Crystalline content

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. 

The crystallization kinetics of commercial polyolefins is to a large extent determined by the chain microstructure [58-60]. The kinetics and the regime [60] of the crystallization process determine not only the crystalline content, but also the structure of the interfaces of the polymer crystals (see also Chapter 7). This has a direct bearing on the mechanical properties like the modulus, toughness, and other end use properties of the polymer in fabricated items such as impact resistance and tear resistance. Such structure-property relationships are particularly important for polymers with high commercial importance in terms of the shear tonnage of polymer produced globally, like polyethylene and polyethylene-based copolymers. It is seen that in the case of LLDPE, which is... 

One of the issues in using solution state NMR for PET analysis is that, due to the high crystallinity content of the polymer, it is fairly difficult to dissolve. Harsh... 

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.)...

In this connection, an interesting relation is shown in Figure 17, where both the tensile strength and the relative crystallinity (from DSC data) are plotted against temperature, for the H2-BBB-30-55 triblock. It can be readily seen that, at 80°C, where the strength has dropped to 10 of its original value, the crystalline content is still over 80% of its initial value. 

Quantitative measurements of the crystallinity content of the block copolymers were made from the determination of the heat of fusion and from the density of the polymer. 

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. 

For the crystallization in present of TPABr a maximum crystallinity is reached already after 10 h with a surprising high value of about 1.6 pretending a crystalline content of more... 

The transition at 19° C involves an expansion of 0.0058 cm3/g (Clark and Muus). Sincethe transition temperatureincreaseswith pressure by about 0.013° C per atmosphere (Beecroft and Swenson), the latent heat is about 3.2 cal/g. These values are for the crystal and would be reduced in proportion to the crystalline content. The transition at 30° C is only about one-tenth as large. The over-all increase in entropy at these transitions is about 0.0108 cal deg-1g-1. The portion due to the increase in volume is (a// ) A V, where a is the volumetric coefficient of thermal expansion and / is the compressibility. Since the compressibility of the crystal is not known, this quantity is somewhat uncertain. Using the average of the values of a (Quinn, Roberts, and Work) and p (Weir, 1951) for the whole polymer above and below the transitions, it appears that (a/P)A V is about 0.0041 cal deg 1g 1. The entropy of the transition corrected to constant volume is, therefore, about 0.0067 cal deg g-1. 

Regenerated cellulose Stable in most organic solvents (typically prepared from cellulose acetate as precursor) High crystalline content 4-9... 

Crystallization of p- nitrotoluene. 8000 1. of crude molten p- nitrotoluene are charged into a tubular crystallizer, cooled to 39-40°C Mid this temperature is maintained for 24 hr. Then the whole is cooled to 18°C for 24 hr and the crystallizer is opened. The mother liquor is collected Mid the crystalline contents heated slowly to 50°C. The oil that was drawn off is collected sepMately and when it reaches... 

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... 

Density is measured using density gradient columns and hydrostatic (displacement) methods. Density is directly related to crystalline content and in fact can be used to estimate % crystallinity in polyethylene. 

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