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A strong, biodegradable and recyclable lignocellulosic bioplastic

An Author Correction to this article was published on 20 August 2021

Abstract

Renewable and biodegradable materials derived from biomass are attractive candidates to replace non-biodegradable petrochemical plastics. However, the mechanical performance and wet stability of biomass are generally insufficient for practical applications. Herein, we report a facile in situ lignin regeneration strategy to synthesize a high-performance bioplastic from lignocellulosic resources (for example, wood). In this process, the porous matrix of natural wood is deconstructed to form a homogeneous cellulose–lignin slurry that features nanoscale entanglement and hydrogen bonding between the regenerated lignin and cellulose micro/nanofibrils. The resulting lignocellulosic bioplastic shows high mechanical strength, excellent water stability, ultraviolet-light resistance and improved thermal stability. Furthermore, the lignocellulosic bioplastic has a lower environmental impact as it can be easily recycled or safely biodegraded in the natural environment. This in situ lignin regeneration strategy involving only green and recyclable chemicals provides a promising route to producing strong, biodegradable and sustainable lignocellulosic bioplastic as a promising alternative to petrochemical plastics.

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Fig. 1: The preparation of high-performance lignocellulosic bioplastic.
Fig. 2: The fabrication process of the lignocellulosic bioplastic by the in situ lignin regeneration method.
Fig. 3: Structural and compositional characterization of the lignocellulosic bioplastic.
Fig. 4: The structure of the regenerated lignin and the interaction between the regenerated lignin and cellulose.
Fig. 5: The biodegradability, recyclability and environmental impacts of the lignocellulosic bioplastic.

Data availability

Data are available on reasonable request from the authors, according to their contributions.

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Acknowledgements

We acknowledge the support of the Maryland Nanocenter, its Surface Analysis Center and AIMLab. We acknowledge J. Gao for his experimental suggestions.

Author information

Authors and Affiliations

Authors

Contributions

L.H., Q.X. and C.C. designed the experiments. Q.X. carried out experiments. Y.G.Y. and S.H. analysed the mechanical data. Y.Z. helped with the preparation of the large-scale bioplastic film. Q.X. and J.L. fabricated the lignocellulosic bioplastic parts by compression moulding. T.L. and X.P. provided some useful suggestions. Y.Y. provided the LCAs. L.H., Q.X. and C.C. collaboratively analysed the data and wrote the paper. All authors commented on the final manuscript.

Corresponding authors

Correspondence to Yuan Yao or Liangbing Hu.

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Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Sustainability thanks Robert Allen, Eun Yeol Lee and Tong-Qi Yuan for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 The fabrication mechanism of the lignocellulosic bioplastic.

Loose and porous wood powder, composed of cellulose, lignin and hemicellulose, serves as the starting material. After DES (ChCl/oxalic acid) treatment, the cellulose fibres are fibrillated into micro/nanofibrils while DES dissolves the lignin. Water can interact with the hydrophobic DES through hydrogen bonding interactions. Thus, water can be added as a green antisolvent in the system, causing the hydrophobic lignin to regenerate. After filtering, we obtain a cellulose–lignin slurry, the solid content of which we can control by varying the water content. The lignocellulosic bioplastic film can then be obtained by casting the slurry at room temperature.

Extended Data Fig. 2 The structure of the wood powder.

a-d, Photograph (a), SEM image (b), magnified SEM image (c) and SAXS pattern (d) of the wood powder. Compared to the isotropic structure of lignocellulosic bioplastic, the wood powder shows more structural inhomogeneity.

Extended Data Fig. 3 The tensile strength and fracture surfaces of the lignocellulosic bioplastic.

a, The tensile stress-strain curves of the cellulose film and lignocellulosic bioplastic. b, The strength and toughness of the cellulose film and lignocellulosic bioplastic. The lignocellulosic bioplastic demonstrates excellent mechanical properties with a high tensile strength of 128 MPa and toughness of 2.8 MJ·m3, which are 7- and 8-times higher than cellulose film (18 MPa and 0.35 MJ·m3), respectively. c-d, Digital and SEM images of the fracture surfaces of the (c) lignocellulosic bioplastic and (d) cellulose film after tensile testing. The samples have ~1 wt.% water content. The cellulose film fractured by macro-fibre slippage from the loose fibre network structure, in which most fibres were not broken, indicating the binding strength between the cellulose fibres in the film is weaker than the strength of the fibres themselves. In contrast, broken fibres appear in the fracture zone of the lignocellulosic bioplastic, suggesting its binding strength is greater than the strength of its constituent fibres due to the intertwining cellulose micro/nanofibrils and lignin network. Such entangled interaction between the micro/nanofibrils and high adhesion mediated by the in situ regenerated lignin matrix with abundant hydrogen bonding and van der Waals forces contribute to the outstanding mechanical properties of the lignocellulosic bioplastic.

Extended Data Fig. 4 The excellent mechanical strength of the lignocellulosic bioplastic.

a, Photographs of the lignocellulosic bioplastic (8 cm×3.5 cm×0.1 cm), b, including under a heavy load (200 g). c-d, The excellent foldability of the lignocellulosic bioplastic. e, The unfolded lignocellulosic bioplastic features a sharp crease. f, Photograph of the unfolded lignocellulosic bioplastic bearing a heavy load (200 g). Although the lignocellulosic bioplastic had undergone folding, the creased material can still easily bear the applied weight without failing.

Extended Data Fig. 5 The water stability of the lignocellulosic bioplastic.

a. Photographs of water droplets on the cellulose film and lignocellulosic bioplastic surfaces over time (0–10 min). The lignocellulosic bioplastic has a higher water contact angle (90.0 ± 8°) than that of pure cellulose film (78.7 ± 10°), demonstrating its slightly greater tendency to repel water. After 10 minutes, the water droplet gradually spreads out and adheres to the cellulose film (28.2 ± 6°), whereas the shape of the droplet on the lignocellulosic bioplastic surface remains relatively stable (71.8 ± 7°). b, Water absorption of the cellulose film and lignocellulosic bioplastic over 140 min. The inset shows photographs of water droplets on a sloping lignocellulosic bioplastic surface (right), demonstrating the material’s excellent water stability, while the water is quickly absorbed on the cellulose film (left). The lignocellulosic bioplastic has exceptionally lower water absorption (~30%) than that of the cellulose film (~100%). In contrast, water droplets easily permeate into the hydrophilic cellulose film even on inclined surfaces. c, Water stability test of cellulose film and lignocellulosic bioplastic in water for 30 days. The cellulose film disintegrates while the lignocellulosic bioplastic film maintains its shape. We immersed the cellulose film and lignocellulosic bioplastic in water for thirty days. After this time, we found the cellulose film completely disintegrated into microfibers, while the lignocellulosic bioplastic showed good stability in the wet environment, retaining its shape without any fractures.

Extended Data Fig. 6 The degradability tests of the lignocellulosic bioplastic and PVC materials.

Direct outdoor exposure was carried out to evaluate the degradability of the lignocellulosic bioplastic, which was placed on grass and exposed to the sun, wind and rain (College Park, Maryland, U.S., from October 20, 2019 to March 10, 2020). After three months, the dimensions of the lignocellulosic bioplastic increased as it became more swollen. After ~4 months, the lignocellulosic bioplastic became cracked and fragmented and its original structure completely degraded after five months. Meanwhile, the PVC remained almost the same as on the first day, demonstrating it cannot be degraded under natural conditions.

Extended Data Fig. 7 Flow diagram for continuous in situ lignin regeneration treatment and the recycling of the DES.

After mixing and heating of the wood powder and DES, followed by the addition of water to in situ regenerate the lignin, we can use an in-line filter to separate the cellulose–lignin slurry and solvent, in which the DES and water make up the filter liquor. DES can then be purified by heating the mixture to remove water. The recovered DES can be recycled in the system to treat new lignocellulosic starting materials. Water can also be collected using a condenser and recycled again to serve as the antisolvent for lignin regeneration.

Extended Data Fig. 8 The universality of in situ lignin regeneration approach.

The lignocellulosic bioplastic can be derived from various lignocellulosic biomass sources, including wood, wheat straw, grass and bagasse, demonstrating the strong universality of this approach.

Extended Data Fig. 9 The life cycle impact assessment results of lignocellulosic and other biodegradable plastics per cm3/MPa.

Across most environmental impact categories, the lignocellulosic bioplastic developed in this work is more environmentally favourable than PHA, PLA, PBS, PCL and PBAT. There are a few exceptions. Compared with PBAT, the lignocellulosic bioplastic has higher impacts in three categories, including eutrophication, human health - carcinogenics and respiratory effects. For all three categories, the impacts of lignocellulosic bioplastics are driven by electricity consumption, which accounted for 71–86% of the results based on the contribution analysis. The electricity was assumed to be the U.S. average grid in this study. The environmental impacts could be lower if renewable energy were used. To estimate the impacts of using renewable energy, a scenario using electricity generated from wind was evaluated and the results are shown in Extended Data Fig. 9 as triangles. The Life Cycle Inventory (LCI) of wind energy was obtained from Ecoinvent database for onshore generation in the U.S. The environmental impacts of the lignocellulosic bioplastic using wind energy are the lowest across all the impact categories except fossil fuel depletion (close to the upper bounds of the results of PLA and PBAT).

Extended Data Fig. 10 Environmental impacts of the moulded lignocellulosic bioplastic compared to PP, PET and ABS.

Compared to PP and ABS, the lignocellulosic bioplastic is at the lower end across all environmental impact categories. Compared to PET, the lignocellulosic bioplastic has lower environmental impacts in categories such as ecotoxicity, eutrophication and human health. For other categories, the lignocellulosic bioplastic has comparable results with PET and close to the higher bounds of PET’s impacts in ozone depletion, smog formation and fossil fuel depletion. Similar to the LCAs for plastic films, we included a renewable energy scenario to investigate the impacts of using wind and the results are shown as triangles (Extended Data Fig. 10). Compared with PP, PET and ABS, the environmental impacts of the lignocellulosic bioplastic using wind energy were the lowest across all the impact categories, except for fossil fuel depletion (which was close to the upper bound of PET’s results).

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Supplementary Notes 1–8, Figs. 1–19, Tables 1–3 and refs. 1–60.

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Xia, Q., Chen, C., Yao, Y. et al. A strong, biodegradable and recyclable lignocellulosic bioplastic. Nat Sustain 4, 627–635 (2021). https://doi.org/10.1038/s41893-021-00702-w

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