In 2011 DG Enterprise and Industry requested the European Commission's DG-JRC to technical evaluate a petition submitted by E. I. du Pont de Nemours and Company (DuPont). This petition requested the creation of a new generic fibre name under the Directive 2008/121/EC on textile names, now repealed by the EU Regulation 1007/2011. This would allow distinguishing between their fibre, polytrimethylene terephthalate (PTT) and, in particular, polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), the two most common types of polyesters. Although the three polyesters are very similar in terms of chemical composition, according to DuPont, PTT fibres have a set of improved properties that justify the petition, such as for example durability, resilience, bleach resistance and comfortstretch properties. As identification and quantification methods are required in order to allow market surveillance of textile products, the JRC was responsible for the verification of the test methods proposed by the applicant and for the development and validation of the new required ones. Regarding identification, optical microscopy cannot differentiate between the three types of polyesters, as they are all man-made fibres with very similar structure. Also chemical solubility methods cannot be used for this purpose. On the contrary, Fourier Transform Infrared Spectroscopy can distinguish between PTT, PET and PBT. This distinction can be achieved also using Differential Scanning Calorimetry (DSC), but only on the basis of their crystallisation peaks, since the melting peaks of PTT and PBT occur at the same temperature. The mechanical properties of PTT were studied. As most PTT fibres cannot reach 50% elongation without breaking, tests were carried out at 25% elongation. In these conditions, PTT showed an elastic recovery and a permanent deformation ranging from 65.7 to 78.1% and from 5.4 to 8.8 %, respectively. On the basis of such results, PTT cannot be considered an elastic fibre. Regarding quantification, the usual pre-treatment protocol described in the EU Regulation 1007/2011 is applicable to PTT fibres. The correction factor b for mass loss during pre-treatment for PTT was established as 0%. The experimental value for the agreed allowance of PTT was determined (0.34%). However, for consistency with the values already adopted for polyester and elastomultiester, the value 1.50% was agreed by the members of the European Network of National Experts on Textile Labelling (ENNETL). PTT is completely soluble in method 14. The following correction factors d for PTT (mass loss due to dissolution methods) were determined: 1.00 for methods 2, 3, 7 and 11; 1.01 for methods 1, 4, 5, 9 and 10; 1.02 for method 13; 1.03 for methods 6, 8 and 16. Method 15 is not applicable to binary mixtures containing PTT. Several binary and ternary blends containing PTT were quantified using both manual separation method and chemical dissolution ones. The JRC developed a new DSC method that was proved to be adequate and accurate for the quantification of PTT in blends with PET. The method uses calibration curves prepared with yarns manually separated from the sample under analysis, thus ensuring a common thermal history. Different types of integration as well as multipoint and single point calibration curves based on PTT or PET melting peaks were evaluated. The JRC organised the validation of the optimised DSC method at European level, as a balanced uniform-level experiment with six levels and 15 laboratories. Statistical analysis showed that the best results were obtained using multipoint calibration curves based on the integration of PTT melting peak with a linear integration. The method was successfully validated and showed good accuracy, in terms of both trueness and precision, as proved by the following parameters: bias values (0.06 -1.30%), confidence limits at 95 % probability level (0.60 - 1.07%) and HORRAT values (0.5 - 2). Results were presented in two meetings of the European Network of National Experts on Textile Labelling, held in Ispra, Italy, on 30th November 2012 and 4th October 2013. The definition proposed by DuPont for PTT ("fibre formed of linear macromolecules comprising at least 85% (by mass) in the chain of an ester of 1,3-propane diol and terephthalic acid) was consistent with the evaluation carried out. As regards the proposed name of the fibre (triexta) there was no consensus among the experts belonging to ENNETL.
