Bitumen Binders Modified with Sulfur/Organic Copolymers.

With the continuing growth of waste sulfur production from the petroleum industry processes, its utilization for the production of useful, low-cost, and environmentally beneficial materials is of primary interest. Elemental sulfur has a significant and established history in the modification of bitumen binders, while the sulfur-containing high-molecular compounds are limited in this field. Herein, we report a novel possibility to utilize the sulfur/organic copolymers obtained via the inverse vulcanization process as modifiers for bitumen binders. Synthesis and thermal characterization (TGA-DSC) of polysulfides derived from elemental sulfur (S8) and unsaturated organic species (dicyclopentadiene, styrene, and limonene) have been carried out. The performance of modified bitumen binders has been studied by several mechanical measurements (softening point, ductility, penetration at 25 °C, frass breaking point, adhesion to glass and gravel) and compared to the unmodified bitumen from the perspective of normalized requirements concerning polymer-modified bitumen. The interaction of bitumen binder with sulfur/organic modifier has been studied by means of FTIR spectroscopy and DSC measurements. The impact of the modification on the performance properties of bitumen has been demonstrated. The bitumen binders modified with sulfur/organic copolymers are in general less sensitive to higher temperatures (higher softening point up to 7 °C), more resistant to permanent deformations (lower penetration depth), and more resistant to aging processes without intrusive deterioration of parameters at lower temperatures. What is more, the modification resulted in significantly higher adhesion of bitumen binders to both glass (from 25% up to 87%) and gravel surfaces in combination with a lower tendency to form permanent deformations (more elastic behavior of the modified materials).

The Fluoride Anion-Catalyzed Sulfurization of Thioketones with Elemental Sulfur Leading to Sulfur-Rich Heterocycles: First Sulfurization of Thiochalcones.

Fluoride anion was demonstrated as a superior activator of elemental sulfur (S8) to perform sulfurization of thioketones leading to diverse sulfur-rich heterocycles. Due to solubility problems, reactions must be carried out either in THF using tetrabutylammonium fluoride (TBAF) or in DMF using cesium fluoride (CsF), respectively. The reactive sulfurizing reagents are in situ generated, nucleophilic fluoropolysulfide anions FS(8-x)-, which react with the C=S bond according to the carbophilic addition mode. Dithiiranes formed thereby, existing in an equilibrium with the ring-opened form (diradicals/zwitterions) are key-intermediates, which undergo either a step-wise dimerization to afford 1,2,4,5-tetrathianes or an intramolecular insertion, leading in the case of thioxo derivatives of 2,2,4,4-tetramethylcyclobutane-1,3-dione to ring enlarged products. In reactions catalyzed by TBAF, water bounded to fluoride anion via H-bridges and forming thereby its stable hydrates is involved in secondary reactions leading, e.g., in the case of 2,2,4,4-tetramethyl-3-thioxocyclobutanone to the formation of some unexpected products such as the ring enlarged dithiolactone and ring-opened dithiocarboxylate. In contrast to thioketones, the fluoride anion catalyzed sulfurization of their α,ß-unsaturated analogues, i.e., thiochalcones is slow and inefficient. However, an alternative protocol with triphenylphosphine (PPh3) applied as a catalyst, offers an attractive approach to the synthesis of 3H-1,2-dithioles via 1,5-dipolar electrocyclization of the in situ-generated α,ß-unsaturated thiocabonyl S-sulfides. All reactions occur under mild conditions and can be considered as attractive methods for the preparation of sulfur rich heterocycles with diverse ring-size.

Anionic Copolymerization of Styrene Sulfide with Elemental Sulfur (S8).

The superior ability of thiiranes (episulfides) to undergo ring-opening polymerization (ROP) in the presence of anionic initiators allows the preparation of chemically stable polysulfide homopolymers. Incorporation of elemental sulfur (S8) by copolymerization below the floor temperature of S8 permits the placement of a large quantity of sulfur atoms in the polysulfide mainchain. The utility of styrene sulfide (2-phenylthiirane; StS) for copolymerization with elemental sulfur is reported here. A few polysulfides differing depending on the initial ratio of S8 to StS and copolymerization time were synthesized. Various spectroscopic methods (1H NMR, 13C NMR, Raman spectroscopy and FTIR spectroscopy) were applied to characterize the chemical structure of the copolymers. Additionally, the phase structure and thermal stability of the synthesized polysulfides were investigated using DSC and TGA, respectively. The successful anionic copolymerization of styrene sulfide and elemental sulfur has been demonstrated.

New Sulfur Organic Polymer-Concrete Composites Containing Waste Materials: Mechanical Characteristics and Resistance to Biocorrosion.

The aim of this study was to develop new sulfur-copolymer concrete composites using waste compounds that have good mechanical characteristics and show a resistance to biocorrosion. The comonomers used to synthesize the sulfur-organic copolymers were-90 wt. % sulfur; 5 wt. % dicyclopentadiene (DCPD); 5 wt. % organic monomers, styrene (SDS), 1-decene (SDD), turpentine (SDT), and furfural (SDF). The concrete composites based on sulfur-organic copolymers were filled with aggregates, sand, gravel, as well as additives and industrial waste such as fly ash or phosphogypsum. The sulfur-organic copolymers were found to be chemically stable (softening temperature, thermal stability, melting temperature, amount of recrystallized sulfur, and shore D hardness). Partial replacement of DCPD with other organic comonomers did not change the thermal stability markedly but did make the copolymers more elastic. However, the materials became significantly stiffer after repeated melting. All the tested copolymers were found to be resistant to microbial corrosion. The highest resistance was exhibited by the SDS-containing polymer, while the SDF polymer exhibited the greatest change due to the activity of the microorganisms (FTIR analysis and sulfur crystallization). The concrete composites with sulfur-organic copolymers containing DCPD, SDS, SDF, fly ash, and phosphogypsum were mechanically resistant to compression and stretching, had low water absorbance, and were resistant to factors, such as temperature and salt. Resistance to freezing and thawing (150 cycles) was not confirmed. The concrete composites with sulfur-organic copolymers showed resistance to bacterial growth and acid activity during 8 weeks of incubation with microorganisms. No significant structural changes were observed in the SDS composites after incubation with bacteria, whereas composites containing SDF showed slight changes (FTIR and microscopic analysis). The concrete composite containing sulfur, DCPD, SDS, sand, gravel, and fly ash was the most resistant to microbiological corrosion, based on the metabolic activity of the bacteria and the production of ergosterol by the molds after eight weeks of incubation. It was found that Thiobacillus thioparus was the first of the acidifying bacteria to colonize the sulfur concrete, decreasing the pH of the environment. The molds Penicillium chrysogenum, Aspergillus versicolor and Cladosporium herbarum were able to grow on the surface of the tested composites only in the presence of an organic carbon source (glucose). During incubation, they produced organic acids and acidified the environment. However, no morphological changes in the concretes were observed suggesting that sulfur-organic copolymers containing styrene could be used as engineering materials or be applied as binders in sulfur-concretes.

Sulfur/Organic Copolymers as Curing Agents for Rubber.

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.