Hc = Heat of crystallization
computed by integrating area of the crystallization peak
This is called the latent heat of crystallization
. Basically it is an energy barrier, and it can cause severe problems in melting and screw wear.
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:
Ikeda and Taniguchi developed a polylactic acid resin consisting of 50-90 wt% polylactic acid and 10-50 wt% polyolefin with a specified heat of crystallization
. The heat of crystallization
of the polyolefin must be 40 J/g or less.
In the medium region indicated by location #2, the heat of crystallization
decreases, although there is still a detectable glass transition.
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.
Crystallization exotherms were characterized by determining: the peak crystallization temperature ([T.sub.c]); the onset crystallization temperature ([T.sub.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
([[DELTA][H.sub.c]) determined from the area under the exotherm.
The latent heat of crystallization
, [H.sub.f], must also be considered and is given in the third term of the RHS of Eq.
where [DELTA][H.sub.f] is the heat of fusion of the blend and [DELTA][H.sub.c] is the heat of crystallization
during the same heating scan.