Flame-retardant, recyclable, and hydrothermally degradable epoxy resins and their degradation products for high-strength adhesives

Abstract

To date, sustainable thermosetting polymers and their composites have emerged to address recyclability issues. However, achieving mild degradation of these polymers compromises their comprehensive properties such as flame retardancy and glass transition temperature (T_g). Moreover, the reuse of degradation products after recycling for upcycling remains a significant challenge. This study introduces phosphorus-containing anhydride into tetraglycidyl methylene diphenylamine via a facile anhydride-epoxy curing equilibrium with triethanolamine as a transesterification modifier to successfully prepare flame-retardant, malleable, reprocessable, and easily hydrothermally degradable epoxy vitrimers and recyclable carbon fiber-reinforced epoxy composites (CFRECs). The composite exhibited excellent flame retardancy and a high T_g of 192 °C, while the presence of stoichiometric primary hydroxyl groups along the ester-bonding crosslinks enabled environmentally friendly degradation (in H₂O) at 200 °C without any external catalyst. Under mild degradation conditions, the fibers of the composite material were successfully recycled without being damaged, and the degradation products were reused to create a recyclable adhesive with a peel strength of 3.5 MPa. This work presents a method to produce flame retardants and sustainable CFRECs for maximizing the value of degradation products, offering a new upcycling method for high-end applications.

Key words： epoxy vitrimer; carbon fiber composites; flame retardancy; upcycling

Competing interests

The authors declare that they have no competing interests.

Acknowledgements

Financial supports by the National Key Research and Development Program of China (Grant No. 2021YFB3700201), the National Science Foundation of China (Grant Nos. 21975166, 51991351, 51991350), the 111 Project (Grant No. B20001) and the Fundamental Research Funds for the Central Universities are sincerely acknowledged.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11705-024-2497-y and is accessible for authorized users.

References

1 Discekici E H , St Amant A H , Nguyen S N , Lee I H , Hawker C J , Read de Alaniz J . Endo and exo Diels-Alder adducts: temperature-tunable building blocks for selective chemical functionalization. Journal of the American Chemical Society, 2018, 140: 5009–5013

2 Yu K , Shi Q , Dunn M L , Wang T J , Qi H J . Carbon fiber reinforced thermoset composite with near 100% recyclability. Advanced Functional Materials, 2016, 26(33): 6098–6106

3 Vollmer I , Jenks M J F , Roelands M C P , White R J , van Harmelen T , de Wild P , van der Laan G P , Meirer F , Keurentjes J T F , Weckhuysen B M . Beyond mechanical recycling: giving new life to plastic waste. Angewandte Chemie International Edition, 2020, 59(36): 15402–15423

4 Chao A , Negulescu I , Zhang D H . Dynamic covalent polymer networks based on degenerative lmine bond exchange: tuning the malleability and self-healing properties by solvent. Macromolecules, 2016, 49(17): 6277–6284

5 Denissen W , Winne J M , Du Prez F E . Vitrimers: permanent organic networks with glass-like fluidity. Chemical Science, 2016, 7(1): 30–38

6 Montarnal D , Capelot M , Tournilhac F , Leibler L . Silica-like malleable materials from permanent organic networks. Science, 2011, 334(6058): 965–968

7 Xu Y Z , Dai S L , Bi L W , Jiang J X , Zhang H B , Chen Y X . Catalyst-free self-healing bio-based vitrimer for a recyclable, reprocessable, and self-adhered carbon fiber reinforced composite. Chemical Engineering Journal, 2022, 429: 132518

8 Capelot M , Unterlass M M , Tournilhac F , Leibler L . Catalytic control of the vitrimer glass transition. ACS Macro Letters, 2012, 1(7): 789–792

9 Jin Y H , Lei Z P , Taynton P , Huang S F , Zhang W . Malleable and recyclable thermosets: the next generation of plastics. Matter, 2019, 1(6): 1456–1493

10 Kloxin C J , Bowman C N . Covalent adaptable networks: smart, reconfigurable and responsive network systems. Chemical Society Reviews, 2013, 42(17): 7161–7173

11 Ding X M , Chen L , Xu Y J , Shi X H , Luo X , Song X , Wang Y Z . Robust epoxy vitrimer with simultaneous ultrahigh impact property, fire safety, and multipath recyclability via rigid-flexible imine networks. ACS Sustainable Chemistry & Engineering, 2023, 11(39): 14445–14456

12 Podgórski M , Fairbanks B D , Kirkpatrick B E , McBride M , Martinez A , Dobson A , Bongiardina N J , Bowman C N . Covalent adaptable networks: toward stimuli-responsive dynamic thermosets through continuous development and improvements in covalent adaptable networks. Advanced Materials, 2020, 32(20): 2070158

13 Liu Y Y , Liu G L , Li Y D , Weng Y X , Zeng J B . Biobased high-performance epoxy vitrimer with UV shielding for recyclable carbon fiber reinforced composites. ACS Sustainable Chemistry & Engineering, 2021, 9(12): 4638–4647

14 Liu T , Hao C , Wang L W , Li Y Z , Liu W C , Xin J N , Zhang J W . Eugenol-derived biobased epoxy: shape memory, repairing, and recyclability. Macromolecules, 2017, 50(21): 8588–8597

15 Liu T , Zhang S , Hao C , Verdi C , Liu W C , Liu H , Zhang J W . Glycerol induced catalyst-free curing of epoxy and vitrimer preparation. Macromolecular Rapid Communications, 2019, 40(7): 1800889

16 Liu T , Zhao B M , Zhang J W . Recent development of repairable, malleable and recyclable thermosetting polymers through dynamic transesterification. Polymer, 2020, 194: 122392

17 Yang Y , Xu Y S , Ji Y , Wei Y . Functional epoxy vitrimers and composites. Progress in Materials Science, 2021, 120: 100710

18 Gu S , Xiao Y F , Tan S H , Liu B W , Guo D M , Wang Y Z , Chen L . Neighboring molecular engineering in Diels-Alder chemistry enabling easily recyclable carbon fiber reinforced composites. Angewandte Chemie International Edition, 2023, 62(51): e202312638

19 Chen J H , Liu B W , Lu J H , Lu P , Tang Y L , Chen L , Wang Y Z . Catalyst-free dynamic transesterification towards a high-performance and fire-safe epoxy vitrimer and its carbon fiber composite. Green Chemistry, 2022, 24(18): 6980–6988

20 Chen J H , Zhang Y R , Wang Y Z , Chen L . Reprocessable, malleable and intrinsically fire-safe epoxy resin with catalyst-free mixed carboxylate/phosphonate transesterification. Polymer, 2023, 281: 126083

21 Feng X M , Fan J Z , Li A , Li G Q . Multireusable thermoset with anomalous flame-triggered shape memory effect. ACS Applied Materials & Interfaces, 2019, 11(17): 16075–16086

22 Ren Q R , Gu S , Liu J H , Wang Y Z , Chen L . Catalyst-free reprocessable, degradable and intrinsically flame-retardant epoxy vitrimer for carbon fiber reinforced composites. Polymer Degradation & Stability, 2023, 211: 110315

23 Zhang Y R , Gu S , Wang Y Z , Chen L . Intrinsically flame-retardant epoxy vitrimers with catalyst-free multi-reprocessability towards sustainable carbon fiber composites. Sustainable Materials and Technologies, 2024, 40: e00883

24 Chen J H , Lu J H , Pu X L , Chen L , Wang Y Z . Recyclable, malleable and intrinsically flame-retardant epoxy resin with catalytic transesterification. Chemosphere, 2022, 294: 133778

25 Hamel C M , Kuang X , Chen K J , Qi H J . Reaction-diffusion model for thermosetting polymer dissolution through exchange reactions assisted by small-molecule solvents. Macromolecules, 2019, 52(10): 3636–3645

26 Kuang X , Zhou Y Y , Shi Q , Wang T J , Qi H J . Recycling of epoxy thermoset and composites via good solvent assisted and small molecules participated exchange reactions. ACS Sustainable Chemistry & Engineering, 2018, 6(7): 9189–9197

27 Liu Z H , Fang Z Z , Zheng N , Yang K X , Sun Z , Li S J , Li W , Wu J J , Xie T . Chemical upcycling of commodity thermoset polyurethane foams towards high-performance 3D photo-printing resins. Nature Chemistry, 2023, 15(12): 1773–1779

28 Liu T , Guo X L , Liu W C , Hao C , Wang L W , Hiscox W C , Liu C Y , Jin C , Xin J , Zhang J W . Selective cleavage of ester linkages of anhydride-cured epoxy using a benign method and reuse of the decomposed polymer in new epoxy preparation. Green Chemistry, 2017, 19(18): 4364–4372

29 Gu S , Xu S D , Lu J H , Pu X L , Ren Q R , Xiao Y F , Wang Y Z , Chen L . Phosphonate-influenced Diels-Alder chemistry toward multi-path recyclable, fire safe thermoset and its carbon fiber composites. EcoMat, 2023, 5(9): e12388

30 Ye C N , Voet V S D , Folkersma R , Loos K . Robust superamphiphilic membrane with a closed-loop life cycle. Advanced Materials, 2021, 33(15): 2008460

31 Denissen W , Droesbeke M , Nicolaÿ R , Leibler L , Winne J M , Du Prez F E . Chemical control of the viscoelastic properties of vinylogous urethane vitrimers. Nature Communications, 2017, 8(1): 14857

32 Ma Z Y , Wang Y , Zhu J , Yu J R , Hu Z M . Bio-based epoxy vitrimers: reprocessibility, controllable shape memory, and degradability. Journal of Polymer Science. Part A, Polymer Chemistry, 2017, 55(10): 1790–1799

33 Delahaye M , Winne J M , Du Prez F E . Internal catalysis in covalent adaptable networks: phthalate monoester transesterification as a versatile dynamic cross-linking chemistry. Journal of the American Chemical Society, 2019, 141(38): 15277–15287

34 Hao C , Liu T , Liu W C , Fei M E , Shao L , Kuang W B , Simmons K L , Zhang J W . Recyclable CFRPs with extremely high Tg: hydrothermal recyclability in pure water and upcycling of the recyclates for new composite preparation. Journal of Materials Chemistry. A, Materials for Energy and Sustainability, 2022, 10(29): 15623–15633

35 Hao C , Liu T , Zhang S , Liu W C , Shan Y F , Zhang J W . Triethanolamine-mediated covalent adaptable epoxy network: excellent mechanical properties, fast repairing, and easy recycling. Macromolecules, 2020, 53(8): 3110–3118

36 Van Lijsebetten F , Spiesschaert Y , Winne J M , Du Prez F E . Reprocessing of covalent adaptable polyamide networks through internal catalysis and ring-size effects. Journal of the American Chemical Society, 2021, 143(38): 15834–15844

37 Zhang J H , Mi X Q , Chen S Y , Xu Z J , Zhang D H , Miao M H , Wang J S . A bio-based hyperbranched flame retardant for epoxy resins. Chemical Engineering Journal, 2020, 381: 122719

38 Liu X F , Liu B W , Luo X , Guo D M , Zhong H Y , Chen L , Wang Y Z . A novel phosphorus-containing semi-aromatic polyester toward flame retardancy and enhanced mechanical properties of epoxy resin. Chemical Engineering Journal, 2020, 380: 122471

39 Zhang A L , Zhang J Z , Liu L N , Dai J F , Lu X Y , Huo S Q , Hong M , Liu X H , Lynch M , Zeng X S . . Engineering phosphorus-containing lignin for epoxy biocomposites with enhanced thermal stability, fire retardancy and mechanical properties. Journal of Materials Science and Technology, 2023, 167: 82–93

40 Bai Z C , Huang T , Shen J H , Xie D , Xu J J , Zhu J H , Chen F Q , Zhang W B , Dai J F , Song P A . Molecularly engineered polyphosphazene-derived for advanced polylactide biocomposites with robust toughness, flame retardancy, and UV resistance. Chemical Engineering Journal, 2024, 482: 148964

41 Huo S Q , Sai T , Ran S Y , Guo Z H , Fang Z P , Song P A , Wang H . A hyperbranched P/N/B-containing oligomer as multifunctional flame retardant for epoxy resins. Composites. Part B, Engineering, 2022, 234: 109701

42 Huo S Q , Song P A , Yu B , Ran S Y , Chevali V S , Liu L , Fang Z P , Wang H . Phosphorus-containing flame retardant epoxy thermosets: recent advances and future perspectives. Progress in Polymer Science, 2021, 114: 101366

43 Velencoso M M , Battig A , Markwart J C , Schartel B , Wurm F R . Molecular firefighting-how modern phosphorus chemistry can help solve the challenge of flame retardancy. Angewandte Chemie International Edition, 2018, 57(33): 10450–10467

44 Zhang L , Li Z , Bi Q Q , Jiang L Y , Zhang X D , Tang E , Cao X M , Li H F , Hobson J , Wang D Y . Strong yet tough epoxy with superior fire suppression enabled by bio-based phosphaphenanthrene towards in-situ formed Diels-Alder network. Composites. Part B, Engineering, 2023, 251: 110490

45 ChenQHuoS QLuY XDingM MFengJ BHuangG BXuHSunZ QWangZ ZSongP A. Heterostructured graphene@silica@iron phenylphosphinate for fire-retardant, strong, thermally conductive yet electrically insulated epoxy nanocomposites. Small, March 1, 2024, 2310724

46 Nie S B , Zhao Z Q , Xu Y X , He W , Zhai W L , Yang J N . A strategy to synthesize phosphorus-containing nickel phyllosilicate whiskers to enhance the flame retardancy of epoxy composites with excellent mechanical and dry-friction properties. Frontiers of Chemical Science and Engineering, 2024, 18(3): 28–35

47 Nie S B , He W , Xu Y X , Zhai W L , Zhang H , Yang J N . Molybdenum disulfide@nickel phyllosilicate hybrid for improving the flame retardancy and wear resistance of epoxy composites. Frontiers of Chemical Science and Engineering, 2023, 17(12): 2114–2126

48 Ding X M , Chen L , Luo X , He F M , Xiao Y F , Wang Y Z . Biomass-derived dynamic covalent epoxy thermoset with robust mechanical properties and facile malleability. Chinese Chemical Letters, 2022, 33(6): 3245–3248

49 Shao L , Chang Y C , Zhao B M , Yan X Y , Bliss B J , Fei M E , Yu C H , Zhang J W . Bona fide upcycling strategy of anhydride cured epoxy and reutilization of decomposed dual monomers into multipurpose applications. Chemical Engineering Journal, 2023, 464: 142735

50 Li P Y , Ma S Q , Wang B B , Xu X W , Feng H Z , Yu Z , Yu T , Liu Y L , Zhu J . Degradable benzyl cyclic acetal epoxy monomers with low viscosity: synthesis, structure-property relationships, application in recyclable carbon fiber composite. Composites Science and Technology, 2022, 219: 109243