Crystallinity change

Dwianto, W., Tanaka, F., Inoue, M. and Norimoto, M. (1996). Crystallinity changes of wood by heat or steam treatment. Wood Research, 83, 47-49. 

Master curves can also be constructed for crystalline polymers, but the shift factor is usually not the same as the one calculated from the WLF equation. An additional vertical shift factor is usually required. This factor is a function of temperature, partly because the modulus changes as the degree of crystallinity changes with temperature. Because crystallinity is dependent on aging and thermal history, vertical factors and crystalline polymer master curves tend to have poor reproducibility. 

Ward, G.H. and Schultz, R.K. (1995). Process-induced crystallinity changes in albuterol sulfate and its effect on powder physical stabilit harm. Res., 12 773-779. 

Tuross N, Behrensmeyer AK, Eanes ED (1989) Strontium increases and crystallinity changes in taphonomic and archaeological bone. J Archaeol Sci 16 661-672... 

Figure 15 compares the crystallinity changes estimated from aH NMR analysis and DSC measurements for a series of the etched powders.24 The crystallinity values for 1H NMR analysis were calculated from the areas in the Fourier-transformed broad-line spectra, simulated for the crystalline, intermediate... 

Melveger AT (1972) Laser-Raman study of crystallinity changes in poly(ethylene Terepthalate). J Polym Sci Part A-2 10 317-322... 

Temperature-resolved X-ray diffraction with a heating cell is widely used. ° Crystalline changes are clearly assigned the X-ray diffraction patterns obtained in situ allow to predict quantitative methods if, for kinetic reasons, forms that are present at high temperatures occur... 

Grade Usually expressed in percent of nitrogen, as 20.5% N, 33.5% N. FGAN is a fertilizer grade, prilled and usually coated with kieselguhr. Also available as an 83% solution. A temperature-stabilized grade is also available that inhibits breakdown of prills due to crystalline changes. 

In the case of titania, the stabilising effect of yttria was not observed below a heat treatment of 600 C as shown in Table 6. Pure titania shifted from anatase to rutile at 900 °C and the phase transformation was accompanied by a very strong decrease of the BET surface area. The doped sample, although it kept the anatase structure until reaching a treatment temperature of 1200 °C, was also characterised by a very strong diminution of its surface area at 900 °C which, however, could not be explained by a sole crystalline change as shown in Table 6. 

The 4 cm round disc at the left front is the actual hot stage of the apparatus. The magnifying glass on the holder immediately to the left of the hot stage is used to magnify the crystals, so you can more easily note small crystalline changes. 

The a-phase crystallites are stable up to maximally 120°C. The a-form crystallinity changes into S-form crystallinity at higher temperatures. This a/S crystal transition is indicated as the Tm -value of PK copolymer. The fusion effect at about 258°C which is important for the processing of the polymer, is thus fusion of S-form material only. 

Annealing of a crystalline polymer, either neat or in a blend, increases the degree of crystallinity, changes the crystallite morphology and relieves built-in stresses in the amorphous phase. Table 12.29 shows the gradual increase of HDT with annealing time. Flexural modulus also increases. Similar effects were reported for amorphous polymers such as PS [Nielsen, 1974]. 

Another example of a product where crystalline changes take place after processing is butter. When butter comes off the processing line, it is still sufficiently fluid or pliable that it can be formed into the desired shape. After packaging, the butter is cooled to refrigeration temperature where further crystallization takes place. 

Turekian KK, Kulp JL (1956) Strontirrm content in human bones. Science 124 405-406 Ttrross N, Behrensmeyer AK, Eanes ED (1989) Strontium increases and crystallinity changes in taphonomic and archaeological bone. J Archaeol Sci 16 661-672 Van der Merwe NJ, Lee-Thorp JA, Thackeray JF, Hall-Martin A, Kmger FJ, Coetzee H, Bell RHV, Lindeque M (1990) Somce-area determination of elephant ivory by isotopic analysis. Nature 346 744-746... 

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