Percent crystallinity

Fig. 4. Plot of crystallite size distribution (width at half-height) and degree of crystallinity, percent from enthalpy of...

The UHMWPE porous preform had a significantly higher percent crystallinity (p < 0.001) compared to the UHMWPE/HA and crosslinked UHMWPE/HA groups due to the introduction of HA and DCP. While statistically significant, the difference between the UHMWPE and UHMWPE/HA was relatively small. The introduction of the compatibilizer (exhibited by the UHMWPE/MA-g-HDPE porous preform) also decreased the percent crystallinity however, the compatibilized porous preform did not have a significantly different percent crystallinity compared to the UHMWPE/HA treatment group. As expected, the crosslinked UHMWPE/HA displayed the lowest crystallinity percent with a significantly lower percent crystallinity (p < 0.001) compared to the compatibilized porous preform and the UHMWPE/HA samples. 

Density, mechanical, and thermal properties are significantly affected by the degree of crystallinity. These properties can be used to experimentally estimate the percent crystallinity, although no measure is completely adequate (48). The crystalline density of PET can be calculated theoretically from the crystalline stmcture to be 1.455 g/cm. The density of amorphous PET is estimated to be 1.33 g/cm as determined experimentally using rapidly quenched polymer. Assuming the fiber is composed of only perfect crystals or amorphous material, the percent crystallinity can be estimated and correlated to other properties. 

Pyrolusite is a black, opaque mineral with a metallic luster and is frequendy soft enough to soil the fingers. Most varieties contain several percent water. Pyrolusite is usually a secondary mineral formed by the oxidation of other manganese minerals. Romanechite, a newer name for what was once known as psilomelane [12322-95-1] (now a group name) (7), is an oxide of variable composition, usually containing several percent water. It is a hard, black amorphous material with a dull luster and commonly found ia the massive form. When free of other oxide minerals, romanechite can be identified readily by its superior hardness and lack of crystallinity. 

Ore. The assay of mercury ores is not simple, owing to the difficulties encountered in obtaining representative ore samples. Crystalline cinnabar is extremely brittie causing it to break loose from adjacent rock and fall into the sample being collected. This uncontrollable salting of the sample can give results as much as several hundred percent over the actual mercury content of the sample. 

Crystalline CaHPO 2H20 loses both water molecules in a single step at moderately elevated temperature or upon storage to yield the anhydrous salt. The presence of free moisture accelerates this dehydration, which results in anhydrous dicalcium phosphate, often as a hard mass. Addition of a few percent of tetrasodium pyrophosphate or trimagnesium phosphate, Mg2(P0 2> stabilizes the dihydrate. The mechanism, however, is not well understood. Nonetheless, these materials are used widely to stabilize CaHPO 2H20, particulady for toothpaste appHcations. 

The pentahalides of phosphorus, PX, in the gas phase exhibit varying tendencies to dissociate into trihaUde and halogen. InstabiUty increases with increasing ionic radius of the halogen. The pentafluoride appears to be thermally stable. Dissociation of the pentachloride, a few percent at 100°C and 101.3 kPa (1 atm), is essentially completed at 300°C (36). The pentabromide is partially dissociated in the Hquid state and totally dissociated above ca 35°C (39). Pentaiodide does not exist. The molecules of PF and PCl in the vapor phase are trigonal bipyramids. In the crystalline state, both pentachloride and pentabromide have ionic stmctures, ie, [PClJ IPClg] and [PBr4]" PBrJ , respectively. The PX" 4 cations are tetrahedral and the PX anion is octahedral (36,37). 

Percent Crystallinity. For samples that consist of a mixture of crystalline and amorphous material, it is possible to determine the percent of crystallinity by measuring the integrated intensity of sharp Bragg reflections and the integrated intensity of the very broad regions due to the amorphous scattering. 

The viscosity range of CN products can be adjusted in advance by choosing the starting cellulose with an appropriate degree of polymerization (DP). A study of the different celluloses examined the impact of various cellulose properties, such as morphological factors (percent crystallinity, fiber length, and distribution), chemical composition (DP, ash content), and hemiceUulose and lignin content, on the nitration behaviors of cellulose (55). 

Purification. Enzyme purity, expressed in terms of the percent active enzyme protein of total protein, is primarily achieved by the strain selection and fermentation method. In some cases, however, removal of nonactive protein by purification is necessary. The key purification method is selective precipitation of the product or impurities by addition of salt, eg, sodium sulfate, or solvent, eg, ethanol or acetone by heat denaturation or by isoelectric precipitation, ie, pH adjustments. Methods have been introduced to produce crystalline enzyme preparations (24). 

Coefficient of Variation One of the problems confronting any user or designer of crystallization equipment is the expected particle-size distribution of the solids leaving the system and how this distribution may be adequately described. Most crystalline-product distributions plotted on arithmetic-probability paper will exhibit a straight line for a considerable portion of the plotted distribution. In this type of plot the particle diameter should be plotted as the ordinate and the cumulative percent on the log-probability scale as the abscissa. 

In the crystalline region isotactic polystyrene molecules take a helical form with three monomer residues per turn and an identity period of 6.65 A. One hundred percent crystalline polymer has a density of 1.12 compared with 1.05 for amorphous polymer and is also translucent. The melting point of the polymer is as high as 230°C. Below the glass transition temperature of 97°C the polymer is rather brittle. 

Fig. 3. Melting point and crystallinity vs. weight percent VA in EVA copolymers. (Courtesy of Exxon Chemical Company.)...

In most ionomers, it is customary to fully convert to the metal salt form but, in some instances, particularly for ionomers based on a partially crystalline homopolymer, a partial degree of conversion may provide the best mechanical properties. For example, as shown in Fig. 4, a significant increase in modulus occurs with increasing percent conversion for both Na and Ca salts of a poly(-ethylene-co-methacrylic acid) ionomer and in both cases, at a partial conversion of 30-50%, a maximum value, some 5-6 times higher than that of the acid copolymer, is obtained and this is followed by a subsequent decrease in the property [12]. The tensile strength of these ionomers also increases significantly with increasing conversion but values tend to level off at about 60% conversion. 

The preparation and properties of a novel, commercially viable Li-ion battery based on a gel electrolyte has recently been disclosed by Bellcore (USA) [124]. The technology has, to date, been licensed to six companies and full commercial production is imminent. The polymer membrane is a copolymer based on PVdF copolymerized with hexafluoropropylene (HFP). HFP helps to decrease the crystallinity of the PVdF component, enhancing its ability to absorb liquid. Optimizing the liquid absorption ability, mechanical strength, and processability requires optimized amorphous/crystalline-phase distribution. The PVdF-HFP membrane can absorb plasticizer up to 200 percent of its original volume, especially when a pore former (fumed silica) is added. The liquid electrolyte is typically a solution of LiPF6 in 2 1 ethylene carbonate dimethyl car-... 

Fig. 15. Percent content of the a form in the crystalline phase (PJ for compression moulded samples from y form powders of s-PS, versus the maximum temperature of heating of the melt (TmsJ [9]. The percent content of the P form is (100 — PJ...

Even when they have a partial crystallinity, conducting polymers swell and shrink, changing their volume in a reverse way during redox processes a relaxation of the polymeric structure has to occur, decreasing the crystallinity to zero percent after a new cycle. In the literature, different relaxation theories (Table 7) have been developed that include structural aspects at the molecular level magnetic or mechanical properties of the constituent materials at the macroscopic level or the depolarization currents of the materials. 

Mixed diacid chlorides with Terephthalate/isophthalate ratio of 50/50 was used during the reactions to inhibit the formation of crystalline ester segments b Composition in weight percent remaining part of the siloxane backbone is dimethylsiloxane ... 

FIGURE 31.2 Plots of crystalline melting point, heat of fusion and percent crystallinity of ethylene-vinyl acetate (EVA) samples versus (a) radiation dose (b) trimethylolpropane trimethacrylate (TMPTMA) level from differential scanning calorimetry (DSC) studies. (From Datta, S.K., Bhowmick, A.K., Chaki, T.K., Majali, A.B., and Deshpande, R.S., Polymer, 37, 45, 1996. With permission.)... 

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