molecules alone. Stronger, but not stiff so that mechanical stress can be processed efficiently. The result is resilient, reliable, and durable rubber products.

At Evonik, we offer two different types of silica systems for two different types of rubber.

• Under the brand SIPERNAT® you will find our product range of precipitated silica for silicone rubbers. And under the brand name AEROSIL® you will find our product range of fumed silica for silicone rubbers. The application areas span from baby products to rubbers with food contact, and medical silicones.
• Under the brand name ULTRASIL® you will find our product range of precipitated silica for industrial rubbers, especially for the tire industry.

Speaking of industrial rubbers, a second ingredient comes into play: silanes. With the use of bifunctional organosilanes as a coupling agent, you can crosslink hydrophilic silica with hydrophobic rubber. The silanes react with the silica surface and the polymer during the vulcanization process, forming a chemical bond between two otherwise non-reacting materials. Which opens doors for new products.

Evonik is the only producer worldwide that provides an advanced silica/silane system. Which means that silica and silane are perfectly paired for maximum resilience and maximum longevity. The reinforcing effect of our silica/silane system has been proven in countless products.

Unfortunately, it’s not easy to find the best filler for your rubber product. But since we are the inventors of synthetic amorphous silica, we have more than seven decades of experience in the rubber industry. Our application experts will use their experience to help you to find the ideal “recipe” for your needs. Usually, our silica and our silica/silane-systems can be added during the regular production process so that no extra equipment is necessary. Just make sure the mixing is not too excessive.

The storage of silica also requires no extra effort: When you keep it in its original packaging in a dry environment, so that it cannot absorb moisture or volatile organic substances, you can store our silica for two years or even more. 

Safety first: All silica products from Evonik are amorphous silicas which are classified as harmless to humans. And the environment.

Evonik’s silica products do not only enhance product performance but also environmental performance. Here are some points at which technology and sustainability go hand in hand:

• ULTRASIL® in combination with silanes reduces the rolling resistance of tires and at the same time the consumption of gas or electricity. Which leads to reduced CO₂ emissions on the streets.
• SIPERNAT®, AEROSIL®, and ULTRASIL® prolong the life of millions of rubber products, from conveyer belts to truck tires, from shoe soles to silicone baking dishes. The reinforcement effect strengthens them for a reliable performance over years or even decades. So, less products have to be dumped due to decay.
• Ask for our variants that do not release any VOCs during processing – even at higher temperatures.

Also good to know: All silica products from Evonik are amorphous silicas. Unlike crystalline silicas, amorphous silicas are classified as harmless to humans and the environment. Or in other words: Evonik silica is safe silica. That’s why our products are approved for use in food, feed, and pharmaceuticals. Or in your baby’s pacifier. The European Food Safety Authority repeatedly confirmed the safety of silica as a food additive. Additionally, our silica agents received an OMRI Listed® Certification. Which means, that they are proven suitable for organic farming. Please find more facts on the safety of silica in our FAQs section.

If you have any questions about the application, processing or storage of silica and silanes, please don’t hesitate to ask. We have expertise accumulated over decades, so we are quite sure that we can offer you a practical solution: Simply drop us a line at ask-se@evonik.com or press the contact button below. Our experts will get back to you as soon as possible.

Our clients will get support from their regional contact and from our application engineers. We are looking forward to helping you.