To retain product value, textiles should ideally be recycled into new textiles. As cellulose-based textiles cannot be indefinitely regenerated due to the degradation of their degree of polymerisation, alternative processes must be used to close the fashion-loop. These fibres which are of a too low degree of polymerisation can be completely depolymerised into glucose, for further production of value-added chemicals and/or fuels. Depolymerisation can be done by acid- or enzymatic hydrolysis. In collaboration with the start-up company ShareTex, this Bachelor thesis has compared the aforementioned hydrolysis processes through both a literature and laboratory study. This was done in order to draw a conclusion on the most sustainable alternative. From this, a bioprocess has been designed to minimise environmental impacts whilst obtaining suitable yields.

According to literature, an optimal acid hydrolysis method would include two process steps, obtaining a yield of at least 90 percent with a purity of 40 grams per litre. In the primary step a concentrated sulfuric acid (H2SO₄) (at least 70 percent) would be used, followed by a diluted H₂SO₄ step (2-5 percent). The acid method should ideally include higher concentrations in both steps, than those reported in literature, to obtain higher purities of the product. Enzymatic hydrolysis should preferably be energetically and chemically integrated with a pulp mill, where the green liquor would be used as an alkali reagent in the pretreatment step, followed by a commercial cellulase cocktail for the hydrolysis step. This method can obtain a 80 percent yield of a purity of 42 grams per litre. If this enzymatic hydrolysis process includes recycling of water and enzymes, the costs and environmental impacts may be reduced enough for this method to be competitive to the acidic process.

From the laboratory study the final yield from the acid hydrolysis was 82 percent with a purity of 33.8 grams per litre. The enzymatic hydrolysis processes achieved a yield of 80 percent and a purity of 43.9 grams per litre using the commercial enzyme cocktail. It was also found that viscose fabric needed less processing time than cotton in regards to the enzymatic process. Thus, the two fabrics should thus be separated prior to the pretreatment.