Crystallinity, crystallisation amorphous content

Savolainen et al. investigated the role of Raman spectroscopy for monitoring amorphous content and compared the performance with that of NIR spectroscopy [41], Partial least squares (PLS) models in combination with several data pre-processing methods were employed. The prediction error for an independent test set was in the range of 2-3% for both NIR and Raman spectroscopy for amorphous and crystalline a-lactose monohydrate. The authors concluded that both techniques are useful for quantifying amorphous content however, the performance depends on process unit operation. Rantanen et al. performed a similar study of anhydrate/hydrate powder mixtures of nitrofurantoin, theophyllin, caffeine and carbamazepine [42], They found that both NIR and Raman performed well and that multivariate evaluation not always improves the evaluation in the case of Raman data. Santesson et al. demonstrated in situ Raman monitoring of crystallisation in acoustically levitated nanolitre drops [43]. Indomethazine and benzamide were used as model... 

A weakness, common to all Karl Fischer-type methods, lies in the limitation that they measure the total water content of the sample, irrespective of the water distribution within the sample. In solids that are partially crystalline and partially amorphous, the residual water will be concentrated in the amorphous phase, thus depressing its Tg. This can accelerate or even promote the crystallisation of small molecule substances within the amorphous matrix. Take as an example crystalline sucrose that contains 0.5% of amorphous material and 0.17% of residual water. Since all the water is concentrated in the amorphous phase, the real water content will be 20% with a Tg of 9°C. It is also instructive to calculate the number of water molecule layers for differently sized sucrose particles. This is shown in Table 1. If the measured water content were to rise to 0.5%, corresponding to 50% in the amorphous phase, then Tg of the amorphous phase would be depressed to —70°C. It is therefore useful, if not essential, to have a reasonable estimate of the amorphous content of a preparation. Several more or less laborious methods for its determination hnd application, and they are... 

The maximum rates of crystallisation of the more common crystalline copolymers occur at 80—120°C. In many cases, these copolymers have broad composition distributions containing both fractions of high VDC content that crystallise rapidly and other fractions that do not crystallise at all. Poly(vinyhdene chloride) probably crystallises at a maximum rate at 140—150°C, but the process is difficult to foUow because of severe polymer degradation. The copolymers may remain amorphous for a considerable period of time if quenched to room temperature. The induction time before the onset of crystallisation depends on both the type and amount of comonomer PVDC crystallises within minutes at 25°C. 

These data show that spontaneous crystallisation during storage under atmospheric conditions occurs for 1,4 trans-BR contents higher than about 75%wt. The amorphous character of system E does not mean that a BR system with an 1,4 trans content of 65.5 %wt. stays amorphous under all circumstances. Comparison of the (scan l) Hf-value with the (scan 2) Hc-value of the systems C and D shows that cooling to lower temperatures promotes the crystallisation process. A decrease of the cooling rate from 20°C/minute to 10°C/minute was already sufficient to obtain also a crystalline phase in system E, see below. 

Several hundred mixed-metal pyrophosphates are known in the solid state. Many of these may be prepared by melting together two pyrophosphates (5.125), or orthophosphoric acid with the appropriate mixture of oxides, or a mixture of metal nitrates with dianunonium phosphate. When solutions of equivalent quantities of a soluble metal salt and sodium pyrophosphate are mixed, a precipitate of a mixed-metal salt is produced. These precipitates are often amorphous and reluctant to crystallise, and sometimes ill defined with a variable water content. In other cases, however, a crystalline compound with a definite composition can be isolated (5.126). Molten nitrates will react with some acid salts to produce double salts [30] (5.127). 

The of the blends depends on many factors. The of P(3HB-co-3HV) copolymer in the blend was lower than that of the pure copolymer. Matzinos et al7° reported that a small decrease in the indicated that a phase separation had occurred. The melting enthalpy of the blend decreased with the increase of starch. Godbole et reported an increase in the Tg value with increasing starch content. The same trend was observed by Seves et al7 using dynamic mechanical thermal behaviour (DMTA). Reis et al7 also reported a decrease in crystallisation enthalpy and as the starch content increased. This indicated that blends had a lower degree of crystallinity compared to the pure P(3HB-co-3HV) copolymer. Any solid polymer can have amorphous, crystalline or both properties. In order to determine this, XRD was used by Reis et al7 There were no crystallinity value from the broad hump for the P(3HB-co-3HV)/starch blends. It was also observed that the crystallinity decreased as the starch content in the blend increased. 

Acid modification of tapioca starch earlier reported to increase the mechanical strength of tablets. The development of ordered structure (double helices) of these starches was monitored using CP MAS NMR and X-ray diffraction. As the hydrolysis time increased, the intensity of the resonance for Cl and C4 amorphous fractions decreased while that for Cl and C4 double helix fractions increased. Relative crystallinity obtained from C CP MAS NMR and X-ray diffraction methods both increased sharply initially and then levelled off with hydrolysis time. The initial increase in relative double helix content and crystallinity was due to a hydrolytic destruction in the amorphous domain, retrogradation of the partially hydrolysed amylose and crystallisation of free amylopectin double helices. ... 

However, as described earlier, amorphousness in lactose samples depends on the method of preparation. The amorphous portions are in a high energy state and should easily absorb water vapour. The amorphous portions will crystallise when the glass temperature has been decreased by the increased water content to below the experimental temperature [151]. Angberg [148] considered that in a sorption isotherm, crystallisation will be shown as a rapid drop in the curve, since the freed crystalline parts desorb the superfluous water. The amount of... 

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