Crystallinity from density

It has also been inferred that differences found between crystallinities measured by density and those from heat of fusion by DSC area determination, as given for polyethylenes in the example of Figure 4 [72], may be related to baseline uncertainties, or not accounting for the temperature correction of AHc. Given that similar differences in crystallinity from density and heat of fusion were reported for isotactic poly(propylene) [43] and polyfaryl ether ether ketone ketone), PEEKK [73], other features of phase structure that deviate from the two-phase model may be involved in the crystallinity discrepancy. 

Crystallinity from density measurements. Crystallinity from broad-line NMR. 

FIGURE 12.16. Ten-second stress relaxation moduli Er(10) of PET crystallized at 227°C to different degrees presented as a function of temperature. Crystallization times are also shown as well as the estimated degree of crystallinity from density measurements. (From Groeninckx, Berghmans, and Smets, by permission, [89].)... 

It has been foimd in a number of cases that from density and WAXD measurements is equivalent within experimental error, but is higher than that from DSC (19,47). These observations have led to the conclusion that DSC provides a measure of the core crystallinity only, while the crystallinity from density and WAXD is a measure of the core crystallinity along with the crystal-amorphous interphase. 

Figure 10 Plot of yield stress as a funetion of degree of crystallinity (from density) for various isotropic polyethylene samples. (Data from Refs. 105 and 106.)...

A major source of error in determining the degree of crystallinity by differential scanning calorimetry arises from the selection of the baseline under the endothermic peak. The problems associated with this procedure were discussed in reference to heat of fusion measurement in Section IV.D. 1. Differential scanning calorimetry also suffers to some extent from poor sample to sample repeatability, which lowers its precision and accuracy. As with the determination of degrees of crystallinity from density, the presence of fillers invalidates this method. From a theoretical standpoint, the determination of crystallinity from a sample s heat of fusion relies on a simple two-phase model of morphology. These drawbacks and an uncertainty in the heat of fusion of 100% crystalline polyethylene limit the accuracy of this method to approximately 5%. 

Figure 21 Plot of degree of crystallinity from density versus that from differential scanning calorimetry.

The chemical and physical properties of limestone vary tremendously, owing to the nature and quantity of impurities present and the texture, ie, crystallinity and density. These same factors also exert a marked effect on the properties of the limes derived from the diverse stone types. In addition, calcination and hydration practices can profoundly influence the properties of lime. 

The large number of commodity and specialty resias collectively known as LLPDE are in fact made up of various resias, each different from the other in the type and content of a-olefin in the copolymer, compositional and branching uniformity, crystallinity and density, and molecular weight and molecular weight distribution (MWD). 

Titanium Dibromide. Titanium dibromide [13873-04-5] a black crystalline soHd, density 4310 kg/m, mp 1025°C, has a cadmium iodide-type stmcture and is readily oxidized to trivalent titanium by water. Spontaneously flammable in air (142), it can be prepared by direct synthesis from the elements, by reaction of the tetrabromide with titanium, or by thermal decomposition of titanium tribromide. This last reaction must be carried out either at or below 400°C, because at higher temperatures the dibromide itself disproportionates. 

Barium acetate [543-80-6] Ba(C2H202)2, crystallines from an aqueous solution of acetic acid and barium carbonate or barium hydroxide. The level of hydration depends on crystallization temperature. At <24.7°C the trihydrate, density 2.02 g/mL is formed from 24.7 to 41 °C barium acetate monohydrate [5908-64-5] density 2.19 g/mL precipitates and above 41 °C the anhydrous salt, density 2.47 g/mL results. The monohydrate becomes anhydrous at 110°C. At 20°C, 76 g of the monohydrate dissolves in 100 g of water. Barium acetate is used in printing fabrics, lubricating grease, and as a catalyst for organic reactions. 

Pelletier and Reber315 present new luminescence and low-energy excitation spectra of Pd(SCN)42 in three different crystalline environments, K2Pd(SCN)4, [K(18-crown-6)]2Pd(SCN)4, and (2-diethylammonium A -(2,6-dimethylphcnyl)acetamide)2Pd(SCN)4, and analyze the vibronic structure of the luminescence spectra, their intensities, and lifetimes as a function of temperature. The spectroscopic results are compared to the HOMO and LUMO orbitals obtained from density functional calculations to qualitatively illustrate the importance of the bending modes in the vibronic structure of the luminescence spectra. 

In the case of a semicrystalline polymer, the two components are the crystalline and amorphous regions. If we know the densities of the crystalline and the amorphous regions, we can calculate a sample s degree of crystallinity from Eq. 7.5. 

The most simple secondary method is die determination of crystallinity from the density of the material. 

Figure 5. A comparison of percent crystallinity obtained from density to that obtained from AHf for the various block copolymers.

The degree of crystallinity is also reflected in the density of the polymer so that the determination of density provides at least a relative measure for crystallinity. Differential scanning calorimetry (DSC) is frequently applied to determine the crystallinity from the heat of crystallization or melting (see Sect. 2.3.4.8). 

The dihydrate, SnCl2 2H20, is a white monoclinic crystalline substance density 2.71 g/cm absorbs oxygen from air forming an oxychloride melts at 37°C on rapid heating decomposes on strong heating very soluble in water forms an insoluble basic salt with excess water very soluble in hydrochloric acid soluble in caustic soda solution, ethanol and ethyl acetate. Thermochemical Properties... 

Fig. 8. Mass fraction of broad component vs. crystallinity obtained from density measurements66. Solid circles indicate data of Mandelkern ef ai.68, 69 Straight line indicates the relation, (l-k)

The distinction between AHf and AHf has not always been borne in mind. Thus to determine AHf from calorimetric measurements it is necessary to know wc. The fraction of crystallinity can be estimated from density measurements through the equation... 

The true densities of crystalline and amorphous PTFE differ considerably, and 100% crystalline PTFE densities of 2.347 at 0°C (32°F) and 2.302 at 25°C (77°F) were calculated from X-ray crystallographic data.21 The density decrease of about 2% between these temperatures includes the decrease of approximately 1% due to the transition at 19°C (66°F), which results from a slight uncoiling of the helical conformation of molecules on heating through the transition. By contrast, the density of amorphous PTFE is not affected by the transition at 19°C and values... 

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...

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