The effect of thermal treatment and uniaxial pressure upon the distribution of segmental dynamics by 1H NMR relaxometry

Abstract Rubber materials undergo structural degradation that can lead to loss of functional performance. In this work, the effects of thermal ageing and uniaxial compression on segmental chain dynamics were investigated for cross-linked natural rubber samples (NR1–NR7) using unilateral NMR relaxometry. Transverse proton relaxation time ( T 2 ) distributions were obtained by Fast Laplace Inversion of CPMG echo decays measured with a Bruker Minispec spectrometer coupled to a unilateral NMR-MOUSE ® sensor. Samples were thermally aged at 90 °C for 24 h. Surface ageing was also induced using a 500 °C heat source at 10 cm distance, and the penetration depth of the thermal effect was estimated at ~ 0.6 mm. Results show that T 2 -distributions depend strongly on cross-link density and ageing conditions. Two relaxation components, short (rigid) and long (mobile), were identified, with the long component showing higher sensitivity to structural changes. A correlation between relaxation parameters and shear modulus confirms the dependence of segmental dynamics on network rigidity. Under uniaxial compression, NR4 exhibited a linear dependence of both T 2 components on pressure, with higher sensitivity than NR1. This correlates with lower mechanical stiffness and leads to failure of NR4 at ~ 3000 kgf/m², while NR1 remains intact up to 9000 kgf/m². These results demonstrate that unilateral NMR relaxometry is an effective non-destructive tool for probing polymer dynamics and evaluating thermal and mechanical degradation in elastomers, with relevance for material characterization and quality control.