# Time Domain NMR in Polymer Science: From the Laboratory to the Industry
## 3 Applications
### Bioplastics  
Synthetic polymers are generally oil-based derivatives, so they are becoming a great environmental pollution issue. Extraction and refining of oil are very polluting processes, and plastics is not biodegradable, impacting on soil and marine life [86]. Therefore, much research is directed towards biodegradable materials, deriving from renewable resources, such as polysaccharides [87], proteins [88] and lipids [89]. These new materials need to be properly characterized, to verify their applicability as substitutes of common plastics. One of the most studied raw materials with this purpose is starch [90; 91; 92], inexpensive and widely available, but with severe limitations in solubility and poor water resistance. Several strategies had been considered to improve its properties, and their consequent changes had been evaluated with the use of various techniques, among which TD-NMR. For example, a clay, such as montmorillonite, was incorporated into starch-based films. MSE and CPMG gave insights into the morphology change upon disruption, plasticization and incorporation of clay as a filler. The formation of agglomerates at high loading proved to have detrimental effects on the composite properties. These effects were also probed through INVREC, that allowed to define two domains and, above all, to establish the dispersion degree of the filler. In fact, according to equation 1/T\({}_{1,\text{para}}\) = 1/T\({}_{1,\text{nancomp}}\) - 1/T\({}_{1,\text{polymer}}\) (where T\({}_{1,\text{nancomp}}\) is the nanocomposite relaxation time and T\({}_{1,\text{polymer}}\) is the relaxation time of the neat polymer) the contribution of the paramagnetic impurities, due to the clay, can be determined and T\({}_{1,\text{para}}\) is then directly proportional to the interlayer distance of the exfoliated or intercalated nanocomposite. Indeed, paramagnetic ions, such as manganese or iron, can be present as metallic substitutes inside the layers of the clays and their additional magnetic field is able to reduce the relaxation times of the surroundings [93; 94]. Their influence is much stronger as lower is the distance between them and the protons of the polymer chains. Determination of longitudinal relaxation in the rotating frame with different spin-locking frequencies allowed to make some considerations about the changes is the molecular dynamics inside the samples [95]. Figure 16: DQ (**a**) and MAPE (**b**) spin diffusion data for PCL (at 27 \({}^{\circ}\)C), exhibiting non-symmetric time evolution of the interphase magnetization. The dashed lines are from simulations based upon simple 1D model of diffusion, well representing the evolution for the DQ-filtered magnetization, but less accuracy for the MAPE (Reprinted with permission from reference [84]. Copyright 2014 Springer). Another way to improve the mechanical properties had been the blending with another biodegradable polymer, such as PLA, and the addition of fillers, such as hydrophilic and hydrophobic silicas and montmorillonite. An intermediate \({}^{1}\)H T\({}_{1}\) between the one for pure starch and pure PLA was found, indicating good miscibility between the two polymers. The addition of fillers promotes an increase in both the crystallinity degree, determined through MSE and \({}^{1}\)H T\({}_{1}\), due to greater overall rigidity. Employing ILT, the \({}^{1}\)H T\({}_{1}\) distributions can be obtained, which had been associated with different domains inside the materials. An increasing amount of montmorillonite appears to create a more heterogeneous system with respect to organolays and silicas [96]. Starch can also be crosslinked with oxidized sucrose. The network structure was probed indirectly, analyzing the mobility of water molecules after swelling of the network. \({}^{1}\)H T\({}_{2}\) measurements pinpointed two water populations associated with bound water molecules and with extra-granular water. Crosslinking increases water mobility, confirming the improvement of hydrophilic properties [97].