An official website of the United States government
Reaction of poly(vinyl chloride) (PVC) with 5 equiv. of triethyl silane in THF, in the presence of in situ generated (xantphos)RhCl catalyst, results in partial reduction of PVC via hydrodechlorination to yield poly(vinyl chloride- co -ethylene). Increasing catalyst loading or using N , N -dimethylacetamide (DMA) as a solvent both diminished selectivity for hydrodechlorination, promoting competitive dehydrochlorination reactions. Reaction of PVC with 2 equiv. of sodium formate in THF in the presence of (xantphos)RhCl affords excellent selectivity for hydrodechlorination along with complete PVC dechlorination, yielding polyethylene-like polymers. Higher catalyst loadings were necessary to activate PVC towards reduction in this case. In contrast, reaction of PVC with 1 equiv. of NaH in DMA, in the presence of (xantphos)RhCl, exhibited good selectivity for dehydrochlorination, as well as much higher reaction rates. These results combined shed light on the interplay between critical reaction parameters that control PVC's mode of reactivity.
more »
« less
Divergent silylium catalysis enables facile poly(vinyl chloride) upcycling to poly(ethylene- co -styrene) derivatives
Tandem hydrodechlorination/Friedel–Crafts alkylation of poly(vinyl chloride) (PVC) is achieved using silylium ion catalysts to prepare new styrenic copolymers of polyethylene. In many cases, conversion of PVC was complete within minutes, indicating facile means of PVC functionalization at low catalyst loadings.
more »
« less
- Award ID(s):
- 2203756
- PAR ID:
- 10463188
- Date Published:
- Journal Name:
- Journal of Materials Chemistry A
- Volume:
- 11
- Issue:
- 5
- ISSN:
- 2050-7488
- Page Range / eLocation ID:
- 2128 to 2132
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Managing water resources has become one of the most pressing concerns of scientists in both academia and industry. Broadening access to nontraditional water feedstocks, such as brackish water, seawater and wastewater, requires a robust pretreatment process to prolong the lifetime and improve the efficiency of reverse osmosis treatment processes. Herein, pretreatment membranes with tunable hydrophilic characteristics and mechanical properties were developed through a facile and scalable technique. Specifically, poly(vinyl alcohol) (PVA) and poly(vinyl chloride) (PVC) were electrospun at various PVA‐to‐PVC mass ratios and then crosslinked with a poly(ethylene glycol) diacid. Fiber diameters and morphologies were characterized using scanning electron microscopy (SEM); Fourier transform infrared spectroscopy and confocal fluorescence microscopy further confirmed the presence of both polymers. Moreover, a rigorous analysis to map the PVA/PVC concentration was established to accurately determine the relative concentrations of the two polymers on the co‐spun mat. The crosslinking reaction noted above tuned the membrane porosity from 500 to 80 nm, as seen using SEM, and the mechanical properties were probed using tensile testing. The data revealed that the PVC content controlled the mechanical strength; moreover, higher PVA contents were expected to increase water permeation by enhancing the hydrophilicity, but the higher degree of crosslinking in these materials actually reduced water permeation. This work introduces a facile, scalable route for the manufacture of pretreatment membranes with tunable porosity, mechanical properties and water permeation behavior. © 2021 Society of Industrial Chemistry.more » « less
-
Abstract Hydrodechlorination of poly(vinyl chloride) (PVC) directly to polyethylene (PE) represents a way to repurpose PVC waste, while avoiding toxic and/or corrosive byproducts that are produced at the end of life of PVC items. Prior studies identified a rhodium‐catalyzed route to hydrodechlorinate PVC to form PE products with sodium formate as a hydrogen source. While all chlorine could be removed to form PE‐like polymers, the reaction was slow and side reactions introduced undesirable cross‐links in the polymer product. In this work, mechanistic studies are pursued to improve catalytic activity for this method. Xantphos and diphenylphosphinoethane (DPPE) both support Rh(I) to promote this reaction to full conversion, effectively removing all chlorine from PVC samples, with Xantphos support providing the fastest metal catalysis for hydrodechlorination to date. However, side reactions to form cross‐links are present for both catalyst systems. Control studies suggest the proposed route for cross‐link formation also deactivates the Rh catalyst, indicating the cross‐link formation can also be the cause for the reaction to slow over time. Other reaction conditions were found to influence the selectivity between hydrodechlorination and cross‐link formation. These results introduce key catalyst design principles to improve methods for hydrodechlorination of PVC, allowing for sustainable repurposing of this toxic polymer waste.more » « less
-
In recent decades, the increased use of polyvinyl chloride (PVC) in industries and households has led to a surge in PVC waste pollution, which mandates developing solutions for the removal of waste PVC from the environment. We report upcycling, the conversion of waste material to a high-value-added product, of PVC-based products to electrospun (ES) fibers (mats). As two common PVC products, waste PVC pipe and waste PVC pool float were upcycled to ES fibers for water treatment. The fabrication process and fiber characteristics, such as morphology, surface charge, and mechanical strength of upcycled fibers, were studied and compared with the same fibers fabricated using research-grade (RG) PVC (commercial PVC powder). In addition, the effect of additives such as calcium carbonate in PVC waste products on the physicochemical properties of upcycled fibers was evaluated. The results showed that upcycling of waste PVC to ES fibers is feasible since the upcycled fibers showed similar or superior properties compared to their equivalent fibers from RG-PVC. Finally, the performance of upcycled fibers on the removal of dyes from the water was evaluated. The upcycled fibers from waste PVC pipes and pool float outperformed the RG PVC fibers in removing methylene blue from water by showing more than 97% removal efficiency. In addition, the upcycled PVC ES fibers showed more than 80% reusability after five adsorption−desorption cycles.more » « less
-
Polyvinyl chloride (PVC) containing municipal solid waste (MSW) streams are difficult to recycle and mostly landfilled due to various detrimental effects PVC causes to waste recycling. In this work, a single-step upcycling of PVC-containing commingled wastes in tetrahydrofuran was investigated using cellulose, PVC, polyethylene (PE), polypropylene (PP), and polystyrene (PS) to model the wastes. During the co-conversion, in-situ produced HCl derived from PVC decomposition acted as an acid catalyst to selectively decompose cellulose into liquid mainly containing levoglucosan (LGA) and furfural. It was also found that the presence of PE, PP, and PS in the mixture synergistically enhanced the cellulose-derived monomer productions and increased the reaction rate for producing the monomers by suppressing secondary reactions of HCl in the solvent. The maximum LGA yield from co-conversion of cellulose, PVC, and PS was 35.4% after a 5 min reaction compared to the 31.7% obtained without PS in the mixture. In addition to converting cellulose to chemicals, PVC-derived polyaromatics and partly decomposed PE, PP, and PS were recovered as solids. The dechlorinated solids had higher heating values up to 46.11 MJ/kg, achieved by co-converting cellulose, PVC, and PP. When used as oil absorbents in water, the solid recovered from converting cellulose, PVC, and PE mixture showed the highest absorption capability. Overall, the presented approach offers a promising way for upcycling PVC-containing wastes in which PVC properties and its molecular structure are leveraged to enhance the conversion.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2TA08142C
