Assessment of Kombucha Leather

[BWalki]

This is a record of the findings and results of a final year project looking into the mechancial properties of kombucha leather. I am completing this as part of a final year university project.

It has been a learning process to produce suitable kombucha scobys, but progress is currently going well. The scoby is being grown in a relatively high sugar concentration of green tea to produce the best scoby rather than good fermented kombucha to drink. Currently the scobys are grown in 300 x 400mm shallow containers after previously growing in 2.5 L jars.

The initial scobys purchased online growing in jars, named of course.

The current thickness of the main kombucha scoby.

The first scoby has been removed and sliced into pieces for ease of drying as well as to be used in further kombucha production. The pieces left to dry on a piece of wood are currently 25mm thick, this may be too thick to produce usable leather but it is all an experiment.

One of the drying scoby sections.

I will continue to update this topic with future findings for growing scoby. The next stage of the project is to perform tensile tests on samples of the material, and to compare to the strength of bovine leather. Comments on technique or questions will be gratefully recieved.

Ben

[BWalki]

The project will also discover any uses of the material replacing bovine leather or in completely alternate situations. Other testing such as producing more supple kombucha leather, or joining/reparing existing kombucha leather products may be performed. It is hoped additional structural observations can be made through examination under a microscope.

[BWalki]

After about 3 weeks of drying this is what the SCOBY now looks like. It has reduced in thickness significantly to a few millimeters and feels leather-like. The next step for material testing will be to perform the tensile testing in the lab, as well as inspection under a microscope.
The kombucha leather, along with bovine and faux leather samples, will be cut into dogbone shapes with the given dimensions:

Once the testing has been completed further results of properties will be released on this forum.

[BWalki]

The tensile testing has been completed on the grown kombucha sheets as well as bovine and vinyl leather materials. Shown are the dog bone shapes that the material was cut into.

The method of cutting the material around a template is not the most accurate available however, press knives were not available. The testing machine used was a Zwick Proline Z020 – Mechanical testing frame with a 20kN load cell, this is a far higher load than would be needed for this material but still provides accurate low load readings.

The bovine leather fracture and the kombucha leather fracture can be seen to look quite different. The kombucha shows necking and a ductile fracture, where the bovine leather appears to be a much more brittle fracture.

The force extension graphs for each material all exhibit differing properties. With the bovine leather having the highest tensile strength and Young’s modulus and vinyl leather the lowest.

The kombucha results were conducted with the material at approximately 17% moisture content. These results overall show kombucha leather to be a viable alternative to bovine leather in terms of the mechanical properties as it shows to be 57% of the Young’s modulus. Kombucha leather also has 70% the tensile strength of bovine, beating out vinyl leather in both.