When crystallization causes an increase of temperature for instance during cooling of a slab or an extruded tube or during sudden stress induced crystallization in fiber spinning, the heat of crystallization
is accounted for by an additional term in the heat transfer equation:
The heat of crystallization
of the polyolefin must be 40 J/g or less.
Equation of energy, taking into account dependence of thermophysical properties upon temperature and release of latent heat of crystallization
within the range of temperatures, is described by Fourier equation of heat conductivity.
By providing more nucleation sites, and, therefore, greater heat of crystallization
during solidification, undercooling is minimized and equilibrium solidification is aided.
The relative degree of crystallinity is calculated from the ratio of the heat evolved up to time t, the area under the curve, divided by the total heat of crystallization
, the total area, according to Eq.
The melting parameters were calculated from the reheating scans and heat of crystallization
from the cooling scans.
0]), which is the temperature where the thermogram initially departs from baseline on the high temperature side of the exotherm; and the heat of crystallization
Numerical Prediction of the Temperature Rise and Latent Heat of Crystallization
The temperature plateau has its physical origin in the release of latent heat of crystallization
, which counterbalances the heat lost from the film by radiation and convection.
c] is the heat of crystallization
during the same heating scan.
The effect of different crystallization kinetics for different materials was approached by arbitrarily varying the degree of crystallinity by changing the latent heat of crystallization
in the calculation.
1/2], and the heat of crystallization
[DELTA]H of LDPE and LDPE/Al composites at various cooling rate [Q.