Study On Microbial Desulfurization Technology And Mechanism Of Waste Latex Rubber

In microbial desulfurization, the desulphurases produced in the metabolic process of microorganisms could directionally catalyze the reactions of sulfur crosslinks in rubber. Microbial desulfurization method has many advantages such as mild desulfurization conditions, simple process, low equipment requirement, and no pollution. Therefore, This method cause extensive attention, and it is great significance for the sustainable development of rubber industry.In this thesis, Alicyclobacillus sp. and Sphingomonas sp. were used to desulfurizated waste latex rubber (WLR). The microbial desulfurization methods were compared with chemical desulfurization method and an amount of valuable data was obtained. The main research contents were showed as follows.In the first part of present thesis (Chapter3,4), two strains of microorganisms, Alicyclobacillus sp. and Sphingomonas sp., were cultured, screened and domesticated. The culture conditions and medium formula of Alicyclobacillus sp. and Sphingomonas sp. were studied, the toxicity effect of the elastomers and the rubber additives on the microorganisms were investigated, detoxification method of WLR and the formulation and the technical conditions in the co-culture desulfurization process were determined. X-ray photoelectron spectrometer (XPS), Fourier transform infrared spectrometer (FTIR), hydrophilic property measurements, crosslink density measurements, mechanical property measurements were used to evaluate the desulfurization effect systematically. The Horikx curve was used to study the desulfurization mechanism, which established the theoretical and applicative bases of microbial desulfurization.The results showed that the optimum conditions for the desulfurization of WLR by Alicyclobacillus sp. with the conventional microbial desulfurization method were detoxification for2h in75%(v/v) ethanol, the addition of5%(w/v) WLR and1.5%o (w/v) polysorbate80(Tween80) in medium, desulfurization for10days at a pH of2.5,50℃, and a stir speed of200prm. the optimum conditions for the desulfurization of WLR by Sphingomonas sp. with the conventional microbial desulfurization method were detoxification for2h in75%(v/v) ethanol, the addition of5%(w/v) WLR and2.0‰(w/v) Tween80in medium, desulfurization for10days at a pH of7.0,30℃, and a stir speed of200prm. After desulfurization by these two microorganisms respectively, the contents of S elements on the surface of WLR were decreased, the contents of oxygenic functional groups increased, and hydrophily was improved. The mechanical property of the vulcanizates filled with desulfurizated waste latex rubber (DWLR) was improved. Both of the desulfurization mechanisms of these two microorganisms were "4S" desulfurization pathway. Alicyclobacillus sp. could break the crosslinked sulfur bonds on the surface of WLR, but leaving the main chains intact. The desulfurization effect of WLR by Sphingomonas sp. was better because Sphingomonas sp. had better tolerance to rubber and additives.In the second part of present theses (Chapter5), a new microbial desulfurization method, half-submerged cultivation method, was proposed. This method was used in desulfurization of waste latex rubber by Sphingomonas sp. The optimum technical condition was determined and the desulfurization effect of this method was evaluated systematically. The reason of achievement good desulfurization effect with this method was analyzed. And this method was also used in desulfurization of ground tire rubber by Sphingomonas sp. The results showed that the optimum conditions for the half-submerged cultivation method were detoxification for2h in75%(v/v) ethanol, the addition of40%(w/v) WLR in medium without polysorbate80(Tween80), desulfurization for10days at a pH of7.0and30℃, and the desulfurization process was without stir. The content of S element on the surface of SDWLR and HDWLR decreased45.8%and62.5%respectively, where SDWLR and HDWLR stand for the WLR desulfurized by the submerged cultivation method and the half-submerged cultivation method respectively. The frequencies of S-S on the surface of SDWLR and HDWLR decreased14.1%and55.6%respectively. The frequencies of S-O on the surface of SDWLR and HDWLR increased47.8%and106.5%respectively. The half-submerged cultivation method had better desulfurization effect on the WLR. There are more sulfoxide groups on the surface of HDWLR than those of SDWLR. The HDWLR/SBR composites had better mechanical property than the SDWLR/SBR composites. The major reason of achievement better desulfurization effect with half-submerged cultivation method was that microorganisms could stick to the surface of WLR with the method easily and evenly. A good desulfurization effect was also achieved in desulfurization of ground tire rubber by Sphingomonas sp. with this method. These results proved that half-submerged cultivation method could not only cut desulfurization costs and improve equipment efficiency, but also could improve desulfurization effect.In the third part of present theses (Chapter6), a disulphide, DBADPDS, was used in desulfurization of WLR in internal mixer. The results showed that with the increasing of the amount of naphthenic oil, the Mooney viscosity and crosslink density were deceased. Naphthenic oil could promote the desulfurization. DBADPDS could promote the desulfurization, but a great number of main chains would be broken if the too many DBADPDS were added. The tensile strength and elongation at break was highest with the addition of0.5phr DBADPDS. The main chains of rubber were broken easily if the temperature was exceeded140℃in internal mixer, which would severely affected the performance of devulcanized rubber. The appropriate temperature was120℃in desulfurization process. Compared to microbial desulfurization, cross bonds were difficult to be broken directionally in chemical desulfurization of WLR.