Inverse Vulcanization Research Articles

Promising Chalcogenide Hybrid Copolymers for Sustainable Applications as Bio-lubricants and Metal Adsorbents

Inverse vulcanization has emerged as a reaction to achieve hybrid inorganic–organic polymeric materials, which allows us to use the high amount of sulfur produced during refining crude oil as a raw material. In this study, a gamut of copolymers has been formulated using a quantitative atom economy, that is, elemental sulfur and castor oil (CO), as can be seen from the appearance of gels to crystalline copolymers. The physical and chemical characterization has been carried out using techniques such as Fourier transform infrared spectroscopy, NMR, differential scanning calorimetry, and thermogravimetric analysis. Furthermore, two types of copolymers have been selected to test their capabilities in different applications. Copolymers with S ratios higher than 30% have been tested for water remediation, with high removal rates for metals such as lead and cadmium. Although copolymers with a percentage of up to 10% sulfur have been tested as bio-based lubricants, showing improvements in terms of viscosities compared to the initial vegetable oil.

Inverse Vulcanization of Elemental Sulfur with Natural Rosin to Prepare High Sulfur Content Polymers with Excellent Solubility and UV‐Blocking Performance

UV Protection Inverse vulcanization of elemental sulfur (S) with natural rosin (Ro) to synthesize high sulfur content Sx-Ro copolymer is presented in article number 2100854 by Li Zhou and co-workers. The Sx-Ro not only shows excellent solubility in low boiling point solvents, but also exhibits superior UV absorption capability in the whole UV region, so it can be utilized as an anti-UV agent to improve the UV-blocking performance of other polymers.

Synthesis of sustainable poly(S-Abietic-co-Pinene) through inverse vulcanization of Kurdica gum and used to fabricate durable and recyclable super-hydrophobic cotton wool filter: Oil-water separation application

The renewable and sustainable poly(S-Abietic-co-Pinene) with a high sulfur content was synthesized by inverse vulcanization of elemental sulfur and natural kurdica gum (extracted from the Pistacia atlantica tree). This hydrophobic polysulfide (KPS) is dip-coated on cotton wool to obtain a super-hydrophobic filter with a water contact angle of 165°. All polysulfide and coated filters are characterized by the FTIR, 13CNMR, TGA, SEM, X-ray map, EDX, and WCA. The 3-Aminopropyltriethoxysilan (APTES) reagent was used to enhance the adhesive forces between cotton and the KPS coating. The super-hydrophobic cotton-KPS wool filters were conducted for six bi-phasic oil-water separations. The high separation efficiencies and permeate fluxes as well as the 100% rejection of the aqueous phase are advantages of cotton-KPS wool filters. Also, no significant change was observed in the separation efficiency after 20 recycling numbers, implying the high durability and stability of the super-hydrophobic coating on the cotton-KPS filter. The use of renewable natural materials for the synthesis of novel polymers and the fabrication of robust super-hydrophobic filters for oil water separation can be based on green chemistry and sustainable development principles.

Highly sulfur-rich polymeric cathode materials via inverse vulcanization of sulfur for lithium–sulfur batteries

In the present study, a new polythiophene derivative bearing an acryloyloxy moiety in the side chain as a functional co-monomer, poly (3-[(2-acryloyloxy) methyl]) thiophene (PAMT), was synthesized to be used for the inverse vulcanization method with elemental sulfur (S8). Highly sulfur-rich graft materials, S- poly (3-[(2-acryloyloxy) methyl]) thiophenes (52 and 74%) (S-PAMT), were prepared by inverse vulcanization of PAMT with different feed ratios of molten sulfur. Their structural characterizations were carried out by using appropriate standard spectroscopic methods such as FT-IR, DSC, TGA, SEM as well as XPS. The electrochemical performance of S-PAMT (74%) as a Li–S battery cathode material was evaluated. It was found that the fabricated cells delivered around 400 mAh·g−1 stable capacity at a C/5 current density over 100 cycles. Electrochemical impedance spectroscopy (EIS) was also performed before and after cycling to further investigate the lithium storage mechanism of S-PAMT (74%).

Polysulfide Synthesis Using Waste Cooking Palm Oil via Inverse Vulcanization

AbstractElemental sulfur and waste cooking palm oil (WCO) are abundant industrial by‐products from petrochemical and food processing industries, respectively. WCO was used as a crosslinker to prepare a high‐sulfur‐content polymer through inverse vulcanization. Polysulfides were generated under vigorous stirring of WCO with elemental sulfur at different temperatures, crosslinking ratios, and reaction times. The physicochemical properties of the produced polysulfides were determined and the thermal stability was analyzed. The FTIR spectra including the breakdown of C=C and formation of C–S bond confirmed the change of functional groups between WCO and produced polymer. The effect of saturated and unsaturated triglycerides of WCO is clearly visible in SEM micrographs. The polysulfide with a 70 wt % sulfur feed ratio showed excellent morphological and thermal properties.

Dark Sulfur: Quantifying Unpolymerized Sulfur in Inverse Vulcanized Polymers

Inverse vulcanization allows polymeric materials to be formed from excess elemental sulfur, promoting polysulfide chains to be stabilized between organic comonomers, rather than reforming as crystalline S8, resulting in high sulfur content materials with interesting properties. The techniques used to determine if free unreacted sulfur remains in the polymers only detect the crystalline and not the amorphous form. A detailed study is presented on the quantification of free amorphous sulfur within inverse vulcanized polymers, in which free sulfur is shown to increase over a period of aging. Postaging regeneration by stimulating homolytic S–S cleavage in the polymer is investigated.

Combining vegetable oils and bioactive compounds via inverse vulcanization for antioxidant and antimicrobial materials

The current great concern about plastic pollution opens up opportunities for the production of more sustainable polymers. Inverse vulcanization has emerged as a novel procedure to obtain inorganic-organic hybrid polymeric materials. Sulfur is attained as a by-product of oil refining production and makes inverse vulcanization a sustainable process due to a large amount of sulfur without a useful life. In previous studies, vegetable oils were used as a comonomer with sulfur to form copolymers based on sustainable raw material. Nevertheless, compounds from agro-wastes, could be a third comonomer that improves new copolymers bio-applications. In this study, a new series of copolymers with castor oil as vegetable oil and sulfur was formulated by adding a third compound bearing double bonds or heteroatoms. A study was conducted to assess the antimicrobial capacity and antioxidant activity of the copolymers obtained to demonstrate the benefits of adding a new comonomer to improve their bioactivity.

Synthesis and Characterization of Disiloxane Cross-Linked Polysulfides

The discovery of inverse vulcanization has resulted in the formation of stable polysulfide materials synthesized from cheap and abundant elemental sulfur. To stabilize the sulfur chains, carbon-based cross-linkers containing alkene moieties have been the focus of the field so far. This research explores the two most basic siloxane dienes, 1,3-diallyl-tetramethyldisiloxane and 1,1,3,3-tetramethyl-1,3-divinyldisiloxane, as cross-linkers. Both cross-linkers successfully underwent inverse vulcanization with different weight percentages of sulfur (wt % S); the traditional method was used for 1,3-diallyl-tetramethyldisiloxane, while the catalytic method was used for 1,1,3,3-tetramethyl-1,3-divinyldisiloxane. Two series of polysulfides, X-poly-(S-r-allyldisiloxane) and X-poly-(S-r-vinyldisiloxane) (X = wt % S), were synthesized. For poly-(S-r-allyldisiloxane), 33 wt % S was the minimum sulfur content required to form a solid material, while for poly-(S-r-vinyldisiloxane), it was 30 wt % S. Both series at and above those wt % S showed great resistance to common laboratory solvents and have thermal stabilities to about 200 °C. Glass transition temperature (Tg) for poly-(S-r-allyldisiloxane) showed an increasing trend with an increase in wt % S, and a maximum Tg at 70 wt % S poly-(S-r-vinyldisiloxane) was measured at 26.4 °C. Elemental analysis and XPS showed inconsistent results due to the presence of unreacted sulfur on the material’s surface, as observed by microscopy. In most cases, excess sulfur could be removed using CS2. The research reported herein provides a direct comparison of the synthesis and characterization of two series of disiloxane cross-linked polysulfides and will stimulate further studies into their applications as well as into future polysulfide materials formed using siloxane or other main-group cross-linkers.

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).

Inverse Vulcanization of Norbornenylsilanes: Soluble Polymers with Controllable Molecular Properties via Siloxane Bonds.

The inverse vulcanization produces high sulfur content polymers from alkenes and elemental sulfur. Control over properties such as the molar mass or the solubility of polymers is not well established, and existing strategies lack predictability or require large variations of the composition. Systematic design principles are sought to allow for a targeted design of materials. Herein, we report on the inverse vulcanization of norbornenylsilanes (NBS), with a different number of hydrolysable groups at the silicon atom. Inverse vulcanization of mixtures of NBS followed by polycondensation yielded soluble high sulfur content copolymers (50 wt % S) with controllable weight average molar mass (MW), polydispersity (Đ), glass transition temperature (T G), or zero‐shear viscosity (η 0). Polycondensation was conducted in the melt with HCl as a catalyst, abolishing the need for a solvent. Purification by precipitation afforded polymers with a greatly reduced amount of low molar mass species.

Inverse Vulcanisation of canola oil as a route to recyclable chopped carbon fibre composites

As a result of crude oil desulfurisation, elemental sulfur is a significant by-product of the petrochemical industry with millions of tonnes produced annually, and a significant portion remains unused. The use of this feedstock for the generation of new materials has seen increased growth, though such materials that utilise inverse vulcanisation have limited practicality in everyday applications due to their poor mechanical properties. Another underutilised waste product is that of carbon fibre composites. The increased need for high performance materials has resulted in a significantly amplified demand for carbon fibre reinforced composites. In line with this demand, an increase in scrap, waste, and fibre offcuts is also increasing in proportion.Within this paper the combination of these two resources was explored: recycled chopped carbon fibre was incorporated into a polymer derived from elemental sulfur and waste canola oil. The aim was to generate composites with improved physical properties, enabling their widespread use in high volume material applications. The introduction of 20 wt% carbon fibre was found to significantly improve tensile strength and modulus in iterative generations of recycling with tensile strength reaching a maximum of 909.1 kPa (+137.4%) and tensile modulus to 94.3 MPa (+160.1%) as compared to the initial introduction of carbon fibre. We demonstrate that fibre and polymer components were able to be repeatedly separated from each other, mechanically or chemically, recombined and processed into new composites.

Charged sulfurous polymers sop up metals

Petroleum refining produces millions of metric tons of excess elemental sulfur each year. Seeking to use this material practically, researchers have incorporated sulfur into polymers to enable them to bind heavy metals for cleaning up water. But because they’re made with hydrophobic monomers, these polymers often suffer from poor solubility, and only sulfur on their surface is available for binding. In an effort to make more-soluble sulfur-containing polymers, chemists Courtney L. Jenkins and Cameron B. Call of Idaho State University and M. Logan Eder of Ball State University combined sulfur with charged monomers, including diallyldimethylammonium chloride, in an inverse vulcanization process ( ACS Appl. Polym. Mater. 2022, DOI: 10.1021/acsapm.1c01536 ). The resulting charged polymer captures gold and silver, precipitating into a complex that can be filtered to leave behind clean water. “Using petroleum waste to create polymers for the remediation of industrial waste helps manage two waste streams with one

Utilizing Reclaimed Petroleum Waste to Synthesize Water-Soluble Polysulfides for Selective Heavy Metal Binding and Detection

Many industrial processes produce waste with toxic and precious metal pollutants. Current remediation strategies lack the selectivity needed to effectively eliminate heavy metals. Thus, materials are needed to effectively treat waste streams and contaminated waterways. Sulfur is well known for its ability to selectively bind heavy metals. Additionally, excess sulfur is produced on large scales during petroleum refinement making it inexpensive and abundant. Inverse vulcanization enables surplus sulfur to be repurposed into high sulfur content materials without the need for solvents. These polysulfides have demonstrated many beneficial applications including heavy metal binding. However, they are plagued by low solubility and dominated by hydrophobic monomers. Here, elemental sulfur and charged monomers, including diallyl dimethylammonium chloride (DADMAC), were combined for the first time in a one-step reaction forming water-soluble polysulfides. The water solubility allows for complete interaction of dissolved metal ions with the polymer, rather than surface-level interaction as is the case for traditional inverse vulcanized polymers. Additionally, the charged polysulfides exhibit enhanced solubility in organic solvents, making solution-based characterization such as NMR more accurate. Poly(S-DADMAC) has demonstrated selective binding to gold and silver inducing the formation of a macromolecular complex that precipitates from solution. Additionally, these polymers interact with other heavy metals including lead and copper demonstrating a visible color change at low concentrations that may be used to detect the presence of these metals in wastewater. The low cost, ease of preparation, and scalability make these polysulfides practical as well as functional.

Removal of Mercury from Acidic Solutions of Mercury Chloride by Means of Sorbents Prepared by Catalyzed Vulcanization of Vegetable Oils

Mercury is a metallic element, dangerous and toxic for the environment. Presently, the incineration of municipal solid waste (MSW) belongs to important sources of Hg emissions. Methods of conversion of metallic mercury and mercury compounds from soluble and toxic forms into water insoluble/non-toxic form (HgS) are sought after. Gaseous HCl and a significant part of HgCl2 vapors present in flue gas from incineration of MSW can be removed there by absorption in hot water. Efficiencies of Hg2+ removal from acidic water solutions by means of sorbents prepared by catalyzed reaction of sulfur with vegetable oils (inverse vulcanization) were studied. These kinds of sorbents were tested and found to be exploitable for selective removal of mercury ions from aqueous solutions, particularly from acidic solutions containing HCl at higher temperatures (50–75 °C). Presence of relatively high concentrations of salts of some other metallic elements (Fe, Zn, Ca) had only very small effects on Hg-sorption. Mercury adsorbed on such sorbents converts relatively quickly into a non-toxic form (HgS). Reactive sulfides and SH‑groups present on the surface of the sorbent particles contribute to a faster sorption of mercury and its conversion to HgS. Leaching of zinc from the catalyst (Zn‑diethyldithiocarbamate) present in the vulcanized sorbents is negligible at neutral conditions and small (about 10 %) at acidic conditions (pH = 1.5).

Inverse Vulcanization of Elemental Sulfur with Natural Rosin to Prepare High Sulfur Content Polymers with Excellent Solubility and UV‐Blocking Performance

AbstractInverse vulcanization of cheap elemental sulfur (S) to prepare polymers that simultaneously possess high sulfur content and good solubility is still in its infancy. In this paper, the authors report the synthesis of a novel S‐rosin (Ro) copolymer (Sx‐Ro) based on the inverse vulcanization of S with natural Ro. The sulfur content of Sx‐Ro can be regulated in a wide range, while Sx‐Ro still presents excellent solubility in low boiling point solvents at high sulfur content. Even if the sulfur content in Sx‐Ro is as high as 50%, its solubility in tetrahydrofuran (THF) can still reach 26 mg mL−1. Moreover, the Sx‐Ro exhibits excellent ultraviolet (UV) absorption capability in the entire UV region (200–400 nm) and can be utilized as an effective anti‐UV agent to enhance the UV‐blocking performance of other polymers (e.g., polymethyl methacrylate [PMMA] and polystyrene [PS]) without compromise of transparency and thermal stability. Considering the fine solubility and superior UV‐blocking properties of Sx‐Ro, this work not only provides a versatile and effective anti‐UV material but also opens new opportunities for value‐added utilization of abundant S and Ro resources.

Covalently Grafting Sulfur-Containing Polymers to Carbon Nanotubes Enhances the Electrochemical Performance of Sulfur Cathodes

Lithium–sulfur (Li–S) batteries have attracted extensive attention due to the high theoretical specific capacity of sulfur (1675 mA h g–1). Despite the advantage, the utility of Li–S batteries is limited by the low electrical conductivities of sulfur and its discharge products (i.e., Li2S2 and Li2S) as well as the “shuttle effect” of polysulfides. Herein, a strategy of covalently grafting sulfur-containing polymers to carbon nanotubes (CNTs) is proposed as a solution to the problems associated with sulfur cathodes. The sulfur-containing polymers are grafted to the CNTs using an “inverse vulcanization” method, wherein elemental sulfur is reacted with CNTs that are previously functionalized with isopropenyl groups. A morphological study of the resulting composite indicates that the material maintains the one-dimensional characteristic of CNTs and effectively establishes a porous network via overlap. Such structural features are found to facilitate electron transport in the composite and also suppress the shuttle effect of polysulfides. When compared to cells that are prepared from elemental sulfur, devices that contain the composite show improved specific capacity (i.e., 1368 mA h g–1 at 0.05 C) and a suppressed capacity fading rate (i.e., 0.074% per cycle at 1 C over 500 cycles). In a broader context, covalently attaching sulfur-containing polymers to CNTs provides design criteria for realizing cathode materials that may be employed in high-performance Li–S batteries.

2,5-Diisopropenylthiophene by Suzuki-Miyaura cross-coupling reaction and its exploitation in inverse vulcanization: a case study.

A novel thiophene derivative, namely 2,5-diisopropenylthiophene (DIT) was synthetized by Suzuki–Miyaura cross-coupling reaction (SMCCR). The influence of reaction parameters, such as temperature, solvent, stoichiometry of reagents, role of the base and reaction medium were thoroughly discussed in view of yield optimization and environmental impact minimization. Basic design of experiment (DoE) and multiple linear regression (MLR) modeling methods were used to interpret the obtained results. DIT was then employed as a comonomer in the copolymerization with waste elemental sulfur through a green process, inverse vulcanization (IV), to obtain sulfur-rich polymers named inverse vulcanized polymers (IVPs) possessing high refractive index (n ≈ 1.8). The DIT comonomer was purposely designed to (i) favor the IV process owing to the high reactivity of the isopropenyl functionalities and (ii) enhance the refractive index of the ensuing IVPs owing to the presence of the sulfur atom itself and to the high electronic polarizability of the π-conjugated thiophene ring. A series of random sulfur-r-diisopropenylthiophene (S-r-DIT) copolymers with sulfur content from 50 up to 90 wt% were synthesized by varying the S/DIT feed ratio. Spectroscopic, thermal and optical characterizations of the new IVPs were carried out to assess their main chemical–physical features.

Investigating the viability of sulfur polymers for the fabrication of photoactive, antimicrobial, water repellent coatings.

Elemental sulfur (S8), a by-product of the petroleum refining industries, possesses many favourable properties including photocatalytic activity and antibacterial activity, in addition to being intrinsically hydrophobic. Despite this, there is a relative lack of research employing elemental sulfur and/or sulfur copolymers within superhydrophobic materials design. In this work, we present the use of sulfur copolymers to produce superhydrophobic materials with advanced functionalities. Using inverse vulcanization and the use of a natural organic crosslinker, perillyl alcohol (PER), stable S8-PER copolymers were synthesised and later combined with silica (SiO2) nanoparticles, to achieve highly water repellent composites that displayed both antimicrobial and photocatalytic properties, in the absence of carcinogenic and/or expensive materials. Here, we investigated the antibacterial performance of coatings against the Staphylococcus aureus bacterial strain, where coatings displayed great promise for use in antifouling applications, as they were found to limit surface adhesion by more than 99%, when compared to uncoated glass samples. Furthermore, UV dye degradation tests were performed, utilizing the commercially available dye resazurin, and it was shown that coatings had the potential to simultaneously exhibit surface hydrophobicity and photoactivity, demonstrating a great advancement in the field of superhydrophobic materials.

High strength composites from low-value animal coproducts and industrial waste sulfur.

Herein we report high strength composites prepared by reaction of sulfur, plant oils (either canola oil or sunflower oil) and brown grease. Brown grease is a high-volume, low value animal fat rendering coproduct that represents one of the most underutilized products of agricultural animal processing. Chemically, brown grease is primarily comprised of triglycerides and fatty acids. The inverse vulcanization of the unsaturated units in triglycerides/fatty acids upon their reaction with sulfur yields CanBGx or SunBGx (x = wt% sulfur, varied from 85–90%). These composites were characterized by infrared spectroscopy, dynamic mechanical analysis (DMA), mechanical test stand analysis, elemental analysis, and powder X-ray diffraction. CanBGx and SunBGx composites exhibit impressive compressive strengths (28.7–35.9 MPa) when compared to other materials such as Portland cement, for which a compressive strength of ≥17 MPa is required for residential building. Stress–strain analysis revealed high flexural strengths of 6.5–8.5 MPa for CanBGx and SunBGx composites as well, again exceeding the range of ∼2–5 MPa for ordinary Portland cements. The thermal properties of the composites were assessed by thermogravimetric analysis, revealing decomposition temperatures ranging from 223–226 °C, and by differential scanning calorimetry. These composites represent a promising new application for low value animal coproducts having limited value to be used as organic crosslinkers in the atom-efficient inverse vulcanization process to yield high sulfur-content materials that have impressive mechanical properties.

Incorporation of fillers to modify the mechanical performance of inverse vulcanised polymers

Inverse vulcanisation stabilises polymeric sulfur to synthesise high sulfur content polymers. Inverse vulcanised polymers were reinforced with carbon black, cellulose microfibres and nanoclay to increase tensile strength.