Crystallinity determination

The scattered intensity is used to calculate the volume integral of the diffracted peak. 

Weight fraction of crystallinity cp is then given by the ratio of the integral of the diffraction intensity scattered by the crystalline fraction to the total coherent scattered intensity  

Alternatively, areas and A of the amorphous and the crystalline peaks, respectively, are used to calculate a crystalline index (C7) defined as 

A diffraction scan over a q range of 0.5-3 A (20 = 10-50, Cu Ka) is used. The areas A and A are determined by resolving the diffractometer scan into amorphous and crystalline peaks (Fig. 2.6a) [49]. 

Crystallinity determination requires that the XRD scan be obtained from an unoriented sample. If the samples are oriented, then numerous scans from different orientations have to be collected and properly weighted to obtain a scan equivalent to that of an unoriented sample [51]. Such randomization can be readily accomplished for uniaxially oriented samples than for samples with biaxial or more complex orientation [52]. A measure of the intensity of the crystalline peak in just a single scan, for example, equatorial 

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Using proton NMR of solutions, the composition of polymers can be analyzed.47 Carbon-13 NMR spectroscopy is a useful tool for studying the sequence length of segments in copolymers and thereby determining the blockiness of the copolymer. With solid-state NMR, the mobility of chain segments can be studied and the crystallinity determined. 

M. J. Pikal, A. L. Lukes, J. E. Lang, and K. J. Gaines, Quantitative crystallinity determinations for beta-lac-tam antibiotics by solution calorimetry correlations with stability, J. Pharm. Sci., 67, 767-773 (1978). 

Both vibrational spectroscopies are valuable tools in the characterization of crystalline polymers. The degree of crystallinity is calculated from the ratio of isolated vibrational modes, specific to the crystalline regions, and a mode whose intensity is not influenced by degree of crystallinity and serves as internal standard. A significant number of studies have used both types of spectroscopy for quantitative crystallinity determination in the polyethylenes [38,74-82] and other semi-crystalline polymers such as polyfethylene terephthalate) [83-85], isotactic poly(propylene) [86,87], polyfaryl ether ether ketone) [88], polyftetra-fluoroethylene) [89,90] and bisphenol A polycarbonate [91]. 

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]. 

If specimen is also crystalline determine DENSITY, UNIT CELL and possible SPACE GROUPS. 

Eoams were extruded from low density polyethylene (LDPE) and blends of LDPE with syndiotactic polypropylene (sPP), using isobutane as the blowing agent. The extruded materials were characterised by measurement of dimensional stability at room temperature, density, tensile properties, dynamic stiffness, and crystallinity determined by differential scanning calorimetry. The sPP, with a slow crystallisation rate, did not interfere with the expansion of the LDPE, and enhanced the temperature resistance by in-situ crystallisation. The blends were flexible, dimensionally... 

The value for the heat of fusion of PPS, extrapolated to a hypothetical 100% crystalline state, is not agreed upon in the literature. Reported values range from approximately 80 J/g (19 cal/g) (36,96,101) to 146 J/g (35 cal/g) (102), with one intermediate value of 105 J/g (25 cal/g) (20). The lower value, 80 J/g, was originally measured by thermal analysis and then correlated with a measure of crystallinity determined by x-ray diffraction (36). The value of 146 J/g was determined independently on uniaxially oriented PPS film samples by thermal analysis, density measurement via density-gradient column, and the use of a calculated density for 100% crystalline PPS to arrive at a heat of fusion for 100% crystalline PPS (102). The value of 105 J/g was obtained by measuring the heats of fusion of well-characterized linear oligomers of PPS and extrapolation to infinite molecular weight. 

Fig. 535 Avrami plots showing the growth of the relative degree of crystallinity (

A routine method for determining relative crystallinity based on the amorphous bands in the spectrum has proved more rapid and precise than the x-ray method. In practice, the ratio of the 778 cm-1 (12.85 ft) and 2367 cm-1 (4.22 ft) band intensities is measured. Use of a ratio eliminates the thickness measurement and increases precision to about 1% at 50% crystallinity and considerably better at higher levels. A density measurement and an infrared crystallinity determination when combined give an estimate of the fraction of microvoids which can occur in molded specimens of polytetrafluoroethylene. The density of a sample is predicted on the basis of its crystallinity as measured by the infrared method and the difference between this density and the actual density measured by displacement in water is a measure of the microvoid content. This determination is precise to about 0,2% voids by volume. By the use of confirmatory infrared measurements, it is possible to check the possibility that the presence of a substantial percentage of voids may have led to erroneous indications of the molecular weight in the standard specific gravity test discussed earlier. 

Pikal, M.J., Lukes, A.L., Lang, J.E., and Gaines, K. (1978). Quantitative crystallinity determinations for /3-lactam antibiotics by solution calorimetry correlations with stabiUtypharm. Sci., 67 767-773. 

Corrections of the apparent crystallinity values of fibers materials have been carried out by taking into account a disorder parameter k, following Ruland s method. Peculiar care was taken about samples preparation (cutting and pelleting of fibers), data collection and reduction, which will be briefly described. Crystallinity and disorder parameter measurements have been performed on main textile fibers (polyester, polyamide, aramid, polypropylene, cellulosic fibers) and the results will be discussed comparatively, with those got by more conventional x-ray crystallinity determinations. The complementarities of these different approaches will be illustrated with several examples. For instance,... 

A linear correlation was observed between crystallinity determined by DSC and MIR for all the studied HDPE samples. As expected, the absolute values are not the same, but a linear correlation can be observed. 

Figure 3. Crystallinities of several melt-processed and annealed-virgin PTFE samples as determined from decomposition of chemical shift lineshapes vj. crystallinities determined from density measurements...

Each of the methods cited yields a measure of average crystallinity, which is really only defined operationally and in which the polymer is assumed artificially to consist of a mixture of perfectly ordered and completely disordered segments. In reality, there will be a continuous spectrum of structures with various degrees of order in the solid material. Average crystallinities determined by the different techniques cannot always be expected to agree very closely, because each method measures a different manifestation of the structural regularities in the solid polymer. 

Comparison of crystallinities determined by gas chromatc r hy and other methods of measurements is usually quite good. In the case of K)lyolefins for which... 

From the examples given in this paper, it is evident that microprocessor control of the molecular probe experiment adds scope and precision to the measurements, as well as avoiding the tediro and operator error involved in repeatedly and reproducibly injecting small volumes of probes (for crystallinity determinations) and permitting quick calculations of adsorption isotherms and BET plots, in the case of surface work. It is hoped that instruments specifically designed for the purpose will be available commercially in the near future. 

The solvent used for crystalline determines which polymorph is formed. Polymorph A (I) is obtained from pyridine, aqueous pyridine3, 60% aqueous isopropanol and potassium tetraborate-water- -, polymorph B (II) from methanol, aqueous methanol3 and dimethylacetamide-water1. ... 

Wide Angle X-rav Scattering. Percent crystallinity determinations were made using wide angle X-ray scattering (WAXS). Samples were compression-molded and then slow-cooled in the mold to promote max-... 

Grant DJW. Report and recommendation of the USP advisory panel on physical test methods crystallinity determination by solution calorimetry. Pharmacop Forum 1999 25 9266-9268. 

The crystal lattice parameters observed for these copolymers by X-ray diffraction are found to be almost identical to those of the P(3HB) homopolymer. The degree of crystallinity determined from the X-ray diffraction decreases steeply from 60 to 23% as the 3HP content in the copolymers increases from 0 to 37 mol%. The trends of composition dependence of the thermal properties and the X-ray diffraction are very similar to those for P(3HB-co-4HB) but not to those for P(3HB-co-3HV), as already mentioned above. Thus, it is reasonable to assume that in the P(3HB-co-3HP) samples containing up to 37 mol% 3HP unit, the 3HB units exist in the crystalline as well as in the noncrystalline regions, while almost all of the 3HP units exist only in the latter. To further investigate this point, the NMR relaxation times have been measured for the films cast from a chloroform solution. 

J. P. Runt, article titled " Crystallinity Determination", Encyclopedia of Polymer Science and Engineering, 4, Wiley-Interscience, New York (1986). 

The stability of drugs in their amorphous form is generally lower than that of drugs in their crystalline form, because of the higher free-energy level of the amorphous state. The relationship between degradation rate and crystallinity determined from heats of dissolution for 13-lactam antibiotics such as sodium cefazolin indicates that a drug with low crystallinity tends to have decreased chemical stability.413... 

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