Microbial And Chmical Desulfurization Technology And Mechanism Of Ground Tire Rubber And Research Of Its Structure And Properties

Microbial desulfurization method uses bacteria which exhibit biologicalactivity towards sulfur to break down sulfur crosslinkds of vulcanized rubberso as to achieve the purpose of regeneration of waste rubber. It is a newmethod for recycling waste rubber in recent years and meets the nationalrequirements of scientific and sustainable development.In this paper, four different bacterias (Thiobacillus ferrooxidans,Thiobacillus sp., Sphingonomas sp., and Yeast) after culture, isolation, andidentification are used for ground tire rubber (GTR) desulfurization. Thetoxicity test about the growth of bacterias in presence of different elastomersand rubber additives are invested. The optimal conditions for each bacteriumco-cultured with GTR such as desulfurization process, medium formulation,pH values, and inoculum are researched. The desulfurization effect on GTR bybacterias is systematically evaluated through analysis of the chemical groups,element content, bonding energy, and sol fraction before and afterdesulfurization. The contribution to the properties of the rubber blend withdesulfurated GTR (DGTR) are quantitatively calculated though evaluation ofprocessing performance, integrated application performance, and morphologystructure. All these results settle the theory and application basis of this newrecycling method.The results show that the toxicity of natural rubber and styrene-butadienerubber is low to the bacterias. Zinc oxide and vulcanization accelerator havehigh toxicity to bacteria. Therefore, GTR must be taken a detoxification byethanol before desulfurization, and then added to medium with vigorousgrowing bacteria. Thiobacillus ferrooxidans has a good effect ondesulfurization GTR when co-cultured time is20days and Fe2+concentrationof medium is25%of9K medium. T. ferrooxidans can oxide sulfur on the surface of GTR to SO₄^2-. A rupture of conjugated C=C bonds and a reductionof sulfur content by52.8%on the surface of GTR have occurred duringdesulfurization. The sol fraction of GTR increases by58%, from its original4.69%to7.43%. When Thiobacillus sp. is co-cultured desulfurization withGTR for7days, S2-2O3in medium has been exhausted and biomass can alsokeep a high level. It is revealed that bacteria can take advantage of sulfur onGTR surface. When continued co-cultured to20days, sulfur content on thesurface of GTR decreses by40.6%, and the content of S-S groups and S-Cgroups are respectivily reduced by18.3%and42.3%. S-O groups are formedon the DGTR surface. The sol fraction of GTR increases by58%.Thiobacillus sp. can oxide C=C bonds to C=O groups. Sphingomonas sp. is anew and relatively moderate strain with high environmental tolerance. It isfirst used for rubber desulfurization. Sphingonomas sp. is co-cultured withGTR for25-50days by replacement medium procress. After desulfurization,sulfur crosslinks are broken down to form S=O sulfoxide groups duringdesulfurization process, and partical sulfoxide groups are continuely oxidizedto form the sulfone O=S=O groups. Sphingonomas sp. can oxide C=C bondsto C=O groups. Sulfur content on the surface decreases by22.9%and solfraction increses by85%. G-SH, thiol-containing product generated duringYeast metabolism, can be used for the desulfurization regeneration of wasterubber. After desulfurization, sulfur content is reduced by56%, S-S groupsare increased by54%, and S-C groups remain unchanged. The sol fraction isincreased by55%. Though comprehensive consideration, desulfurizationeffect on GTR by Sphingonomas sp. is more remarkable and economy.Compared with rubber composites filled with GTR, DGTR filled rubbercomposites has better mechnical properties, dynamic mechnical properties,and improved interface between DGTR and rubber matrix.Sulfur crosslined squalene is used as a model of vulcanized rubbercompounds for revealing sulfur crosslink bonds metabolism mechanism bySphingomonas sp. Medium has no effect on the structure of modelcompounds. After inoculation of Sphingomonas sp., the color of the modelcompounds fades and the peak values of the model compounds aresignificantly reduced by Liquid chromatography-ultraviolet (HPLC-UV)test. Mass spectrometry furthur indicates that the monosulfide bonds anddisulfide bonds decrease slightly, trisulfide bonds decrease significantly and four-sulfur cross-linked model compounds disappeares. The relsutessuggest that Sphingomonas sp. indeed has desulfurization effect on GTRand mainly cut polysulfur cross-linked bonds during desulfurizationprocess.Desulfurization regeneration activitor420(RA420) is widely used forindustrial recycling waste rubber. Both main chain scissions and crosslinkscissions are ocuured during desulfurization process. The total amount ofcrosslink as well as the fraction of the polysulfidic crosslink obviouslydecreases, whereas the disulfidic crosslink slightly decreases and themonosulfidic crosslink remains constant. After reclaiming, the crosslinksstill present in waste rubber are mainly disulfide and monosulfidecrosslink. Extending the desulfurization time can increase thedesulfurization and the optimal temperature for desulfurization180°C.