Polymers crystallization kinetics

Before we start to describe thoroughly the kinetics of mineralorganic-filled thermoplasts we would note that in Ref. [13], with the example of PE keroplasts, it was proved that kerogens only very slightly influence polymer crystallization kinetics, and, consequently can be classified as low-energy surface fillers. 

Ravindranath, K., and J.P. Jog, Polymer Crystallization Kinetics Poly(ethylene tereph-talate) and Poly(phenylene sulfide), J. Appl. Pol. Sci. 49 1395-1403 (1993). 

J. N. Hay, Application of the modified Avrami equation to polymer crystallization kinetics, Brit. Polym. J. 3,74 (1971). 

Nucleation of the embryonic crystals in the liquid phase followed by growth or accretion of the solid phase onto the nucleus in the mechanism usually used to describe polymer crystallization kinetics as with metals. 

DSC results showed a melting temperature depression of HOPE caused by the dilution effect of the non-crystalline EVA and the probable co-crystallization of some EVA chains with HD PE chains [38, 40]. Changes in the crystallization and melting temperatures of EVA were determined mainly by the nucleation effect of HDPE crystals and the effect of partial miscibility between these polymers. Crystallization kinetics results showed that the addition of more HDPE into an EVA matrix caused more heterogeneous nucleation, while the addition of EVA would delay the nucleation of HDPE at the beginning of the cooling process. Intermolecular interaction in the melt facilitated the crystallization of both EVA and HDPE. 

J. D. Hoffman and R. L. Miller, Polymer, 38, 3151 (1997). (General review of polymer crystallization kinetics.)... 

Ozawa extended the Avrami model to quantify polymer crystallization kinetics using noniso-thermal data [289]. It was reasoned that nonisothermal crystallization amounted to infinitesimal short crystallization times at isothermal conditions, given a crystallization temperature T [290]. This analysis led to the following equation ... 

In a previous work [31], practical guidelines were given for the Avrami equation fitting to DSC isothermal polymer crystallization kinetics. It was recommended that ... 

Lorenzo A, Arnal M, Albueme J, Muller AJ. DSC isothermal polymer crystallization kinetics measurements and the use of the Avrami equation to fit the data guidelines to avoid common problems. Polym Test 2007 26(2) 222-31. 

The development of solid-state structure in semicrystalline block copolymers has been studied extensively over the past decade. Most of the earlier studies are covered in a recent review by Hamley [1999] the present chapter complements this earlier review by highlighting recent advances in this field, with a particular focus on how the processes of microphase separation and crystallization interact. We begin by providing a brief overview of synthetic routes to near-monodisperse semicrystalline block copolymers. We then enumerate the key experimental techniques used to examine the crystallization behavior and morphology of semicrystalline block copolymers. The remainder of the chapter focuses on the solid-state structures that these materials exhibit, the pathways by which these structures develop, and the impact of melt microphase separation on polymer crystallization kinetics. 

The present discussion will focus on the physical principles of the measurement and how to interpret the recorded data under nonisothermal conditions. This technique is also useful to study the polymer crystallization kinetics however, this topic is beyond the scope of this discussion. Fully detailed description and... 

Albeit somewhat different in detail, the principles governing static melt-crystallization also apply to the crystallization of oriented melts. Therefore, in the following discussion emphasis is placed on qualitative principles rather than quantitative considerations. A full exposition of the quantitative aspects of polymer crystallization kinetics can be found in the works of Mandelkem and Wunderlich listed in the bibliography at the end of this chapter. 

Chan TW, Shyu GD, Isayev AI. Master curve approach to polymer crystallization kinetics. In Annual Technical Conference, Vol. 52, issue 2. Society of Plastics Engineers, 1994 pp. 1480-1484. 

The fundamental equilibrium relationships we have discussed in the last sections are undoubtedly satisfied to the extent possible in polymer crystallization, but this possibility is limited by kinetic considerations. To make sense of the latter, both the mechanisms for crystallization and experimental rates of crystallization need to be examined. 

In order to carry out an experimental study of the kinetics of crystallization, it is first necessary to be able to measure the fraction d of polymer crystallized. While this is necessary, it is not sufficient we must also be able to follow changes in the fraction of crystallinity with time. So far in this chapter we have said nothing about the experimental aspects of determining 6. We shall now briefly rectify this situation by citing some of the methods for determining 6. It must be remembered that not all of these techniques will be suitable for kinetic studies. 

A crystalline or semicrystalline state in polymers can be induced by thermal changes from a melt or from a glass, by strain, by organic vapors, or by Hquid solvents (40). Polymer crystallization can also be induced by compressed (or supercritical) gases, such as CO2 (41). The plasticization of a polymer by CO2 can increase the polymer segmental motions so that crystallization is kinetically possible. Because the amount of gas (or fluid) sorbed into the polymer is a dkect function of the pressure, the rate and extent of crystallization may be controUed by controlling the supercritical fluid pressure. As a result of this abiHty to induce crystallization, a history effect may be introduced into polymers. This can be an important consideration for polymer processing and gas permeation membranes. 

Crystallization kinetics have been studied by differential thermal analysis (92,94,95). The heat of fusion of the crystalline phase is approximately 96 kj/kg (23 kcal/mol), and the activation energy for crystallization is 104 kj/mol (25 kcal/mol). The extent of crystallinity may be calculated from the density of amorphous polymer (d = 1.23), and the crystalline density (d = 1.35). Using this method, polymer prepared at —40° C melts at 73°C and is 38% crystalline. Polymer made at +40° C melts at 45°C and is about 12% crystalline. 

Since interactions at the molecular level between polymer components in the blends occur only in the amorphous phase, it is reasonable to assume that these effects are due to kinetic factors and, in particular, to the influence of a polymer component on the nucleation or crystallization kinetics of the other one. 

Modified amino acids such as N-acyl-dehydroalanine polymers and copolymers with N-vinyl-N-methyl acetamide seem to be particularly effective [396]. The crystallization kinetics in the presence of polyvinylpyrrolidone and tyrosine have been tested by time-resolved experiments [981]. An influence is evident on the particle size distribution of the hydrate [1433]. 

Many polymers solidify into a semi-crystalline morphology. Their crystallization process, driven by thermodynamic forces, is hindered due to entanglements of the macromolecules, and the crystallization kinetics is restricted by the polymer s molecular diffusion. Therefore, crystalline lamellae and amorphous regions coexist in semi-crystalline polymers. The formation of crystals during the crystallization process results in a decrease of molecular mobility, since the crystalline regions act as crosslinks which connect the molecules into a sample spanning network. 

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... 

In what follows, we use simple mean-field theories to predict polymer phase diagrams and then use numerical simulations to study the kinetics of polymer crystallization behaviors and the morphologies of the resulting polymer crystals. More specifically, in the molecular driving forces for the crystallization of statistical copolymers, the distinction of comonomer sequences from monomer sequences can be represented by the absence (presence) of parallel attractions. We also devote considerable attention to the study of the free-energy landscape of single-chain homopolymer crystallites. For readers interested in the computational techniques that we used, we provide a detailed description in the Appendix. ... 

In the dynamic Monte Carlo simulations described earlier, we used a crystalline template to suppress supercooling (Sect. A.3). If this template is not present, there will be a kinetic interplay between polymer crystallization and liquid-liquid demixing during simulations of a cooling run. In this context, it is of particular interest to know how the crystallization process is affected by the vicinity of a region in the phase diagram where liquid-liquid demixing can occur. 

The fascinating issues relating to polymer structures preceding crystallization are still largely open to investigation. More specific and articulated models of such states may provide a better understanding of polymer crystallization, both from the thermodynamic and the kinetic viewpoint. Furthermore, the different mechanisms that lead polymers to crystallize may eventually be understood in a coherent, more unified picture. 

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