Crystallinity index standard

Toraya s WPPD approach is quite similar to the Rietveld method it requires knowledge of the chemical composition of the individual phases (mass absorption coefficients of phases of the sample), and their unit cell parameters from indexing. The benefit of this method is that it does not require the structural model required by the Rietveld method. Furthermore, if the quality of the crystallographic structure is poor and contains disordered pharmaceutical or poorly refined solvent molecules, quantification by the WPPD approach will be unbiased by an inadequate structural model, in contrast to the Rietveld method. If an appropriate internal standard of known quantity is introduced to the sample, the method can be applied to determine the amorphous phase composition as well as the crystalline components.9 The Rietveld method uses structural-based parameters such as atomic coordinates and atomic site occupancies are required for the calculation of the structure factor, in addition to the parameters refined by the WPPD method of Toraya. The additional complexity of the Rietveld method affords a greater amount of information to be extracted from the data set, due to the increased number of refinable parameters. Furthermore, the method is commonly referred to as a standardless method, since the structural model serves the role of a standard crystalline phase. It is generally best to minimize the effect of preferred orientation through sample preparation. In certain instances models of its influence on the powder pattern can be used to improve the refinement.12... 

All compositions were either single phase or nearly single phase as determined by X-ray powder diffraction. In the least pure sample there was only one diffraction peak with 3% of the maximum intensity which could not be indexed in the orthorhombic La2CuOA.y structure (Cmca). None of the samples to which K2C03 had been added showed diffraction peaks which could be attributed to either K20 or K2C03, suggesting that either K20 sublimed out of the sample, or was present in a poorly crystalline form. The lattice parameters calculated for all seven compositions are the same within two standard deviations, and are consistent with the published values for the lattice parameters for La2Cu04.y. Thus, the implicatons is that in all cases the bulk of the sample is stoichiometric,... 

For syndiotactic polypropylene, the band at 11.54 ja has been very useful for the determination of the helix content and, indirectly, of the steric structure. The ratio Is between the absorbance of this band and the mean value of the two bands at 2.32 and 2.35 p has been called the index of syndiotacticity (97). The proportionality between Is and the content of crystalline form in the samples was checked by density measurements these, combined with a knowledge of the volume of the unit cell, allowed a direct, though approximate, evaluation of the crystallinity of the samples. The concept of syndiotacticity index was extended to C3— butene 1 copolymers (96) and can be applied to C2-C3 copolymers as well (98). Its value is strongly dependent upon the preliminary thermal treatment of the copolymer (spectra are recorded on samples annealed at 80° C for 12 hours) this is why standard values are not usually given. 

Isotacticity level has a stronger effect on crystallinity and related properties of polypropylene. PP grades with an isotactic index (II) of 0.96-0.98 are obtainable which can offer a 20% increase in flexural modulus in comparison to standard grades (II = 0.93-0.95). This enhanced stereoregularity has very interesting consequences on the properties of bio-rientated PP films (BOPP). A 25% increase in flexural stiffness and 25%... 

Small differences in crystallinity affect the density. For an exact and reproducible density determination the specimen must be eonditioned and the history of the specimen preparation must be known. Density is often measured together with the melt mass-flow rate and both serve as characteristic material parameters. Therefore, preparation and conditioning method based on the ASTM D2839-87 Standard Practice for Use of a Melt Index Strand for Determining Density of Polyethylene has proved suitable The density is determined on extrudates fi om the melt mass-flow rate measurement after boiling in water for one hour. 

The melt flow index, melting and crystallization temperatures, and heat of fusion of the samples are shown in Table 1. The difference in the melting point between the reference and the branched samples are caused by the presence of the branching and the reduced crystallinity. The molecular weights are shown in Table 2 based on a calibration curve determined using PMMA standards. 

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