# Opportunities and Limitations in Recycling Fossil Polymers from Textiles
## 2 Sorting of Textiles: Techniques and Facilities  
### Sorting Methodologies  
High volumes of textile materials are often incinerated and landfilled due to the lack of specific collection of post-consumer textile waste, difficulties in separating the discarded textiles and costs associated with their sorting [67]. Nonetheless, reusing and recycling of end-of-life textiles are still considered to be better choices when compared to incineration or landfilling [68]. Regardless of the recycling process to be followed (i.e., chemical, mechanical or physical), textiles must be sorted before according to their colour, fabric type or raw material, quality and style [69].  
Textile waste sorting is often carried out manually. Even though this is feasible, the high costs, low speed, and lack of automatization associated with it makes its implementation not suitable for the processing of large volumes of materials [67]. Moreover, this method is prone to misclassifications since it depends on the material content listed on the product labels (might be faulty) and the expertise of the workers, who in turn experience high intensity and poor working conditions [68; 70].  
Other sorting methodologies can also be carried out, and these are divided into physical and chemical methods. Chemical methods (i.e., dissolution) are not usually considered for sorting waste textiles because they are destructive, hazardous and pollutant.  
On the other hand, physical methods include density and melting point measurements, among others [70]. In general terms, all the above-mentioned methods are expensive, time-consuming, and demand high training from the operator [71]. For this reason, a fast, non-destructive, and reliable method that is able to analyse large volumes of textile materials and can be implemented in-line is urgently needed for the waste textile recycling industry [68].  
Some alternative physical methods have been explored during the last years to identify textile materials, such as the usage of radio frequency (RFID) tags that store information about the textile and could be read remotely. However, RFID tags being able to withstand several laundry cycles have not been developed yet. Furthermore, other methodologies based on the use of optical sensors have recently arisen. For example, colour sorting can be accomplished with the help of computer vision techniques based on an RGB camera [72, 73, 74]. RGB cameras are usually combined with infrared (IR) sensors to give further information about the textiles.  
In this regard, Fourier-transform mid-infrared spectroscopy (FT-MIR) can be used to determine the material content of fabrics through the analysis of their spectral features that arise from the different molecular vibrations of the different textile components. For example, [PERSON] et al. [67] classified textile samples based on synthetic (i.e., polyamide and polyester) and natural fibres (i.e., cotton, wool, and silk) by means of combining FT-MIR spectroscopy coupled to powerful mathematical recognition methods (such as principal component analysis, PCA). However, this technique cannot be implemented in-line and so is considered a complementary technique/extension to manual sorting [67, 69].