Amorphous crystalline content

Solution calorimetry can also be used to evaluate amorphous/crystalline content in a binary mixture. The enthalpy of solution for the amorphous compound is an exothermic event, whereas that of the crystalline hydrate is endothermic. Enthalpy of solution is a sum of several thermal events, that is, heat of wetting (incorporating sorption process, such as surface sorption and complexation), disruption of the crystal lattice, and solvation. The order of magnitude of solution enthalpy for the crystalline compound suggests that the disruption of the crystal lattice predominates over the heat of solvation. In addition, the ready solubility of the compotmd in aqueous media is probably governed by entropy considerations. 

Chemical methods to determine the crystalline content in silica have been reviewed (6). These are based on the solubility of amorphous silica in a variety of solvents, acids or bases, with respect to relatively inert crystalline silica, and include differences in reactivity in high temperature fusions with strong bases. These methods ate qualitative, however, and fail to satisfy regulatory requirements to determine crystallinity at 0.1% concentration in bulk materials. 

Figure 5 Raman spectra of orthorhombic ethylene 1-hexene copolymer with band fitting. The crystalline band at 1,416 cm-1, and amorphous bands at 1,303 cm- and 1,080 cm- are used to compute the crystallinity content ac = 0.52, and the amorphous content aa = 0.42. (See Color Plate Section at the end of this book.)...

Correlation between Co and Fe contents in Israeli arid soils. Correlation between Cu and MnO contents in Israeli arid soils. Effects of soil pH on the Zn amount bound to the Fe oxide fraction (amorphous/crystalline Fe oxide and overall Fe oxide bound fractions) in soils from China with pH 3.73 - 8.1 and 0 -14.7% CaC03 (after Han et al., 1995. Reprinted from Geoderma, 66, Han F.X., Hu A.T., Qi H.Y., Transformation and distribution of forms of zinc in acid, neutral and calcareous soils of China, p 128, Copyright (1995), with permission from Elsevier). 

As with ceramics and metals, polymer crystals can have multiple crystal forms. Polyethylene has a metastable monoclinic form and a orthohexagonal high pressure form. A list of some of the more common polymers and their corresponding crystal strnctnres is given in Table 1.24. Finally, X-ray diffraction can be used to determine the amorphous to crystalline ratio in semicrystalUne polymers in much the same way that Eq. (1.61) can be used. Figure 1.66 shows a schematic illustration of the X-ray diffraction patterns for semicrystalline and amorphous polyethylene. The estimation of crystalline content is based upon a ratio of the peak areas in the two samples. 

Othfer properties of the PMMA-PVdF system are consistent with the amorphous-crystalline blend model. Thus, the light transmission of films of these blends at room temperature (Figure 5) decreases fairly abruptly as the the PVdF content increases, coincident with the appearance of a crystalline phase. 

Fig. 15.6 Raman spectra recorded along the diameter of an iPP spherulite during isothermal crystallization from the melt at Tj, = 130°C. The variation in Raman bands at 809 cm and 841 cm indicating the amorphous and crystalline content of iPP are matched -with their positions on the polymer (Reprinted from [38])...

At temperatures below the melting point of the polymer, in region CD, retention proceeds by bulk sorption but the polymer-solute interaction is restricted to the amorphous domains of the stationary phase. Upon meltir, in r on DF, the fraction of amorphous material increases, leading to an incre in retention volume. At temperatures above the melting point, segment FG, a linear retention diagram, corresponding to bulk sorption into the completely amorphous polymer, is obtained. By extrapolation of this line to lower temperatures (dashed line FE), the crystalline content of the stationary phase can be determined by comparison of the experimental retention volume with the extrapolated value. 

An exothermic transition can sometimes be observed by DSC on crystallization of the amorphous form. This can be used to quantify the amorphous content of crystalline drugs. A calibration curve that consists of a plot of the enthalpy of crystallization as a function of crystalline content was used to determine if the lyophilized MK-0591 drug substance was... 

Amorphous phase content was determined by subtracting the total concentration of crystalline phases from unity (see reference 8 for example),... 

Figure X. Effect of amorphous phase content on the solubility coefficients of various gases in semi-crystalline polyethylene. (Data taken from Ref. 19.)...

As demonstrated before, the shifting involves three shift factors, one horizontal, usually expressed as aj, = b rip(T)/rip(Tp), where b = p T /pT is the hrst vertical shift factor that originates in the thermal expansion of the system (p is density). The subscript o indicates reference conditions, dehned by the selected reference temperature T, usually taken in the middle of the explored T-range. For homopolymer melts, as well as for amorphous resins, the two shift factors, aj, and b.j, are sufficient. However, for semi-crystalline polymers, a second vertical factor, v., has been found necessary — it accounts for variation of the crystallinity content during frequency scans at different temperatures [Ninomiya and Ferry, 1967 Dumoulin, 1988]. 

The presence of mineral reinforcements such as talc or mica, as foreign solid particles embedded into a polypropylene matrix, usually induces a nucleation effect. A signihcant increase in the crystalline content of the polymer is evidenced if compared with the neat polymer when processed at the same setup conditions that are necessary to ensure a good accommodation of the solid particles into the amorphous phase of the polymer in order to obtain a material with a good mechanical performance (27). The comparison between PP/mica and PP/talc composites in terms of their mechanical behavior under dynamic conditions in the solid state agrees with the morphological features derived from their chemical structures of both minerals (28). 

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