Research On Acoustic Properties Of The Diaphragm Based On Bacterial Cellulose

As the medium of information transmission, voice affects people's daily lives. The speaker, as a major tool of the sound transmission, plays a key role in the reduction of the sound distortion and the satisfaction of high-speed vibration transmission and the high friction. Especially, the quality of speaker depends on the diaphragm. Therefore, this article attempts to explore the potential application ability of bacterial cellulose membrane as a diaphragm.Bacterial cellulose (BC), synthesized by Gluconacetobacter xylinum, is a kind of ultra-fine and highly pure fiber. In comparison with other high plant cellulose in nature, BC displays unique properties, including higher purity, higher crystallinity, higher mechanical properties and biodegradable properties. Owing to these characteristics, BC membrane has a great potential to be an ideal diaphragm material. Adopting the immerse-adsorption method and the homogeneous modification, we produced the carbon nanotubes (CNTs)/BC composite diaphragm and acetylization BC based diaphragm, respectively. In addition, though measuring the dynamic elastic modulus, the elastic modulus ratio and the loss factor etc, we studied their acoustic performances. The specific works are mainly concentrated on the following parts:1. Preparation and acoustical behavior of BC diaphragmThe wet BC membrane prepared by bio-cultivation was dehydrated by freeze drying, vacuum drying, oven drying, press drying and film-reforming of beating in order to produce BC diaphragm. The basic physical and acoustic performance of the diaphragm was characterized by scanning electron microscopy and dynamic mechanical analysis, etc. According to the scanning electron microscopy, the vacuum-drying diaphragm was the maximum extent possible to maintain the micro nanostructure of BC. The results of dynamic mechanical analysis revealed that the dynamic elastic modulus of BC membrane dried by vacuum was far higher than others and the density of which was lower. Therefore, the elastic ratio of vacuum-drying BC membrane, which reached to 10.27m2/s2, was relatively higher and its loss factor was up to 4.3.2. Preparation and acoustical properties of CNTs/BC composite diaphragmAdopting the immerse-adsorption method, we combined the multi-walled CNTs with BC membrane to get CNTs/BC composite diaphragm and characterized it by scanning electron microscopy and elemental analysis, respectively. Simultaneously, we study its performance as a diaphragm. The elemental analysis results showed that the acoustic properties of CNTs/BC composite diaphragm were considerably improved by adding a reasonable amount of the carbon nanotubes and that CNTs/BC composite diaphragm modified by the surfactant owned more uniform dispersion of carbon nanotubes. In terms of acoustic parameters, with the CNTs content increasing, the density, elastic ratio and loss factor of composite diaphragm were climbing up. When the CNTs content reached to lwt%, however, the upward tendency leveled off. Finally, the optimal preparation process was confirmed, that under the surfactant conditions, the carbon nanotubes concentration was 1 wt% and the adsorption time was 24 hours. In this case, the elastic ratio reached to 15.85m2/s2 and the loss factor was 4.7.3. Preparation and acoustical properties of acetylization BC based diaphragmAcetylization BC based diaphragm was prepared by BC membrane, acetic anhydride and iodine. Scanning electron microscopy, infrared spectrum and substitution degree analysis etc were used to characterize it. The results suggest that the modified acetylization in 60 minutes under 80℃, adding 0.125 mmol catalyst, can get the higher substitution degree acetylization BC membrane. Dynamic mechanical analysis confirmed that we obtained the modified acoustic diaphragm, whose performance was best, under this condition, and that the elastic rate was 10.78m2/s2, the loss factor was 4.2. In addition, the acetylization improved the diaphragm's hydrophobicity, and rendered it operate successfully under a relatively humid environment.