Melt Strength and Elastic Behaviour of LLDPE/LDPE Blends

Abstract

Differences in processability between linear low denisty polyethylene (LLDPE) and low density polyethylene (LDPE) as well as for their blends subjected to extensional flow were assessed in terms of melt strength and elastic parameters from shear flow such as storage modulus (G' ), and first normal stress difference (N 11 -N 22 ). The results revealed similar synergistic effects for these parameters in the LDPE rich blends. A DSC test carried out on these LLDPE/LDPE blends when fast cooled disclosed the existence of two phases in the molten blends for the same composition range where the melt strength synergism was observed. The results are discussed in terms of the influence of the different molecular structures of the blend polymers and their miscibility on the measured melt strength. A mechanism is suggested to explain the observed synergistic phenomenon.

Melt strength and film bubble instability of LLDPE/LDPE blends

“…In our previous work, 20,21 this melt strength synergism was discussed and related to the immiscible melt morphology of these blend compositions.…”

“…The principles of the operation of this apparatus have been described elsewhere. 20 The tester consists of two counter-rotating toothed rollers which are mounted on a sensitive balance beam. A melt strand extruded vertically downwards from an extruder die is drawn by the rotating rollers with increasing haul-off velocity (constant acceleration) and the drawing-off force is measured.…”

Melt Miscibility and Mechanical Properties of Metallocene LLDPE blends with HDPE: Influence of Mw of LLDPE

“…[1][2][3][4][5][6][7] However, this enhancement of processing and properties is dictated by phase homogeneity or heterogeneity of these blends in the melt and solid state. A large number of studies utilizing different techniques were devoted to investigate the phase morphology and characterization of polyolefin blends.…”

“…A large number of studies utilizing different techniques were devoted to investigate the phase morphology and characterization of polyolefin blends. These techniques include transmission electron spectroscopy, [8][9][10][11] small angle neutron scattering, [11][12][13] differential scanning calorimetry, 2,5,11,[14][15][16][17][18][19][20][21][22][23] rheology, 3,4,6,7,[16][17][18][24][25][26][27][28][29][30] X-ray diffraction 11,14,31 and more recently thermal fractionation techniques. 33,34 Mechanical characterization of polyolefin blends has also been a subject of interest.…”

“…Two sets of blends were prepared and compared to study the influence of short chain branching (SCB) and M w . A hexene based m-LLDPE ( ¼ 0:918 g/cm 3 ) and an octene based m-LLDPE ( ¼ 0:902 g/cm 3 ) with some long chain branching (LCB) were melt blended with two different LDPEs of varying melt indices. The hexene m-LLDPE/LDPE blend was reported to be immiscible, whereas, octene m-LLDPE/LDPE blend was found to be miscible at all compositions.…”