Practical State of Cure Measurements by NMR

The use of Nuclear Magnetic Resonance (NMR) spin echo measurements (T2 relaxation) for assessing the state of cure of crosslinked rubber systems is becoming more popular in the rubber industry.  Knowledge of the state of cure of finished rubber products is paramount in order to quantify the effectiveness not only of the rubber formulation but also of the processing conditions used in preparing the final part.  Numerous technical papers have been published dealing with the measurement of crosslink density on commodity based elastomers systems such as natural rubber, SBR and EPDM.   In cases where an absolute value of crosslink density is not necessarily required, a relative state of cure with comparison to reference samples is largely sufficient. FNGP has developed an internal analysis method of NMR relaxation data which provides a state of cure value that can largely reduce the error which is inherent during the NMR data analysis.   Correlations of this technique with conventional data analysis results and state of cure by volume swell measurements will be presented.  Furthermore, the use of NMR to quantify state of cure in specialty elastomers for automotive applications such as HNBR, ACM and FKM will be presented.