To decrease the environmental footprint, the textile industry needs to become more circular. One company that is trying to close the textile lifecycle loop is the Swedish company Renewcell. In the Renewcell process, discarded clothes and other textile waste are turned into a dissolving pulp that can be used for production of new textiles. For this to work, it is important to generate a non-colored dissolved pulp. Therefore, it is of great interest to be able to optimize the bleaching process and evaluate different starting materials. Today, there are different methods that have been used for quantification of specific dyes and for identification of raw materials in textiles. However, there is no complete method that can be used for all types of dyes and raw materials. This master thesis will therefore investigate the bleaching step and the raw materials used in Renewcell’s recycling process. The aim with this project is to develop a method, to be able to analyse the presence of dyes qualitatively and quantitatively in the dissolved pulp from the recycled cotton-based textiles. To do so, different chemical analysing methods were used. These include kappa number measurements, UV-VIS and FTIR. Nine different types of jeans, one yarn, three raw materials (cotton, PET and elastane), and two pure dyes (indigo and black sulfur dye) were selected for this project. The result from the kappa number measurements shows that only the blue jeans, blue yarn and black jeans could be bleached and measured by using the original kappa number method at 25 degrees C. But when the same procedure was done manually and the temperature was increased to 70 degrees C, almost all materials could be bleached and measured. Therefore, the conclusion is that this method can be a successful quantification method. However, the temperature correction equation needs to be developed further to be able to quantify the exact amount of dyes. The kappa number was also compared with the absorbance factor, i.e. the k-value from the UV-VIS results. A correlation could be seen for the blue jeans, blue yarn, and black jeans. So, the UV-VIS method could also be a possible method for quantification of dyes in textiles. For the qualitative analyses, FTIR was used. The results showed that the raw materials could be identified by comparing the resulting FTIR spectra with a reference spectrum. For the jeans and yarn materials, indigo dye was identified for the blue jeans, blue yarn, and black jeans. However, for the other materials, the amount of dyes was too low to be able to draw conclusions about the chemical structure. With further development, these methods could be used as successful qualitative and quantitative methods for analysing dyes in textiles. This would generate positive consequences in several ways. The usage of bleaching chemicals could be optimized, and the quality of the final textile material could be improved. This would benefit both the manufacturer of these recycled textiles (economically) and the consumer who will buy the final product (quality). Indirectly, this would help to decrease the environmental footprint from the textile industry.

The structure and composition of denim jeans is complex. In addition to cotton, which is the dominating type of textile fibre, there may be up to about 20 % synthetic fibres. The synthetic fibres are found in the sewing thread and in the elastic yarns that are used to make stretch denim jeans. In total it was found that up to six different types of textile fibres may be present in the material. To be able to recycle cotton in jeans by producing regenerated cellulose fibres a very high purity with respect to cotton is required. The purpose with this project was to investigate the possibility to fractionate the textile material found in denim jeans to obtain a pure cotton fraction that can be used in the viscose process to produce regenerated cellulose fibres, which then can be used to manufacture new clothes. In this project traditional wet mechanical separation equipment found in the pulp and paper industry, in the form of a laboratory screen (used as a model for a pressure screen) and hydrocyclone, was used to fractionate the textile material from cut and shredded denim jeans. The degree of separation of synthetic fibres from cotton fibres was quantitatively evaluated by measuring the glucose content after acid hydrolysis. The results from the experimental work showed that there were runnability problems both regarding disintegration and fractionation. Regarding the fractionation, plugging was found to be a problem and no significant separation of synthetic fibres from cotton fibres was obtained with the conditions of the experiment. / Strukturen och sammansättningen i denimjeans är komplex. Utöver bomull, vilken är den dominerande typen av textilfiber, kan de innehålla upp till 20 % syntetiska fibrer i tyget. De syntetiska fibrerna finns i sytråden och i elastiska garner som används för att tillverka stretchdenimjeans. Den här studien visade att upp till sex olika typer av textilfibrer kan förekomma i materialet. För att kunna återvinna bomull i denimjeans genom att producera regenererade cellulosafibrer krävs en mycket hög renhet med avseende på bomull. Syftet med projektet var att undersöka möjligheten att fraktionera textilmaterialet i denimjeans för att erhålla en ren bomullsfraktion som kan användas i viskosprocessen för att tillverka regenererade textilfibrer, vilka sedan kan användas för att tillverka nya kläder. I projektet användes, inom massa och pappersindustrin traditionell våtmekanisk separationsutrustning i form av en laboratoriesil (här använd som en modell av en trycksil) och en hydrocyklon, för att fraktionera textilmaterialet från klippta och sönderslitna denimjeans. Separationsgraden av syntetiska fibrer från bomullsfibrer bestämdes kvantitativt genom att mäta glukoshalten efter sur hydrolys. Resultatet från det experimentella arbetet visade att det finns körbarhetsproblem både gällande uppslagning och fraktionering. För fraktioneringen visade sig pluggning vara ett problem och ingen signifikant separation av syntetiska fibrer från bomullsfibrer erhölls med förhållandena i experimentet.

Denna uppsats syftar till att utforska vilka textilfibrer och färgningsmetoder som har låg miljöpåverkan och hur dessa ska införas i modeindustrin. För att undersöka detta har jag använt intervju och tematisk analys som metod där jag intervjuat två forskare, en återvinningsanläggning och två modeföretag. Drivkrafter och hinder som driver på och försvårar användning av miljövänligare textilfibrer och färgningsmetoder belyses där ett stort hinder för cirkulärt mode är ekonomi där företag och kunder tjänar mer på billigare och sämre textilfibrer samt färgningsmetoder. Ett alternativ för att sänka kostnaden är subventioner eller skatteavdrag på miljömärkta kläder i butik samt skattepålägg på syntetkläder som säljs. Modeindustrin är den näst mest förorenande industrin efter oljeindustrin med 10% av världens koldioxidutsläpp. Textilindustrin är en av tio industrier som förbrukar mest vatten. Sverige är en stor aktör i modebranschen där flera svenska företag är etablerade internationellt och samtidigt ses som en representant för cirkulärt mode. Internationellt är polyester den vanligaste använda textilfibern idag och svenska företag går emot normen förde använder främst bomull som är en förnybar textilfiber. Användning av hållbara textilfibrer är större än hållbara färgningsmetoder i Sverige men en väletablerad modekedja har utvecklat miljövänligare färgningsmetoder med sina leverantörer. Slutsatser jag dragit är att återvunna och cellulosafibrer kommer öka i framtiden samt att ekonomiska incitament är viktiga för miljöarbete med textilfibrer och färgningsmetoder. Kunskap och information är också en viktig komponent för att göra miljövänliga val i modeindustrin. / This essay aims to explore which textile fibers and dyeing methods have a low environmental impact and how these will be introduced in the fashion industry. I have used interview and thematic analysis as a method to investigate this area where I have interviewed two scientists, one recycling facility and two fashion companies. Drivers and obstacles that drives and complicates utilization of more environmentally friendly textile fibers and dyeing methods are casted light on, where a big obstacle for circular fashion is economy where companies and customers earn money on cheaper and inferior textile fibers and dyeing methods. An option to lowering the cost is subsidies or tax deductions for environmentally marked clothes in stores and tax additions for synthetic clothes which is for sale. The fashion industry is the most polluting industry after the oil industry with 10% of the carbon emissions in the world. The textile industry is one of ten industries which consumes the most water. Sweden is a large actor in the fashion industry with several international established Swedish companies and is seen as a representative of circular fashion at the same time. The most common textile fiber today is polyester but Swedish companies foremost utilize cotton which is a renewable textile fiber. Utilization of sustainable textile fibers is more common than sustainable dyeing methods in Sweden, but a well-established fashion chain has developed more environmentally friendly dyeing methods with their suppliers. Conclusions I have made are that recyclable and cellulosic fibers will increase in the future and economic instruments are crucial for the environmental work with textile fibers and dyeing methods. Knowledge and information are also important components to make environmentally friendly choices in the fashion industry.