Environmental contamination by plastic waste is a growing threat to the environment and human health. Unfortunately, most post‐consumer plastics are still disposed of in landfills, even plastics that could be easily recycled via simple chemical processes. This disconnect between technology and implementation is partly due to the economic barrier posed by multi‐step processes that convert plastic waste into commodity goods. There is an urgent need for green methods to convert plastic waste directly into marketable commodities via simple processes. Herein we report a simple, single‐stage process to chemically recycle poly(ethylene terephthalate) (PET) to yield composites having thermal and mechanical properties that are competitive with commercial structural materials like Portland cement. In this protocol, a mixture of PET and geraniol are heated with elemental sulfur. In this process, transesterification between geraniol and PET with concomitant thiocracking of the PET backbone leads to the formation of a highly‐crosslinked sulfur–PET–geraniol (SPG) network composite. The composite exhibited compressive strength (23.1 MPa) greater than that required for Portland cement to be used in building foundations. This new, single‐stage chemical recycling strategy thus employs a bio‐olefin and waste sulfur to convert PET waste into a durable composite that could serve as a sustainable alternative to traditional cements.
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
- NSF-PAR ID:
- 10455228
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Polymer Science
- Volume:
- 61
- Issue:
- 23
- ISSN:
- 2642-4150
- Format(s):
- Medium: X Size: p. 3075-3086
- Size(s):
- ["p. 3075-3086"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
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
-
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
-
more » « less
Abstract 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 network
SPC 90 . The composition, thermal, morphological, and mechanical properties ofSPC 90 were characterized by FT‐IR spectroscopy, TGA, DSC, elemental analysis, SEM/EDX, compressive strength tests, and flexural strength tests. The compositeSPC 90 (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. -
more » « less
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
x (x = wt% S, varied from 80%–90%). The compressive strengths of GBS80(27.5 ± 2.6 MPa) and GBS90(19.2 ± 0.8 MPa) exceed the compressive strength required of ordinary Portland cement (17 MPa) for its use in residential building foundations. The current route represents a way to repurpose waste plastic, energy sector by‐product sulfur, and agricultural by‐product brown grease to give high strength composites with mechanical properties suggesting their possible use to replace less sustainably sourced legacy structural materials.
