- Award ID(s):
- 1708844
- NSF-PAR ID:
- 10199240
- Date Published:
- Journal Name:
- RSC Advances
- Volume:
- 9
- Issue:
- 54
- ISSN:
- 2046-2069
- Page Range / eLocation ID:
- 31460 to 31465
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Fossil fuel refining produces over 70 Mt of excess sulfur annually from for which there is currently no practical use. Recently, methods to convert waste sulfur to recyclable and biodegradable polymers have been delineated. In this report, a commercial bisphenol A (BPA) derivative, 2,2′,5,5′-tetrabromo(bisphenol A) (Br4BPA), is explored as a potential organic monomer for copolymerization with elemental sulfur by RASP (radical-induced aryl halide-sulfur polymerization). Resultant copolymers, BASx (x = wt% sulfur in the monomer feed, screened for values of 80, 85, 90, and 95) were characterized by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Analysis of early stage reaction products and depolymerization products support proposed S–Caryl bond formation and regiochemistry, while fractionation of BASx reveals a sulfur rank of 3–6. Copolymers having less organic cross-linker (5 or 10 wt%) in the monomer feed were thermoplastics, whereas thermosets were accomplished when 15 or 20 wt% of organic cross-linker was used. The flexural strengths of the thermally processable samples (>3.4 MPa and >4.7 for BAS95 and BAS90, respectively) were quite high compared to those of familiar building materials such as portland cement (3.7 MPa). Furthermore, copolymer BAS90 proved quite resistant to degradation by oxidizing organic acid, maintaining its full flexural strength after soaking in 0.5 M H2SO4 for 24 h. BAS90 could also be remelted and recast into shapes over many cycles without any loss of mechanical strength. This study on the effect of monomer ratio on properties of materials prepared by RASP of small molecular aryl halides confirms that highly cross-linked materials with varying physical and mechanical properties can be accessed by this protocol. This work is also an important step towards potentially upcycling BPA from plastic degradation and sulfur from fossil fuel refining.more » « less
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Herein we report a method for the chemical recycling of poly(ethylene terephthalate) (PET) by a three-stage process employing sustainably-sourced organic materials and industrial byproduct sulfur. In this protocol, PET was subject to glycolysis with diethylene glycol to yield low molecular weight oligomers with hydroxyl end groups. The glycolyzed PET (GPET) was then reacted with oleoyl chloride to yield esterified PET (EPET) containing vulcanizable olefin units. The oligomers constituting GPET and EPET were elucidated by MALDI-TOF spectrometry. EPET underwent inverse vulcanization with elemental sulfur (90 wt%) for 35 min or 24 h to yield xPES or mPES, respectively. The composition, thermal, morphological, thermal and mechanical properties were characterized. The composites exhibited good to excellent mechanical properties that were improved significantly by extending the reaction time from 35 min used to prepare xPES (compressive strength = 10.5 MPa, flexural strength = 2.7 MPa) to 24 h used to prepare mPES (compressive strength = 26.9 MPa, flexural strength = 7.7 MPa). Notably, the compressive and flexural strengths of mPES represent 158% and 208% of the values required for residential building foundations made from traditional materials such as ordinary Portland cement. The three-stage approach delineated herein thus represents a way to mediate chemical recycling of waste plastic with green coreagents to yield composites having mechanical properties competitive with existing commercial structural materials.more » « less
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Sulfur cements have drawn significant attention as binders because sulfur is a byproduct of fossil fuel refining. Sulfur cements that can be formed by the vulcanization of elemental sulfur and plant-derived olefins such as terpenoids are particularly promising from a sustainability standpoint. A range of terpenoid–sulfur cements have shown compressional and flexural properties exceeding those of some commercial structural mineral cements. Pozzolans such as fly ash (FA), silica fume (SF), and ground granulated blast furnace slag (GGBFS) and abundant clay resources such as metakaolin (MK) are attractive fines for addition to binders. Herein, we report 10 composites prepared by a combination of sulfur, terpenoids (geraniol or citronellol), and these pozzolans. This study reveals the extent to which the addition of the pozzolan fines to the sulfur–terpenoid cements influences their mechanical properties and chemical resistance. The sulfur–terpenoid composites CitS and GerS were prepared by the reaction of 90 wt% sulfur and 10 wt% citronellol or geraniol oil, respectively. The density of the composites fell within the range of 1800–1900 kg/m3 and after 24 h submersion in water at room temperature, none of the materials absorbed more than 0.7 wt% water. The compressional strength of the as-prepared materials ranged from 9.1–23.2 MPa, and the percentage of compressional strength retained after acid challenge (submersion in 0.1 M H2SO4 for 24 h) ranged from 80–100%. Incorporating pozzolan fines into the already strong CitS (18.8 MPa) had negligible effects on its compressional strength within the statistical error of the measurement. CitS-SF and CitS-MK had slightly higher compressive strengths of 20.4 MPa and 23.2 MPa, respectively. CitS-GGBFS and CitS-FA resulted in slightly lower compressive strengths of 17.0 MPa and 15.8 MPa, respectively. In contrast, the compressional strength of initially softer GerS (11.7 MPa) benefited greatly after incorporating hard mineral fines. All GerS derivatives had higher compressive strengths than GerS, with GerS-MK having the highest compressive strength of 19.8 MPa. The compressional strengths of several of the composites compare favorably to those required by traditional mineral cements for residential building foundations (17 MPa), whereas such mineral products disintegrate upon similar acid challenge.more » « less
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Abstract 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 composite
CPS (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. -
Abstract A three‐stage route to chemically upcycle post‐consumer poly(ethylene terephthalate) (PET) to produce high compressive strength composites is reported. This procedure involves initial glycolysis with diethylene glycol to produce a mixture (GPET) comprising oligomers of 2–7 terephthalate units followed by trans/esterification of GPET with fatty acid chains supplied by brown grease, an agricultural by‐product of animal fat of relatively low nutritional or fuel value. This process yields PGB comprising a mixture of mono‐terephthalate ester derivatives. The olefin units provided by unsaturated fatty acid chains in brown grease were crosslinked by an inverse vulcanization reaction with elemental sulfur to give composites GBS
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