# Time Domain NMR in Polymer Science: From the Laboratory to the Industry
## 3 Applications
### Industrial Applications
Detailed investigation of the limit of detection (LOD), the limit of quantification (LOQ), discriminating power (DP) of the instrument was conducted to find out almost undetectable differences in forensics traces of polyurethane (PU) samples [111]. Proton content, determined by proton counting through the maximum intensity of FID and comparison with a calibration line, previously constructed using liquid samples with known proton fraction, was calculated for each PU sample. T\({}_{2}\) of the mobile phase, measured with a SE  
Figure 19: Evolution of FID-MSE signals of a biodiesel mixture, from pure fuel (zero days) and after the immersion of CB-filled vulcanized NR (Reprinted with permission from reference [108]. Copyright 2016 Elsevier). to refocus the magnetization of the rather constrained chains with a quite long initial echo time to exclude the contribution from the rigid phase, was also determined for each PU sample. Reporting T\({}_{2}\) values as function of the proton content in a graph, revealed to give very scattered, uncorrelated results, that can be used to discriminate the samples (Figure 20). The DP, meaning the number of discriminated pairs respect to all possible sample pairs, was therefore calculated, applying statistical analysis methods, obtaining a 96% of DP. The degree of correlation between results conveyed by TD-NMR and other techniques, such as FTIR or TGA, has been calculated using the principal component analysis, highlighting the better performances of TD-NMR. The developed protocol could be applied in quality control analysis. Discrimination capability can be also needed in evaluating the suitability of a material in respect to another, for a specific purpose in a specific environment. Probing the interaction existing between the material and a surrounding medium can be employed to achieve that. In fact, it proved effective in characterizing different fabrics for swimming, simply measuring MSE-FIDs of the fabrics in \"dry\" and \"wet\" conditions. T\({}_{2}\) distributions after ILT, characterized by several peaks, were assigned to the solid component, for the lower T\({}_{2}\), and to the subpopulation of water in the swelled sample, interacting in various ways with the fabrics' fibers. Surfaces are, in fact, relaxation sinks, whose impact on water T\({}_{2}\) reduction depends on water molecules interaction magnitude with the surface [112]. T\({}_{2}\) can also inform about the effect of processing parameters, monitoring, for example, the morphology change. SE can be used, in alternative to MSE, to refocus the rigid phase. In Nylon 6 fibers, a three phases model has been considered adequate to describe the composition, with a good agreement of the crystal content with XRD. Increased drawing and winding speed of dried fibers, since water has a plasticizing effect, increase the degree of crystallinity at the expenses of the soft-amorphous phase. Nonetheless, spin-line crystallization was speculated to explain an increment of the soft-amorphous fraction at a high winding speed [113]. Morphological evaluation can also support the determination of the exact composition of polymers characterized by microphase separation, as in thermoplastic elastomers. It was attempted with SBR samples, where simple components analysis of T\({}_{2}\) gave results compatible with the known content of butadiene only when the homopolymer blocks of styrene and butadiene were completely separated. Better resolution of the rubber fraction is achieved for blends of PS and SBR if the relaxation behavior of the rubber is known [114]. The good correspondence between the experimental T\({}_{2}\) distributions for a 50/50 blend and the calculated one is presented in Figure 21a. The same approach is valuable to study the swelling process, for different pairs polymer-solvent/mixture of solvents. Polymer dispersions  
Figure 20: T\({}_{2}\) relaxation time, measured with solid echo, versus % proton fraction of different polyurethane samples.