Growing environmental and health concerns have led to a considerable attention to the formulation of sustainable and non-toxic elastomer blends to be used in the tire industry. For this purpose, one of the long-shot aims is to replace petroleum-based resins with renewable, biocompatible and non-toxic resins, without altering the processability and the mechanical features of the final product.[1] To accomplish this task, it is important to understand what happens at the molecular level between polymer and resin in a vulcanizate and to relate this with its macroscopic behavior. This knowledge is in fact necessary to guide the design of innovative materials which fulfill specific mechanical requirements. In this context, Time-Domain Nuclear Magnetic Resonance (TD-NMR) spectroscopy represents a powerful tool to characterize the molecular dynamics of polymer and plasticizer in a vulcanizate, as well as their miscibility, as it allows to measure parameters which depend on the modulation of 1H-1H homonuclear dipolar interactions by molecular motions.[2] Indeed, from one side, 1H T2 relaxation times can be correlated with the different dynamic behavior of protons belonging to different molecular environments.[3] Furthermore, 1H-1H residual dipolar couplings (Dres) can be exploited to evaluate the cross-link density, as they depend on the amount of topological constraints, such as entanglements and cross-links, to polymer chain motions. [4] From the other side, 1H T1 relaxation times allow to assess the degree of mixing of different phases in the sample: in fact, in multiphase systems with domain sizes lower than ~10 nm, the T1's of protons in different dynamic environments tend to be averaged to a single value, due to the spin diffusion phenomenon. In this work, several TD-NMR experiments were performed at different temperature on vulcanized and non-vulcanized styrene-butadiene rubber samples, in the presence of petroleum-based or natural resins. In particular, Magic Sandwich Echo and Carr-Purcell-Meiboom-Gill experiments were acquired to measure 1H T2, while Inversion Recovery experiments were exploited to measure 1H T1, thus allowing to evaluate the molecular mobility of the polymeric and resin phases, as well as their miscibility. Moreover, Double-Quantum NMR experiments were acquired for the measurement of 1H-1H Dres to monitor the cross-link density in all vulcanized samples. References [1] B.L. Wadey, B.L. Wadey, Encyclopedia of Physical Science and Technology, 3rd ed, (2003) [2] K. Saalwachter, Rubber Chemistry and Technology, 85, 350-386, (2012) [3] K. Müller, M. Geppi, Solid State NMR: Principles, Methods, and Applications, (2021) [4] F. Nardelli, L. Calucci, E. Carignani, S. Borsacchi, M. Cettolin, M. Arimondi, L. Giannini, M. Geppi, F. Martini, Polymers, 14, 767-782, (2022)
STUDY OF THE MISCIBILITY OF BIOCOMPATIBLE PLASTICIZERS IN ELASTOMERIC MATERIALS BY TIME-DOMAIN NMR TECHNIQUES
L Calucci;
2022
Abstract
Growing environmental and health concerns have led to a considerable attention to the formulation of sustainable and non-toxic elastomer blends to be used in the tire industry. For this purpose, one of the long-shot aims is to replace petroleum-based resins with renewable, biocompatible and non-toxic resins, without altering the processability and the mechanical features of the final product.[1] To accomplish this task, it is important to understand what happens at the molecular level between polymer and resin in a vulcanizate and to relate this with its macroscopic behavior. This knowledge is in fact necessary to guide the design of innovative materials which fulfill specific mechanical requirements. In this context, Time-Domain Nuclear Magnetic Resonance (TD-NMR) spectroscopy represents a powerful tool to characterize the molecular dynamics of polymer and plasticizer in a vulcanizate, as well as their miscibility, as it allows to measure parameters which depend on the modulation of 1H-1H homonuclear dipolar interactions by molecular motions.[2] Indeed, from one side, 1H T2 relaxation times can be correlated with the different dynamic behavior of protons belonging to different molecular environments.[3] Furthermore, 1H-1H residual dipolar couplings (Dres) can be exploited to evaluate the cross-link density, as they depend on the amount of topological constraints, such as entanglements and cross-links, to polymer chain motions. [4] From the other side, 1H T1 relaxation times allow to assess the degree of mixing of different phases in the sample: in fact, in multiphase systems with domain sizes lower than ~10 nm, the T1's of protons in different dynamic environments tend to be averaged to a single value, due to the spin diffusion phenomenon. In this work, several TD-NMR experiments were performed at different temperature on vulcanized and non-vulcanized styrene-butadiene rubber samples, in the presence of petroleum-based or natural resins. In particular, Magic Sandwich Echo and Carr-Purcell-Meiboom-Gill experiments were acquired to measure 1H T2, while Inversion Recovery experiments were exploited to measure 1H T1, thus allowing to evaluate the molecular mobility of the polymeric and resin phases, as well as their miscibility. Moreover, Double-Quantum NMR experiments were acquired for the measurement of 1H-1H Dres to monitor the cross-link density in all vulcanized samples. References [1] B.L. Wadey, B.L. Wadey, Encyclopedia of Physical Science and Technology, 3rd ed, (2003) [2] K. Saalwachter, Rubber Chemistry and Technology, 85, 350-386, (2012) [3] K. Müller, M. Geppi, Solid State NMR: Principles, Methods, and Applications, (2021) [4] F. Nardelli, L. Calucci, E. Carignani, S. Borsacchi, M. Cettolin, M. Arimondi, L. Giannini, M. Geppi, F. Martini, Polymers, 14, 767-782, (2022)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
