Crystallinity estimation

AppHcations of soHd-state nmr include measuring degrees of crystallinity, estimates of domain sizes and compatibiHty in mixed systems from relaxation time studies in the rotating frame, preferred orientation in Hquid crystalline domains, as weU as the opportunity to characterize samples for which suitable solvents are not available. This method is a primary tool in the study of high polymers, zeoHtes (see Molecular sieves), and other insoluble materials. 

In a comparative study of the crystallinity of isomeric aliphatic polyamides by NMR, DSC and X-ray, the NMR-based crystallinity was obtained by a two component fit of the proton broad-line spectra and their associated mobilities by Tip determination. Compared to the crystallinity estimates from DSC and WAXS, the content of rigid material obtained from NMR is significantly higher, but comparable to the crystallinity determined by SAXS. The difference with the DSC value was associated with a fraction of intermediate order within the crystalline phase [193]. 

The evidence presented fails to suggest the causes for the large variations in crystallinity estimates which have been reported for similar cellulosic materials. There is a possibility that the different methods may not measure precisely the same characteristic of the material. It also may be that relative crystallinity is not a fixed quantity in any case but depends on circumstances involved in the measurement, such as the amount of swelling. The estimates reached by different methods need to be reconciled. At present, crystallinity estimates which depend wholly or in part on X-ray diffraction seem to be much higher than those obtained by chemical methods. The fact is that X-ray diffraction methods are ideal for studies of the crystalline fraction but are necessarily indirect in application to the non-crystalline fraction. The converse is true for the chemical approach. Apparently a combination of diffraction and chemical methods may adjust the existing differences. 

The conditions of swelling during the measurement undoubtedly have an important bearing on crystallinity estimates. Area determinations by Assaf, Haas and Purves89 indicate that up to 98% of the surface of moist cellulose is obliterated by direct drying while about 75% remains (39) A. G. Assaf, R. H. Haas and C. B. Purves, J, Am. Chem. Soc., 08, 68 (1944). 

In the case of optical studies, better agreement in the case of crystallinity estimates, let us say, might be expected between the calorimetric and infrared measurements than between calorimetric and x-ray calcu-... 

Figure 3. Degree of crystallinity estimated from X-ray powder diffraction data versus crystallization time.

Figure 15 Comparison of etching time dependencies of crystallinity, estimated from DSC and hi NMR FID analyses for a series of nascent and etched powders. For the latter case, the percentage of the crystalline component is plotted.

The FTIR spectroscopy studies on PTT (refer Figure 9) subjected to isothermal ciystallization for 40 min at 200"C, shows the following result. The area ratio of the absorption band which is assigned to the % of gauche conformation, is calculated to be 1.39 while the ratio which denotes the trans conformation of the methylene groups is found to be 0.28, indicating reasonable amount of crystallinity in the sample (refer Table 8). The crystallinity estimated by DSC analysis after isothermal crystallization at 200°C for 40 min shows a value of 40.8%. ... 

Morphologically cotton cellulose is highly crystalline. Estimations of the extent of crystallinity vary, depending upon the measurement method used, from 75% to 95%. This configuration is almost a rectangular parallelepiped containing a cellobiose unit in each corner, with a central cellobiose unit in the center, antiparallel to the other four. 

For many polymers, however, the degree of crystallinity estimated from the two-component analysis was found to be appreciably larger than that obtained from WAXD or density measnrements on the same materials. In addition, although the crystallinity of PE determined by density methods remains constant below room temperature ( 60%), the breadline NMR crystallinity increases continuously to 100% at temperatin-es approaching Tg (55). Thus the area imder the broad portion of the derivative cnrve is proportional to the number of immobile protons in both crystalline and rigid noncrystalUne phases. As a result, methods to decompose such spectra into three components were developed (56,57). 

The ratio of the absorbance intensities of the infrared bands at 1265 and 1235 cm is commonly used in fibroin crystallinity estimations (27,28,29). The band at 1235 cm" is assigned to the Amide III mode of the random coil conformation, and the corresponding band of the P-sheet confonnation has been identified at 1265 cm" (30). Since these two peaks were not well resolved in the spectra under consideiation, intensity measurement of the two peaks was... 

The catalytic activities of coprecipitated Sn02 M0O3 with various Mo/Sn ratios for the dehydration-dehydrogenation of 2-butanol have been studied in relation to the surface composition measured by XPS and the crystallinity estimated by XRD. The results are shown in Fig. 4.32. The Sn02 phase dissolving Mo in its lattice has been... 

The derived activation energy for SPS chain mobility at the crystal-growing front is 5.4kJ/mol, which is lower than that of isotactic polystyrene, which is 6.5kJ/mol. Despite a wide range of Tc used, however, the sample crystallinity estimated by Fourier transform infrared spectroscopy remains unchanged. Interconnected domains with a width of approximately 1.8 pm are readily observable in all the crystallized samples under phase contrast microscopy, and the phase-separated structure is conserved within SPS spherulites whose diameters are increased with increasing Tc. 

Depends upon chain branching data given are representative values of typical commercial poly(ethylenes) (22). Crystallization from melt by rapid cooling at ambient temperature crystallinity estimated from density. ... 

The Xc Dsc values of the VUV-irradiated and unirradiated PLA manbranes evaluated by Equation 3.1 are sununarized in Table 3.6. The Xc dsc values clearly increased in the range of irradiation time from 0 to 6 min and settled to 4.3% as irradiation time increased from 6 to 100 min. Figures 3.17 and 3.18 show that Xq DSC result differs from the WAXD pattern. In the WAXD pattern, crystallinity can be estimated by dividing the halo pattern, whereas crystallinity estimated by DSC value is directly determined by enthalpy change. Given this factor, the Xc dsc values obtained higher accuracy when compared with the values obtained by WAXD analysis. A sharp halo of crystalline PLA was buried in the broad halo of amorphous PLA. 

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