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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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Robust, remeltable and remarkably simple to prepare biomass–sulfur composites
Lignocellulosic biomass holds a tremendous opportunity for transformation into carbon-negative materials, yet the expense of separating biomass into its cellulose and lignin components remains a primary economic barrier to biomass utilization. Herein is reported a simple procedure to convert several biomass-derived materials into robust, recyclable composites through their reaction with elemental sulfur by inverse vulcanization, a process in which olefins are crosslinked by sulfur chains. In an effort to understand the chemistry and the parameters leading to the strength of these composites, sulfur was reacted with four biomass-derivative comonomers: (1) unmodified peanut shell powder, (2) allyl peanut shells, (3) ‘mock’ allyl peanut shells (a mixture containing independently-prepared allyl cellulose and allyl lignin), or (4) peanut shells that have been defatted by extraction of peanut oil. The reactions of these materials with sulfur produce the biomass–sulfur composites PSx , APSx , mAPSx and dfPSx , respectively, where x = wt% sulfur in the monomer feed. The influence of biomass : sulfur ratio was assessed for PSx and APSx . Thermal/mechanical properties of composites were evaluated for comparison to commercial materials. Remarkably, unmodified peanut shell flour can simply be heated with elemental sulfur to produce composites having flexural/compressive strengths exceeding those of Portland cement, an effect traced to the presence of olefin-bearing peanut oil in the peanut shells. When allylated peanut shells are used in this process, a composite having twice the compressive strength of Portland cement is attained.
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- Award ID(s):
- 1708844
- PAR ID:
- 10199254
- Date Published:
- Journal Name:
- Materials Advances
- Volume:
- 1
- Issue:
- 7
- ISSN:
- 2633-5409
- Page Range / eLocation ID:
- 2271 to 2278
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Lignin is the most abundant natural source of aromatics but remains underutilized. Elemental sulfur is a plentiful by-product of fossil fuel refining. Herein we report a strategy for preparing a durable composite by the one-pot reaction of elemental sulfur and lignin oil comprising lower molecular weight lignin derivatives. A lignin oil-sulfur composite (LOS90) was prepared by reacting 10 wt. % lignin oil with 90 wt. % elemental sulfur. The composite could be remelted and reshaped over several cycles without loss of properties. Results from the study showed thatLOS90has properties competitive with or exceeding values for commercial ordinary Portland cement and brick formulations. For example,LOS90displayed impressive compressive strength (22.1 MPa) and flexural strength (5.7 MPa).LOS90is prepared entirely from waste materials with 98.5% atom economy of composite synthesis, a lowEfactor of 0.057, and lignin char as the only waste product of the process for its preparation. These results suggest the potential applications of lignin and waste sulfur in the continuous efforts to develop more recyclable and sustainable materials.more » « less
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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 GBSx(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.more » « less
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1039/d0ma00538j
