Poly crystal growth rates

Figure 2.13 Variation of the crystal growth rate with temperature for poly(ethy-lene terephlhalate), T , = 280°C. (From Ref. 11.)...

Accordingly, the influence of MW on the crystallization behaviors of semicrystalline polymers has been studied in various articles. For example, linear crystal growth rates of poly(ethylene oxide) and poly(ethylene succinate) (PES) reach a minimum value at a critical MW. This value is related to the crystallization transition from an extended chain to a folded chain conformation [96,97], suggesting that high MW polymers require sufficient reconformation time to achieve an ordered structure. As evidence of this MW dependence of the semicrystalline polymer on... 

Irrstead of the molar flux derrsity ft the crystal growth rate is often described by the displacement rate v of a crystal face (for irrstance v, for the 111 face). Note that every face can have different growth rates v at the same supersaturation. Let us assume spherical (poly)crystals. The growth rate is eqttal to the derivative of the radius with respect to time t (y = dr/dt) or the derivative G = 6L/6t with/, as the decisive length which is the diameter L for spheres. With the volume shape factor a = V /L and the srrrface shape factor P =. 4p/Z,, the following relationship between the mass flux density m (m = n M), the displacement rate v of the crystal surface, and the rate G = 2v of crystalhne particles is given... 

Hu WB (2005) Molecular segregation in polymer melt crystallization simulation evidence and unified-scheme interpretation. Macromolecules 38 8712-8718 Hu WB, Cai T (2008) Regime transitions of polymer crystal growth rates molecular simulations and interpretation beyond Lauritzen-Hoffman model. Macromolecules 41 2049-2061 Jeziomy A (1971) Parameters characterizing the kinetics of the non-isothermal crystallization of poly(ethylene terephthalate) determined by DSC. Polymer 12 150-158 Johnson WA, Mehl RT (1939) Reaction kinetics in processes of nucleation and growth. Trans Am Inst Min Pet Eng 135 416-441... 

Spherulitic growth is a special case in crystallization. Spherulites form only within a specific temperature range for example, with it-poly(propylene) with a melting point of ITO C, they are first formed below IIS C. With spherulites, the rate of advance of the spherulite boundary is followed. This boundary encloses the crystalline portion of the spherulite. Since spherulites also contain noncrystalline material, however, the spherulite growth rate thus corresponds to the linear crystal growth rate. As the molecular weight increases, the rate of crystallization falls, since the rate of diffusion of segments and molecules decreases. 

Fig. 19.1. Temperature dependencies of the primary nucleation rate (I) (A) and the linear crystal growth rate (G) (Q) for poly(ethylene succinate) (PEISU) [14] with a molecular weight (M) of 8,770. The solid and broken lines are results from the best fitting procedure for G based on Eq. (19.2) and for I based on Exj. (19.11) by the Arrhenius and the WLF expressions of the molecular transport term, respectively...

Fig. 19.3. Temperature dependence of common logarithm of crystal growth rate from the melt for a variety of crystalline materials Glycreine [1], Li20-2Si02 [9, PBO-2B2O3 [12] and isotactic poly(styrene) [19] (i-PS). Solid lines are best fitting by Arrhenius expression of the molecular transport term...

Spherulitic and Single Crystal Growth Rates.—Rate measurements have been made on poly(ethylene oxide), plasticized polycarbonate, and polydioxolan. ... 

Fig. 4.25 Dependence of crystal growth rate v upon crystallization temperature Tc, for different fractions of poly(tetramethyl-p-phenylene) siloxane (molar mass given in g mol ) (after Magill).

Among many more linear polymers, poly(ethylene terephthalate) (PET) is of particular relevance since its maximum crystal growth rate is slow. The enhanced crystallization of PET has been, and still is, a topic of technological relevance. Following extended work by Legras, Mercier, and Nield [21], the impact of chemical nucleation (as opposed to epitaxial, i.e., physical interactions) has been widely publicized and is indeed... 

In order to evaluate the application of modulated-temperature differential scanning calorimetry (M-TDSC) to the study of the crystallisation kinetics of semicrystalline polymers, isothermal crystallisation kinetics in poly(e-caprolactone)-SAN blends are investigated. The temperature dependence of d In G/dT (G =crystal growth rate), determined by M-TDSC agrees approximately with previous experimental data and theoretical values. These were obtained from direct measurements of spherulite growth rate by optical microscopy. Here, theoretical and M-TDSC experimental results show that the d In G/dT versus temperature plots are not sensitive to the noncrystalline component in the poly(e-caprolactone)-SAN blends. 15 refs. 

The temperature dependencies of spherulitic and crystal growth rate have been claimed to correspond closely (65) under comparable conditions of undercooling, but there are results to the contrary. In monodisperse poly(oxyethylene)... 

The lateral growth rate (V) of crystals of linear chain polymers strongly depends on molecular weight (M) [37]. Although the M dependence of V of folded chain crystals (FCCs) of polymers has been rather well studied, it is still an important unresolved problem. Magill et al. presented an experimental formula, V ocM-0-5, for poly (tetramethyl-p-silpenyline siloxane), poly (ethylene terephthalate), etc [38]. 

---