Auswahl der wissenschaftlichen Literatur zum Thema „Peroxide devulcanization“

Abstract The thermochemical recycling of natural rubber (NR) and ethylene-propylene-diene rubber (EPDM) vulcanizates with disulfides was studied. NR sulfur vulcanizates were completely plasticized when heated with diphenyldisulfide at 200 °C. It could be concluded that both main chain scission and crosslink scission caused the network breakdown. NR peroxide vulcanizates were less reactive towards disulfide at 200 °C, and only reacted through main chain scission. For EPDM a temperature range of 200–275 °C was studied. In the presence of diphenyldisulfide at 200 °C there was almost no devulcanization of EPDM sulfur vulcanizates, and at 225 and 250 °C there was only slightly more devulcanization. A decrease in crosslink density of 90% was found when 2×10−4 mol diphenyldisulfide/cm3 vulcanizate was added and the EPDM sulfur vulcanizates were heated to 275 °C. EPDM peroxide vulcanizates showed a decrease in crosslink density of ca. 40% under the same conditions. The lower reactivity of EPDM towards disulfide compared with NR is the result of higher crosslink densities, the presence of a higher percentage of more stable monosulfidic crosslinks and the fact that EPDM is less apt to main chain scission relative to NR.

Rubber-based wastes represent challenges facing the global community. Human health protection and preservation of environmental quality are strong reasons to find more efficient methods to induce degradation of latex/rubber products in order to replace devulcanization, incineration, or simply storage, and electron beam irradiation is a promising method that can be can be taken into account. Polymeric composites based on natural rubber and plasticized starch in amounts of 10 to 50 phr, obtained by benzoyl peroxide cross-linking, were subjected to 5.5 MeV electron beam irradiation in order to induce degradation, in the dose range of 150 to 450 kGy. A qualitative study was conducted on the kinetics of water absorption in these composites in order to appreciate their degradation degree. The percentages of equilibrium sorption and mass loss after equilibrium sorption were found to be dependent on irradiation dose and amount of plasticized starch. The mechanism of water transport in composites was studied not only through the specific absorption and diffusion parameters but also by the evaluation of the diffusion, intrinsic diffusion, permeation, and absorption coefficients.

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.

Waste management of vulcanized rubber is a serious environmental problem as the molecular structure formed during the process complicates recycling. Due to this, researchers have developed a process that can break the strong bonds and return the rubber to its original state. This process is called devulcanization and is developed for the tire industry due to the large amount of waste formed from this sector. This rubber is vulcanized with sulfurs like 90 % of other rubber products. However, there exist other products that are vulcanized with peroxides where much less research has been done. Due to this, it is unclear if devulcanization is possible as a different type of bond is formed in the vulcanization process. This work therefore investigates the possibilities with recycling by devulcanization of peroxide cured rubber where a collaboration is done with Roxtec International AB. The work also investigates the possibilities with reuse of the cooperating partner’s particular rubber and how everything can be implemented to understand the efficiency of these two waste management strategies and to share knowledge.  The used method for this work is a combination of the Participatory Action Research (PAR) and the Design thinking (DT) framework. A systematic literature review has also been conducted to collect relevant material for one of the research questions. The result showed that there exist many methods and possibilities with devulcanization of peroxides if sufficient energy is provided. However, the quality of the reclaimed rubber will be lacking as the bonds in the polymers main chain are degraded which affects the mechanical properties. Due to this only a small percentage can be reused by mixing it with virgin rubber. The efficiency for peroxides is therefore lower than for sulfurs. Regarding reuse many alternative usage areas were brainstromed but once the concepts were evaluated against the limitations with the material, the needs and the sustainability factor, only few solutions survived. The winning concept became a punching bag filled with granulated rubber crumbs. When investigating how everything can be implemented it turned out that a lot of effort is needed. For example, to get favorable results, the solution will require the punching bag company to also want to work towards sustainability by adapting take back systems. Devulcanization will then require that the waste is sorted which requires a big investment in both time and money to achieve. The conclusion of this work is that devulcanization and reuse is possible and the developed system solution can take care of parts of the waste. However, the possibilities are limited and to get rid of all the waste and develop a long-term solution that is both sustainable and further prepared for the future, more actions are needed. It is therefore of high interest to start investigating the possibilities with a new material that is easy to recycle or are degradable.
Avfallshantering av vulkaniserat gummi är ett allvarligt miljöproblem eftersom den molekylära strukturen som bildas under processen komplicerar återvinning. På grund av detta har forskare utvecklat en process som kan bryta de starka bindningarna och återställa gummit till sitt ursprungliga tillstånd. Denna process kallas devulkanisering och är främst utvecklad för däck-industrin på grund av den stora mängden avfall som bildas från denna sektor. Detta gummi vulkaniseras med svavel som 90% av andra gummiprodukter. Det finns dock andra produkter som vulkaniseras med peroxider där mycket mindre forskning har gjorts. På grund av detta är det oklart om devulkanisering är möjlig eftersom en annan typ av bindning bildas i vulkaniseringsprocessen. Detta arbete undersöker därför möjligheterna med återvinning genom devulkanisering av peroxid härdat gummi där ett samarbete görs med Roxtec International AB. Arbetet undersöker också möjligheterna med återanvändning av samarbetspartners specifika gummi spill och hur allt kan implementeras för att förstå effektiviteten i dessa två avfallshanterings strategier och för att sprida kunskap. Den använda metoden för detta arbete var en kombination av PAR (Participatory Action Research) och design thinking (DT). En systematisk litteraturstudie har också genomförts för att samla in relevant material för en av forskningsfrågorna. Resultatet visade att det finns många metoder och möjligheter för devulkanisering av peroxider om tillräcklig energi tillhandahålls. Dock kommer kvalitén på det återvunna gummit att försämras markant då bindningarna i polymerens huvudkedja bryts vilket påverkar de mekaniska egenskaperna. På grund av detta kan endast en liten andel återanvändas genom att blanda med jungfruligt gummi. Effektiviteten för peroxider är därför lägre än för svavel. När det gäller återanvändning, brainstormades många alternativa användningsområden, men när koncepten utvärderades mot begränsningarna med materialet, behoven och hållbarhetsfaktorer överlevde bara ett fåtal lösningar. Det vinnande konceptet blev en slagsäck fylld med granulerat gummi. När det undersöktes hur allt kan implementeras visade det sig att det krävs mycket ansträngningar. Till exempel, för att få gynnsamma resultat kommer lösningen att kräva att boxsäck företaget också vill arbeta för hållbarhet genom att anpassa take back system. Devulkaniserings-processen kommer även kräva att avfallet sorteras vilket kräver en stor investering i både tid och pengar för att uppnå. Slutsatserna av detta arbete är att devulkanisering och återanvändning är möjligt och den utvecklade systemlösningen kan ta hand om delar av avfallet. Men möjligheterna är begränsade och för att bli av med allt avfall och utveckla en långsiktig lösning som både är hållbar och ytterligare förberedd för framtiden, kommer fler åtgärder att behövas. Det är därför av stort intresse att börja undersöka möjligheterna med ett nytt material som är lätt att återvinna eller är nedbrytbart.