Cure Characteristics of Devulcanized Rubber:the Issue of Low Scorch

Abstract

We investigate the reasons behind the observed low scorch during the revulcanization of devulcanized rubber. Mechanically devulcanized carbon black filled natural rubber vulcanizates originally cured by conventional vulcanization (CV), semiefficient vulcanization (semi EV), efficient vulcanization (EV), and peroxide systems as well as buffing dust obtained from pre-cured tread with known formulation were used. Revulcanization of these devulcanized samples using sulfur/sulfonamide system led to the following observations; irrespective of the type of sulfur cure system used for the initial vulcanization of the rubber, (i) the devulcanized samples cured without pre-vulcanization induction time and (ii) devulcanized samples prepared from peroxide vulcanized rubber cured with scorch safety. Based on the earlier reports that solvent extraction of devulcanized rubber did not improve the scorch time during revulcanization, the role of zinc bound non-extractable moieties was investigated using devulcanized rubber prepared from activator-free vulcanizates, which disproved the role of such moieties. This confirmed that the scorch reducing moieties should be attached to the rubber main chain, which can be unreacted crosslink precursors and cyclic sulfides left after the initial accelerated sulfur vulcanization of the original sample. The ability of pre-vulcanization inhibitor to induce scorch safety when devulcanized rubber is revulcanized as such, without adding any virgin rubber, proved that mercaptobenzothiazole (MBT) generated from crosslink precursors is the cause of low scorch. Acetone extracted devulcanized rubber samples prepared from tetramethyl thiuramdisulfide (TMTD) cured natural rubber, which does not follow the MBT pathway when revulcanized, cured with scorch safety, which further proved the role of MBT. Based on the previous reports and our results, it is obvious that powdering of rubber vulcanizate and devulcanization processes have no role on the low process safety of these materials, but it is inherent to the initial accelerated sulfur vulcanization chemistry undergone by these materials.

Synergistic Effects of Bitumen Plasticization and Microwave Treatment on Short-Term Devulcanization of Ground Tire Rubber

“…This process, sometimes called in the literature as devulcanization, is related to the transformation of waste rubber using thermal, mechanical or chemical energy, in order to destroy the three-dimensional network of a cross-linked rubber. Compared to untreated waste rubber, the obtained reclaimed rubber can be easily processed, shaped, and vulcanized [9,10].…”

Preparation and characterization of maleic anhydride‐grafted desulfurization rubber powder by free‐radical polymerization

“…The molecular structure of desulfurized rubber obtained after force degradation and desulfurization is shown in Figure 8. [ 39–41 ] It can be seen from the molecular structure that there was a double bond in every four main chain carbon atoms of desulfurization rubber. According to the reaction conditions, both free‐radical reaction and ionic reaction can occur.…”

Evaluation of vulcanization nanoactivators with low zinc content: characterization of zinc oxides, cure, physico‐mechanical properties, Zn2+ release in water and cytotoxic effect of EPDM compositions

“…, which is further discussed based in the cellular viability results. During the first step, ZnO 30 and ZnO 40 have smaller particle sizes compared to sZnO; thus, ZnO 30 and ZnO 40 could penetrate easily into the elastomer matrix and react like polar pathway with the co‐activator, accelerator and sulfur molecules embedded between the EPDM chains . On the other hand, the samples without ZnO and with sZnO react mainly through a radical pathway due to the difficulty of dispersion of sZnO particles in the rubber matrix .…”