Mechano-chemical recycling of sulfur cured natural rubber

Abstract

The disposal of cured rubber has become a major environmental problem. Discarded rubber was devulcanized by an open two-roll cracker-cum mixing mill both in the presence or absence of diphenyl disulfide at 120 o C (Mechano-Chemical Process, MCP), and then the obtained devulcanized mass was revulcanized again by the addition of sulfur and N-cyclohexyl-2-benzothiazyl sulfonamide (CBS). A new look at the devulcanization mechanism and the influence of the devulcanizing agent on the mechanical properties of the ultimate revulcanized rubber are presented in this paper. Rheometric characteristics show that both the scorch time and curing rate were low for revulcanized rubber. One of the most interesting observations is that the mechanical properties of revulcanized rubber obtained by devulcanizing in the presence of disulfide were better than of the revulcanized rubber obtained by devulcanizing in absence of disulfide. The formation of extra crosslinking in disulfide containing revulcanized rubber was confirmed by crosslinking density data. By adopting this devulcanization technique mechanical properties of vulcanized natural rubber were retained in more than 87 %. MECHANOCHEMICZNY RECYKLING KAUCZUKU NATURALNEGO WULKANIZOWANEGO ZA POMOC¥ SIARKIStreszczenie -Opisano metodê recyklingu odpadów gumowych polegaj¹c¹ na ich dewulkanizacji w walcarce mieszankowej (rys. 1) w temp. 120 o C z dodatkiem lub bez disiarczku difenylu, a nastêpnie rewulkanizacji otrzymanej masy za pomoc¹ siarki i N-cykloheksylo-2-benzotioazol-sulfonamidu (CBS) jako przyspieszacza (tabele 1-3). Pomiary reometryczne wykazywa³y, ¿e czas podwulkanizacji i szybkooeae wulkanizacji próbek rewulkanizowanych s¹ mniejsze w porównaniu z tymi wielkooeciami dotycz¹cymi odpowiadaj¹cym im próbkom oryginalnych wulkanizatów (rys. 2-4). Stwierdzono, ¿e u¿ycie w procesie dewulkanizacji disiarczku difenylu daje lepsze w³aoeciwooeci mechaniczne i wy¿sz¹ gêstooeae sieciowania rewulkanizowanych kauczuków w porównaniu z analogicznymi próbkami otrzymanymi bez tego dodatku (tabela 4, rys. 5-7). S³owa kluczowe: proces mechanochemiczny, dewulkanizacja, rewulkanizacja, mechanizm dewulkanizacji, w³aoeciwooeci mechaniczne, gêstooeae sieciowania.

Effective Thermal-Oxidative Reclamation of Waste Tire Rubbers for Producing High-Performance Rubber Composites

“…8,9 High scission of crosslinked rubbers with a high scission efficiency (>50 wt% soluble rubber) is highly desirable in order to facilitate the dispersion of RGTR and the associated CB in rubber matrices for high performance rubber products. 10,11 Traditional reclamation of GTR include mechanical, [12][13][14] mechano-chemical, [15][16][17] thermo-mechanical and thermo-chemical, 18,19 or other physical and chemical methods. [20][21][22][23] To further improve the reclamation degree with a high content of soluble rubber for ultrafine dispersion, Tripathy et al reclaimed vulcanized natural rubber (NR) by a "high-pressure high-temperature sintering (HPHTS)" method and obtained a viscous reclaimed rubber at high temperature (310 °C) for 1 h under nitrogen, but this process involved high energy consumption and operational hazards.…”

“…Traditional reclamation techniques for GTR include mechanical, − mechanochemical, − thermo-mechanical and thermo-chemical, , or other physical and chemical methods. − To further improve the reclamation degree with a high content of soluble rubber for ultrafine dispersion, Tripathy et al reclaimed vulcanized natural rubber (NR) by a “high-pressure high-temperature sintering (HPHTS)” method and obtained a viscous reclaimed rubber at high temperature (310 °C) for 1 h under nitrogen, but this process involved high energy consumption and operational hazards . Shi et al reclaimed GTR by a corotating twin-screw extruder at 300 °C using pine tar as the chemical agent.…”

Use of Diels–Alder Chemistry for Thermoreversible Cross-Linking of Rubbers: The Next Step toward Recycling of Rubber Products?

“…Sulfur vulcanization and peroxide curing are currently the main industrial cross-linking techniques in the rubber industry. These yield irreversible chemical cross-links, preventing melt reprocessing. , Considerable efforts have been devoted to the devulcanization of a variety of cross-linked rubbers. − For iso-based rubbers such as natural rubber and butyl rubber, such reclaiming processes have been commercially practiced for decades. − Rubbers like EPDM with the unsaturations in the side group are less reactive and therefore more difficult to recycle. Nevertheless, some workable reclaiming processes have been developed for these materials. , These processes combine thermal and mechanical treatment for selective cleavage of the sulfur cross-links.…”

Mechanical Properties of the Regenerated Rubber Prepared by Waste Tire Powders and Fillers

“…Many attempts have been made for reclaiming of waste rubber products [2][3][4][5][6]. Generally, the process could be categorized into two groups: physical reclaiming process and chemical reclaiming process.…”