Research ArticleMATERIALS SCIENCE

Bioinspired polymeric woods

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Science Advances  10 Aug 2018:
Vol. 4, no. 8, eaat7223
DOI: 10.1126/sciadv.aat7223
  • Fig. 1 Fabrication scheme of the bioinspired polymeric woods and kinds of composite woods based on PF and MF.

    (A) Starting solution (sol) including water-soluble thermoset resins, CTS, and acetic acid (HAc), forming a homogeneous polymer solution. (B) Predesigned matrix prepared by the ice template–induced self-assembly and freeze-drying process. (C) Final polymeric woods after thermocuring the predesigned matrix. The resins are completely cross-linked. (D) Photographs of the artificial polymeric woods based on phenolic resin (top, cellular CPF-4-5) and melamine resin (bottom, CMF-3-5). (E) Scheme illustration showing the fabrication of various composite woods by adding ions or functional nanomaterials into the polymer solution, followed by the above self-assembly and thermocuring process. (F) Photographs of various composite woods based on melamine resin, including MF/Co (CMF-2/Co-0.2), MF/SiO2 (CMF-2/SiO2-1), MF/SiC (CMF-2/SiC@RF-5), and MF/GO (CMF-2/GO-1). Size of the composite woods, ~1 cm × 1 cm × 1 cm.

  • Fig. 2 The structural characterization of the balsa and polymeric woods.

    (A) Balsa wood with a density of ~90 mg cm−3. (B and C) SEM images of the cross section (perpendicular to the channel direction) and the longitudinal section (parallel to the channel direction) of the balsa wood. (D) Artificial CPF wood (CPF-4-5) with a density of ~280 mg cm−3. (E and F) SEM images of the cross section and the longitudinal section of the CPF wood. (G) Artificial CMF wood (CMF-3-5) with a density of ~560 mg cm−3. (H and I) SEM images of the cross section and the longitudinal section of the CMF wood. (J) PF/GO composite wood (CPF-1/GO-1) with a density of ~85 mg cm−3. (K and L) SEM images of the cross section and the longitudinal section of the PF/GO composite wood. The inset in (L) shows the enlarged image of the node of the walls. (M) 3D reconstruction of the CPF wood (CPF-4-5) derived from x-ray microtomography, and microtomography images display the straight, parallel tubular pores. Sale bars, 200 μm.

  • Fig. 3 Compressive performances and failure mechanisms of the polymeric woods.

    (A) Axial compressive stress-strain curves of typical polymeric woods. (B) Relative strength and modulus as functions of the relative density of CPF woods. (C) Ashby chart plotting compressive yield strength versus density for polymeric woods and other engineered materials, including cast resin Embedded Image (14), SiC foam Embedded Image (15), 3D-printed honeycomb Embedded Image (14), mullite-ZrO2 foam Embedded Image(16), PF carbon foam Embedded Image (24), and RF aerogel Embedded Image (25). Symbols ‖ and ⊥ represent the compressive directions that are parallel and perpendicular to the channels, respectively. (D and E) The compressive stress-strain curve, photograph, and micrographs show the bending-dominated failure of CPF-1-5 and the brittle cracking failure of CPF-5-5. The black boxes in (E) display the damage induced by the exfoliation of little blocks before the fracture appeared. (F and G) FEM simulations of thin- and thick-walled honeycomb structures for the low- and high-density polymeric woods. The honeycomb structures are colored by the total displacement of element nodes. (F) Bending-dominated wall buckling of thin-walled honeycomb structure. (G) Cracking failure of thick-walled honeycomb structure.

  • Fig. 4 Corrosion resistance and thermal conductivities of polymeric woods.

    (A) Axial compressive stress-strain curves of two typical polymeric woods before and after immersing in water or acid solution for 30 days. (B) Thermal conductivities of balsa, commercial PF foam, and polymeric woods. (C) Schematic illustration showing the difference of thermal conductivity in the radial and axial directions. (D) Thermal conductivity λ versus specific strength for Embedded Image polymeric woods, traditional aerogel-like materials, and other cellular ceramic materials, including polyurethane PU aerogels Embedded Image (38, 39), PF foams Embedded Image (40), nanocellulose aerogels Embedded Image (41), SiO2 aerogels Embedded Image (42), cellular CNF/GO/boric acid (BA)/sepiolite nanorods (SEP) aerogels Embedded Image (31), SiC foams Embedded Image (15), and mullite-ZrO2 aerogels Embedded Image (16). The polymer/SiO2 aerogels include pectin/SiO2 aerogels Embedded Image (43), cellulose/SiO2 aerogels Embedded Image (44), isocyanate/SiO2 aerogels Embedded Image (45, 46), and polyurethane/SiO2 aerogels Embedded Image (47).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/8/eaat7223/DC1

    Fig. S1. The chemical structures of matrix materials.

    Fig. S2. SEM images of various MF-based composite woods.

    Fig. S3. Large-scale fabrication of the polymeric wood.

    Fig. S4. Photography of the homemade equipment to control the freezing rate.

    Fig. S5. SEM images showing the changing trend of the microstructures of CPF woods with the increasing resol content and freezing rate, respectively.

    Fig. S6. Statistical analysis of area distribution of the channels of CPF woods prepared at different freezing rates.

    Fig. S7. Statistical analysis of wall thickness.

    Fig. S8. SEM images showing the changing trend of the microstructures of CPF woods with the increasing resol content and curing temperature, respectively.

    Fig. S9. Statistical analysis of area distribution of the channels of CPF woods prepared by using different curing temperatures.

    Fig. S10. Statistical analysis of wall thickness.

    Fig. S11. The averaged pore area and averaged wall thickness of CPF woods.

    Fig. S12. SEM images of the CMF woods.

    Fig. S13. Densities and porosities of the polymeric woods.

    Fig. S14. The mechanical performances of CPF woods prepared at different freezing rates.

    Fig. S15. The mechanical performances of CPF woods prepared at different curing temperatures.

    Fig. S16. The mechanical performances of CMF woods prepared at different freezing rates.

    Fig. S17. An Ashby chart plotting compressive stiffness versus density for CPF and CMF woods.

    Fig. S18. The radial compression tests of balsa, CPF, and CMF woods.

    Fig. S19. The axial compression of the balsa wood.

    Fig. S20. The in situ micrographs show the failure of polymeric woods with relatively low density.

    Fig. S21. The in situ micrographs show the failure of different polymeric woods with relatively high density.

    Fig. S22. Thin-walled model for the compression simulations of low-density polymeric woods.

    Fig. S23. The simulation models and results.

    Fig. S24. A similar thin-walled model was also simulated as a comparison.

    Fig. S25. Three-point bending test of balsa woods, polymeric woods, and a typical composite wood.

    Fig. S26. The contact angles of the typical polymeric woods.

    Fig. S27. The water resistance of balsa woods.

    Fig. S28. The fire resistance of polymeric woods and balsa wood under an alcohol flame.

    Fig. S29. The contrasts of CMF woods with various CMF-based composite woods in mechanical performance.

    Table S1. The details of the synthesis of typical CPF and CMF woods and their respective parameters.

    Table S2. Vertical burning test and LOI of the balsa (~300 mg cm−3) and polymeric woods.

    Movie S1. 3D observation of a typical CPF wood by x-ray microtomography.

    Movie S2. The in situ observation of failure process of the low-density CPF-1-5 during the compression, revealing the gradual plastic bending of cell walls.

    Movie S3. The in situ observation of failure process of the low-density CMF-1-5 during the compression, revealing the gradual plastic bending of cell walls.

    Movie S4. The in situ observation of failure process of the high-density CPF-5-5 during the compression, revealing the brittle fracture behaviors.

    Movie S5. The in situ observation of failure process of the high-density CMF-2-5 during the compression, revealing the brittle fracture behaviors.

    Movie S6. The burning test of the CPF-1/GO-1 composite wood by using an alcohol lamp flame.

    Movie S7. The burning test of the balsa wood by using an alcohol lamp flame.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. The chemical structures of matrix materials.
    • Fig. S2. SEM images of various MF-based composite woods.
    • Fig. S3. Large-scale fabrication of the polymeric wood.
    • Fig. S4. Photography of the homemade equipment to control the freezing rate.
    • Fig. S5. SEM images showing the changing trend of the microstructures of CPF woods with the increasing resol content and freezing rate, respectively.
    • Fig. S6. Statistical analysis of area distribution of the channels of CPF woods prepared at different freezing rates.
    • Fig. S7. Statistical analysis of wall thickness.
    • Fig. S8. SEM images showing the changing trend of the microstructures of CPF woods with the increasing resol content and curing temperature, respectively.
    • Fig. S9. Statistical analysis of area distribution of the channels of CPF woods prepared by using different curing temperatures.
    • Fig. S10. Statistical analysis of wall thickness.
    • Fig. S11. The averaged pore area and averaged wall thickness of CPF woods.
    • Fig. S12. SEM images of the CMF woods.
    • Fig. S13. Densities and porosities of the polymeric woods.
    • Fig. S14. The mechanical performances of CPF woods prepared at different freezing rates.
    • Fig. S15. The mechanical performances of CPF woods prepared at different curing temperatures.
    • Fig. S16. The mechanical performances of CMF woods prepared at different freezing rates.
    • Fig. S17. An Ashby chart plotting compressive stiffness versus density for CPF and CMF woods.
    • Fig. S18. The radial compression tests of balsa, CPF, and CMF woods.
    • Fig. S19. The axial compression of the balsa wood.
    • Fig. S20. The in situ micrographs show the failure of polymeric woods with relatively low density.
    • Fig. S21. The in situ micrographs show the failure of different polymeric woods with relatively high density.
    • Fig. S22. Thin-walled model for the compression simulations of low-density polymeric woods.
    • Fig. S23. The simulation models and results.
    • Fig. S24. A similar thin-walled model was also simulated as a comparison.
    • Fig. S25. Three-point bending test of balsa woods, polymeric woods, and a typical composite wood.
    • Fig. S26. The contact angles of the typical polymeric woods.
    • Fig. S27. The water resistance of balsa woods.
    • Fig. S28. The fire resistance of polymeric woods and balsa wood under an alcohol flame.
    • Fig. S29. The contrasts of CMF woods with various CMF-based composite woods in mechanical performance.
    • Table S1. The details of the synthesis of typical CPF and CMF woods and their respective parameters.
    • Table S2. Vertical burning test and LOI of the balsa (~300 mg cm−3) and polymeric woods.

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mov format). 3D observation of a typical CPF wood by x-ray microtomography.
    • Movie S2 (.mov format). The in situ observation of failure process of the low-density CPF-1-5 during the compression, revealing the gradual plastic bending of cell walls.
    • Movie S3 (.mov format). The in situ observation of failure process of the low-density CMF-1-5 during the compression, revealing the gradual plastic bending of cell walls.
    • Movie S4 (.mov format). The in situ observation of failure process of the high-density CPF-5-5 during the compression, revealing the brittle fracture behaviors.
    • Movie S5 (.mov format). The in situ observation of failure process of the high-density CMF-2-5 during the compression, revealing the brittle fracture behaviors.
    • Movie S6 (.mov format). The burning test of the CPF-1/GO-1 composite wood by using an alcohol lamp flame.
    • Movie S7 (.mov format). The burning test of the balsa wood by using an alcohol lamp flame.

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