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Dynamic crosslinking compatibilizes immiscible mixed plastics

Nature volume 616, pages 731–739 (2023)Cite this article

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Abstract

The global plastics problem is a trifecta, greatly affecting environment, energy and climate1,2,3,4. Many innovative closed/open-loop plastics recycling or upcycling strategies have been proposed or developed5,6,7,8,9,10,11,12,13,14,15,16, addressing various aspects of the issues underpinning the achievement of a circular economy17,18,19. In this context, reusing mixed-plastics waste presents a particular challenge with no current effective closed-loop solution20. This is because such mixed plastics, especially polar/apolar polymer mixtures, are typically incompatible and phase separate, leading to materials with substantially inferior properties. To address this key barrier, here we introduce a new compatibilization strategy that installs dynamic crosslinkers into several classes of binary, ternary and postconsumer immiscible polymer mixtures in situ. Our combined experimental and modelling studies show that specifically designed classes of dynamic crosslinker can reactivate mixed-plastics chains, represented here by apolar polyolefins and polar polyesters, by compatibilizing them via dynamic formation of graft multiblock copolymers. The resulting in-situ-generated dynamic thermosets exhibit intrinsic reprocessability and enhanced tensile strength and creep resistance relative to virgin plastics. This approach avoids the need for de/reconstruction and thus potentially provides an alternative, facile route towards the recovery of the endowed energy and materials value of individual plastics.

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Fig. 1: Design of UDCs and their molecular and macromolecular features.
Fig. 2: Thermomechanical performance of crosslinked polyethylene and UDC compatibilization of immiscible polyethylene–polyester blends.
Fig. 3: Reprocessability, recyclability and UDC compatibilization of immiscible polyolefin/polyester binary and ternary blends.
Fig. 4: Coarse-grained MD simulations of a binary polymer blend.

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The data that support the finding of this study are present in the paper and/or the Supplementary Information and are available from the corresponding authors on request.

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Acknowledgements

The work done at Colorado State University (CSU) was supported in part by the US Department of Energy, Office of Science, Basic Energy Sciences under award no. DE-SC0022290, and by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office and Bioenergy Technologies Office, performed as part of the BOTTLE Consortium, which includes members from CSU, and funded under contract no. DE-AC36-08GO28308 with the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy. This research used resources of the Argonne Leadership Computing Facility and Center for Nanoscience Materials, which are DOE Office of Science User Facilities supported under contract no. DE-AC02-06CH11357. Research conducted at Columbia used resources supported by the Office of The Director, National Institutes of Health of the National Institutes of Health under award no. S10OD026749. The work done at IIT Madras was supported in part by the Science and Engineering Research Board (SRG/2020/001045) and the National Supercomputing Mission (DST/NSM/R&D_HPC_Applications/2021/40), Government of India. T.S. thanks the Swiss National Science Foundation for a fellowship. D.R. thanks the Alexander von Humboldt Foundation for a Feodor Lynen Research Fellowship.

Author information

Author notes

  1. These authors contributed equally: Ryan W. Clarke, Tobias Sandmeier, Kevin A. Franklin

Authors and Affiliations

  1. Department of Chemistry, Colorado State University, Fort Collins, CO, USA

    Ryan W. Clarke, Kevin A. Franklin & Eugene Y.-X. Chen

  2. Department of Chemistry, Columbia University, New York, NY, USA

    Tobias Sandmeier, Dominik Reich, Xiao Zhang & Tomislav Rovis

  3. Department of Chemical Engineering, Center for Carbon Capture Utilization and Storage, and Center for Atomistic Modeling and Materials Design, India Institute of Technology Madras, Chennai, India

    Nayan Vengallur & Tarak K. Patra

  4. Department of Chemical Engineering, Columbia University, New York, NY, USA

    Robert J. Tannenbaum, Sabin Adhikari & Sanat K. Kumar

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Contributions

E.Y.-X.C. and T.R. conceived the project and directed research. R.W.C., T.S., K.A.F., D.R., X.Z. and R.J.T. designed and conducted experiments and analysed results. N.V., S.A., T.K.P. and S.K.K. performed MD modelling studies and analysed results. R.W.C. and T.S. wrote the initial manuscript and revised subsequent versions. E.Y.-X.C. edited the initial draft and S.K.K., T.R. and E.Y.-X.C. edited various subsequent versions.

Corresponding authors

Correspondence to Sanat K. Kumar, Tomislav Rovis or Eugene Y.-X. Chen.

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A patent (US 2022 63/332,197) has been filed by Colorado State University Research Foundation on findings reported here.

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Extended data figures and tables

Extended Data Fig. 1 Additional cross-sectional SEM images of LMWPE-PLLA blends.

a, Virgin immiscible LMWPE-PLLA. b. Compatibilized LMWPE-PLLA blend processed with 5% UDC2. c, Uncompatibilized blend processed with 5% USC. d, Uncompatibilized blend processed with 5% MDC.

Extended Data Fig. 2 Additional cross-sectional SEM images of LMWPE-P3HB blends.

a, Virgin immiscible LMWPE-P3HB. b, Compatibilized blend processed with UDC1. c, Compatibilized blend processed with UDC2. d, Compatibilized blend processed with UDC3. e, Uncompatibilized blend processed with USC. f, Uncompatibilized blend processed with MDC.

Extended Data Fig. 3 Additional cross-sectional SEM images of LDPE-PLLA blends.

a, Extruded immiscible virgin LDPE-PLLA blend. b, Compatibilized blend via reactive extrusion with 5% UDC1. c, Compatibilized blend via reactive extrusion with 5% UDC2. d, Compatibilized blend via reactive extrusion with 5% UDC3. e, Extruded immiscible virgin blend of LDPE bag and PLLA cup flakes. f, Compatibilized blend of LDPE bag and PLLA cup flakes via reactive extrusion with 5% UDC3.

Extended Data Fig. 4 Additional cross-sectional SEM images of LDPE-P3HB blends.

a, Extruded immiscible virgin LDPE-P3HB. b, Compatibilized blend via reactive extrusion with 5% UDC1. c, Compatibilized blend via reactive extrusion with 5% UDC2. d, Compatibilized blend via reactive extrusion with 5% UDC3.

Extended Data Fig. 5 Additional cross-sectional SEM images of binary blends.

a, Extruded immiscible virgin LDPE-iPP blend. b, Compatibilized LDPE-iPP blend via reactive extrusion with 5% UDC3.

Extended Data Fig. 6 Additional cross-sectional SEM images of binary blends.

a, Extruded immiscible virgin polystyrene (PS)-PLLA blend. b, Compatibilized PS-PLLA blend via reactive extrusion with 5% UDC3.

Extended Data Fig. 7 Additional sectional SEM images of ternary blends.

a, Low-magnification image of extruded immiscible LDPE-iPP-PLLA ternary blend. b, High-magnification image of extruded immiscible LDPE-iPP-PLLA ternary blend. c, Low-magnification image of compatibilized LDPE-iPP-PLLA ternary blend via reactive extrusion with 5% UDC3. d, High-magnification image of compatibilized LDPE-iPP-PLLA ternary blend via reactive extrusion with 5% UDC3.

Extended Data Fig. 8 SAXS/WAXS profile for LDPE-PLLA blends.

a, Domain-averaged combination SAXS/WAXS curves for crosslinked LDPE-PLLA blends relative to the virgin blend and reference homopolymers. b, Effect of temperatures above the component Tm’s on domain-averaged combination SAXS/WAXS curves for UDC3 compatibilized LDPE-P3HB blend.

Extended Data Fig. 9 Stability of the interface with all three types of dynamic crosslinks and mixing binary melts with longer chains, n = 100.

a, Total crosslink fraction = 0.1, (AB fraction = 0.01). b, Total crosslink fraction = 0.21, (AB fraction = 0.013). The interface width is stable when all three crosslinks are allowed. c, MD snapshot of a system with all three types of crosslinks allowed showing no mixing. d, Radial distribution functions of three systems – binary melt with no crosslinks (red), and binary melt with all three types of dynamic crosslinks (green) indicate unmixed states, and binary melt with only AB dynamic crosslinks (blue) indicates mixing.

Extended Data Fig. 10 Time evolution of crosslink fraction and stability of the interface with static AB crosslinks.

a, AB crosslink fraction versus time-step for the static (red) and the dynamic (blue) crosslinks. For the static case, the crosslink fraction, f, monotonically increases and reaches 0.16 whereas for the dynamic case it equilibrates at around 0.10. b, The interface width remains stationary at long time showing no further mixing. c, Completely overlapping gAB(r) (at t = 23 × 106 and 28 × 106 time-steps), further showing that the interface is stable and there is no more progress in mixing.

Supplementary information

Supplementary Information

This file contains Supplementary methods, discussion, Figs.1–82, Tables 1–23 and references.

Supplementary Video 1

Video recording of a reactive melt-extrusion of LDPE-PLLA (50/50 wt%) embedded with UDC3 (5 wt%) in a HAAKE Minilab 3 Micro-Compounder (twin-screw extruder) on manual mode. The compatibilized blend extrudate is shown flowing out through the slit die facet.

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Clarke, R.W., Sandmeier, T., Franklin, K.A. et al. Dynamic crosslinking compatibilizes immiscible mixed plastics. Nature 616, 731–739 (2023). https://doi.org/10.1038/s41586-023-05858-3

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