Preparation And Characterization Of Microcapsules Sulfur And Application In Natural Rubber

Sulfur vulcanization system is widely used in rubber industry. Due to the solubility of sulfur in rubber varies with temperature variation a phenomenon named blooming usually occurs in rubber processing.Sulfur in rubber is difficult to be dispersed evenly due to the different polarities of sulfur and rubber matrix.This causes uneven internal curing structure and usually has serious impact on rubber mechanic properties.In addition, the toxicity of sulfur is another consideration factor, especially when the sulfur is heated and get vaporized.In this thesis work,pure sulfur particle is coated by several different types of polymer materials.The coated sulfur is expected to solve the problems stated above.Coated sulfur could realize controlled release at certain conditions by the way of tuning the polymer molecular and structure.Controlled release of sulfur is good to improve the effective use of sulfur and increase the scorch time properly,which benefits rubber processing.A series of different molecular weight of low molecular weight polyvinyl alcohol,poly(vinyl alcohol-co-vinyl triethoxysilane),methyl hydrogen dichlorosilane modified polyvinyl alcohol,polystyrene were synthesized.Purchased polyethylene wax and the synthesized polymers were characterized by DSC to characterize the melting temperature range of the coating materials to meet the required melting temperature range of120-140℃.Polarized light microscopy.infrared spectroscopy and electron scanning microscopy were used to characterize the coating effects;laster particle analyzer was used to characterize the particle size and distribution of the coated sulfurs by different methods.The results showed the particle size of the prepared coated sulfur are less than100μm.The coated sulfurs were applied into rubber processing.Results found that the concentrations of10%,15%,20%polyethylene wax,concentrations of2.5%,5%polyvinyl alcohol coated sulfur obtained significantly higher performance than the uncoated sulfur;Concentration of5%polyethylene wax, polystyrene prepared coated sulfur vulcanizations mechanical properties than the uncoated sulfur,but not obvious; Concentration of5%vinyl alcohol vinyl triethoxysilane copolymer coated sulfur vulcanizations mechanical properties enhanced the elongation at break are slightly lower than the vulcanized rubber coated sulfur; Concentration of5%by the exception of the elongation at break, based hydrogen dichlorosilane modified polyvinyl alcohol prepared coated sulfur vulcanizations mechanical properties are significantly lower than the vulcanized rubber coated sulfur; Concentration of7.5%,10%polyvinyl alcohol prepared coated sulfur vulcanizations mechanical properties are poor.The same kinds of coating materials coated sulfur were applied into rubber processing.Results found that vulcanization time and scorch time increasing with the increasing of the corresponding coating layer thickness.The coated sulfur were applied into natural rubber processing as vulcanizing agent, polyethylene wax coated sulfur, polystyrene coated sulfur, raw rubber, sulfur were dispersed well in raw rubber.However, uncoated sulfur particles appeared, and blooming phenomenon occurred after parking three weeks; Raw rubber whose vulcanizing agent is the low molecular weight polyvinyl alcohol or silicone modified polyvinyl alcohol coated sulfur, the sulfur dispersion is poor than sulfur coated with polyethylene wax and polystyrene.But in the surface of the corresponding raw rubber sulfur particles and the blooming phenomenon did not occur after parked three weeks; Curing agent for the uncoated sulfur, the sulfur in raw rubber matrix dispersed well after milling.However, three weeks later.in the surface of raw rubber blooming phenomenon gradually occur,and sulfur particles could be founded by naked eye in longitudinal section.Researches shows that sulfur coated by the non-polar materials such as non-polar polyethylene wax and polystyrene preparation were applied into the non-polar rubber processing, can effectively inhibit the blooming phenomenon, promote the dispersion of sulfur, and improve the mechanical properties of rubber;Sulfur coated by polar materials such as polyvinyl alcohol were applied into the non-polar natural rubber processing, can inhibit blooming, as well as the sulfur dispersed,however,do not meet the expectation.Control the dosage of polyvinyl alcohol can improve mechanical properties of the rubber. Though sulfur coated by silicone modified polyvinyl alcohol-poly (vinyl alcohol-b-vinyl triethoxysilane) methyl hydrogen dichlorosilane modified polyvinyl alcohol can reduce the polarity,these sulfur still do not meet the intended purpose.