How tight the network is
In rubber, chemical crosslinks tie the polymer chains into a network. The tighter the network, the more restricted the motion of the chains, and the faster the NMR signal fades. A relaxation time is therefore a measure of the crosslink density, which decides hardness, elasticity, fatigue and ageing behaviour.
Where it is used
- Natural and synthetic rubber compounds, including tyre compounds
- EPDM, silicone and polyurethane elastomers
- Filled and unfilled compounds, before and after vulcanisation
- Thermosets and adhesives, to follow the cure
Typical tasks are following the cure of a compound, comparing recipes and cure systems, checking batch-to-batch consistency, and finding out why a batch behaved differently.
From a decay to a number
A small piece of the compound is placed in the instrument and the decay of the signal is recorded. Pulse sequences such as spin echoes, and in research also multiple-quantum methods, give relaxation times that depend on the restriction of motion in the network. The values are compared between samples, or calibrated against a reference such as a swelling test or a measure of hardness.
What it adds
- Small samples and little preparation
- No solvents, as are needed for swelling tests
- The same sample can be followed during the cure
- Compounds with different fillers can be compared on the same scale
Points that matter in practice
- The relaxation time reflects the restriction of chain motion. Fillers also restrict motion, so interpret the result together with the filler content, or compare compounds with the same filler
- Absolute crosslink densities need a calibration for each type of compound. Without it, the method is excellent for ranking and for consistency checks
- For this reason, much of the work is still research and development, and the step to a routine quality check needs a validated calibration
- Control the temperature of the sample, and keep the thermal history of the samples comparable
From your compound to a method
Send or bring representative samples. MSY Consulting runs feasibility measurements, helps you compare the results with your own reference tests, and trains your team in the measurement and the analysis.
Let's talk about your application
Send an email describing your instrument and your application, and you will get a reply.
contact@msyconsulting.euMSY CONSULTING SAS · Wissembourg, France · LinkedIn