Crystallization ,Morphological Structure ,and Melting of Polymer Blends

Introduction:
The concept of a crystal-amorphous (also order-disorder) interface was first proposed by Flory [1962] for binary semi-crystalline/amorphous
blends. The order-disorder interphase was defined as the region of loss of crystalline order.
Kumar and Yoon [1991] examined this interface and found that in blends the thickness of this transition zone was essentially independent of the interaction parameter between the two polymers (when ?12 varied from -1 to -0.005).
Following the theoretical predictions the thickness of this region increases only slightly when stiffer chains are considered. Due to the higher degree of order of segments of the crystallizable component in this zone, the penetration of the amorphous component is limited.
The compositional interphase, however, is influenced by the stiffness of both chains and by the interaction parameter (the interfacial thickness varies with the reciprocal of |?12|1/2) .

When the melt of a crystalline polymer is cooled to a temperature between the glass-transition and the equilibrium melting point, the thermodynamic requirement for crystallization is fulfilled.
The crystallization of miscible and immiscible polymer blends can differ remarkably from that of the neat crystallizable component(s).
The overall crystallization kinetics of blends can often be described by the Avrami equation:

Where:
?: is the weight fraction of crystallinity at time t,
n: is the Avrami index depending on the type of nucleation and the crystal growth geometry
k: is the Avrami constant related to the crystallization rate:

Where :
tn1/2 : is the half time of crystallization (the time for half the crystallinity to develop), which is often used as a measure for the
overall rate of crystallization.