The reinforcing effect of carbon black is mainly that the addition of carbon black changes the structure of the rubber and produces a C-phase structure.
In vulcanized rubber, if the carbon black is well dispersed, and a C-phase structure is formed on the surface of each carbon black particle , Phase C plays a skeleton role to connect phase A and phase B. Forming an overall network of rubber macromolecules and fillers, changing the structure of the vulcanized rubber, thus improving the physical and mechanical properties of the vulcanized rubber.
Reinforcement mechanism of carbon black Surface adsorption layer theory
This theory believes that Black carbon and rubber generate a microscopic multi-phase inhomogeneous structure, which is a reinforcing mechanism of composite materials.
Nuclear magnetic resonance studies have confirmed that there is an adsorption layer composed of two types of rubber macromolecules on the surface of carbon black. The inner layer of about 0.5nm close to the carbon surface is in a glassy state; the rubber within a range of 0.5-5.0nm away from the Black carbon surface is somewhat mobile and in a subglassy state. This layer is called the outer layer.
These two layers constitute a double shell layer on the surface. The thickness of the double shell layer is basically within the above range. The binding energy in the interface layer of this cool shell must continuously decrease from the inside to the outside, that is, the surface of the special carbon black has a greater The constraints on molecular mobility continue to decrease, and finally the rubber molecules reach a free state where they are not constrained.
The reinforcing mechanism of black carbon on rubber.
During mixing, the rubber molecules break into free radicals, which combine with the active centers on the black carbon surface, or the oxygen-containing groups and free radicals on the carbon black surface cross-link with the rubber molecules during vulcanization to form chemical bonds.
Reinforcement mechanism of carbon black Molecular chain sliding theory
The core of this theory is that rubber macromolecules can slide on the surface , thus explaining the reinforcement phenomenon. The surface activity of carbon black particles is not uniform, with many strong active points and a series of adsorption points with different energies. The rubber chains adsorbed on the black carbon surface can have various binding energies, ranging from mostly weak van der Waals adsorption to at least a few strong chemical adsorptions. The adsorbed rubber segments will slide and elongate under stress.
Why do silica and carbon black have good reinforcing properties?
Because rubber is an organic matter, mainly composed of C atoms and H atoms, and the C in black carbon and the Si in silica belong to the same column in the periodic table of elements. They both have 4 electrons outside their nuclei, that is It is said that during the rubber mixing and vulcanization process, they may be able to participate in the chemical reactions that occur inside and form bonds with rubber molecules, thus enhancing the binding force between rubber molecules and achieving a reinforcing effect.