Networking Skills: The Effect of Graphene on the Crosslinking of Natural Rubber Nanocomposites with Sulfur and Peroxide Systems

Abstract

Tailored crosslinking in elastomers is crucial for their technical applications. The incorporation of nanoparticles with high surface-to-volume ratios not only leads to the formation of physical networks and influences the ultimate performance of nanocomposites, but it also affects the chemical crosslinking reactions. The influence of few-layer graphene (FLG) on the crosslinking behavior of natural rubber is investigated. Four different curing systems, two sulfur-based with different accelerator-to-sulfur ratios, and two peroxide-based with different peroxide concentrations, are combined with different FLG contents. Using differential scanning calorimetry (DSC), vulcametry (MDR) and swelling measurements, the results show an accelerating effect of FLG on the kinetics of the sulfur-based curing systems, with an exothermic reaction peak in DSC shifted to lower temperatures and lower scorch and curing times in the MDR. While a higher accelerator-to-sulfur ratio in combination with FLG leads to reduced crosslinking densities, the peroxide crosslinkers are hardly affected by the presence of FLG. The good agreement of crosslink densities obtained from the swelling behavior confirms the suitability of vulcameter measurements for monitoring the complex vulcanization process of such nanocomposite systems in a simple and efficient way. The reinforcing effect of FLG shows the highest relative improvements in weakly crosslinked nanocomposites.

The quantification of anisotropy in graphene/natural rubber nanocomposites: Evaluation of the aspect ratio, concentration, and crosslinking

“…The samples SulEV and 3Perox clearly show the strongest reinforcement of the four vulcanization systems, namely the highest shear modulus G ' perpendicular to the plane of the graphene platelets, compared to their unfilled samples with 0 phr; see Table 1 and Figure 4e. For SulEV a first decrease in G' was detected (from 0 to 1 phr FLG), which corresponds to a reported prevention of crosslinking with the presence of FLG 45 . The values for 1Perox were lower overall than for the other three vulcanization systems.…”

“…For SulEV a first decrease in G' was detected (from 0 to 1 phr FLG), which corresponds to a reported prevention of crosslinking with the presence of FLG. 45 The values for 1Perox were lower overall than for the other three vulcanization systems.…”

“…An influence on the sorption kinetics of the presence of the nanoparticles or their aspect ratio was therefore not detected. The respective curves of mass uptake over time and kinetics for the vulcanization systems and FLG contents are part of a previous study 45 …”

“…The respective curves of mass uptake over time and kinetics for the vulcanization systems and FLG contents are part of a previous study. 45 When the polymer chains are oriented or the reinforcing effect of the fillers is more pronounced in one direction than the other, the swelling becomes anisotropic. Furthermore, these two effects may be mutually amplified.…”

“…Our previous studies were focused on the improvements of technical properties, 8,17,19 potential replacements of conventional fillers by small amounts of graphene 14,16,18,20 as well as the influence of graphene on the crosslinking kinetics and crosslinking density 45 in elastomers. In this study, different natural rubber (NR) nanocomposites are evaluated regarding their anisotropic behavior.…”