However, most plastic films are difficult to degrade, creating an enormous impact on the environment 13, 14, 15. In particular, plastic thin films are used ubiquitously in commercial speakers as they are low cost and easy to process with controllable thickness and high modulus. In the past few decades, tremendous efforts have been dedicated to developing various acoustic thin film materials based on plastic 7, metal 8, ceramic 9, and carbon-based materials 10, 11, 12 for the purpose of enhancing the quality of the sound output. Acoustic membranes, for example, are generally very thin (micron-scale) and must be mechanically robust with a high modulus to enable a highly sensitive frequency response and high vibrational amplitude. Thin films of several microns or even nanometers in thickness are used in a wide range of applications, including solar cells 1, food packaging 2, water treatment 3, personal electronics 4, 5, and acoustic sensors 6. The ultrathin wood film with excellent mechanical property and acoustic performance is a promising candidate for next-generation acoustic speakers. As a proof-of-concept, we directly use the ultrathin wood film as a diaphragm in a real speaker that can output music. The material’s ultrathin thickness and exceptional mechanical strength enable excellent acoustic properties with a 1.83-times higher resonance frequency and a 1.25-times greater displacement amplitude than a commercial polypropylene diaphragm found in an audio speaker. Benefiting from this aligned and laminated structure, the ultrathin wood film exhibits excellent mechanical properties with a high tensile strength of 342 MPa and a Young’s modulus of 43.6 GPa, respectively. Here we demonstrate that natural wood can be directly converted into an ultrathin film with a record-small thickness of less than 10 μm through partial delignification followed by densification. Thin films of several microns in thickness are ubiquitously used in packaging, electronics, and acoustic sensors.
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