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1. A role for terpenoid cyclization in the atom economical polymerization of terpenoids with sulfur to yield durable composites

   https://doi.org/10.1039/D0MA00474J  

   Maladeniya, Charini P. ; Karunarathna, Menisha S. ; Lauer, Moira K. ; Lopez, Claudia V. ; Thiounn, Timmy ; Smith, Rhett C. ( September 2020 , Materials Advances)

   null (Ed.)

   Renewably-sourced, recyclable materials that can replace or extend the service life of existing technologies are essential to accomplish humanity's quest for sustainable living. In this contribution, remeltable composites were prepared in a highly atom-economical reaction between plant-derived terpenoid alcohols (10 wt% citronellol, geraniol, or farnesol) and elemental sulfur (90 wt%). Investigation into the microstructures led to elucidation of a mechanism for terpenoid polyene cyclization initiated by sulfur-centered radicals. The formation of these cyclic structures contributes significantly to understanding the mechanical properties of the materials and the extent to which linear versus crosslinked network materials are formed. The terpenoid–sulfur composites can be thermally processed at low temperatures of 120 °C without loss of mechanical properties, and the farnesol–sulfur composite so processed exhibits compressive strength 70% higher than required of concrete for residential building. The terpenoid–sulfur composites also resist degradation by oxidizing acid under conditions that disintegrate many commercial composites and cements. In addition to being stronger and more chemically resistant than some commercial products, the terpenoid–sulfur composites can be used to improve the acid resistance of mineral-based Portland cement as well. These terpenoid–sulfur composites thus hold promise as elements of sustainable construction on their own or as additives to extend the operational life of existing technologies, while the cyclization behaviour could be an important contributor in other polymerizations of terpenoids. 

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2. Transesterification‐vulcanization route to durable composites from post‐consumer poly(ethylene terephthalate), terpenoids, and industrial waste sulfur

   https://doi.org/10.1002/pol.20230503  

   Derr, Katelyn M. ; Lopez, Claudia V. ; Maladeniya, Charini P. ; Tennyson, Andrew G. ; Smith, Rhett C. ( September 2023 , Journal of Polymer Science)

   Despite improvements in chemical recycling, most post‐consumer plastics are still deposited in landfills where they pose a significant threat to ecological health. Herein we report a two‐stage method for chemically recycling poly(ethylene terephthalate) (PET) using terpenoids and waste sulfur to yield composites. In this method, post‐consumer PET (from beverage bottles) undergoes transesterification with a terpenoid alcohol (citronellol or geraniol) to yield low‐molecular PET oligomers. The terpene‐derived alkenes in these PET oligomer derivatives then served as reaction sites for inverse vulcanization with 90 wt% elemental sulfur to form compositeCPS(using citronellol) orGPS(using geraniol). Composition, mechanical, thermal, and morphological properties were characterized by NMR spectroscopy, MALDI, FT‐IR spectroscopy, compressive and flexural strength analysis, TGA, DSC, elemental analysis, and SEM/EDX. The compositesCPS(compressive strength = 5.20 MPa, flexural strength = 3.10 MPa) andGPS(compressive strength = 5.8 MPa, flexural strength = 2.77 MPa) showed mechanical strengths comparable to those of commercial bricks (classification C62 for general building). The approach delineated herein thus represents a method to chemically recycle waste plastic with industrial waste sulfur and plant‐derived terpenoids to yield composites having favorable properties comparable to existing building materials.

    

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3. Influence of pozzolans on plant oil‐sulfur polymer cements: More sustainable and chemically‐resistant alternatives to Portland cement

   https://doi.org/10.1002/app.53684  

   Graham, Matthew J. ; Lopez, Claudia V. ; Maladeniya, Charini P. ; Tennyson, Andrew G. ; Smith, Rhett C. ( February 2023 , Journal of Applied Polymer Science)

   Low cost and high durability have made Portland cement the most widely‐used building material, but benefits are offset by environmental harm of cement production contributing 8–10% of total anthropogenic CO₂gas emissions. High sulfur‐content materials (HSMs) are an alternative that can perform the binding roles as cements with a smaller carbon footprint, and possibly superior chemical, physical, and mechanical properties. Inverse vulcanization of 90 wt% sulfur with 10 wt% canola oil or sunflower oil to yield CanS or SunS, respectively. Notably, these HSMs prepared at temperatures ≤180 °C compared to >1200 °C hours for Portland cement CanS was combined with 5 wt% fly ash (FA), silica fume (SF), ground granulated blast furnace slag (GGBFS), or metakaolin (MK) to give composites CanS‐FA, CanS‐SF, CanS‐GGBFS, and CanS‐MK, respectively. The analogous protocol with SunS likewise yielded SunS‐FA, SunS‐SF, SunS‐GGBFS, and SunS‐MK. Each of these HSMs exhibit high compressive mechanical strength, low water uptake values, and exceptional resistance to acid‐induced corrosion. All of the composites also exhibit superior compressive strength retention after exposure to acidic solutions, conditions under which Portland cement undergoes dissolution. The polymer cement‐pozzolan composites reported herein may thus serve as greener alternatives to traditional Portland cement in some applications.

    

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4. Durable composites by vulcanization of oleyl-esterified lignin

   https://doi.org/10.1039/D2RA07082K  

   Karunarathna, Menisha S. ; Maladeniya, Charini P. ; Lauer, Moira K. ; Tennyson, Andrew G. ; Smith, Rhett C. ( January 2023 , RSC Advances)

   Productive utilization of lignocellulosic biomass is critical to the continued advancement of human civilization. Whereas the cellulose component can be efficiently upconverted to automotive fuel-grade ethanol, the lack of upconversion methods for the lignin component constitutes one of the grand challenges facing science. Lignin is an attractive feedstock for structural applications, in which its highly-crosslinked architecture can endow composite structures with high strengths. Prior work suggests that high-strength composites can be prepared by the reaction of olefin-modified lignin with sulfur. Those studies were limited to ≤5 wt% lignin, due to phase-separation of hydrophilic lignin from hydrophobic sulfur matrices. Herein we report a protocol to increase lignin hydrophobicity and thus its incorporation into sulfur-rich materials. This improvement is affected by esterifying lignin with oleic acid prior to its reaction with sulfur. This approach allowed preparation of esterified lignin–sulfur (ELS) composites comprising up to 20 wt% lignin. Two reaction temperatures were employed such that the reaction of ELS with sulfur at 180 °C would only produce S–C bonds at olefinic sites, whereas the reaction at 230 °C would produce C–S bonds at both olefin and aryl sites. Mechanistic analyses and microstructural characterization elucidated two ELS composites having compressive strength values (>20 MPa), exceeding the values observed with ordinary Portland cements. Consequently, this new method represents a way to improve lignin utilization to produce durable composites that represent sustainable alternatives to Portland cements. 

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5. One‐pot method for upcycling polycarbonate waste to yield high‐strength, BPA ‐free composites

   https://doi.org/10.1002/pol.20230724  

   Derr, Katelyn M. ; Smith, Rhett C. ( December 2023 , Journal of Polymer Science)

   Environmental damage caused by waste plastics and downstream chemical breakdown products is a modern crisis. Endocrine‐disrupting bisphenol A (BPA), found in breakdown products of poly(bisphenol A carbonate) (PC), is an especially pernicious example that interferes with the reproduction and development of a wide range of organisms, including humans. Herein we report a single‐stage thiocracking method to chemically upcycle polycarbonate using elemental sulfur, a waste product of fossil fuel refining. Importantly, this method disintegrates bisphenol A units into monoaryls, thus eliminating endocrine‐disrupting BPA from the material and from any potential downstream waste. Thiocracking of PC (10 wt%) with elemental sulfur (90 wt%) at 320 °C yields the highly crosslinked networkSPC₉₀. The composition, thermal, morphological, and mechanical properties ofSPC₉₀were characterized by FT‐IR spectroscopy, TGA, DSC, elemental analysis, SEM/EDX, compressive strength tests, and flexural strength tests. The compositeSPC₉₀(compressive strength = 12.8 MPa, flexural strength = 4.33 MPa) showed mechanical strengths exceeding those of commercial bricks and competitive with those of mineral cements. The approach discussed herein represents a method to chemically upcycle polycarbonate while deconstructing BPA units, and valorizing waste sulfur to yield structurally viable building materials that could replace less‐green legacy materials.

    

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