Correlation between Macroscopic Elasticity and Chain Dynamics of Natural Rubber during Vulcanization as Determined by a Unique Rheo-NMR Combination

Abstract

The cross-linking process of natural rubber (NR) is studied for the first time by a unique combination of rheology and time-domain (TD) NMR, two methods that are commonly conducted separately. The combined setup consists of a high-end rheometer and a compact 25 MHz 1 H NMR relaxometer (rheo-NMR), which allows rheological characterization and NMR relaxometry to be operated simultaneously on the same sample. During vulcanization, the elastic modulus G′(t), representing the macroscopic elasticity, was directly correlated to the molecular dynamic parameters derived from NMR, including the populationaveraged transverse relaxation rate, 1/T 2ave , and the logarithmic mean of the residual dipolar coupling constant, D̅ res . It is found that, at the same level of macroscopic elasticity, the conformational flexibility of network chains in NR cross-linked with the so-called efficient vulcanization (EV) is more restricted than that with conventional vulcanization (CV). This can be attributed to the shorter and consequently less flexible (monosulfidic) cross-links formed by EV, whereas polysulfidic links dominate in the CV vulcanizate as confirmed by high-field 13 C NMR spectroscopy.

From Formulation to Application: Effects of Plasticizer on the Printability of Fluoro Elastomer Compounds and Additive Manufacturing of Specialized Seals

“…Post-print shrinkage was found in this research to be one of the most, if not the most, critical issues in MatEx AM of fully compounded rubbers or thermoset elastomers. This phenomenon can be attributed to the inherent characteristic of polymeric chains to revert to their initial state of relaxation (random coil chain) after they have been stretched [34][35][36]. During the printing process, the FKM compounds were extruded through the small opening of the printer nozzle.…”

“…Due to the lower viscosity, the FKM compound with plasticizer experienced less induced stress during the extrusion process compared to the FKM compound without plasticizer. The reduced stress experienced by the polymer chains during extrusion for the plasticized FKM meant they were less stretched compared to the FKM without plasticizer [34][35][36]. Consequently, upon relaxation to their coiled configuration, FKM with plasticizer displayed a lower degree of postprint shrinkage in comparison to FKM without plasticizer.…”

Rheo-NMR at the Phase Transition of Liquid Crystalline Poly-γ-benzyl-l-glutamate: Phase Kinetics and a Valuable Tool for the Measurement of Residual Dipolar Couplings

“…Rheo-NMR is a well-established technique that allows revealing detailed properties of viscous liquids – and liquid crystalline phases (LCs) under applied shear. – Particularly the combination of rheo-NMR and deuterium NMR with the residual quadrupolar coupling of deuterated solvents provides a highly sensitive measure for alignment properties of LCs and has been used extensively. – Experiments, however, are usually performed in a steady rheological state using specialized NMR-probehead that show excellent distribution of shear forces but compromised sensitivity and shim. ,, A better setup for our intended applications adds the rheology in a modular way . Not long ago, the Scheler group developed an apparatus for use with a conventional 5 mm high-resolution NMR probehead to study the effect of shear forces on a protein in solution with the highest currently available sensitivity. – The modular and relatively simple apparatus has led to important novel insights, but applicable shear forces are limited by the weak built-in sample spinning capabilities of the NMR spectrometer and only allow steady-state rheological conditions.…”

Time-Resolved Extensional Rheo-NMR Spectroscopy for Investigating Polymer Nanocomposites under Deformation

“…The Rheo-NMR, which combines rheometer and NMR, becomes a versatile instrument to capture the molecular-level information under shear or deformation. Most of the Rheo-NMR instruments are designed based on various shear cells, − whereas reports related to the tensile mode are quite limited . Nishi et al first investigated the chain dynamics and strain-induced crystallization of various elastomers, i.e., natural rubber, by measuring the NMR of a deformed sample with a fixed stretch ratio.…”