Tensile test for hydrated gel-films of bacterial cellulose

Bacterial cellulose (BC) finds multiple applications due to unique physicochemical properties and biocompatibility. The mechanical characteristics of hydrated BC such as Young modulus, tear strength, and tensile elongation under maximum load are crucial in some instances. The diversity of test methods does not allow correct comparison of the results of BC thermomechanical analysis (TMA) obtained by different researchers. However, current standards for determination of the mechanical characteristics are not intended for highly hydrated samples and do not take into account conditions for their use. The goal of the study is to develop a tensile test method for hydrated gel films of bacterial cellulose and to compare their relative elongation when tested in air and in an aqueous medium. Test samples were produced in a synthetic nutrient broth using Medusomyces gisevii Sa-12 symbiont. Physico-mechanical analysis was performed on a TMA-60 thermomechanical analyzer. The loading rate was selected proceeding from the requirement that the specimen will not dry out when tested in air. The microfibrillar structure of BC samples was studied before and after stretching using scanning electron microscope (JSM-840). The results showed that at different loading rate, tensile strength varies by a factor of 16, Young’s modulus, and elongation at maximum load by a factor of 1.3 and 1.5, respectively. The maximum tensile elongation of hydrated BC in an aqueous medium (51.4%) is 3.1 times larger compared to that determined for the test specimen tested in air. The recommended loading rate is 20 g/min. The BC structure changes during tension: after testing the BC fibers line up along the load vector and thus structured bacterial cellulose acquires the anisotropic properties.

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