Systems magnetic resonance crystalline solids

Plasticisers are added to PVC to achieve flexibility and workability. The flexibility or softness is determined by the type of plasticiser and level used in relation to the PVC (phr). They also operate as an internal lubricant between the PVC molecules. Based on organic esters, e.g., phthalates, adipates, trimellitates, phosphates, etc., addition levels can be as low as 20 phr for semi-rigid to 100 phr for very flexible applications. The effect on the thermal stability significantly depends on the physical state of the PVC-plasticiser system (260). The relative amount of crystalline PVC in PVC/diethylhexyl phthalate has been identified on the basis of a combination of carbon-13 solution and solid state nuclear magnetic resonance (NMR) (361). 

In file Avrami mcxlel, F is, in fact, a reduced ctystallinity since it asscxiiates the crystallinity of the system at a given time to the total crystallinity achieved under the experimental conditions. The F value is measured with a property proportional to the change in solid phase or crystallinity developed in the system as a function of time (i.e., light transmitted or reflected. X-ray diffraction, DSC measurements, solid-fat index by nuclear magnetic resonance). In general, F is calculated as F = (X, - Xg)l(X - Xq) where Xg is the concentration of solid (i.e., TAG in the solid phase) at time zero, Xj is the concentration of solid at time t, and X is the maximum concentration of solid obtained in the ciystallization process. When DSC is used, the F values are calculated from the crystallization exotherm as F = where AW, is the area... 

To the contrary, study of the second moment and various relaxation times of the resonance line as a function of temperature and other parameters often yidLds important data on the polymer such as degree of crystallinity, chain axis orientation, and degree of molecular motion. Indeed, so-called wide-line NMR has been one of the primary methods of characterizing the bulk state of polymeric systems. Nonetheless, it might be assumed that if a high-resolution NMR spectrum of a solid could be obtained, new detail on the nature of the solid state might be uncovered. Recent advances in magnetic resonance have now made possible the partial realization of this... 

In cementitious systems, TGA (or also DSC or DTA) is generally used to identify hydration phases, to confirm the presence of both crystalline and amorphous phases found by XRD, nuclear magnetic resonance (NMR) or scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) analysis and/or to quantify the amount of solids present. The discussion presented in this chapter will mainly focus on TGA only Section... 

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