Kinetics crystallisation

Taddei and co-workers [42] investigated the kinetics and mechanism of in vitro and in vivo degradation of Vicryl (lactide-glycolide copolymer) periodontal mesh, using Fourier-Transform Raman, attenuated total reflectance/Fourier-Transform-infrared (FT-IR) spectroscopy and DSC. A saline phosphate buffer and a sodium hydroxide solution were used as the aqueous media to study the hydrolytic in vitro degradation and the membrane implanted in vivo for four weeks. 

Other polymers which have been subjected to a study of crystallisation kinetics include amorphous cellulose [45], PE and chlorinated polyethylene [46-48], aliphatic polyesters [49], Nylon 8 [50], Nylon 6.6 and 6.10 [51] and perfluorocyclobutyl networks [52], polyethylene oxide-PS star polymers [53] and poly(e-caprolactone) [54]. 

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The examples of this section summarise the recent application of the solvent-drop grinding approach to solid-state cocrystal preparation. The approach has been shown in certain instances to provide for either acceleration of CO crystallisation kinetics or selection of a particular polymorph via solid-state grinding. The approach is attractive, as it appears to incorporate some of the beneficial aspects of solvent participation while maintaining an essentially green, eco-friendly process. 

Sequence distribution studies on several types of rubber by 13C-NMR technique have been reported. Some of the more recent reports include silicone rubbers [28-30], SBR [31], acrylonitrile-butadiene rubber (NBR) [32,33], polyurethane [34,35], polyepichlorohydrin [36], ethylene-norbonene [37] and ethylene-propylene rubber [4, 16, 25, 38-44]. The NMR studies on EPDM have been carried out extensively, because it is one of the important parameters, which control the physical properties of the elastomer. For example, ethylene sequence can influence the crystallisation kinetic and melting behaviour of the rubber [38]. 

This is illustrated in Fig. 19.8. He explains the lower and upper limit in the following way. In practice, Tg/Tm is not less than 0.4 for any known polymer for which melt crystallisation data are currently available, so that the lower limit (0.35) of the validity of Eq. (19.26a) has not been reached. The upper limit (0.79) suggests that if Tm is not sufficiently large xc max will be zero. The reason is that the polymer will not have enough driving force for crystallisation and it will be amorphous, at least over the relatively short time periods used in typical crystallisation kinetic studies. 

Because of the difficulties associated with the characterisation of heteronuclei in solution, few studies have attempted to explain experimental results in a quantitative way. If it is assumed that, once nucleation occurs, the particles grow without recrystallisation, then it is possible to get information about the particle density from a consideration of the geometry of the particles and the growth kinetics. One approach is to add heteronuclei to supersaturated solutions and measure the crystallisation kinetics and, from the data obtained, estimate the surface area of the growing crystals. In this way, it is feasible to obtain information about the nucleation capability of different heteronuclei and the effects of pretreatments on the nucleation capability. An example of such an application will be discussed in Sect. 5.4. 

Arellano, M.P., Aguilera, J.M., and Bouchon, P. (2004). Development of a digital video microscopy technique to study lactose crystallisation kinetics in situ. Carbohydr. Res. 339,2721-2730. 

Aside textile and packaging applications the use of PET (Poly(ethylene Terephthalate) for structural applications is rather limited compared to equivalent polymers such as polyamides. Two main reasons can be given. Firstly, the high sensitivity of PET toward hydrolysis and its slow crystallisation kinetics constrain its processing. Secondly, its low glass transition temperature constrains its use if amorphous, whereas its weak impact resistance if semicrystalline constrains its use when crystallised. The industrial objective of this work deals with the latter of these points increasing the impact resistance of semi-crystalline PET. 

Nucleation and crystallisation kinetics generally follow S-shaped crystallisation curves as shown for zeolite A in Figs. 8.28 and 8.29. This means that a rather long incubation time or nucleation period precedes the crystallisation (compare Figs. 8.28b for zeolite A and 8.29b for ZSM5). The general trend in the kinetics of zeolite (ZSM5) synthesis can be summarised as follows ... 

Hubert, L. David, L. Seguela, R. Vigier, G. Degoulet, C. Germain, Y. Physical and mechanical properties of polyethylene for pipes in relation to molecular architecture. I. Microstructure and crystallisation kinetics. Polymer 2001, 42, 8425-8434. 

In a typical zeolite synthesis, the first definite evidence for a successful reaction is the appearance of crystals of the product. As noted above (section 6.1), this signal for the end of the induction period is dependent upon the method of detection most commonly a combination of visual inspection or microscopy with X-ray diffraction. Thereafter, crystal growth can be monitored by the same techniques and the resulting S-shaped growth curve of bulk crystallinity against time is by far the most commonly reported measurement of zeolite crystallisation kinetics (fig- 2). 

The purpose of this research is to study the crystallisation kinetics of ET(Zr)S-4 starting from mixed systems containing titanium and zirconium and to connect the results obtained to the observation, through electron microscopy (SEM), of the crystal morphology of ETS(Zr)-4 synthesised at different reaction times. The Si NMR data suggest that zirconium occupies framework tetrahedral positions. 

The crystallisation kinetics of PET suit the process (Fig. 3.26). A glassy preform can be injection moulded with a wall thickness of up to 4 mm. If the mould is kept at 10 °C, the inner layers of the polymer cool fast enough for the crystallinity to be negligible. High molecular weight PET, with Mn — 24 000, is used so that the rate of crystallisation is suitably low. 

The possibility of obtaining photographic patterns with short exposure time permits the following of rapid changes with time. This approach has bwn used, for example, for following the crystallisation kinetics of isotactic polystyrene. By utilisation of a high speed motion picture camera, it has been possible to follow the rapid extension of samples at rates of several hundred frames per second. ... 

On the other hand, the incorporation of a small content of ethylene units in the polypropylene chains has an influence on the regularity of the molecular structure. In fact, a change in tacticity induced by the shortening of isotactic sequences was observed (Zimmermann, 1993). Although this has a negative influence on crystallisation kinetics, an opposite effect should come from the enhanced mobility due to the presence of the ethylene sequences. As a result of these counteracting effects, a relatively narrow window of cooling rates exists in which an enhancement of crystallization kinetics sets in (Foresta et al., 2001). 

K. Watanabe and K. Hoshi, Crystallisation Kinetics of Fine Barium Hexaferrite, BaFei20i9, Particles in a Glass Matrix, Phys. Chem. Glasses 40, 75-78 (1999). 

Lebreton B, Zomerdijk M, Ottens M, van der Widen LAM (1999) Effect of impurities upon crystallisation kinetics of j3-lactam antibiotics. Proc Annual Meeting AlChE, November 1999... 

The effects due to very slow processes in the sample, however, may not be removed even in the quasi-isothermal MTDSC with data collection after 10 min. The analysis of the slow response of the sample in the glass transition region will be treated in Section 4.3. The decrease in the heat capacity due to cold crystallisation can easily be converted into a plot of the crystallisation kinetics. Additional points for the kinetics plot can be generated at shorter and longer analysis times of the quasi-isothermal runs. The time-scale can easily be adjusted to modulations from 1 min to many hours, limited only by the patience of the operator and the stability of the calorimeter. 

Figure 4.67. Analysis of the crystallisation kinetics. [A] Isothermal analysis with a DSC by quick cooling to the crystallisation temperature and analysis after steady state has been reached. [B] Step-wise analysis by heating after different times of crystallisation of PEEK by direct measurement from the crystallisation temperamre.

Plastics—Differential Scanning Calrimetry (DSC)—Part 7 Determination of Crystallisation Kinetics... 

The crystallisation kinetics of the composites are affected by the nucleating effects of the polymer liquid crystal interlayer and the glass fibre. When both components are present the glass fibres dominate the nucleation kinetics. This is also reflected in the degradation kinetics, where complete degradation of the matrix occurs at lower temperatures for the glass reinforced materials. 

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