Elastomers are polymeric materials extensively used in the tire industry. These materials are obtained by vulcanization of one (or more) polydiene polymer(s) in the presence of sulfur and other additives (accelerators, activators, plasticizers, fillers, etc.). During this process, chemical crosslinks are formed between the polymeric chains, providing the final product's elasticity and durability. Depending on the formulation and the vulcanization conditions, other mechanical properties can be obtained. Importantly, such properties are strongly related to the microscopic structure of the polymeric network [1]. Consequently, the investigation of microscopic and macroscopic properties giving access to information on the network structure in relation to the vulcanization conditions is fundamental for the design of optimized elastomeric materials. In this context, 1H time-domain NMR (TD-NMR) represents a valuable tool to gain insights into the molecular dynamics of the polymeric chains. This technique allows to measure NMR observables (1H T1 and T2 relaxation times and 1H-1H residual dipolar couplings (Dres)), which depend on the modulation of 1H-1H dipolar couplings by segmental motions. These motions are quite fast in elastomers above the glass transition temperature, but are anisotropic, resulting in residual 1H-1H dipolar interactions, which depend on the amount and distribution of topological constraints in the polymeric network [2]. In this work, natural and isoprene rubbers vulcanized at different curing temperatures and different sulfur contents have been investigated by exploiting 1H TD-NMR techniques, including 1H multiple-quantum experiments for the measurements of Dres, Carr-Purcell-Meiboom-Gill pulse sequence for the evaluation of 1H T2 relaxation times, and field cycling NMR relaxometry for the measurements of 1H T1 relaxation times on a wide range of Larmor frequencies (10 kHz-35 MHz). The NMR observables were compared with the crosslink density or macroscopic properties of the material that depend on this quantity, obtained using routinely employed methods in industrial analyses, allowing to gain insight into the effects of the formulation and the vulcanization conditions on the structure and dynamics of the polymeric networks [3]. References [1] S. P. O. Danielsen, H. K. Beech, S. Wang, B. M. El-Zaatari, X. Wang, L. Sapir, T. Ouchi, Z. Wang, P. N. Johnson, Y. Hu, D. J. Lundberg, G. Stoychev, S. L. Craig, J. A. Johnson, J. A. Kalow, B. D. Olsen and M. Rubinstein Chem. Rev. 121, 5042-5092 (2021) [2] K. Saalwächter Rubber Chem. Technol. 85, 350-386 (2012) [3] F. Nardelli, L. Calucci, E. Carignani, S. Borsacchi, M. Cettolin, M. Arimondi, L. Giannini, M. Geppi and F. Martini Polymers 14, 767 (2022)
INFLUENCE OF SULFUR-CURING CONDITIONS ON THE DYNAMICS AND CROSSLINKING OF RUBBER NETWORKS: A TIME-DOMAIN NMR STUDY
F Nardelli;L Calucci;E Carignani;S Borsacchi;
2022
Abstract
Elastomers are polymeric materials extensively used in the tire industry. These materials are obtained by vulcanization of one (or more) polydiene polymer(s) in the presence of sulfur and other additives (accelerators, activators, plasticizers, fillers, etc.). During this process, chemical crosslinks are formed between the polymeric chains, providing the final product's elasticity and durability. Depending on the formulation and the vulcanization conditions, other mechanical properties can be obtained. Importantly, such properties are strongly related to the microscopic structure of the polymeric network [1]. Consequently, the investigation of microscopic and macroscopic properties giving access to information on the network structure in relation to the vulcanization conditions is fundamental for the design of optimized elastomeric materials. In this context, 1H time-domain NMR (TD-NMR) represents a valuable tool to gain insights into the molecular dynamics of the polymeric chains. This technique allows to measure NMR observables (1H T1 and T2 relaxation times and 1H-1H residual dipolar couplings (Dres)), which depend on the modulation of 1H-1H dipolar couplings by segmental motions. These motions are quite fast in elastomers above the glass transition temperature, but are anisotropic, resulting in residual 1H-1H dipolar interactions, which depend on the amount and distribution of topological constraints in the polymeric network [2]. In this work, natural and isoprene rubbers vulcanized at different curing temperatures and different sulfur contents have been investigated by exploiting 1H TD-NMR techniques, including 1H multiple-quantum experiments for the measurements of Dres, Carr-Purcell-Meiboom-Gill pulse sequence for the evaluation of 1H T2 relaxation times, and field cycling NMR relaxometry for the measurements of 1H T1 relaxation times on a wide range of Larmor frequencies (10 kHz-35 MHz). The NMR observables were compared with the crosslink density or macroscopic properties of the material that depend on this quantity, obtained using routinely employed methods in industrial analyses, allowing to gain insight into the effects of the formulation and the vulcanization conditions on the structure and dynamics of the polymeric networks [3]. References [1] S. P. O. Danielsen, H. K. Beech, S. Wang, B. M. El-Zaatari, X. Wang, L. Sapir, T. Ouchi, Z. Wang, P. N. Johnson, Y. Hu, D. J. Lundberg, G. Stoychev, S. L. Craig, J. A. Johnson, J. A. Kalow, B. D. Olsen and M. Rubinstein Chem. Rev. 121, 5042-5092 (2021) [2] K. Saalwächter Rubber Chem. Technol. 85, 350-386 (2012) [3] F. Nardelli, L. Calucci, E. Carignani, S. Borsacchi, M. Cettolin, M. Arimondi, L. Giannini, M. Geppi and F. Martini Polymers 14, 767 (2022)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
