Next Article in Journal
Tourism Development in a Wellbeing Economy
Previous Article in Journal
State-of-the-Art and Practice Review in Concrete Sandwich Wall Panels: Materials, Design, and Construction Methods
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Sustainability
Volume 17
Issue 8
10.3390/su17083702
sustainability-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Upcycled Composite Derived from Polyacrylonitrile and Elemental Sulfur: Thermomechanical Properties and Microstructural Insight

by
Shalini K. Wijeyatunga
and
Rhett C. Smith
*
Department of Chemistry, Clemson University, Clemson, SC 29634, USA
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(8), 3702; https://doi.org/10.3390/su17083702
Submission received: 16 March 2025 / Revised: 9 April 2025 / Accepted: 15 April 2025 / Published: 19 April 2025
(This article belongs to the Section Sustainable Materials)
Browse Figures
Versions Notes

Abstract

:
Herein, a method to upcycle polyacrylonitrile (PAN) into high-sulfur-content materials (HSMs) by reacting 10 wt. % PAN with 90 wt. % elemental sulfur at 220 °C is reported. The resulting composites (PANS90) form glassy solids that display compressive, flexural, and tensile strengths comparable to or exceeding some common construction materials, including C62 brick. Comparison to other plastic-derived HSMs indicates that PANS90 exhibits mechanical properties including compressional strength (11.4 MPa), flexural strength (3.6 MPa) and tensile strength (2.5 MPa) within a similar or slightly improved range. Mechanistic investigations using small-molecule analogs (e.g., adiponitrile) suggest that thiophene ring formation and radical-driven sulfur–carbon bond formation are key reaction pathways, contributing to the composite’s crosslinked microstructure. Preliminary life cycle assessments estimate a global warming potential for PANS90 (0.33 kg CO2e/kg) that is about three times lower than that of Ordinary Portland Cement, underscoring its reduced environmental footprint. Overall, this sulfur-based upcycling strategy addresses two pressing waste-management concerns—surplus sulfur from petroleum refining and unrecycled PAN—while furnishing robust composites suitable for applications ranging from lightweight construction materials to specialty polymer systems.

1. Introduction

Over the past several decades, global plastic manufacturing has risen dramatically, with production totals now surpassing 450 million metric tons (Mt) annually, predominantly encompassing large-scale production of polypropylene, polyethylene, polyethylene terephthalate, and polystyrene [1]. Although polyacrylonitrile (PAN) is generated in comparatively smaller quantities, it serves vital functions in industry—most notably as the principal component in acrylic fibers (representing nearly 90% of PAN usage) and as a precursor for high-strength carbon fibers. Despite its significance, sustainable management of post-consumer PAN remains underdeveloped. This is partly because PAN’s elevated glass transition temperature and strong dipole–dipole interactions of the nitrile moieties make melt-reprocessing challenging. In addition, numerous PAN-containing products (e.g., textiles, industrial tows, coatings) are discarded alongside heterogeneous waste streams, limiting their recovery for downstream recycling operations [2]. Consequently, discarded PAN persists in landfills, where it can degrade into microplastics that exacerbate environmental pollution across both terrestrial and aquatic ecosystems.
Recycling rates for PAN-based materials are remarkably low, with less than 1% of used acrylic fibers or blends receiving a second life via existing recycling pathways [3]. The nitrile group in PAN can produce noxious and toxic byproducts during thermal processing, emphasizing the need for novel upcycling avenues that capture the material’s value without introducing additional health or ecological hazards [4]. Recent endeavors toward more responsible disposal of PAN have included depolymerization into functional intermediates, incorporation into reinforced polymer blends, and carbonization into advanced carbon materials. However, there remains a critical need for processes that combine economic viability with minimal environmental impact.
Simultaneously, petroleum refining generates abundant elemental sulfur—in the order of 80 Mt per year—through desulfurization procedures [5]. Many refining sites struggle with surplus sulfur heaps, which pose significant environmental and safety challenges. This predicament has motivated the search for technologies that transform elemental sulfur into versatile commodities. For example, inverse vulcanization (InV, Scheme 1) [6,7,8,9,10,11,12,13,14,15,16] has emerged as a particularly promising approach: by subjecting sulfur to thermal conditions, sulfur radicals are generated (Scheme 1A) and react with unsaturated bonds (e.g., alkenes), creating crosslinked high-sulfur-content materials (HSMs, Scheme 1B) [7,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38]. These HSMs can possess extraordinary properties, including optical responsiveness [39], mechanical robustness [18,22,29,30,32,40], strong adhesion [19,28,41,42,43], excellent coating properties [44], effective sorbent capabilities [45,46,47,48] and as structural materials to replace mineral cements [49,50,51,52,53,54,55,56].
Although most demonstrations of InV have centered on monomers featuring C=C bonds [23,57,58,59], recent work suggests that sulfur radicals may also engage in reactions with activated carbon sites—even in polymers not traditionally associated with alkene chemistry [60,61]. The ability of thermally generated sulfur radicals to react with a diverse range of functional groups has led to its use in upcycling or thiocracking waste comprised of lignin [62], cellulose [54], poly(ethylene terephthalate) [63], polycarbonate [64], poly(methyl methacrylate) [65] and polystyrene [61]. Polyacrylonitrile, with its nitrile functionalities and potentially radical-reactive sites along its backbone, represents a new candidate for such transformations. Harnessing sulfur’s reactivity to modify or upcycle PAN offers a dual advantage: mitigating environmental burdens from sulfur stockpiles while granting new life to PAN wastes that would otherwise accumulate in landfills. Herein, we investigate how sulfur can be employed to produce novel PAN-based composites under radical-generating conditions, aiming to develop sustainable strategies for managing both sulfur and PAN waste streams.
Herein, the reactions of 90 wt. % S8 with 10 wt. % PAN at 220 °C to give the HSM PANS90 are reported. Spectroscopic and thermal analyses are presented and compared to previously reported HSMs incorporating post-consumer plastic waste. Mechanical properties are analyzed and compared to both HSMs and representative construction materials. Lastly, the sustainability of PANS90 is evaluated against representative construction materials. Reactivity studies on model compounds are also reported, providing insight into the mechanism of reactivity of elemental sulfur and cyanoalkanes as well as the microstructures present in PANS90.

2. Materials and Methods

2.1. Materials

Sulfur (Dugas Diesel, Houma, LA, USA), glutaronitrile (Thermo Scientific, Mumbai, India), succinonitrile (TCI, Portland, OR, USA), adiponitrile (Thermo Scientific, Fair Lawn, NJ, USA), 2-methyloctanenitrile (Enamine, Kyiv, Ukraine), sodium borohydride (Oakwood Chemical, Estill, SC, USA), tetrahydrofuran (Sigma-Aldrich, St. Louis, MO, USA), ethyl acetate (VWR, Delaware, PA, USA), hydrochloric acid (MACRON, Delaware, PA, USA) and dichloromethane (VWR, Ottawa, ON, Canada) were used as received. PAN (Mw = 150,000) was obtained from AmBeed, Arlington Hts, IL, USA and used as received.

2.2. Instrumentation

SEM and EDX were acquired on a Schottky Field Emission Scanning Electron Microscope SU5000 (Hitachi High-Tech, Tokyo, Japan) operating in variable pressure mode with an accelerating voltage of 15 keV.
Thermogravimetric analysis (TGA) data were recorded on a Mettler Toledo TGA 2 STARe system (Mettler Toledo, Columbus, OH, USA) over the range 25 to 800 °C, with a heating rate of 10 °C min–1 under a flow of N2 (20 mL min–1).
DSC data were acquired (Mettler Toledo DSC 3 STARe System, Mettler Toledo, Columbus, OH, USA) over a temperature range from −60 to 140 °C with a heating rate of 10 °C·min–1 under a flow of N2 (200 mL·min–1). Each DSC measurement was carried out over three heat–cool cycles.The GC-MS was carried out on a Shimadzu QP2010SE system (Shimadzu U.S.A. Manufacturing, Inc., Canby, OR, USA)with an auto-injector (AOC-20i) equipped with a mass selective detector, with an interface temperature of 250 °C, a solvent cut time of 3.50 min, threshold of 70 eV and mass range of 45 to 900 m/z. Compounds were separated using a SH-Rxi-5 MS capillary column (Restek Company, Bellefonte, PA, USA: crossbond 5% diphenyl/ 95% dimethyl polysiloxane) with dimensions of 30 m (length) × 0.25 mm (diameter) × 0.25 μm (film thickness). Samples were analyzed using one of the following methods. For Method 1, the temperature of the injector was initialized to 280 °C. The temperature was programmed to 40 °C for 1 min, then from 40 °C to 320 °C at a rate of 20 °C/min, and then held at 320 °C for 5 min. For Method 2, the temperature of the injector was initialized to 180 °C. The temperature was programmed to 40 °C for 1 min, then from 40 °C to 180 °C at a rate of 10 °C/min, and then held at 180 °C for 10 min.
UV–vis data were collected on an Agilent Technologies Cary 60 UV-Vis (Agilent Technologies, Inc., Santa Clara, CA, USA) using Simple Reads software (Version 5.0.0.999) over the range of 200–800 nm, with the dark sulfur content being reported at 275 nm.
Mechanical testing was performed in accordance with modified ASTM standards: compressive testing followed a protocol adapted from ASTM D695 [66], tensile testing from ASTM D638 [67] (dog bone geometry), and flexural testing from ASTM D790 [68] (single cantilever mode).
Compressional and tensile analyses were performed on a Mark-10 ES30 (Mark-10 Corporation, Copiague, NY, USA) test stand equipped with a M3-200 force gauge (1 kN maximum force with ±1 N resolution) with an applied force rate of 3–4 N·s–1. Compression cylinders were cast from silicone resin molds (Smooth-On Oomoo® 25 tin-cure, Oomoo Corp., Richmond, BC, Canada) with diameters of approximately 6 mm and heights of approximately 10 mm. Samples were manually sanded to ensure uniform dimensions and measured with a digital caliper with ±0.01 mm resolution. Compressional and tensile analyses were performed in triplicate for each composite, and the results were averaged.
Flexural strength analysis was performed using a Mettler Toledo DMA 1 STARe System (Mettler Toledo, Columbus, OH, USA) in single cantilever mode. The samples were cast from silicone resin molds (Smooth-On Oomoo® 25 tin-cure, Oomoo Corp., Richmond, BC, Canada). The sample dimensions were approximately 1.5 × 10 × 18 mm. Flexural analysis was performed in triplicate and the results were averaged. The clamping force was 1 cN·m.
CAUTION: Heating elemental sulfur with organics can result in the formation of H2S or other gases. Such gases can be toxic, foul-smelling, and corrosive. Temperature must be carefully controlled to prevent thermal spikes, contributing to the potential for H2S or other gas evolution. Rapid stirring shortened heating times, and very slow addition of reagents can help avoid unforeseen temperature spikes. Reactions should be conducted in a well-ventilated fume hood equipped with H2S and SO2 sensors or scrubbers to ensure operator safety.

2.3. PANS90

Elemental sulfur (36.0 g, 1.12 mol) was introduced into a round bottom flask with a magnetic stir bar. First, sulfur was melted in an oil bath at 180 ± 2 °C. Then, PAN (4.04 g, 76.1 mmol of repeat unit) was added to the molten sulfur in the round bottom flask while stirring. After PAN addition, a reflux condenser was connected to the round bottom flask and purged with nitrogen. The temperature was gradually increased from 180 °C to 220 °C. The reaction mixture was stirred for an additional 24 h at 220 °C after PAN addition. The reaction mixture became black over the course of heating. After cooling to room temperature, the product was isolated as a black solid (38.0 g, 94.8% yield). Elemental analysis calculated: C,6.78; H, 0.57; N, 2.65; S, 90.00%. Found: C, 9.49; H, 0.51; N, 2.99; S, 87.07%. (Atlantic Microlab, Inc., Norcross, GA, USA).

2.4. General Procedure for 8 h Reaction of Model Compounds

The indicated model compounds were combined with sulfur in a 2:1 sulfur-to-organic mass ratio with magnetic stir bars in three separate round-bottom flasks. Reflux condensers with interconnected tubing were attached, and the setups were purged with nitrogen. The oil bath temperature was gradually increased to 220 °C and maintained at that temperature for 8 h. After cooling to room temperature, the crude solid was recovered and partially dissolved in 4.0 mL dichloromethane.
  • Glutaronitrile–Sulfur
Prepared according to the general procedure using glutaronitrile (0.167 g, 1.77 mmol) and sulfur (0.333 g, 10.4 mmol) to give 0.500 g of the title compound (100%).
  • Succinonitrile–Sulfur
Prepared according to the general procedure using succinonitrile (0.167 g, 2.08 mmol) and sulfur (0.333 g, 10.4 mmol) to give 0.500 g of the title compound (100%).
  • Adiponitrile–Sulfur
Prepared according to the general procedure using adiponitrile (0.169 g, 1.56 mmol) and sulfur (0.333 g, 10.4 mmol) to give 0.500 g of the title compound (100%).
  • 2–Methyloctanenitrile–Sulfur
Prepared according to a modification of the general procedure as follows. In a reaction vial, 2–methyloctanenitrile (0.0482 g, 0.346 mmol) and sulfur (0.0963 g, 3.00 mmol) were combined in a 2:1 sulfur-to-organic mass ratio with a magnetic stir bar to give 0.144 g of title compound (100%). A reflux condenser was attached, and the setup was purged with nitrogen. The oil bath temperature was gradually increased to 220 °C and maintained at that temperature for 8 h. After cooling to room temperature, the crude solid was recovered and partially dissolved in 4.0 mL dichloromethane.

2.5. Procedure for 4 h Reaction of Model Compounds

In three separate round-bottom flasks, the indicated model compounds were combined with sulfur in a 2:1 sulfur-to-organic mass ratio with magnetic stir bars. Reflux condensers with interconnected tubing were attached, and the setups were purged with nitrogen. The oil bath temperature was gradually increased to 220 °C and maintained at that temperature for 4 h. After cooling to room temperature, the crude solid was recovered and partially dissolved in 4.0 mL dichloromethane. To the final products in the round-bottom flasks, 12.0 mL of dichloromethane was added. The flasks were then sonicated for 5 min at room temperature with dichloromethane. The dichloromethane was removed using a Pasteur pipette, and the insoluble solid was air-dried in a watch glass and used directly in reaction with NaBH4 as outlined below.
  • Glutaronitrile–Sulfur
Prepared according to the general procedure using glutaronitrile (1.67 g, 17.7 mmol) and sulfur (3.33 g, 104 mmol) to give 5.00 g of title compound (100%).
  • Succinonitrile–Sulfur
Prepared according to the general procedure using succinonitrile (1.67 g, 20.8 mmol) and sulfur (3.34 g, 104 mmol) to give 5.01 g of title compound (100%).
  • Adiponitrile–Sulfur
Prepared according to the general procedure using adiponitrile (1.67 g, 15.4 mmol) and sulfur (3.34 g, 104 mmol) to give 5.01 g of title compound (100%).

2.6. Procedure for Reaction of Model Compound/Sulfur Products with NaBH4

This was an adaptation of the reported procedure [69]. To a solution of the model compound–sulfur (0.383 g) in 9.0 mL tetrahydrofuran at 0 °C, a solution of NaBH4 (0.133 g) in water (1.00 mL) was added dropwise. The reaction mixture was stirred at room temperature for 24 h. Approximately 1.00 mL of the sample was taken, and diluted with 9.0 mL of distilled water. About 0.1 mL of 5% (v/v) HCl was added gradually while monitoring the pH until it reached 5. The solution was then transferred to a separatory funnel and 10.0 mL of ethyl acetate was added. The ethyl acetate layer was collected after separation. The extraction was repeated with an additional 10.0 mL of ethyl acetate and the combined ethyl acetate layers were filtered using vacuum filtration. The collected filtrate was evaporated at 60 °C.

3. Results and Discussion

3.1. Preparation and Compositional Characterization of Composite from PAN

The reaction of PAN (10 wt. %) with sulfur (90 wt. %) was performed at 220 °C, affording the HSM PANS90 as a glassy black solid (Figure 1). The 10:90 PAN-to-sulfur ratio was selected based on preliminary trials and extensive data in the literature on other plastic-derived HSMs (vide infra), which have largely used this ratio. Higher organic content resulted in incomplete mixing and reduced processability due to elevated melt viscosity. The reaction led to detectable mass loss (5%) due to the loss of volatiles (see mechanistic discussion), as observed in some HSM preparations [9,70].
Scanning electron microscopy with energy dispersive X-ray analysis (SEM–EDX) was used to assess the microscopic structure and homogeneity of PANS90. The images in Figure 2 demonstrate that the absence of sulfur in the sulfur map corresponds to regions with a higher abundance of carbon. This observation suggests a spatial separation between sulfur-rich and organic-rich domains at this length scale.
Sulfur atoms within high-sulfur-content materials (HSMs) can take several distinct forms: (a) oligo/polysulfide chains covalently bonded to organic moieties (via C–S bonds), (b) crystalline sulfur incorporated non-covalently into the HSM matrix, or (c) amorphous oligo/polysulfur domains without C–S bonds that are merely physically entrapped in the network [71,72]. While both covalently attached oligo/polysulfur chains and crystalline sulfur are detectable by differential scanning calorimetry (DSC), amorphous sulfur species are not. These amorphous species also evade detection by IR or NMR spectroscopy and, as such, have been termed “dark sulfur” [71,72]. Despite lacking direct covalent attachments to the HSM framework, dark sulfur can substantially affect the thermomechanical behavior of the material.
Fortunately, dark sulfur content can be quantified through UV–visible spectroscopy by extracting the dark sulfur into an organic solvent and measuring its concentration at 275 nm [72]. From this concentration and the total volume of the extract, the mass of dark sulfur removed from each HSM can be determined. Dividing this mass by the original mass of the HSM yields the relative weight percentage of dark sulfur present in the material.
This approach revealed that PANS90 has a dark sulfur content of 30 wt. % (Table 1), a value consistent with those of HSMs made from recycled plastics [64,65,73] or small-molecular olefins [72,74,75].

3.2. Thermal and Mechanical Properties of PANS90

A 5% mass loss (Td,5%) for PAN was observed at 305 °C, which is attributed to the loss of ammonia and hydrogen cyanide after the complete cyclization [4]. However, the thermogravimetric analysis (TGA) of PANS90 (Figure S1) revealed a Td,5% value of 209 °C, indicating mass loss due to sulfur sublimation. This value is slightly lower than the Td,5% value of 229 °C reported for cyclo-S8. The initial study of PAN revealed a glass transition at 98 °C, which is consistent with literature-reported values for the glass transition of PAN, typically ranging from 90 to 150 °C [76]. Differential scanning calorimetry (DSC) showed a melting temperature for PANS90 (Tm =119 °C) (Figure S2) that compares favorably with that of pure S8 (Tm = 118 °C). Less than 0.1 wt. % water absorption was measured for PANS90, consistent with the highly hydrophobic nature of the polysulfur chains, which are the major component of the HSM composite. Extractable sulfur, quantified at 30 wt. %, may volatilize or leach under elevated temperature or solvent exposure. However, the composite’s hydrophobic nature and low water absorption (<0.1 wt. %) and thermal stability up to 209 °C suggest limited risk under ambient or moderate environmental conditions. Long-term leaching studies under accelerated aging conditions are planned to fully assess environmental safety.
Samples of PANS90 were remeltable, allowing them to be poured into molds to cast shapes required for compressional, flexural, and tensile strength measurements (Figure 1; stress–strain plots are provided as Figures S3–S5). Table 2 summarizes these mechanical tests from three independently prepared samples for each test, with standard deviations provided.
Cylinders were made to evaluate compressive strength (Table 2; Figure S3 of the SI presents a stress–strain plot). The compressive strength of PANS90 was comparable to that of SPC90 (made from 90 wt. % sulfur 10 wt. % Poly(bisphenol A carbonate), compressive strength = 12.8 MPa) [64], as the values were statistically identical. PANS90 exhibited lower compressive strength than mPES (made from 90 wt. % sulfur and 10 wt. % esterified PET, compressive strength = 26.9 MPa) [63] and PGMA–S (made from 90 wt. % sulfur and 10 wt. % geranyl-derivatized PMMA, compressive strength = 17.5 MPa) [65]. In contrast, PANS90 demonstrated higher compressive strength than PSP90 (made from 90 wt. % sulfur and 10 wt. % polystyrene packaging material particulate, compressive strength = 9.8 MPa) [61]. All materials are previously reported HSMs containing other plastic wastes.
In addition, flexural strength was measured using rectangular prisms of PANS90 in single cantilever mode at room temperature (Table 2; Figure S4 of the SI presents a stress–strain plot). The flexural strength of PANS90 (flexural strength = 3.6 MPa) falls within the mid-range compared to previously reported HSMs. The flexural strengths of mPES (flexural strength = 7.7 MPa) and PGMA–S (flexural strength = 4.8 MPa) exceed that of PANS90, while PANS90 exhibits a flexural strength comparable to SPC90 (flexural strength = 3.1 MPa) as the values were statistically identical. In contrast, PSP90 (flexural strength = 2.4 MPa) demonstrates lower flexural strength than PANS90.
Tensile strength analysis of PANS90 was conducted using dog bone specimens, revealing an ultimate tensile strength (UTS) of 2.5 MPa and an elongation at break of 11.5% (Table 2; Figure S5 of the SI presents a stress–strain plot). Previously reported HSMs derived from plastic waste, such as PGMA–S (Tensile strength = 3.9 MPa), exhibited higher UTS compared to PANS90, while PSP90 (Tensile strength = 2.0 MPa) and mPES (tensile strength = 0.2 MPa) demonstrated lower UTS values.
The mechanical strength of PANS90 is also competitive with that of some mineral-based structural products. Ordinary Portland Cement (OPC) displays a higher compressive strength (17 MPa) than PANS90 and the flexural strength of OPC (3.7 MPa) is comparable to that of PANS90 (3.6 MPa). Moreover, the compressive strength of PANS90 exceeds that of C62 Brick, a common structural masonry material with a compressive strength of 8.6 MPa. These findings underscore the possibility of employing PANS90 prepared from post-consumer polyacrylonitrile and sulfur as a byproduct of fossil fuel refining as sustainable alternatives to certain conventional building materials.

3.3. Preliminary Environmental Impact Estimates

The preparation of PANS90 employs only PAN and elemental sulfur, providing a simple and low-cost approach to recycling PAN with 95% atom economy and an E factor of 0.05. The E factor is a tool for assessing the efficiency and sustainability of a chemical process by determining the amount of waste generated per unit of the desired product obtained [77,78,79]. The favorable atom economy and E factor, however, do not comprehensively inform on the energy expenditures that also impact the sustainability of a product [78,80,81,82]. The global warming potential (GWP), defined as kilograms of CO2 emitted per kilogram of material produced (expressed as kg CO2e/kg), is a useful metric for discussing sustainability that includes estimates of energy required [83,84,85,86]. To assess the GWP for PANS90, it is necessary to consider the GWP of PAN (~5.4 kg CO2e/kg) [87], energy needed to grind the PAN (estimated to be the same as for PET, reported as 0.092 kg CO2e/kg) [88,89,90,91,92,93], and the energy requirements for heating the reaction mixture from 20 °C to 220 °C followed by holding constant temperature for 24 h. To estimate this energy, metrics for sulfur, which makes up 90 wt. % of the mixture, were used here. A value of 0.025 kg CO2e/kg for the heating process was calculated using the heat capacity and heat of fusion of sulfur [94] assuming 90% heat retention efficiency and 0.50 kg CO2e/kWh for electricity generation, as previously reported [61]. It is also assumed that polyacrylonitrile would be incinerated if not used to make PANS90, a process that would produce 2.48 kg CO2e/kg PAN. Calculations based on these assumptions (summarized in Table 3) indicate that the overall process, while slightly carbon positive, is about three times lower than that of mineral products like Ordinary Portland Cement, which has a GWP of ~1.0 kg CO2e/kg [95,96].
Industrial-scale validation of the reported GWP (0.33 kg CO2e/kg) will require pilot plant data encompassing batch energy usage; solvent recovery rates; and material handling logistics. Co-location of PAN and sulfur waste sources could significantly reduce transportation-related emissions, while integration with existing waste valorization infrastructures may further enhance sustainability.

3.4. Microstructural Insight from Model Studies

Determining the microstructural features of PANS90 using solution-phase analytical methods was hindered by the insolubility of this highly crosslinked material. Several small-molecule models—glutaronitrile, succinonitrile, adiponitrile, and 2-methyloctanenitrile—were selected for assessing how structural motifs present in PAN react with elemental sulfur (Figure 3). These small-molecule models were selected to model the reactivity of majority chain constituents resulting from head-to-tail monomer coupling (glutaronitrile), minor contributors resulting from defects such as head-to-head (succinonitrile) or tail-to-tail (adiponitrile) monomer coupling, and for the potential for reactivity between a nitrile-bearing site and more remote chain sites (2-methyloctanenitrile). Even though tail-to-tail or head-to-head linkages in PAN are minor, the formation of aromatic or fused thiophene structures (vide infra) may still be important for ultimate crosslinking and property development. Following an adaptation of mechanistic model studies reported by Pyun [13], each model compound was reacted with elemental sulfur in a 2:1 sulfur: organic mass ratio at 220 °C with mechanical stirring for 4–8 h. A portion of each reaction mixture was extracted with dichloromethane and the soluble molecules were analyzed by GC-MS. Another portion of each reaction mixture was reduced with NaBH4, which cleaves S–S bonds, while C–S units are left intact, [69] thus removing oligo/polysulfur crosslinks and providing additional soluble species for analysis by GC-MS (Figures S6–S17 and Scheme 2). In addition to any sulfur-specific reactivity that may be taking place, PAN is known to undergo radical-mediated thermal decomposition to form extended networks comprising pyridine rings (Scheme 3) [4]. This pathway would also be expected to occur in the presence of sulfur at elevated temperatures due to sulfur-centered radicals. The 1H NMR spectrum of the product obtained from the insoluble fraction after the reaction of succinonitrile with elemental sulfur at 220 °C for 4 h, followed by NaBH4 treatment, showed no peaks (Figure S18) corresponding to aromatic species. In contrast, the product obtained from adiponitrile under identical conditions displayed peaks at 7.0 ppm and 8.1 ppm (Figure S19). Similarly, the product from glutaronitrile under the same conditions exhibited peaks at 7.0 ppm, 7.1 ppm, and 8.2 ppm (Figure S20). In each case, the insoluble fraction was isolated after removing the soluble portion via dichloromethane extraction before NaBH4 treatment. These results were consistent with the structures elucidated from GC-MS analysis for succinonitrile–sulfur, adiponitrile–sulfur and glutaronitrile–sulfur.
Several S–C bond-forming reactions, including the formation of thiophene rings, were observed in GC-MS analyses of model compound reaction mixtures (Scheme 2). Several reactivity pathways consistent with established reactions of elemental sulfur [60,61,97,98,99,100] with small molecules were deduced based on the compounds observed by GC-MS analysis. Succinonitrile (Scheme 2A) undergoes H-atom abstraction from the nitrile a-carbon followed by reaction with a polysulfur chain that leads to Motif A, which, under thermal conditions, could lead to thiol 1,as observed by GC-MS. Thiol 1 could also form by conversion of the initially formed radical to the olefin, followed by olefin addition, analogous to the pathway reported for reactions of benzylic radicals with elemental sulfur under the same reaction conditions used here [61].
Adiponitrile undergoes a more complex series of reactions (Scheme 2B), ultimately leading to the observation of thiophene derivative 2, corresponding to Motif B if analogous segments of PAN undergo reaction via this pathway. The cyclization and aromatization steps involved here are analogous to the Gewald reaction, but mediated by radicals rather than the anions involved in the Gewald mechanism [97]. A similar radical-mediated pathway to thiophene formation has also been reported by Lai et al. [60] from the reaction of 1,3,5-triisopropylbenzene with elemental sulfur, and by our group from the reaction of cumene or 2,4-diphenylpentane with elemental sulfur. The final step leading to 2 is deamination mediated by concomitant protonation by an H–S moiety, analogous to deamination by H–Br, which occurs even at 50 °C, a considerably lower temperature than the 220 °C temperature used in the current study [101]. The observation of 2 as the primary product is driven by the irreversible loss of ammonia and the formation of aromatic species.
Although the reaction of adiponitrile with elemental sulfur in Scheme 2B only models the reactivity of the minor (<3%) tail-to-tail segments in the PAN backbone, formation of thiophene and even thieno [3,2-b]thiophene moieties is observed in reactions of 2-methyloctanenitrile with elemental sulfur (Scheme 2C). The reaction of elemental sulfur with 2-methyloctanenitrile models shows how activation of reactive nitrile and α-carbon sites by sulfur radicals leads to a reaction with more distal segments of the polymer backbone in PAN. Scheme 2C shows a proposed pathway to thiophene derivative 3, observed by GC-MS, that relies on established H-atom transfer, olefin formation, S-chain transfer, and olefin addition steps [61,98,99]. The corresponding reactivity of the PAN backbone would lead to Motif C in PANS90. A second pathway occurs when initially formed 2-methyl-2-octenenitrile undergoes olefin addition rather than H-atom transfer. Once olefin addition occurs, initial cyclization to form a thiophene ring positions the remaining carbon skeleton for ring fusion, leading to the formation of thieno [3,2-b]thiophene derivative 4, as observed by GC-MS. This reactivity would manifest as Motif D when this reactivity takes place along the PAN backbone, in which case the thieno [3,2-b]thiophene moiety could contain corresponding nitrile moieties from the polymer side chains.
Reaction of glutaronitrile (Scheme 2D) results in the formation of thiophene-bearing 5, observed by GC-MS and formed via pathways analogous to those illustrated in Scheme 2B,C. Additionally, the formation of thione 6 is observed by GC-MS. Formation of the thione at the nitrile a-carbon is easily envisioned via a Willgerodt–Kindler-type mechanism (formation of thione at an iminium a-carbon) [100]. It should be noted that the formation of thiones by this pathway requires the removal of two protons on the a-carbon, whereas the a-carbons in PAN have only one proton, so this is not likely to contribute to the microstructure in PANS90 except possibly at the chain ends.
Taken together, the model studies illustrated in Scheme 2 and Scheme 3 reveal that PANS90 likely exhibits S–C crosslinks that can form between elemental sulfur and PAN backbone carbons, thiophene rings can form involving both backbone and nitrile carbon atoms, resultant thiophene rings can fuse to form thieno [3,2-b]thiophene moieties. Because the PANS90 matrix is highly crosslinked and largely insoluble, GC-MS analysis of model compounds serves as the most effective probe of species formed in this complex mixture. It is noteworthy, however, that GC-MS cannot detect non-volatile intermediates or large oligomeric species. The data from this technique are most useful in assessing the types of C–S bonds formed under these conditions.

4. Conclusions

This work demonstrates a promising strategy for converting polyacrylonitrile (PAN), a major constituent of acrylic fibers, into robust sulfur-rich composites via reaction with elemental sulfur at elevated temperatures. By incorporating 10 wt. % of PAN and 90 wt. % sulfur, the resulting material (PANS90) achieves compressive, flexural, and tensile strengths that match or exceed those of certain commonly used construction materials such as C62 brick. The global warming potential (GWP) analysis also suggests a favorable carbon footprint relative to Ordinary Portland Cement. Such an outcome highlights the potential for using sulfur-derived composites to mitigate both plastic waste and surplus elemental sulfur generated during petroleum refining.
Model studies using small-molecule analogs provide mechanistic support for the formation of thiophene-based linkages and other sulfur–carbon crosslinks, thus offering valuable clues about the microstructure of PANS90.
Despite these encouraging outcomes, several limitations merit consideration. First, while the method of generating PANS90 is straightforward and potentially scalable, controlling the precise extent of crosslinking remains challenging, given the reactive and radical-based nature of sulfur chemistry. Significant amounts of dark sulfur indicate that some fraction of sulfur remains only physically entrapped, potentially leading to material heterogeneities. More detailed life cycle assessment studies would also be necessary to confirm initial GWP estimates on a large industrial scale. Overall, these results establish a foundation for sustainable PAN–sulfur upcycling and encourage future efforts to refine, diversify, and scale up this approach for managing two critical industrial wastes.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/su17083702/s1: Figure S1: Mass loss curve from thermogravimetric analysis for PANS90. Figure S2: Differential scanning calorimetry (DSC) traces for PANS90. Figure S3: Stress–strain plot for compressive strength analysis of PANS90. Figure S4: Stress–strain plot for flexural strength analysis of PANS90. The trendline is a propagation of the linear region of the curve from initial reversible deformation and is used to calculate the modulus. Figure S5: Stress–strain plot for tensile strength analysis of PANS90. Figure S6: The zoomed-in GC trace for the product obtained after the final reaction mixture from succinonitrile and elemental sulfur (2:1 sulfur: organic mass ratio), heated at 220 °C for 8 h, extracted with dichloromethane (GC-MS Method 1). Figure S7: Mass spectrum of (GC-MS)1 corresponding to the retention time (10.989 min) for peak labelled 1 in the GC trace shown in Figure S6. Figure S8: The zoomed-in GC trace for the product obtained after the final reaction mixture from adiponitrile and elemental sulfur (2:1 sulfur: organic mass ratio), heated at 220 °C for 4 h, extracted with dichloromethane (GC-MS Method 2). Figure S9: Mass spectrum of (GC-MS)2 corresponding to the retention time (8.871 min) for peak labelled 2 in the GC trace shown in Figure S8. Figure S10: The zoomed-in GC trace for the products obtained after the final reaction mixture from 2-methyloctanenitrile and elemental sulfur (2:1 sulfur: organic mass ratio), heated at 220 °C for 8 h, extracted with dichloromethane (GC-MS Method 1). Figure S11: Mass spectrum of (GC-MS)3 corresponding to the retention time (8.276 min) for peak labelled 3 in the GC trace shown in Figure S10. Figure S12: Mass spectrum of (GC-MS)4 corresponding to the retention time (10.536 min) for peak labelled 4 in the GC trace shown in Figure S10. Figure S13: The zoomed-in GC trace for the products obtained after the final reaction mixture from glutaronitrile and elemental sulfur (2:1 sulfur: organic mass ratio), heated at 220 °C for 8 h, extracted with dichloromethane (GC-MS Method 1). Figure S14: Mass spectrum of (GC-MS)6 corresponding to the retention time (8.854 min) for peak labelled 6 in the GC trace shown in Figure S13. Figure S15: Mass spectrum of (GC-MS)5 corresponding to the retention time (13.338 min) for peak labelled 5 in the GC trace shown in Figure S13. Figure S16: The zoomed-in GC trace of the products obtained from the remaining insoluble fraction after the soluble portion was removed by dichloromethane extraction of the final reaction mixture from glutaronitrile and elemental sulfur (2:1 sulfur-to-organic mass ratio) heated at 220 °C for 4 h, followed by reaction with NaBH4 (GC-MS Method 2). Figure S17: Mass spectrum of (GC-MS)7 corresponding to the retention time (10.850 min) for peak labelled 7 in the GC trace shown in Figure S16. Figure S18: The zoomed-in proton nuclear magnetic resonance (NMR) (300 MHz, CDCl3) of the product obtained from the remaining insoluble fraction after the soluble portion was removed by dichloromethane extraction of the final reaction mixture from succinonitrile and elemental sulfur (2:1 sulfur-to-organic mass ratio) heated at 220 °C for 4 h, followed by reaction with NaBH4. Figure S19: The zoomed-in proton nuclear magnetic resonance (NMR) (300 MHz, CDCl3) of the product obtained from the remaining insoluble fraction after the soluble portion was removed by dichloromethane extraction of the final reaction mixture from adiponitrile and elemental sulfur (2:1 sulfur-to-organic mass ratio) heated at 220 °C for 4 h, followed by reaction with NaBH4. Figure S20: The zoomed-in proton nuclear magnetic resonance (NMR) (300 MHz, CDCl3) of the product obtained from the remaining insoluble fraction after the soluble portion was removed by dichloromethane extraction of the final reaction mixture from glutaronitrile and elemental sulfur (2:1 sulfur-to-organic mass ratio) heated at 220 °C for 4 h, followed by reaction with NaBH4.

Author Contributions

Conceptualization, R.C.S.; methodology, R.C.S.; formal analysis, S.K.W.; investigation, S.K.W.; resources, R.C.S.; data curation, S.K.W.; writing—original draft preparation, all authors; writing—review and editing, all authors; supervision, R.C.S.; funding acquisition, R.C.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research is funded by the National Science Foundation grant number CHE-2203669 awarded to RCS.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are provided in the Supplementary Materials file or can be requested from the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
PANPolyacrylonitrile
HSMHigh-sulfur-content material
PANS90Composite made from 90 wt. % sulfur and 10 wt. % PAN
InVInverse vulcanization
SEM–EDXScanning electron microscopy with energy dispersive X-ray analysis
DSCDifferential scanning calorimetry
PSP90Composite made from 90 wt. % sulfur and 10 wt. % polystyrene packaging material particulate
mPESComposite made from 90 wt. % sulfur and 10 wt. % esterified PET
PGMA–SComposite made from 90 wt. % sulfur and 10 wt. % geraniol-transesterified PMMA
SPC90Composite made from 90 wt.% sulfur 10 wt. % poly(bisphenol A carbonate).
TGAThermogravimetric analysis
GWPGlobal warming potential

References

  1. Geyer, R. Production, use, and fate of synthetic polymers. In Plastic Waste and Recycling; Letcher, T.M., Ed.; Academic Press: New York, NY, USA, 2020; pp. 13–32. [Google Scholar]
  2. Patti, A.; Cicala, G.; Acierno, D. Eco-sustainability of the textile production: Waste recovery and current recycling in the composites world. Polymers 2021, 13, 134. [Google Scholar] [CrossRef] [PubMed]
  3. Athanasopoulos, P.; Zabaniotou, A. Post-consumer textile thermochemical recycling to fuels and biocarbon: A critical review. Sci. Total Environ. 2022, 834, 155387. [Google Scholar] [CrossRef] [PubMed]
  4. Xue, T.J.; McKinney, M.A.; Wilkie, C.A. The thermal degradation of polyacrylonitrile. Polym. Degrad. Stab. 1997, 58, 193–202. [Google Scholar] [CrossRef]
  5. Harpp, D.N.; Smith, R.A. Organic sulfur chemistry. 42. Sulfur-sulfur bond cleavage processes. Selective desulfurization of trisulfides. J. Am. Chem. Soc. 1982, 104, 6045–6053. [Google Scholar] [CrossRef]
  6. Marshall, C.M.; Molineux, J.; Kang, K.-S.; Kumirov, V.; Kim, K.-J.; Norwood, R.A.; Njardarson, J.T.; Pyun, J. Synthesis of Polycyclic Olefinic Monomers from Norbornadiene for Inverse Vulcanization: Structural and Mechanistic Consequences. J. Am. Chem. Soc. 2024, 146, 24061–24074. [Google Scholar] [CrossRef]
  7. Orme, K.; Fistrovich, A.H.; Jenkins, C.L. Tailoring Polysulfide Properties through Variations of Inverse Vulcanization. Macromolecules 2020, 53, 9353–9361. [Google Scholar] [CrossRef]
  8. Wickramasingha, Y.A.; Stojcevski, F.; Eyckens, D.J.; Hayne, D.J.; Chalker, J.M.; Henderson, L.C. Exploring Inverse Vulcanized Dicyclopentadiene As a Polymer Matrix for Carbon Fiber Composites. Macromol. Mater. Eng. 2024, 309, 2300298. [Google Scholar] [CrossRef]
  9. Wu, X.; Smith, J.A.; Petcher, S.; Zhang, B.; Parker, D.J.; Griffin, J.M.; Hasell, T. Catalytic inverse vulcanization. Nat. Commun. 2019, 10, 647. [Google Scholar] [CrossRef]
  10. Molineux, J.; Lee, T.; Kim, K.J.; Kang, K.-S.; Lyons, N.P.; Nishant, A.; Kleine, T.S.; Durfee, S.W.; Pyun, J.; Norwood, R.A. Fabrication of Plastic Optics from Chalcogenide Hybrid Inorganic/Organic Polymers for Infrared Thermal Imaging. Adv. Opt. Mater. 2024, 12, 2301971. [Google Scholar] [CrossRef]
  11. Qureshi, M.H.; Bao, J.; Kleine, T.S.; Kim, K.-J.; Carothers, K.J.; Molineux, J.; Cho, E.; Kang, K.-S.; Godman, N.P.; Coropceanu, V.; et al. Synthesis of Deuterated and Sulfurated Polymers by Inverse Vulcanization: Engineering Infrared Transparency via Deuteration. J. Am. Chem. Soc. 2023, 145, 27821–27829. [Google Scholar] [CrossRef]
  12. Bischoff, D.J.; Lee, T.; Kang, K.-S.; Molineux, J.; O’Neil Parker, W., Jr.; Pyun, J.; Mackay, M.E. Unraveling the rheology of inverse vulcanized polymers. Nat. Commun. 2023, 14, 7553. [Google Scholar] [CrossRef] [PubMed]
  13. Bao, J.; Martin, K.P.; Cho, E.; Kang, K.-S.; Glass, R.S.; Coropceanu, V.; Bredas, J.-L.; Parker, W.O.N., Jr.; Njardarson, J.T.; Pyun, J. On the Mechanism of the Inverse Vulcanization of Elemental Sulfur: Structural Characterization of Poly(sulfur-random-(1,3-diisopropenylbenzene)). J. Am. Chem. Soc. 2023, 145, 12386–12397. [Google Scholar] [CrossRef] [PubMed]
  14. Lee, T.; Dirlam, P.T.; Njardarson, J.T.; Glass, R.S.; Pyun, J. Polymerizations with Elemental Sulfur: From Petroleum Refining to Polymeric Materials. J. Am. Chem. Soc. 2022, 144, 5–22. [Google Scholar] [CrossRef] [PubMed]
  15. Kang, K.-S.; Iyer, K.A.; Pyun, J. On the Fundamental Polymer Chemistry of Inverse Vulcanization for Statistical and Segmented Copolymers from Elemental Sulfur. Chem.-A Eur. J. 2022, 28, e202200115. [Google Scholar] [CrossRef]
  16. Lim, J.; Pyun, J.; Char, K. Recent Approaches for the Direct Use of Elemental Sulfur in the Synthesis and Processing of Advanced Materials. Angew. Chem. Int. Ed. 2015, 54, 3249–3258. [Google Scholar] [CrossRef]
  17. Eder, M.L.; Call, C.B.; Jenkins, C.L. Utilizing Reclaimed Petroleum Waste to Synthesize Water-Soluble Polysulfides for Selective Heavy Metal Binding and Detection. ACS Appl. Polym. Mater. 2022, 4, 1110–1116. [Google Scholar] [CrossRef]
  18. Smith, J.A.; Green, S.J.; Petcher, S.; Parker, D.J.; Zhang, B.; Worthington, M.J.H.; Wu, X.; Kelly, C.A.; Baker, T.; Gibson, C.T.; et al. Crosslinker Copolymerization for Property Control in Inverse Vulcanization. Chem.-A Eur. J. 2019, 25, 10433–10440. [Google Scholar] [CrossRef]
  19. Herrera, C.; Ysinga, K.J.; Jenkins, C.L. Polysulfides Synthesized from Renewable Garlic Components and Repurposed Sulfur Form Environmentally Friendly Adhesives. ACS Appl. Mater. Interfaces 2019, 11, 35312–35318. [Google Scholar] [CrossRef]
  20. Westerman, C.R.; Jenkins, C.L. Dynamic Sulfur Bonds Initiate Polymerization of Vinyl and Allyl Ethers at Mild Temperatures. Macromolecules 2018, 51, 7233–7238. [Google Scholar] [CrossRef]
  21. Newman, B.; Doeven, E.H.; Francis, P.S.; Stojcevski, F.; Hayne, D.J.; Chalker, J.M.; Henderson, L.C. A high value application of reclaimed carbon fibers: Environmental remediation and redeployment in structural composites. Sustain. Mater. Technol. 2023, 35, e00546. [Google Scholar] [CrossRef]
  22. Yan, P.; Zhao, W.; Tonkin, S.J.; Chalker, J.M.; Schiller, T.L.; Hasell, T. Stretchable and Durable Inverse Vulcanized Polymers with Chemical and Thermal Recycling. Chem. Mater. 2022, 34, 1167–1178. [Google Scholar] [CrossRef]
  23. Stojcevski, F.; Stanfield, M.K.; Hayne, D.J.; Mann, M.; Lundquist, N.A.; Chalker, J.M.; Henderson, L.C. Inverse Vulcanisation of canola oil as a route to recyclable chopped carbon fibre composites. Sustain. Mater. Technol. 2022, 32, e00400. [Google Scholar] [CrossRef]
  24. Mann, M.; Pauling, P.J.; Tonkin, S.J.; Campbell, J.A.; Chalker, J.M. Chemically Activated S-S Metathesis for Adhesive-Free Bonding of Polysulfide Surfaces. Macromol. Chem. Phys. 2022, 223, 2100333. [Google Scholar] [CrossRef]
  25. Gupta, A.; Worthington, M.J.H.; Patel, H.D.; Johnston, M.R.; Puri, M.; Chalker, J.M. Reaction of sulfur and sustainable algae oil for polymer synthesis and enrichment of saturated triglycerides. ACS Sust. Chem. Eng. 2022, 10, 9022–9028. [Google Scholar] [CrossRef]
  26. Mann, M.; Luo, X.; Tikoalu, A.D.; Gibson, C.T.; Yin, Y.; Al-Attabi, R.; Andersson, G.G.; Raston, C.L.; Henderson, L.C.; Pring, A.; et al. Carbonisation of a polymer made from sulfur and canola oil. Chem. Commun. 2021, 57, 6296–6299. [Google Scholar] [CrossRef]
  27. Bu Najmah, I.; Lundquist, N.A.; Stanfield, M.K.; Stojcevski, F.; Campbell, J.A.; Esdaile, L.J.; Gibson, C.T.; Lewis, D.A.; Henderson, L.C.; Hasell, T.; et al. Insulating Composites Made from Sulfur, Canola Oil, and Wool. ChemSusChem 2021, 14, 2352–2359. [Google Scholar] [CrossRef]
  28. Tonkin, S.J.; Gibson, C.T.; Campbell, J.A.; Lewis, D.A.; Karton, A.; Hasell, T.; Chalker, J.M. Chemically induced repair, adhesion, and recycling of polymers made by inverse vulcanization. Chem. Sci. 2020, 11, 5537–5546. [Google Scholar] [CrossRef]
  29. Lundquist, N.A.; Tikoalu, A.D.; Worthington, M.J.H.; Shapter, R.; Tonkin, S.J.; Stojcevski, F.; Mann, M.; Gibson, C.T.; Gascooke, J.R.; Karton, A.; et al. Reactive Compression Molding Post-Inverse Vulcanization: A Method to Assemble, Recycle, and Repurpose Sulfur Polymers and Composites. Chem.-A Eur. J. 2020, 26, 10035–10044. [Google Scholar] [CrossRef]
  30. Hanna, V.; Graysmark, M.; Willcock, H.; Hasell, T. Liquid polybutadiene reinforced inverse vulcanised polymers. J. Mater. Chem. A 2024, 12, 1211–1217. [Google Scholar] [CrossRef]
  31. Dop, R.A.; Neill, D.R.; Hasell, T. Sulfur-Polymer Nanoparticles: Preparation and Antibacterial Activity. ACS Appl. Mater. Interfaces 2023, 15, 20822–20832. [Google Scholar] [CrossRef]
  32. Dale, J.J.; Hanna, V.; Hasell, T. Manipulating Inverse Vulcanization Comonomers to Generate High-Tensile-Strain Polymers. ACS Appl. Polym. Mater. 2023, 5, 6761–6765. [Google Scholar] [CrossRef]
  33. Zhang, B.; Petcher, S.; Dop, R.A.; Yan, P.; Zhao, W.; Wang, H.; Dodd, L.J.; McDonald, T.O.; Hasell, T. Inverse vulcanised sulfur polymer nanoparticles prepared by antisolvent precipitation. J. Mater. Chem. A 2022, 10, 13704–13710. [Google Scholar] [CrossRef]
  34. Yan, P.; Zhao, W.; McBride, F.; Cai, D.; Dale, J.; Hanna, V.; Hasell, T. Mechanochemical synthesis of inverse vulcanized polymers. Nat. Commun. 2022, 13, 4824. [Google Scholar] [CrossRef]
  35. Jia, J.; Liu, J.; Wang, Z.-Q.; Liu, T.; Yan, P.; Gong, X.-Q.; Zhao, C.; Chen, L.; Miao, C.; Zhao, W.; et al. Photoinduced inverse vulcanization. Nat. Chem. 2022, 14, 1249–1257. [Google Scholar] [CrossRef]
  36. Dop, R.A.; Neill, D.R.; Hasell, T. Antibacterial Activity of Inverse Vulcanized Polymers. Biomacromolecules 2021, 22, 5223–5233. [Google Scholar] [CrossRef]
  37. Dodd, L.J.; Omar, O.; Wu, X.; Hasell, T. Investigating the Role and Scope of Catalysts in Inverse Vulcanization. ACS Catal. 2021, 11, 4441–4455. [Google Scholar] [CrossRef]
  38. Zhang, B.; Gao, H.; Yan, P.; Petcher, S.; Hasell, T. Inverse vulcanization below the melting point of sulfur. Mater. Chem. Front. 2020, 4, 669–675. [Google Scholar] [CrossRef]
  39. Anderson, L.E.; Kleine, T.S.; Zhang, Y.; Phan, D.D.; Namnabat, S.; LaVilla, E.A.; Konopka, K.M.; Ruiz Diaz, L.; Manchester, M.S.; Schwiegerling, J.; et al. Chalcogenide Hybrid Inorganic/Organic Polymers: Ultrahigh Refractive Index Polymers for Infrared Imaging. ACS Macro Lett. 2017, 6, 500–504. [Google Scholar] [CrossRef]
  40. Hanna, V.; Yan, P.; Petcher, S.; Hasell, T. Incorporation of fillers to modify the mechanical performance of inverse vulcanised polymers. Polym. Chem. 2022, 13, 3930–3937. [Google Scholar] [CrossRef]
  41. Meredith, H.J.; Jenkins, C.L.; Wilker, J.J. Enhancing the Adhesion of a Biomimetic Polymer Yields Performance Rivaling Commercial Glues. Adv. Funct. Mater. 2014, 24, 3259–3267. [Google Scholar] [CrossRef]
  42. Davis, A.E.; Sayer, K.B.; Jenkins, C.L. A comparison of adhesive polysulfides initiated by garlic essential oil and elemental sulfur to create recyclable adhesives. Polym. Chem. 2022, 13, 4634–4640. [Google Scholar] [CrossRef]
  43. Wickramasingha, Y.A.; Simon, Z.; Hayne, D.J.; Eyckens, D.J.; Dharmasiri, B.; Chalker, J.M.; Henderson, L.C. Adhesives made from sulfur copolymer composites reinforced with recycled carbon fiber. Ind. Eng. Chem. Res. 2024, 63, 12490–12501. [Google Scholar] [CrossRef]
  44. Mann, M.; Zhang, B.; Tonkin, S.J.; Gibson, C.T.; Jia, Z.; Hasell, T.; Chalker, J.M. Processes for coating surfaces with a copolymer made from sulfur and dicyclopentadiene. Polym. Chem. 2022, 13, 1320–1327. [Google Scholar] [CrossRef]
  45. Worthington, M.J.H.; Kucera, R.L.; Albuquerque, I.S.; Gibson, C.T.; Sibley, A.; Slattery, A.D.; Campbell, J.A.; Alboaiji, S.F.K.; Muller, K.A.; Young, J.; et al. Laying Waste to Mercury: Inexpensive Sorbents Made from Sulfur and Recycled Cooking Oils. Chem.-Eur. J. 2017, 23, 16106. [Google Scholar] [CrossRef]
  46. Chalker, J.M.; Mann, M.; Worthington, M.J.H.; Esdaile, L.J. Polymers Made by Inverse Vulcanization for Use as Mercury Sorbents. Org. Mater. 2021, 3, 362–373. [Google Scholar] [CrossRef]
  47. Worthington, M.J.H.; Mann, M.; Muhti, I.Y.; Tikoalu, A.D.; Gibson, C.T.; Jia, Z.; Miller, A.D.; Chalker, J.M. Modelling mercury sorption of a polysulfide coating made from sulfur and limonene. Phys. Chem. Chem. Phys. 2022, 24, 12363–12373. [Google Scholar] [CrossRef]
  48. Crockett, M.P.; Evans, A.M.; Worthington, M.J.H.; Albuquerque, I.S.; Slattery, A.D.; Gibson, C.T.; Campbell, J.A.; Lewis, D.A.; Bernardes, G.J.L.; Chalker, J.M. Sulfur-Limonene Polysulfide: A Material Synthesized Entirely from Industrial By-Products and Its Use in Removing Toxic Metals from Water and Soil. Angew. Chem. Int. Ed. 2016, 55, 1714–1718. [Google Scholar] [CrossRef]
  49. Lauer, M.K.; Karunarathna, M.S.; Tennyson, A.G.; Smith, R.C. Recyclable, Sustainable, and Stronger than Portland Cement: A Composite from Unseparated Biomass and Fossil Fuel Waste. Mater. Adv. 2020, 1, 590–594. [Google Scholar] [CrossRef]
  50. Smith, A.D.; Smith, R.C.; Tennyson, A.G. Sulfur-Containing Polymers Prepared from Fatty Acid-Derived Monomers: Application of Atom-Economical Thiol-ene/Thiol-yne Click Reactions and Inverse Vulcanization Strategies. Sustain. Chem. 2020, 1, 209–237. [Google Scholar] [CrossRef]
  51. Lauer, M.K.; Tennyson, A.G.; Smith, R.C. Green Synthesis of Thermoplastic Composites from a Terpenoid-Cellulose Ester. ACS Appl. Polym. Mater. 2020, 2, 3761–3765. [Google Scholar] [CrossRef]
  52. Lauer, M.K.; Karunarathna, M.S.; Tennyson, A.G.; Smith, R.C. Robust, remeltable and remarkably simple to prepare biomass-sulfur composites. Mater. Adv. 2020, 1, 2271–2278. [Google Scholar] [CrossRef]
  53. Maladeniya, C.P.; Karunarathna, M.S.; Lauer, M.K.; Lopez, C.V.; Thiounn, T.; Smith, R.C. A Role for Terpenoid Cyclization in the Atom Economical Polymerization of Terpenoids with Sulfur to Yield Durable Composites. Mater. Adv. 2020, 1, 1665–1674. [Google Scholar] [CrossRef]
  54. Lauer, M.K.; Tennyson, A.G.; Smith, R.C. Inverse vulcanization of octenyl succinate-modified corn starch as a route to biopolymer-sulfur composites. Mater. Adv. 2021, 2, 2391–2397. [Google Scholar] [CrossRef]
  55. Karunarathna, M.S.; Lauer, M.K.; Smith, R.C. Facile route to an organosulfur composite from biomass-derived guaiacol and waste sulfur. J. Mater. Chem. A 2020, 8, 20318–20322. [Google Scholar] [CrossRef]
  56. Lopez, C.V.; Smith, A.D.; Smith, R.C. High strength composites from low-value animal coproducts and industrial waste sulfur. RSC Adv. 2022, 12, 1535–1542. [Google Scholar] [CrossRef]
  57. Pyun, J.; Carrozza, C.F.; Silvano, S.; Boggioni, L.; Losio, S.; de Angelis, A.R.; O’Neil Parker, W., Jr. Nuclear magnetic resonance structural characterization of sulfur-derived copolymers from inverse vulcanization. Part 1: Styrene. J. Polym. Sci. 2022, 60, 3471–3477. [Google Scholar] [CrossRef]
  58. Dodd, L.J.; Sandy, W.; Dop, R.A.; Zhang, B.; Lunt, A.; Neill, D.R.; Hasell, T. Inverse vulcanisation of self-activating amine and alkyne crosslinkers. Polym. Chem. 2023, 14, 4064–4078. [Google Scholar] [CrossRef]
  59. Sayer, K.B.; Miller, V.L.; Merrill, Z.; Davis, A.E.; Jenkins, C.L. Allyl sulfides in garlic oil initiate the formation of renewable adhesives. Polym. Chem. 2023, 14, 3091–3098. [Google Scholar] [CrossRef]
  60. Lai, Y.-S.; Liu, Y.-L. Reaction between 1,3,5-Triisopropylbenzene and Elemental Sulfur Extending the Scope of Reagents in Inverse Vulcanization. Macromol. Rapid Commun. 2023, 44, e2300014. [Google Scholar] [CrossRef]
  61. Wijeyatunga, S.K.; Tennyson, A.G.; Smith, R.C. High-Sulfur-Content Materials Derived from Postconsumer Polystyrene Wastes: Thermomechanical Properties, Environmental Impacts, and Microstructural Insights. ACS Sustain. Resour. Manag. 2024, 1, 2173–2183. [Google Scholar] [CrossRef]
  62. Karunarathna, M.S.; Maladeniya, C.P.; Lauer, M.K.; Tennyson, A.G.; Smith, R.C. Durable composites by vulcanization of oleyl-esterified lignin. RSC Adv. 2023, 13, 3234–3240. [Google Scholar] [CrossRef] [PubMed]
  63. Lopez, C.V.; Smith, R.C. Chemical recycling of poly(ethylene terephthalate) via sequential glycolysis, oleoyl chloride esterification and vulcanization to yield durable composites. Mater. Adv. 2023, 4, 2785–2793. [Google Scholar] [CrossRef]
  64. Derr, K.M.; Smith, R.C. One-Pot Method for Upcycling Polycarbonate Waste to Yield High-Strength, BPA-Free Composites. J. Polym. Sci. 2023, 62, 1115–1122. [Google Scholar] [CrossRef]
  65. Wijeyatunga, S.K.; Derr, K.M.; Maladeniya, C.P.; Sauceda-Oloño, P.Y.; Tennyson, A.G.; Smith, R.C. Upcycling waste PMMA to durable composites via a transesterification-inverse vulcanization process. J. Polym. Sci. 2024, 62, 554–563. [Google Scholar] [CrossRef]
  66. ASTM D695−23; Standard Test Method for Compressive Properties of Rigid Plastics. ASTM International: West Conshohocken, PA, USA, 2023.
  67. ASTM D638-22; Standard Test Method for Tensile Properties of Plastics. ASTM International: West Conshohocken, PA, USA, 2022.
  68. ASTM D790-03; Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials. ASTM International: West Conshohocken, PA, USA, 2003.
  69. Eom, T.; Khan, A. Disulfides as mercapto-precursors in nucleophilic ring opening reaction of polymeric epoxides: Establishing equimolar stoichiometric conditions in a thiol–epoxy ‘click’ reaction. Chem. Commun. 2020, 56, 7419–7422. [Google Scholar] [CrossRef]
  70. Griebel, J.J.; Li, G.; Glass, R.S.; Char, K.; Pyun, J. Kilogram scale inverse vulcanization of elemental sulfur to prepare high capacity polymer electrodes for Li-S batteries. J. Polym. Sci. Part A Polym. Chem. 2015, 53, 173–177. [Google Scholar] [CrossRef]
  71. Dale, J.J.; Petcher, S.; Hasell, T. Dark Sulfur: Quantifying Unpolymerized Sulfur in Inverse Vulcanized Polymers. ACS Appl. Polym. Mater. 2022, 4, 3169–3173. [Google Scholar] [CrossRef]
  72. Dale, J.J.; Stanley, J.; Dop, R.A.; Chronowska-Bojczuk, G.; Fielding, A.J.; Neill, D.R.; Hasell, T. Exploring inverse vulcanization mechanisms from the perspective of dark sulfur. Eur. Polym. J. 2023, 195, 112198. [Google Scholar] [CrossRef]
  73. Derr, K.M.; Lopez, C.V.; Maladeniya, C.P.; Tennyson, A.G.; Smith, R.C. Transesterification-vulcanization route to durable composites from post-consumer poly(ethylene terephthalate), terpenoids, and industrial waste sulfur. J. Polym. Sci. 2023, 61, 3075–3086. [Google Scholar] [CrossRef]
  74. Hoefling, A.; Lee, Y.J.; Theato, P. Sulfur-Based Polymer Composites from Vegetable Oils and Elemental Sulfur: A Sustainable Active Material for Li-S Batteries. Macromol. Chem. Phys. 2017, 218, 1600303. [Google Scholar] [CrossRef]
  75. Wreczycki, J.; Bielinski, D.M.; Anyszka, R. Sulfur/organic copolymers as curing agents for rubber. Polymers 2018, 10, 870. [Google Scholar] [CrossRef] [PubMed]
  76. Furushima, Y.; Nakada, M.; Takahashi, H.; Ishikiriyama, K. Study of melting and crystallization behavior of polyacrylonitrile using ultrafast differential scanning calorimetry. Polymer 2014, 55, 3075–3081. [Google Scholar] [CrossRef]
  77. Sheldon, R.A. The E Factor: Fifteen years on. Green Chem. 2007, 9, 1273–1283. [Google Scholar] [CrossRef]
  78. Sheldon, R.A. Green chemistry, catalysis and valorization of waste biomass. J. Mol. Catal. A Chem. 2016, 422, 3–12. [Google Scholar] [CrossRef]
  79. Sheldon, R.A. Recent advances in green catalytic oxidations of alcohols in aqueous media. Catal. Today 2015, 247, 4–13. [Google Scholar] [CrossRef]
  80. Clark, J.H.; Matharu, A.S. Waste to wealth using green chemistry. Issues Environ. Sci. Technol. 2013, 37, 66–82. [Google Scholar]
  81. Anastas, P.; Eghbali, N. Green Chemistry: Principles and Practice. Chem. Soc. Rev. 2010, 39, 301–312. [Google Scholar] [CrossRef]
  82. Anastas, P.T.; Warner, J.C. Green Chemistry: Theory and Practice; Oxford University Press: New York, NY, USA, 1998. [Google Scholar]
  83. Farquharson, D.; Jaramillo, P.; Schivley, G.; Klima, K.; Carlson, D.; Samaras, C. Beyond Global Warming Potential: A Comparative Application of Climate Impact Metrics for the Life Cycle Assessment of Coal and Natural Gas Based Electricity. J. Ind. Ecol. 2017, 21, 857–873. [Google Scholar] [CrossRef]
  84. Joos, F.; Roth, R.; Fuglestvedt, J.S.; Peters, G.P.; Enting, I.G.; von Bloh, W.; Brovkin, V.; Burke, E.J.; Eby, M.; Edwards, N.R.; et al. Carbon dioxide and climate impulse response functions for the computation of greenhouse gas metrics: A multi-model analysis. Atmos. Chem. Phys. 2013, 13, 2793. [Google Scholar] [CrossRef]
  85. Peters, G.P.; Aamaas, B.; Lund, M.T.; Solli, C.; Fuglestvedt, J.S. Alternative “Global Warming” Metrics in Life Cycle Assessment: A Case Study with Existing Transportation Data. Environ. Sci. Technol. 2011, 45, 8633–8641. [Google Scholar] [CrossRef]
  86. Fuglestvedt, J.S.; Shine, K.P.; Berntsen, T.; Cook, J.; Lee, D.S.; Stenke, A.; Skeie, R.B.; Velders, G.J.M.; Waitz, I.A. Transport impacts on atmosphere and climate: Metrics. Atmos. Environ. 2010, 44, 4648–4677. [Google Scholar] [CrossRef]
  87. Yacout, D.M.; Abd El-Kawi, M.; Hassouna, M. Cradle to gate environmental impact assessment of acrylic fiber manufacturing. Int. J. Life Cycle Assess. 2016, 21, 326–336. [Google Scholar] [CrossRef]
  88. Passarini, F.; Ciacci, L.; Santini, A.; Vassura, I.; Morselli, L. Auto shredder residue LCA: Implications of ASR composition evolution. J. Clean. Prod. 2012, 23, 28–36. [Google Scholar] [CrossRef]
  89. Arena, U.; Ardolino, F. Technical and environmental performances of alternative treatments for challenging plastics waste. Resour. Conserv. Recycl. 2022, 183, 106379. [Google Scholar] [CrossRef]
  90. Jeswani, H.; Krüger, C.; Russ, M.; Horlacher, M.; Antony, F.; Hann, S.; Azapagic, A. Life cycle environmental impacts of chemical recycling via pyrolysis of mixed plastic waste in comparison with mechanical recycling and energy recovery. Sci. Total Environ. 2021, 769, 144483. [Google Scholar] [CrossRef]
  91. Wüstenberg, D.; Kasper, J. Required energy and structural breakdown at the process of dynamic cutting—Comminution of polypropylene and aluminium. Int. J. Miner. Process. 2004, 74, S417–S424. [Google Scholar] [CrossRef]
  92. Schubert, G.; Bernotat, S. Comminution of non-brittle materials. Int. J. Miner. Process. 2004, 74, S19–S30. [Google Scholar] [CrossRef]
  93. Peukert, W. Material properties in fine grinding. Int. J. Miner. Process. 2004, 74, S3–S17. [Google Scholar] [CrossRef]
  94. Lewis, G.N.; Randall, M. The heat content of the various forms of sulfur. J. Am. Chem. Soc. 1911, 33, 476–488. [Google Scholar] [CrossRef]
  95. Scrivener, K.L.; John, V.M.; Gartner, E.M. Eco-efficient cements: Potential economically viable solutions for a low-CO2 cement-based materials industry. Cem. Concr. Res. 2018, 114, 2–26. [Google Scholar] [CrossRef]
  96. Scrivener, K.L.; Fullmann, T.; Gallucci, E.; Walenta, G.; Bermejo, E. Quantitative study of Portland cement hydration by X-ray diffraction/Rietveld analysis and independent methods. Cem. Concr. Res. 2004, 34, 1541–1547. [Google Scholar] [CrossRef]
  97. Tayebee, R.; Ahmadi, S.J.; Rezaei Seresht, E.; Javadi, F.; Yasemi, M.A.; Hosseinpour, M.; Maleki, B. Commercial Zinc Oxide: A Facile, Efficient, and Eco-friendly Catalyst for the One-Pot Three-Component Synthesis of Multisubstituted 2-Aminothiophenes via the Gewald Reaction. Ind. Eng. Chem. Res. 2012, 51, 14577–14582. [Google Scholar] [CrossRef]
  98. Kapuge Dona, N.L.; Maladeniya, C.P.; Smith, R.C. Reactivity of Biomass-Derived Olefins with Elemental Sulfur: Mechanistic Insight. Eur. J. Org. Chem. 2024, 27, e202301269. [Google Scholar] [CrossRef]
  99. Tisdale, K.A.; Kapuge Dona, N.L.; Smith, R.C. The Influence of the Comonomer Ratio and Reaction Temperature on the Mechanical, Thermal, and Morphological Properties of Lignin Oil–Sulfur Composites. Molecules 2024, 29, 4209. [Google Scholar] [CrossRef]
  100. Priebbenow, D.L.; Bolm, C. Recent advances in the Willgerodt–Kindler reaction. Chem. Soc. Rev. 2013, 42, 7870–7880. [Google Scholar] [CrossRef]
  101. Monascal, Y.; Cartaya, L.; Álvarez-Aular, Á.; Maldonado, A.; Chuchani, G. The ion pair mechanism in the thermal deamination of primary amines catalyzed by HBr in the gas phase: DFT and AIM analysis. Chem. Phys. Lett. 2018, 703, 117–123. [Google Scholar] [CrossRef]
Sustainability 17 03702 sch001
Scheme 1. General scheme depicting the generation of sulfur radicals from S8 (A) and their reaction with alkenes during inverse vulcanization (B).
Scheme 1. General scheme depicting the generation of sulfur radicals from S8 (A) and their reaction with alkenes during inverse vulcanization (B).
Sustainability 17 03702 sch001
Sustainability 17 03702 g001
Figure 1. Photos of PANS90 that have been shaped into cylinders for compressional strength analysis, rectangular prisms for flexural strength analysis and dog bones for tensile strength analysis.
Figure 1. Photos of PANS90 that have been shaped into cylinders for compressional strength analysis, rectangular prisms for flexural strength analysis and dog bones for tensile strength analysis.
Sustainability 17 03702 g001
Sustainability 17 03702 g002
Figure 2. Left to right: SEM image of PANS90 and EDX elemental mapping for carbon (green), nitrogen (blue), and sulfur (red).
Figure 2. Left to right: SEM image of PANS90 and EDX elemental mapping for carbon (green), nitrogen (blue), and sulfur (red).
Sustainability 17 03702 g002
Sustainability 17 03702 g003
Figure 3. Structure of major and minor PAN chain segments and structures of small-molecule model compounds used in this study to probe their reactivity with elemental sulfur.
Figure 3. Structure of major and minor PAN chain segments and structures of small-molecule model compounds used in this study to probe their reactivity with elemental sulfur.
Sustainability 17 03702 g003
Sustainability 17 03702 sch002aSustainability 17 03702 sch002b
Scheme 2. Proposed microstructure motifs observed from model compound reactions with sulfur. Two hydrogens on each structure are explicitly represented in blue to illustrate where the polymer backbone would be found in analogous PAN-derived HSMs.
Scheme 2. Proposed microstructure motifs observed from model compound reactions with sulfur. Two hydrogens on each structure are explicitly represented in blue to illustrate where the polymer backbone would be found in analogous PAN-derived HSMs.
Sustainability 17 03702 sch002aSustainability 17 03702 sch002b
Sustainability 17 03702 sch003
Scheme 3. Known decomposition pathway for PAN (A) and formation of 7 (observed by GC-MS) from glutaronitrile via an analogous mechanism (B).
Scheme 3. Known decomposition pathway for PAN (A) and formation of 7 (observed by GC-MS) from glutaronitrile via an analogous mechanism (B).
Sustainability 17 03702 sch003
Table 1. Thermal and morphological properties of PANS90 compared to some other plastic-derived HSMs and S8.
Table 1. Thermal and morphological properties of PANS90 compared to some other plastic-derived HSMs and S8.
MaterialsTd [a]
(°C)		Tm [b]
(°C)		Tg, DSC [c]
(°C)		Dark Sulfur
(wt. %)
PANS90209119NA30 [d]
PSP90 [g]220118−3942 [d]
mPES [h]215117−3620 [e]
PGMA–S [i]211117NA79 [f]
SPC90 [j]219116−3462 [f]
S8229118NANA
[a] The temperature at which the 5% mass loss was observed. [b] The temperature at the peak maximum of the endothermic melting. [c] Glass transition temperature. [d] Percent of ethyl acetate-extractable sulfur species. [e] Percent of CS2-extractable sulfur species. [f] Percent of toluene-extractable sulfur species. [g] Composite made from 90 wt. % sulfur and 10 wt. % polystyrene packaging material particulate. [h] Composite made from 90 wt. % sulfur and 10 wt. % esterified PET. [i] Composite made from 90 wt. % sulfur and 10 wt. % geraniol-transesterified PMMA. [j] Composite made from 90 wt. % sulfur 10 wt. % poly(bisphenol A carbonate).
Table 2. Mechanical properties of PANS90, other plastic-derived HSMs, and conventional building materials.
Table 2. Mechanical properties of PANS90, other plastic-derived HSMs, and conventional building materials.
Compressional Strength (MPa)Flexural Strength/Modulus (MPa)Ultimate Tensile Strength (MPa)
PANS9011.4 ± 0.73.6 ± 0.4/975 ± 952.5 ± 0.2
PSP90 [a]9.8 ± 1.22.4 ± 0.1/341 ± 232.0 ± 0.2
mPES [b]26.9 ± 0.67.7 ± 0.2/320 ± 50.2 ± 0.0
PGMA–S [c]17.5 ± 2.84.8 ± 0.7/642 ± 493.9 ± 1.2
SPC90 [d]12.8 ± 1.63.1 ± 0.5ND
C62 Brick8.6ND [e]ND
Portland Cement17.03.7/580ND
[a] Composite made from 90 wt. % sulfur and 10 wt. % polystyrene packaging material particulate. [b] Composite made from 90 wt. % sulfur and 10 wt. % esterified PET. [c] Composite made from 90 wt. % sulfur and 10 wt. % geraniol-transesterified PMMA. [d] Composite made from 90 wt.% sulfur 10 wt. % poly(bisphenol A carbonate). [e] Not determined.
Table 3. Metrics used in the calculation of the global warming potential of PANS90.
Table 3. Metrics used in the calculation of the global warming potential of PANS90.
ProcessCost (+) or Credit (–)?Value
(kg CO2e)
Make PAN (0.10 kg × 5.4 kg CO2e/kg)+0.54
Grinding (0.100 kg of PAN × 0.092 kg CO2e/kg)+0.0092
Heating (1.00 kg mixture × 0.025 kg CO2e/kg)+0.025
Prevent Incineration of PAN (0.100 kg × 2.5 kg CO2e/kg)–0.25
Total0.33 kg CO2e/kg
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Wijeyatunga, S.K.; Smith, R.C. Upcycled Composite Derived from Polyacrylonitrile and Elemental Sulfur: Thermomechanical Properties and Microstructural Insight. Sustainability 2025, 17, 3702. https://doi.org/10.3390/su17083702

AMA Style

Wijeyatunga SK, Smith RC. Upcycled Composite Derived from Polyacrylonitrile and Elemental Sulfur: Thermomechanical Properties and Microstructural Insight. Sustainability. 2025; 17(8):3702. https://doi.org/10.3390/su17083702

Chicago/Turabian Style

Wijeyatunga, Shalini K., and Rhett C. Smith. 2025. "Upcycled Composite Derived from Polyacrylonitrile and Elemental Sulfur: Thermomechanical Properties and Microstructural Insight" Sustainability 17, no. 8: 3702. https://doi.org/10.3390/su17083702

APA Style

Wijeyatunga, S. K., & Smith, R. C. (2025). Upcycled Composite Derived from Polyacrylonitrile and Elemental Sulfur: Thermomechanical Properties and Microstructural Insight. Sustainability, 17(8), 3702. https://doi.org/10.3390/su17083702

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop