Rubber active agent also known as vulcanizing active agent. An inorganic or organic substance used to make a vulcanization accelerator active. It can maximize the capacity of the accelerator, reduce the amount of accelerator, and shorten the vulcanization time. Most of the inorganic additives are metal oxides, hydroxides and basic carbonates, such as zinc oxide, lead oxide, calcium hydroxide, lead carbonate, etc., the most important thing in organic additives is fatty acids, followed by amines, soaps, etc. Such as stearic acid, dibutyloleic acid amine, zinc stearate, etc. The general dosage is less than 5% of the weight of rubber.

Rubber Additives: Detailed Properties, Advantages, and Applications

1. Zinc Oxide (ZnO)

Properties:

• White, odorless powder with high specific gravity (5.6 g/cm³).

• Melting point: 1,975°C; refractive index: 2.008–2.029.

• High reactivity as a vulcanization activator.

• UV-blocking and antimicrobial properties.

Advantages:

• Accelerates sulfur vulcanization (reduces curing time by 20–30%).

• Improves mechanical properties (tensile strength +15–25%, elongation at break +10–15%).

• FDA-approved for food-contact applications (21 CFR 172.480).

• Environmentally friendly (non-toxic, recyclable).

Applications:

• Tires: Steel-belted radial tire carcasses (enhances adhesion between rubber and steel).

• Footwear: Outsole compounds (improves abrasion resistance, ASTM D5963: 50–80 mm³ loss).

• Medical: Surgical gloves (antimicrobial protection, ASTM E2149).

• Adhesives: Rubber-to-metal bonding (increases peel strength by 30–40%).

2. Phenolic Resin

Properties:

• Thermosetting polymer with high crosslink density.

• Heat resistance: Continuous use up to 180°C (intermittent 250°C).

• High rigidity (modulus: 2–4 GPa) and dimensional stability.

• Chemical resistance to acids, bases, and solvents.

Advantages:

• Provides structural reinforcement (increases hardness by 10–20 Shore A).

• Flame retardant (UL94 V-0 rating without halogen additives).

• Cost-effective compared to specialty thermoplastics.

• Customizable curing systems (acid-catalyzed or heat-activated).

Applications:

• Tires: Sidewall compounds (improves cut resistance, ASTM D624).

• Industrial Belts: Conveyor belts for high-temperature environments (e.g., cement plants).

• Friction Materials: Brake pads (maintains coefficient of friction at 0.35–0.45 under 200°C).

• Foundry: Core sand binders (reduces gas evolution during casting).