Research ArticleMATERIALS SCIENCE

Recycling of multilayer plastic packaging materials by solvent-targeted recovery and precipitation

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Science Advances  20 Nov 2020:
Vol. 6, no. 47, eaba7599
DOI: 10.1126/sciadv.aba7599
  • Fig. 1 Overview of the STRAP process.

    Schematic representation of a multilayer plastic film consisting of three common polymer resins, and key steps in the solvent-targeted recovery and precipitation (STRAP) process for segregating these component resins into pure, recyclable streams using a series of solvent washes.

  • Fig. 2 Computational tools used to guide the solvent selection for the STRAP process.

    (A) Process of selecting solvents using a combination of HSPs, classical MD simulations, and COSMO-RS calculations. The solubility of PE, EVOH, and PET was estimated using HSPs for 22 common solvents (values in Supplementary Materials). Solvents selective to each polymer were then used for subsequent calculations. Classical MD simulations were performed to provide input oligomer configurations for COSMO-RS, which uses ab initio methods to calculate the screening charge density of each molecule. COSMO-RS calculations then determine thermodynamic properties, such as solubilities. (B) PE-, EVOH-, and PET-selective solvents and antisolvents (in which none of the polymers are soluble) determined from HSP calculations. DMSO, dimethyl sulfoxide; DMF, N,N-dimethylformamide; THFA, tetrahydrofurfuryl alcohol; THF, tetrahydrofuran; NMP, N-methylpyrrolidinone; GVL, γ-valerolactone; IPA, isopropyl alcohol. (C) Predicted solubility versus temperature for PE, EVOH, and PET in pure toluene (PE selective) and DMSO (EVOH selective) computed using COSMO-RS. (D) Predicted solubility versus solvent-antisolvent mass ratio for PE (red curve) and EVOH (green curve). Acetone and water were used as antisolvents for the dissolution of PE and EVOH, respectively. Black dashed lines in (C) and (D) are the temperatures and mass ratios selected for the STRAP process.

  • Fig. 3 STRAP process separates PE, EVOH, and PET mixtures.

    (A) Process schematic for deconstructing an Amcor Evolution multilayer film into its constituent resins using the STRAP process. (B) Photographs of the Evolution film and the recovered resin using the STRAP process in (A). The mass balance for this process is 100.44 wt % with respect to the initial mass of the evolution film, with an SE of ±1.39 wt %. Photo credit: Theodore W. Walker, University of Wisconsin-Madison. (C) Photographs of comingled plastic resin beads consisting of 7:2:2 PE, EVOH, and PET and the recovered resins using the same procedure in (A). The mass balance for this process is 99.40 wt % with respect to the initial mass of the physical mixture, with an SE of ±0.19 wt %. Photo credit: Theodore W. Walker, University of Wisconsin-Madison.

  • Fig. 4 Total capital investment and MSP for the combined, recycled PE, EVOH, and PET streams derived from an Amcor Evolution multilayer film using the STRAP process, both as a function of feed capacity in tons of Amcor Evolution film per year (circles, MSP; squares, Capital Investment).

    Market price of virgin PET is shown as a dotted line for reference.

  • Table 1 Solubilities of PE, EVOH, and PET in select solvent systems determined by HSPs (Ra/R0), COSMO-RS calculations, and experiments.

    Ra/R0 is the ratio of the polymer-solvent distance to the interaction radius of the polymer (R0) in δD − δP − δH space. Ra/R0 less than unity means that the polymer is likely to dissolve in the solvent, whereas Ra/R0 greater than unity means that the polymer is insoluble in the solvent. ND indicates nondetected solubilities.

    Component resinSolvent systemTemperature (°C)Ra/R0COSMO-RS solubility
    (wt %)
    Experimental
    solubility (wt %)
    PEToluene1100.3733.6214.56*
    PEDMSO952.662.690.04
    PE1:4 toluene:acetone251.311.57ND
    PE1:4 DMSO:water255.530.00ND
    EVOHToluene1102.000.270.00
    EVOHDMSO951.0332.5414.05
    EVOH1:4 toluene:acetone251.530.13ND
    EVOH1:4 DMSO:water253.530.82ND
    PETToluene1101.061.330.00
    PETDMSO951.650.250.02
    PET1:4 toluene:acetone250.910.00ND
    PET1:4 DMSO:water254.800.00ND

    *upper limit of PE wt% in toluene tested, as higher concentrations resulted in a viscous solution that was difficult to stir. This value therefore represents a lower limit for PE solubility in toluene at the temperature indicated.

    Supplementary Materials

    • Supplementary Materials

      Recycling of multilayer plastic packaging materials by solvent-targeted recovery and precipitation

      Theodore W. Walker, Nathan Frelka, Zhizhang Shen, Alex K. Chew, Jesse Banick, Steven Grey, Min Soo Kim, James A. Dumesic, Reid C. Van Lehn, George W. Huber

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      The PDF file includes:

      • Supplementary Materials and Methods
      • Supplementary Text
      • Sections S1 to S6
      • Figs. S1 to S5
      • Legend for fig. S6
      • Tables S1 to S5
      • Legends for tables S6 to S18
      • References

      Other Supplementary Material for this manuscript includes the following:

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