Probing Rubber Cross-Linking Generation of Industrial Polymer Networks at Nanometer Scale

Abstract

We present improved analyses of rheometric torque measurements as well as (1)H double-quantum (DQ) nuclear magnetic resonance (NMR) buildup data on polymer networks of industrial compounds. This latter DQ NMR analysis allows finding the distribution of an orientation order parameter (Dres) resulting from the noncomplete averaging of proton dipole-dipole couplings within the cross-linked polymer chains. We investigate the influence of the formulation (filler and vulcanization systems) as well as the process (curing temperature) ending to the final polymer network. We show that DQ NMR follows the generation of the polymer network during the vulcanization process from a heterogeneous network to a very homogeneous one. The time variations of microscopic Dres and macroscopic rheometric torques present power-law behaviors above a threshold time scale with characteristic exponents of the percolation theory. We observe also a very good linear correlation between the kinetics of Dres and rheometric data routinely performed in industry. All these observations confirm the description of the polymer network generation as a critical phenomenon. On the basis of all these results, we believe that DQ NMR could become a valuable tool for investigating in situ the cross-linking of industrial polymer networks at the nanometer scale.

Topological Insight into Superabsorbent Hydrogel Network Structures: a 1H Double‐Quantum NMR Study

“…It should be noted, however, that the RDC distribution reaching 0 at D res = 0 Hz coupling is physically not correct, which limits the significance of this kernel. Similar findings are summarized in literature . Most recently, Naumova et al have applied an empirical single‐orientation A‐l kernel function to study the anisotropically mobile protonated molecular segments …”

“…Similar findings are summarized in literature. [33,36,39,50,51] Most recently, Naumova et al have applied an empirical single-orientation A-l kernel function to study the anisotropically mobile protonated molecular segments. [52] In summary, the S nDQ data obtained with the proposed user-independent tri-exponential model and the conventional stepwise fit procedure through careful choice of two fitting ranges are nearly identical within the experimental error.…”

Influence of Sulfur-Curing Conditions on the Dynamics and Crosslinking of Rubber Networks: A Time-Domain NMR Study

“…Moreover, a linear dependence of M h on ν c,sw can be found (Figure S1), ascribable to the increase in viscosity of the polymer network. In fact, a direct proportionality between M h and crosslink density is documented in the literature [8,36]. It is worth noting that since the ν c,sw values are in the range 2-8 × 10 −5 mol/g, our samples can be considered as moderately crosslinked.…”

“…Information on the average crosslink density (or on the average mass between consecutive crosslinks, M c ) of the network formed by the vulcanization of elastomers can be obtained via different experimental approaches; the most commonly used are equilibrium swelling experiments, mechanical measurements, and proton time-domain NMR (TD-NMR) spectroscopy [1,7,9,10,13,17,18,21,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. In several studies, correlations have been drawn between crosslink density measurements obtained by different methods, and origins for discrepancies have been discussed in relation to experimental uncertainties and models adopted in data analysis in the different cases [25,26,28,29,32,37].…”

Design of “Zn2+ Salt-Bondings” Cross-Linked Carboxylated Styrene Butadiene Rubber with Reprocessing and Recycling Ability via Rearrangements of Ionic Cross-Linkings

“…Developing eco-friendly recyclable rubber products is always a crucial and hot issue in sustainable development of the rubber industry . To meet the requirements of high mechanical performance in various practical applications, rubbers must be chemically cross-linked to form a 3D covalent network . Afterward, however, the formation of a chemical cross-linked network classifies rubber as a thermoset material, which prevents reshaping and recycling …”