Crystallization kinetics regimes

The crystallization kinetics of commercial polyolefins is to a large extent determined by the chain microstructure [58-60]. The kinetics and the regime [60] of the crystallization process determine not only the crystalline content, but also the structure of the interfaces of the polymer crystals (see also Chapter 7). This has a direct bearing on the mechanical properties like the modulus, toughness, and other end use properties of the polymer in fabricated items such as impact resistance and tear resistance. Such structure-property relationships are particularly important for polymers with high commercial importance in terms of the shear tonnage of polymer produced globally, like polyethylene and polyethylene-based copolymers. It is seen that in the case of LLDPE, which is... 

Table 6 Schematic representation of the effects of branching and molecular weight on the crystallization kinetics and the appearance of the Regimes in crystallization...

Sanchez and DiMarzio identified [41] a crossover regime 11 [Fig. 1.15(c)], where g is more rapid than in 1 and less than in 111. On the basis of the LH model, crystallization kinetics in these three regimes are obtained as follows. 

The SR spectnun of an intense energy continuum of radiation makes possible rapid data collection in the sub-second regime by the Laue diffraction method. This rate of data collection is sufficient to investigate some of the crystal kinetics and catalytic intermediate reaction states that can be produced. 

Figure 3. Kinetics of solidification illustrating how various cooling programmes (pathways 1 to 3) can affect the final inventory of phases which differ in their respective crystallization kinetics. The characteristic times are in the microsecond regime for metallic alloys but extend into the time-scales of days for compounds such as oxides.

Microphase-assisled aulocatalysis in the production of citric acid Anaiysis of rale enhancement through a study of controlling regimes and crystallization kinetics... 

In this section experimental results are discussed, concerned with analyses of melting and crystallization kinetics, as well as reversibility of the phase transition. The frame of the discussion is set by Fig. 3.76, which will be supported by experimental data on poly(oxyethylene). The thermal analysis tools involved are TMDSC, optical and atomic-force microscopy, DSC, adiabatic calorimetry, and dilatometry. Most of these techniques are described in more detail in Chap. 4. Results from isothermal crystallization, and reorganization are attempted to be fitted to the Avrami equation. This is followed by a short remark on crystallization regimes and finally some data are presented on the polymerization and crystallization of trioxane crystals. 

Three Regimes of Crystallization Kinetics Hoffman defined three regimes of crystallization kinetics from the melt, which differ according to the rate that the chains are deposited on the crystal surface. 

Similar results have been found upon analysis of the crystallization kinetics by differential scanning calorimetry [151, 152] of polyethylene fractions encompassing a very wide range of molecular masses, from 2900 to 8 X 10 . This is the widest range in molecular masses to have been reported for the crystallization kinetics of this polymer. The influence of molecular mass on regime formation has been explored. 

Figure 11.8a shows how the LH theory was applied to fit overall crystallization kinetics data of 1/t5q% versus 7). for the PPDX . Here, we have also assumed that crystal growth occurs under Regime II and the values of all parameters employed for the LH theory calculation are listed as a footnote in Table 11.4. 

Before discussing the effect of short-chain branching on the kinetics of crystallization process, it is necessary to revisit the theory of secondary nucleation and the concept of regimes as given by Lauritzen and Hoffmann... 

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