SYNOPSISBinary blend of high-density polyethylene ( HDPE ) and linear low-density polyethylene (LLDPE) , prepared by melt mixing in an extruder, in the entire range of blending ratio, is studied for crystallization behavior by differential scanning calorimetry (DSC) and Xray diffraction measurements. Cocrystallization was evident in the entire range of blend composition, from the single-peak character in both DSC crystallization exotherms and meltingendothermsand theX-raydiffractionpeaks.AdetailedanalysisofDSCcrystal1ization exotherms revealed a systematic effect of the addition of LLDPE on nucleation rate and the subsequently developed crystalline morphology, which could be distinguished in the three regions of blending ratio, viz., the "HDPE-rich blend," "LLDPE-rich blend," and the "middle range from 30-70% LLDPE content." Variations in crystallinity, crystallite size, and d spacing are discussed in terms of differences in molecular structure of the components.
SYNOPSISThe binary blend of high-density polyethylene ( HDPE ) and linear low-density polyethylene (LLDPE) in the range of composition from 100% HDPE to 100% LLDPE has been investigated for tensile and flexural properties and the morphology in the deformed state on tensile fracture. Tensile properties (initial modulus, yield stress, and elongation-at-yield, ultimate tensile strength and elongation-at-break, and work of yield and work of rupture) and flexural properties (flexural modulus and flexural yield stress) are studied as a function of blend composition. Behavior, in terms of these properties, is distinguishable in three zones of blend composition, viz. ( i ) HDPE-rich blend, (ii) LLDPE-rich blend, and (iii) the middle zone. In zones ( i ) and (ii) , the variations of these properties are more or less linear, whereas in the middle region [ i.e., zone (iii) 1, there is a reversal of trends in variation or sometimes a behavior opposite to the expected one. The results are explained on the basis of the effects of cocrystallization and the presence of octene-containing segments in the amorphous phase. Scanning electron micrographs of the tensile fracture surfaces are presented to illustrate the occurrence of transverse bands interconnecting the fibrils.
The crystallization studies revealed that the high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) formed strong cocrystalline mass when they were melt blended in a single screw extruder. The progress of crystallization was observed through a small-angle light scattering instrument, scanning electron microscope, and differential scanning calorimeter. Analysis showed that these constituents followed individual nucleation and combine growth of crystallites in blends. The growth of crystallites all through the blend compositions were two-dimensional. Interestingly, the crystallites resembled each other for a particular blend composition; however, they differ widely as the composition changes. The rate of crystallization depends greatly to the number of crystallites and their interfacial boundary in contact with the amorphous phase pool. The t 1/2 and percentage of crystallinity showed a mutually exclusive trend and were seen to be varied in the following three regions of blend composition: the HDPE-rich, the LLDPE-rich, and the middle region of blend composition. The percentage of crystallinity decreases in both the HDPE-rich and LLDPE-rich blends, and it showed a plateau value in the middle region of blend composition. The t 1/2 showed opposite trend to that of % crystallinity.
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