How to improve the tear strength of silicone rubber products?

Rubber tearing is a destructive phenomenon caused by the rapid expansion of cracks or fissures in materials due to stress. The load per unit thickness during sample tearing is the tear strength. Tear strength is an important mechanical property of silicone rubber products. Generally, the national standard GB/T 529-2008 "Determination of Tear Strength of Vulcanized Rubber or Thermoplastic Rubber" is used for testing. This standard specifies three types of specimens for determining the tear strength of vulcanized rubber or thermoplastic rubber, with the most commonly used being the right angle specimen without notches.

Pant shaped sample (knife): For samples with gaps, the tear strength of the pants is determined by dividing the force required to tear the sample by the thickness of the sample;

Right angle sample (B-knife): cut and uncut. Place the right angled specimen on a tensile machine and continuously stretch it at a certain speed until it tears, at the maximum force required per unit thickness;

Crescent shaped (C-section): also known as curved or waist shaped. Apply an external force perpendicular to the plane of the incision on a specified right angle or crescent shaped specimen, and divide the maximum force required to fracture the incision by the thickness of the specimen.

The tear strength of ordinary silicone rubber (ShoreA 70) (B-knife test) is around 20kN/m.

How to improve the tear strength of silicone rubber products? The tear strength of silicone rubber is mainly affected by raw rubber, reinforcing agents, and vulcanizing agents.

Raw rubber: Used together with high and low vinyl content silicone rubber products. When the ethylene mole fraction of the composite adhesive is less than 0.15%, an appropriate mix ratio will significantly improve the tear resistance of the composite adhesive. When the ethylene mole fraction of silicone rubber is 0.15% and 0.06%, and the ethylene mole fraction of silicone rubber is used in a 50/50 combination, the highest tear strength is achieved when the ethylene mole fraction of the combined rubber is 0.15%, reaching 45.8 kN/m. When the ethylene mole fraction in the composite rubber exceeds 0.15%, the combination ratio of silicone rubber has little effect on the tear performance of vulcanized rubber.

Enhancer: The most important factor affecting tear strength is the reinforcement system. The commonly used reinforcing agents include gas-phase white carbon black and precipitated white carbon black, among which precipitated white carbon black has a better reinforcing effect on gas-phase white carbon black. According to the influence of silica particle size on reinforcement effect, the smaller the particle size, the larger the specific surface area, and the stronger the ability of white carbon black surface to adsorb rubber molecules, resulting in better reinforcement effect. According to this principle, try to choose gas-phase white carbon black with smaller particle size. Therefore, white carbon black modification is also the main way to improve the tear strength of silicone rubber products.

Vulcanizing agent: The commonly used vulcanizing agent for silicone rubber products is peroxide, which is used for molding and extrusion. Taking the Eken Silicone HCR 9170 UE as an example. After adding the first level platinum vulcanizing agent, the tear strength reached 47.8kN/m, which is higher than peroxide vulcanization. Therefore, for products with high tear requirements, platinum vulcanizing agent can be considered.