# Time Domain NMR in Polymer Science: From the Laboratory to the Industry
## 3 Applications
### Bioplastics
Cellulose is another polysaccharide that had been evaluated as an alternative to synthetic polymers [98]. Cellulose properties are determined by its supramolecular structure, realized through hydrogen bonding between the polymer chains. The high content of hydroxyl groups makes cellulose structure highly susceptible to water, therefore TD-NMR was applied to examine the morphological changes with moisture. MSE was employed to determine the phase composition, fitting the FID with a three components function, obtaining the water uptake, the degree of crystallinity and the amorphous content. A decrease of crystallinity and increment of the amorphous phase are observed with increasing water content. Spin diffusion was exploited to assess the linear size of fibrils. Goldman-Shen sequences were introduced at two times in the FID, corresponding to the polarization transfer from amorphous to crystalline and from water to the solid phase. The extrapolation to 0 amorphous amplitude of the initial region of the dispersion curves and the T\({}_{2}\) for the amorphous phase allowed to calculate the domain sizes and the spin diffusion coefficient in 1D, that changes upon water uptake. Comparison with the trend of R\({}_{1}\) = 1/T\({}_{1}\) helped to describe the mechanism of uptake as infiltration of water inside the micropores, forming a monolayer at the surface of elementary fibrils, followed by deepening in the micropores [99]. Morphological studies with MSE were carried out on blends of PHB (polyhydroxybutyrate) and PCL, where PHB is a biodegradable polymer with properties close to PP. Three fractions (crystalline, amorphous and interphase) are identified, and their composition was hypothesized according to their dynamics: amorphous phase is constituted prevalently by PCL, while interphase pertains to both polymers. R\({}_{1}\) gave an indication about the miscibility degree of the two components, with better miscibility at high PHB levels. These results were in agreement with DSC and XRD data [100]. Resins can also be obtained by biobased precursors, such as polyfurfuryl alcohol (PFA). T\({}_{2}\) measurements were performed by applying CPMG to monitor the curing kinetics as a function of catalyst concentration and filler type and content. R\({}_{2}\) (=1/T\({}_{2}\)) increases with curing time, and its variation is accelerated with increasing catalyst concentration. Two models of catalysis were employed to fit the data, with a better agreement including diffusion rates at an early stage of the reaction. Nanoparticles are able to increase the reaction rate at low loadings, after that reaction rate is reduced, because of hindered diffusion and chain mobility. Even the type of filler modifiers is decisive, related to the different chemical groups interacting with the matrix chains [101]. A polysaccharide with active moieties, as chitosan (CHI), could be used as a functional material for optoelectronics or sorption, due to its metal binding properties. The mechanism of interaction with different metals has been investigated, through simultaneous T\({}_{1}\) and T\({}_{2}\) determination with CP-CWFP sequence as function of pH in aqueous solutions. pH has a strong effect on the relaxation profiles, with the existence of two plateaus (low T\({}_{1}\), T\({}_{2}\) at acidic pH and high T\({}_{1}\), T\({}_{2}\) at basic pH) and a transition zone between the two, indicating coagulation of CHI. Interaction between CHI and ions can be appreciated confronting the values of relaxation times for the solution containing both CHI and ion with the CHI-free solution. Interaction is apparent for Fe\({}^{3+}\), Cu\({}^{2+}\), and Mn\({}^{2+}\), with the formation of a stable complex with Cu\({}^{2+}\), as hypothesized analyzing the results of Figure 17a. Analysis of supernatant after centrifugation showed the good capability of CHI in removing metal ions from solution, evidenced by the different behavior between the supernatant of the CHI-solutions and free ions solutions (Figure 17b) [102].