Sulfur/Organic Copolymers as Curing Agents for Rubber

Abstract

It is widely acknowledged that waste sulfur generated from the petroleum industry creates huge storage and ecological problems. Therefore, the various methods of utilization are becoming increasingly attractive research topics worldwide. The thermal ability of elemental sulfur to homolytic cleavage of S8 rings enables its free radical copolymerization with unsaturated organic species and the obtaining of chemically stable polymeric materials. Here we report a novel possibility to use sulfur/organic copolymers obtained via “inverse vulcanization” as curatives for rubber. For this purpose, several various sulfur/organic copolymers were synthesized and analyzed from the point of view of their performance as rubber crosslinking agents. Solvent extraction was used to purify sulfur/organic copolymers from unreacted (elemental) sulfur. Thermal properties of the prepared copolymers were characterized by thermogravimetric analysis and differential scanning calorimetry (TGA–DSC). Crosslink density and structure of cured elastomers was studied by equilibrium swelling, thiol-amine analysis and freezing point depression. Mechanical properties of the vulcanizates were determined under static and dynamic conditions (DMA—dynamic mechanical analysis). It is proved that the utilization of sulfur/organic copolymers as curatives enables an effective crosslinking process of rubbers. Taking into account the results of a crosslink density analysis and mechanical properties of the vulcanizates cured with purified copolymers, it is evident that relatively long copolymer macromolecules are also involved in the formation of chemical bonds between unsaturated rubber macromolecules.

Density-Adjustable Bio-Based Polysulfide Composite Prepared by Inverse Vulcanization and Bio-Based Fillers

“…Some residual sulfur did not participate in inverse vulcanization. These results were confirmed by Wręczycki [ 10 ] and Valle et al [ 36 ]. The results showed that the amount of sulfur had a great influence on the appearance of bio-based polysulfides.…”

“…Orthorhombic sulfur (S α ) is the most thermodynamically stable form of elemental sulfur. S α presents in the form of eight-membered rings (S 8 ) [ 10 ]. The heating of S α leads it to be converted into monoclinic sulfur (S β , S 8 ) at 95.6 °C.…”

“…When the temperature continues to rise to 159 °C, sulfur S 8 rings opening polymerization forms the deep red liquid sulfur (S μ ). S μ continues to spontaneously polymerize, resulting in the formation of linear sulfur radical high polymer (S w ) [ 6 , 10 , 11 , 12 , 13 , 14 ].…”

“…The reaction between sulfur and unsaturated compound is known as “inverse vulcanization” [ 5 ]. Polysulfides usually exhibit excellent properties preferring them suitable for direct use or as intermediates for further functionalization for various applications [ 15 , 16 ] such as solar cell [ 17 ], hydrogen fuel cell [ 18 ], lithium-ion batteries [ 11 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ], high refractive index and IR transmitting optical devices [ 27 , 28 , 29 , 30 ], sulfur-doped carbon materials [ 31 ], heavy metal remediation [ 14 , 31 , 32 , 33 , 34 , 35 ], rubber [ 10 ], fertilizer [ 36 , 37 ], and other advanced materials [ 38 , 39 , 40 ].…”

Mercury Sorbents Made By Inverse Vulcanization of Sustainable Triglycerides: The Plant Oil Structure Influences the Rate of Mercury Removal from Water

“…The T g was found to be −17 °C for poly(S‐r‐Canola), −13 °C for poly(S‐r‐Rice Bran), and −24 °C for poly(S‐r‐Castor). DSC also revealed an endotherm between 100 and 150 °C, which corresponds to the transition of sulfur from an orthorhombic to monoclinic crystalline state and then melting and conversion to liquid sulfur ( Figure ) 31. An estimation of free, non‐polymeric sulfur content was made by integrating the area of these endothermic peaks after constructing a standard curve with crystalline S 8 standards (Supporting Information S24–S26).…”