True silk is the secretion of the silkworm, Bombyx mori L. It accounts for only about 0.1% of the world's textile fibre production, but its price, which is 20 times that of cotton, makes it an important textile raw material. The demand for real silk on the world market has been growing over the last two decades for textile purposes, as well as for the cosmetics and medical industries. In Europe, the arrival of synthetic fibres has finally destroyed silk farming and silk milling, and with it the knowledge of, among other things, cocoon unravelling and the production of silk yarn. The revival of silk farming in Slovenia began in 2016 with the objectives of establishing “green” silk farming without the use of environmentally harmful plant protection products and breeding resistant breeds of silkworms without the use of antibiotics. The aim of the MSc thesis was to analyse the cocoons of 20 samples that differed in the origin of the silkworm food, i.e. white mulberry leaves, and in the breeding practices, in particular the way the caterpillars were fed, and the cocoons were dried. An electronic device with two winding points was developed, which enabled at least two cocoons to be unwound simultaneously and the length of the raw silk filament (bava) to be recorded electronically. The weight, length, thickness, and appearance of the cocoons were measured before unwinding. For each sample, 10 cocoons were unwound. The length of the raw silk without breakage, the mass of the silk remnants and of the cocoon were measured. The longest raw silk fibre was obtained from sample 2/4 (year 2017, breeder from Hungary, mulberry genotype Old Hu ge. (wild)) with an average silk cocoon length of 1.27 km and a length mass of 2.63 dtex. All cocoons were very well unwound. The best sample among Slovenian breeders was 2/9 (year 2017, breeder ISS RLB(Maribor), Old Slo genotype) with an average silk cocoon length of 1,205 km and a length mass of 2,48 dtex. The cocoons contained an average of 5.49 % air moisture before threshing and an average of 4.7 % sericin and other proteins were removed during threshing. There is a linear correlation between the weight of the cocoon and the silk envelope, and for our samples it was found that the silk of the bale represented a good third of the weight of the cocoon, i.e. an average of 33.4 %. The length of the unwound silk was strongly influenced by the farming performance. Superior cocoons yielded over 950 m, while poor breeding yielded between 650 m and 700 m of silk bale/cocoon. Based on the cocoons analysed, it can be said that the 2017 and 2021 cocoons were on average very similar in weight, length and thickness, but the raw silk in 2017 was on average finer (2.5 dtex) than in 2021 (2.8 dtex).
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