Temperature dissolution

On the other hand, water-soluble PVA fibers are available on the market. They are stable in cool water but shrink in warm water and dissolve at 40 to 90°C. The dissolution temperature is controlled by the degree of polymerization and hydrolysis of PVA, he at-treatment conditions after spinning, etc. 

A different melting point, and hence supercooling, is predicted for the strained sector. This is the basis for a different interpretation of the (200) growth rates a regime //// transition occurs on (110) but not on (200). This is despite the fact that the raw data [113] show a similar change in slope when plotted with respect to the equilibrium dissolution temperature (Fig. 3.15). It is questionable whether it is correct to extrapolate the melting point depression equation for finite crystals which is due to lattice strain caused by folds, to infinite crystal size while keeping the strain factor constant. 

Ti/Zr reaction time Acetic acid amount Acetic acid reaction time Solution Concentration Pb dissolution temperature Refluxing... 

Samples should be weighed out (typically 30-120 jug) in bottles. The submitter should check which is the appropriate amount for a particular test. The sample should be labeled with the contents, exact amount of polymer, and test type. Any other information, such as expected molecular weight range, ENB or other monomer content, dissolution temperature..., is helpful for optimizing the analysis. Typically, a single GPC run takes approximately 2lA hours, except for GPC/FTIR which can take five hours for the fractionation and additional time for the FTIR data acquisition. 

Figure 2.25 The dissolution temperature method for determining polymer solubility parameters. Reprinted with permission from J. E. Mark, Physical Chemistry of Polymers, ACS Audio Course C-89, American Chemical Society, Washington, DC, 1986. Copyright 1986, American Chemical Society.

When nitrobenzene alone is used as a solvent (170 C) and with slow cooling, lamellar single crystals are obtained. Their electron diffractograms have an oblique cell (plane group p2). With a mixture of nitrobenzene/decane (65/35) or nitrobenzene/ hexane the dissolution temperature is reduced to about 70 C. 

Nucleation inhibition studies show that the crystallization of both diastereoisomeric salts is inhibited, whereas the dissolution temperatures remain more or less identical. This results in a larger operating window in which to perform a resolution and in a higher efficiency. In addition to nucleation inhibition, the crystal growth also seems to be inhibited by the additive. 

Fig. 14 Binary phase diagram for C246H494 in octacosane. The top curve shows the equilibrium liquidus for extended-chain crystals, and the bottom line the metastable liquidus for once-folded crystals. Experimental dissolution temperatures are fitted to the Flory-Huggins equation with / = 0.15 (solid lines). Vertical dotted lines (a) and (b) indicate the concentrations at which the growth rates were determined as a function of Tc in [29]. Horizontal dotted lines indicate the temperatures at which the rates were determined in [45] as a function of concentration. G(c) at Tc = 106.3 °C, measured along line (c), is shown in Fig. 12. The shading indicates schematically the crystal growth rate (black = fast), and the dashed line the position of the growth rate minimum...

Except for theophyllin, the solubilities are similar at a dissolution temperature (Td) and a dissolution pressure (Pd) of 65°C and 250bar, respectively, the mole fractions are of 2.5e-4 for anthracene, 5e-4 for caffeine and 6.5e-4 for salicylic acid. Theophyllin is an order of magnitude lower, with a value of 0.2e-4. The mole fractions allow one to estimate the maximum production rate for the experimental set up. Assuming a recovery of produced particles of 100%, and no dilution required for processing, the production rates are 1.0, 1.2, 0.5 and 0.04 g/h for caffeine, salicylic acid, anthracene and theophyllin, respectively (conditions Pd = 220bar, Td=65°C, capillary =1.5cm x 75pm flow rate of liquid C02=11.2ml/min)... 

Earlier investigations in our laboratory 56) have shown that several chain reaction polymerizations at temperatures below the melting or dissolution temperature of the final polymer lead to a thermodynamically more stable state than crystallization of the identical polymer from the polymer melt. Bawn and Ledwith mentioned in a review on stereoregular addition polymerization 57) that crystallization of the growing polymer chain might influence the polymerization step such that a more stereoregular polymer results. Ham 58—60) has finally pointed out a possible influence of the crystallization on the tacticity of the preceeding poljonerization which should only be possible when both processes are practically simultaneous. 

Figure 34. Initial crystal growth rate (Gt, along [010]) vs crystallization temperature from 1.1 wt % ( . ) and 4.2 wt % solutions (A, a) of CigsThgs in 1-phenyldecane. ( , a) extended chain, ( , a) once-folded chain crystals. 7 and 7 are the dissolution temperatures of extended-chain and once-folded-chain crystals. The retardation in growth around 7dF is caused by self-poisoning (from ref 192 by permission of American Physical Society).

Fig. 18 Dissolution temperature of additive 3 (red filled circles) and surface potential of 50 pm-thick i-PP films after annealing at 90 °C for 720 min, as a function of the additive concentration of 3 for two independently prepared series (filled triangles, open triangles). The end of the region II (grey) at 0.15 wt% marks the concentration below which the additive is completely soluble in the polypropylene melt at 260°C (horizontal dashed line) [29]. Reprinted by permission of Elsevier Ltd...

Experimental results showed that with equimolar quantity of acid at an appropriate reaction volume, extent of dissolution of the spent catalyst powder increased sharply with temperature. Thus while quite low at 60°C, it became appreciable at higher temperature. For all practical purpose, a dissolution temperature of 90°C was found to be appropriate. 

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