Paper Title
Investigation of the Damping Ability of Biopolymer Foam Structures by Extending the Excitation Frequency Range

Abstract
Biopolymers and their foams offer a promising alternative in applications, for example, short life cycle products. However, their field of application is currently not well defined. The primary function of polymeric foam structures can be mechanical protection, sound, and vibration damping; therefore, these structures' energy absorption capacity has paramount importance. Mechanical characterization of foam structures can be performed using dynamic mechanical analysis (DMA). The great advantage of the dynamic mechanical analysis is that it provides information on the material's viscoelastic properties (storage and loss modulus) over a wide frequency range. Furthermore, using the principle of time-temperature- equivalence (TTS), the frequency range of the test can be extended, especially with respect to the frequency range of the audible sound (e.g., 36 to 20.000 Hz). In our research, we created several poly(lactic acid) (Ingeo 4060D) based biopolymer syntactic foam sheets using 2, 4, and 8 wt% of thermally expandable foaming agent. Subsequently, we tested the produced sheet foam samples with the help of a dynamic mechanical analyzer. After which, using the principle of time-temperature- equivalence (TTS), we implemented the test frequency range extension. The master curves thus created provide information on the value of the loss modulus characteristic of biopolymer structures as a function of the frequency. Acknowledgments: This research was supported by the ÚNKP-20-3 New National Excellence Program of the Ministry for Innovation and Technology from the source of the National Research, Development and Innovation Fund (ÚNKP-20-3-II-BME-158). This research was also supported by János Bolyai Research Scholarship of the Hungarian Academy of Sciences. Keywords - poly(lactic acid), thermally expandable microspheres, polymer foam, damping