# Time Domain NMR in Polymer Science: From the Laboratory to the Industry
## 3 Applications
### Industrial Applications  
So far, the review has explored mainly academic applications concerning materials at a very early stage of development or very elegant and thorough characterization for providing experimental evidence for theoretical models. However, the LF-TD-NMR methods revised in the previous sections can also be applied to draw straightforward conclusions about common polymeric materials, such as degradation state or subtle differences between similar materials or effect of processing or formulation changes, that can be easily transferred in industrial routines. In this section, we would like to propose examples of possible industrial relevance to demonstrate a great deal of opportunities that this technique can offer as support in industrial development and quality control. TD-NMR can represent a very fast instrument to verify the consequences of exposure of materials to environmental conditions that could affect materials' properties, analyzing the potentially induced molecular changes. Thermal aging, for example, can occur both in elastomers and thermoplastics after the permanence at high temperatures. FTIR results show generally the occurrence of oxidation processes at the material surface, monitored through the carbonyl index. Nitrile rubber (NBR) behavior at a prolonged exposition to temperatures above 100 \({}^{\circ}\)C was investigated, together with the effect of lubricating oil. The degree of oxidation and loss of additives were correlated to the steady increase of crosslink density throughout the process (Figure 18a), which was prevented partially by the presence of oils, with better protection provided by base oil. Full oil contains, in fact, additives with active moieties that could accelerate the oxidation of rubber [103]. Instead, in a thermoplastic semi-crystalline polymer, the effect of thermal aging induces an increase in the rigid fraction, with the reconstruction of crystallites, that become larger driving out defects. While simple annealing induces a concomitant increase of the mobility of the soft-amorphous phase [104; 105], the additional contribution of chemical reactions, such as oxidation, causes a reduction, at short times, in the overall mobility, because of a higher confinement of the mobile-amorphous part and at longer exposure times, mobility increases because of oxidative chain cleavage [104; 106]. Lately, the employment of NMR-MOUSE devices allowed to analyze the  
Figure 17: Relaxation profiles of T\({}_{1}\) (full squares) and T\({}_{2}\) (empty circles) against pH for Cu\({}^{2+}\)-CHI solutions (**a**) and the supernatant after centrifugation of the aqueous solution (**b**). Solid lines are the sigmoidal fittings for the experimental data of the Cu\({}^{2+}\)-CHI solutions, while dotted lines are the fittings for free Cu\({}^{2+}\) ions in solution (Reprinted with permission from reference [102]. Copyright 2017 Elsevier). depth-dependent changes by aging, which are known to greatly compromise the mechanical properties. T2 was measured with an NMR-MOUSE for a polyamide 12 (PA12), even though this should be better defined as a T2 eff, data showed a biexponential decay. The two components were assigned to the rigid and semi-rigid fraction for the short relaxing component and to the mobile-amorphous phase for the long relaxing component. The variation of these components was more pronounced for the non-stabilized sample, reported in Figure 18b, confirming the protective action of the stabilizer and its role as a plasticizer. At the surface higher degradation and hardening occurs, with increasing exposure time the penetration depth of thermo-oxidation increases, as resulting from higher rigid fraction and lower T2 eff in both cases [106]. Similar studies were carried out on polyethylene, confirming the increase of crystalline phase with aging time and consequent decrease of T2 eff, that is of overall mobility, which changes faster at a higher temperature, incrementing at longer times, because of chain scission.