In this work, we present a method for strain determination. This method is based on random points sprayed on the surface of the examined material. The method does not require vacuum deposition or the use of any difficult sample preparation method. Markers are embedded under room conditions. Another advantage of this method is that it can be used for materials with different moisture contents. This method was applied to observe Young’s modulus and the breaking force of biodegradable films produced from thermoplastic starch (TPS) during their storage in air and in soil. In our study, we consider the samples of thermoplastic starch obtained from a mixture of potato starch and glycerol with added polyvinyl alcohol (PVA) and keratin. We observed that the value of Young’s modulus after sample preparation is higher for the samples with a higher content of PVA and keratin. It was found that after two weeks of storage, the value of Young’s modulus significantly decreased for all samples stored in air. Young’s modulus increases for stor-age in the soil. The crystallinity does not depend on the screw rotational speed.

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