Enthalpy crystallization

The melt mixed 80/20 PS/iPP blend displays a set of exotherms, where the amount of the iPP component that was heterogeneously nucleated is substantially reduced as indicated by the decrease of the crystallization enthalpy in the temperature region where the iPP crystallizes in bulk, i.e., at 109-111 °C (exotherm labeled A). This effect is due to the confinement of iPP into a large number of droplets. If the number of droplets of iPP as a dispersed phase is greater than the number of heterogeneities present in the system, fractionated crystallization occurs. The number of droplets for this composition is known (by scanning electron microscopy observations) to be of the order of 1011 particles cm-3 and polarized optical microscopy (POM) experiments have shown that this iPP contains approximately 9 x 106 heterogeneities cm-3. In fact, it can be seen in Fig. 1 that the fractionated crystallization of the iPP compon-... 

The amount of freezing water in the water-NaLS system can be calculated from the enthalpy, assuming the crystallization enthalpy of water to be 333 J/g (7). Thus,... 

The displayed data are T crystallization temperature AH apparent crystallization enthalpy Tm melting temperature AHm apparent melting enthalpy X. degree of crystallinity, obtained by DSC (a) and WAXS experiments. D ]0 cystallite size perpendicular to the diffraction plane (110). 

Wu and Woo [26] compared the isothermal kinetics of sPS/aPS or sPS/PPE melt crystallized blends (T x = 320°C, tmax = 5 min, Tcj = 238-252°C) with those of neat sPS. Crystallization enthalpies, measured by DSC and fitted to the Avrami equation, provided the kinetic rate constant k and the exponent n. The n value found in pure sPS (2.8) points to a homogeneous nucleation and a three-dimensional pattern of the spherulite growth. In sPS/aPS (75 25 wt%) n is similar (2.7), but it decreases with increase in sPS content, whereas in sPS/PPE n is much lower (2.2) and independent of composition. As the shape of spherul-ites does not change with composition, the decrease in n suggests that the addition of aPS or PPE to sPS makes the nucleation mechanism of the latter more heterogeneous. 

Where 2RT (R denotes the universal gas constant) represents a correctional factor for the difference between the gas phase enthalpy and vibrational contribution to the crystal enthalpy. 

Fusion Entropy (kJmor ) Crystallization Enthalpy (kJmoP )... 

Fig. 8. Crystallization of an amorphous alloy (a) into a stable (cy) or metastable compound (C2). The values given in parentheses represent an order of magnitude estimate of the activation energy for crystallization A act and the crystallization enthalpy AHcr.

Fig. 51. Traces of measurements on Gd0 64Co0 36 made using a differential scanning calorimeter operated at two different heating rates. The positions of the glass transition temperature Tg and the crystallization temperature 7X are indicated for the higher heating rate. The inset shows the level scheme for the amorphous-to-crystalhne transformation. The experimental values for the activation enthalpy AE = Eac — Ea is 3. 29 eV or 317 kJ mol 1. The value for the crystallization enthalpy A Hc, = Ec — EA is 3.8...

Structural Investigations. The melting and crystallization points and the melting and crystallization enthalpies of styrene graft polymers with different styrene contents and different grafting efficiencies were determined by differential scanning calorimetry. The melting and crystallization points were... 

Crystallization enthalpies of the irradiated blends were lower than predicted by the additivity rule. The crosslinking of the amorphous domains lowered the melting enthalpies. Irradiated blends showed separated crystallizations, at their characteristic temperatures of crystallization, independent of composition. On irradiation, the crystallization temperature of PE did not change, whereas that of UHMWPE slightly decreased. Separate irradiation of UHMWPE and PE favored molecular scission over the crosslinking, whereas irradiation of the blends favored crosslinking. The melting temperature, T, increased linearly with... 

Table 11.10. Melting and crystallization enthalpies of ultra-high molecular weight polyethylene (UHMWPE) and normal molecular weight polyethylene (NMWPE) blends [Minkova and Mihailov, 1990]...

It can be seen that, as the alkoxy chain is extended, the broad enthalpy peak in the isotropic liquid regime becomes more pronounced, and when TGB phases are present the peak is well-separated from the liquid to liquid crystal enthalpy peak. 

The effect of pigments on the behavior of PP was studied by thermal analysis in isothermal and non-isothermal modes. The crystallization enthalpy, AH, was measured for every isothermal run. 

The degree of crystallinity for all PP samples were obtained from the crystallization enthalpy, AH, using dynamic DSC measurements, as follows ... 

Calorimetric analysis by DSC provides information on the melting temperature, crystallization, enthalpy, polymorphic transition, and degree of crystallinity of the particles. XRD, on the other hand, also evaluates the crystallinity and polymorphic transition events that may eventually occur in microparticles. 

The thermal parameters of the crystallization temperature T ), melting temperature (Tin), crystallization enthalpy (A/fc), heat of fusion (AiA), supercooling temperature (AT = T - Tc) and percentage of crystallinity (Zc) were obtained and reported in Table 8.1. 

Figure 11.29. Crystallization enthalpy of polylactide plasticized with variable amounts of polypropylene glycol having molecular weight of 1000. [Data from Paul M-A Alexandre M Degee P Pluta M Gleski A Dubois P, New Nanocomposite Materials Based on Plasticized Poly(l-lactide) and Organo-modified Montmorillonites, Belgian Polymer Group Meeting 2002, Mens, Belgium.]...

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