Low-field NMR method for determining the content of the curing agent.

During the mixing process, the large molecules of rubber chemically and physically bond with the surface of active fillers (such as carbon black particles). This causes some of the rubber to bind to the surface of the carbon black particles, making it insoluble in organic solvents, which is known as bound rubber.

The formation of bound rubber helps break up and disperse the carbon black aggregates evenly during mixing. However, if too much bound rubber is generated too early in the mixing process, particularly before the carbon black-rubber agglomerates break and disperse, it forms a hard film around the carbon black aggregates, making it more difficult for the high-concentration carbon black-rubber agglomerates to break up and disperse further. Therefore, for diene-based rubbers with high unsaturation, especially natural rubber, strict control of the mixing conditions in the early stages is essential to prevent excessive formation of bound rubber, and the mixing temperature should not be raised too quickly, allowing only limited bonding between the carbon black and rubber.

The determination of bound rubber content has always been a challenging issue in the industry. Traditional chemical methods have low precision and are subject to significant human error. With nuclear magnetic resonance (NMR), the relaxation decay curve of elastomeric materials changes in response to variations in the internal composition of the sample, allowing rapid, non-destructive determination of bound rubber content.

The relaxation decay curve of elastomeric materials changes according to the internal composition of the sample. NMR uses the principle that different components within elastomeric materials have different relaxation times to measure bound rubber content.

Low-field NMR technology does not require specific shapes or colors for the test samples, as long as they can fit into the detection probe. Using NMR, bound rubber content can be quickly and accurately measured.