Relation between activation energy and induction in rubber sulfur vulcanization: An experimental study

Abstract

The article presents the possibility to use the so‐called frequency factors in order to select the optimal temperature to mix rubber blend recipes before vulcanization without inducing premature crosslinking. As secondary result of the research, it provides a very simple approach to evaluate induction assuming a first order kinetic approach. It has been frequently observed that the activation energy in a first order rubber vulcanization scheme appears to be function of the particular activators used and that activation energy links to the so‐called waiting time (and induction) by means of the frequency factor through an exponential relationship. A total of 212 rheometer curves are experimentally obtained and suitably postprocessed, consisting of pure natural rubber (NR), polybutadiene (PB), and 50–50 or 70%–30% NR‐PR blends in presence of different concentrations of sulfur and accelerants (diphenyl guanidine [DPG] and N‐t‐butylbenzothiazole‐sulfenamide [TBBS]). Data reduction is carried out to have an insight into the most suitable temperature to utilize in the different cases in order to: (a) Obtain the best mixed blends without risking premature vulcanization and (b) design the induction phase without over vulcanize the blend and/or delaying curing because the time required is too long. Waiting time and induction are evaluated by means of a well‐established exponential law requiring the knowledge of the activation energy (assuming for the sake of simplicity that crosslinking occurs following a first order reaction kinetic law) and a constant called “frequency factor”. Frequency factor, considering all reactions monomolecular for the sake of simplicity, is assumed of the order of magnitude of 10−13–10−14 s. All experimental data carried out are critically compared and a wide explanation of the expected induction times and most suitable temperatures to use in the mixing phase is provided in the different cases considered. The article provides a meaningful insight into the importance of the link existing among activation energy, vulcanization recipe (with particular regard to concentration of accelerants, blend between two rubbers with very different activation energies and interaction between two accelerants) and mixing temperature to adopt before curing.

Experimental and simulative investigation of a multistage 2K injection molding process of PA6 and EPDM

“…It is about 85 kJ mol À1 . The crosslinking kinetics of the vulcanization or an ideal temperature process window for the internal mixer process could be described in more depth by mathematical kinetic models, for example by Milani et al 13,14,15 based on the available MDR data.…”

Anti‐migration performance of EPDM composite improved by octadecylamine‐functionalized graphene oxide

“…The GA nanofillers were mixed with EPDM to prepare EPDM/GA composites with GA contents of 0, 1, 3, 5, and 7 phr, recorded as EPDM/GA‐0, EPDM/GA‐1, EPDM/GA‐3, EPDM/GA‐5, and EPDM/GA‐7, respectively. The EPDM and other fillers were prepared using an XK‐160 mixing roll mill at 60°C, and then left to stand for 24 h. The elastomer compounds were molded into 2‐mm‐thick slabs, the vulcanizates were cured at 160°C for 30 min under 15 MPa according to the vulcanization curves 22,23 . The basic recipe is as follows: EPDM, 100 phr; DCP, 2 phr; TAIC, 2 phr; sulfur, 1 phr; N‐isopropyl‐N0‐phenyl‐4‐phenylenediamine (4010 NA), 2 phr; ZnO, 5 phr; stearic acid, 1 phr; N‐cyclohexyl‐2‐benzothiazole (CZ), 2.2 phr.…”

Hybrid reinforcement of styrene‐butadiene rubber nanocomposites with carbon black, silica, and graphene

“…Considering that these mechanical properties closely correlate with cross-link density, it can be argued that the curing system of rubbers also have a strong influence on abrasion resistance. [14][15][16][17][18][19] Carbon black and silica have been in use for decades in the tyre manufacturing industry. Their role in achieving today's high-quality standards is irrefutable.…”