Microbial Desulfurization Technology Of Crosslinked Elastomer And Research Of Its Structure And Properties

Waste rubber is an important renewable resource, and microbial desulfurization is a novel reclaiming method of waste rubber. This paper involved microbial desulfurization for ground rubber (natural rubber and styrene butadiene rubber) with four bacteria with sulfur desulfurization ability: Thiobacillus ferrooxidans, Thiobacillus, Sphingonomas, and Alicyclobacillus.The optimal culture conditions for each bacterium were fully researched, such as temperature, pH value, stirring speed, culture medium and nutrition compositions. The possible microbial desulfurization pathways for sulfur vulcanized natural rubber and styrene butadiene rubber were discussed. The similarities and differences between desulfurization mechanism of various kinds of bacteria were compared through surface analysis of elements structure and contents. When desulfurized ground rubber was incorporated with virgin rubber, crosslink densities, mechanical properties, stress-strain properties, dynamic mechanical properties, the morphologies of tensile and tear fracture surfaces of filled vulcanizates and the situation of ground rubber particles on the fracture surfaces were studied.All these results proved that microbial desulfurization technology improved the dispersion of desulfurized ground rubber in rubber matrix, and also strengthed interphase bonding forces between dispersion ground rubber phases and rubber matrix, and therefore increased the mechanical properties of filled rubber vulcanizates.The major work of this paper is as follows: 1. Two Thiobacillus ferrooxidans strains with high desulfurization ability were selected:Thiobacillus ferrooxidans YT-1 and Thiobacillus ferrooxidans T-1. The biomasses in different culture mediums were studied, and then several modified 9K mediums were determined as desulfurization culture medium. FTIR and XPS measurements were tested for desulfurized NR and SBR vulcanizates, and sulfate concentration in desulfurization medium was monitored. All results supported that desulfurization mechanism of Thiobacillus ferrooxidans for NR and SBR matched the 4S pathway. The crosslink density of desulfurized NR ground rubber decreased after desulfurization. NR and SBR vulcanizates filled with desulfurized NR ground rubber showed good mechanical properties and dynamic mechanical properties, and the interphase bonding forces were improved. Disinfection of NR ground rubber by ethanol was proved to be very important for microbial desulfurization. Compared with strictly autotrophic Thiobacillus ferrooxidans T-1, facultative heterotrophic Thiobacillus ferrooxidans YT-1 was more effective for microbial desulfurization of NR ground rubber.2. Several Thiobacillus strains were screened. The influences of ground rubber to the growth of Thiobacillus sp. HB122 were characterized in order to obtain the proper loading of ground rubber. FTIR, XPS analysis and Schiff agent staining experiments proved that Thiobacillus sp. HB122 not only disrupted the sulfur crosslink bonds of NR and SBR vulcanizates, but also oxidized the carbon-carbon double bonds of polymers to aldehyde groups. The desulfurization effect of Thiobacillus sp. HB122 for NR ground rubber was better than that of Thiobacillus sp. HB062 and Thiobacillus sp. X4. Tensile strength and enlongation at break of vulcanizates filled with desulfurized NR ground rubber improved obviously. After desulfurized for 15 days, the mechanical properties of vulcanizates filled with desulfurized NR ground rubber were better than that filled with desulfurized ground rubber for 30 days. Desulfurized SBR ground rubber rarely increased the mechanical properties of filled vulcanizates, which indicated that the desulfurization effect of Thiobacillus sp. HB122 was not very good for SBR vulcanizates.3. A new Sphingomonas species strain was cultured. And the growth of it with different amounts of NR ground rubber and SBR ground rubber was investigated, and then the contents of ground rubber was obtained when desulfurization was processing. The evidences of S=O and C=O on the surface of desulfurized vulcanizates were shown in FTIR spectra. XPS spectra found that C=C double bonds decreased for desulfurized vulcanizates. Therefore, Sphingomonas oxidized the carbon-carbon double bonds of rubber main chains to carboxyl group. And it also oxidized the sulfur bonds and sulfur-carbon bonds to sulfoxide, sulfone and sulfonic acid groups. Tensile strength and elongation at break of NR vulcanizates filled with desulfurized SBR ground rubber were improved. So were SBR vulcanizates filled with desulfurized SBR ground rubber. Dynamic mechanical properties and SEM morphologies of vulcanizates filled with desulfurized SBR ground rubber proved the better interphase bonding between ground rubber and rubber matrix. Because of the stronger interphase bonding, the abrasion resistances of filled vulcanizates were also improved.4. A novel thermophilic Alicyclobacillus species bacterium was obtained. FTIR spectra reflected that Alicyclobacillus did not change carbon-carbon bonds or carbon-carbon double bonds of NR and SBR vulcanizates. XPS analysis of desulfurized rubber also found that carbon element was not oxidized, but sulfur element content decreased and oxygen element content increased due to the oxidantion of sulfur crosslink bonds. Crosslink density of filled vulcanizes decreased if compared with untreated ground rubber. Tensile strength and elongation at break of SBR vulcanizates filled with desulfurized NR ground rubber increased. So were SBR vulcanizates filled with desulfurized SBR ground rubber. The abrasion resistances of SBR vulcanizates filled with desulfurized SBR ground rubber also improved. Dynamic mechanical properties and SEM morphologies proved that vulcanizates filled with desulfurized NR and SBR ground rubber exhibited a better interphase bonding.