heat of crystallization


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heat of crys·tal·li·za·tion

the quantity of heat liberated or absorbed per mole when a substance passes into the crystalline state.
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Obviously, the heat of crystallization cannot be transferred fast enough to the outer layers of the sample.
where [V.sub.f] is the volume fraction of crystalline, [DELTA][H.sub.xm] is the heat of crystallization when it is full amorphous, and [DELTA][H.sub.xc] is the heat of crystallization when there are some crystalline phases in the amorphous sample.
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.
The value of [T.sub.p], the initial crystallization temperature [T.sub.c0], the half-time of crystallization [t.sub.1/2], and the heat of crystallization [DELTA]H of LDPE and LDPE/Al composites at various cooling rate [Q.sub.-] are listed in Table 1, which shows that in the case of nanocomposites, the values of [T.sub.c0] are a little lower than those of the neat LDPE, whereas for the microcomposites, the values of [T.sub.c0] are larger than their corresponding values of the neat LDPE.
The heat of crystallization decreases on passing from neat sPP to sPPc, and a further regular decrease is obtained when OLS is added.
where [DELTA]h is heat of crystallization of the sample and [DELTA][h.sub.100] is the heat of crystallization for a 100% crystalline sample, taken as 288 J/g [10].
Therefore the glass transition temperature ([T.sub.g]), crystallization temperature ([T.sub.c]), exothermic heat of crystallization ([DELTA][H.sub.c]), crystalline melting temperature ([T.sub.m]), and heat of fusion of polymer crystalline ([DELTA][H.sub.m]) for the sPS and sPS/clay nanocomposites are recorded.
The degree of conversion or relative crystallinity [phi](t), defined as the ratio of heat of crystallization [DELTA][H.sub.c](t) at time t to the total heat of crystallization [DELTA][H.sub.c]([infinity]), is calculated according to (9, 15, 17)
Sample Cooling Rate [T.sub.p] [DELTA][H.sub.c] Designation ([degrees]C/min) ([degrees]C) (J/g) PET 20 193.7 -41.74 10 203.6 -42.09 5 212.2 -42.2 2.5 218.9 -43.95 DMP6 20 171.5 -36.42 10 185.1 -37.29 5 194.6 -39.81 2.5 201.7 -40.75 DMP11 20 160.7 -26.23 10 171.2 -31.94 5 180.8 -31.72 2.5 189.8 -32.59 DMP18 20 155.7 -25.49 10 169.3 -30.84 5 180.7 -29.21 2.5 188.9 -29.69 Sample [X.sub.c] (a) Designation (%) PET 35.49 35.79 35.90 47.37 DMP6 30.97 31.71 33.85 34.65 DMP11 22.30 27.16 26.97 27.71 DMP18 21.68 26.22 24.84 25.25 (a) Estimated from the measured heat of crystallization using the heat of fusion (117.6 J/g) of the fully crystallized PET polymer.
From the heat of crystallization as given in Table 1, it is known that the original iPP has the lowest crystallinity; plastication enhances the latter crystallization of iPP.
But these models require the actual temperature profile in the polymer for calculating the crystallinity, and various schemes have been presented to couple the effect of latent heat of crystallization with the melt temperature profile.
The heat of fusion and the heat of crystallization and thus the overall order of the PBT crystallinity in blends remains almost the same (after normalization).