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

Abstract

ABSTRACT:The influence of M w of LLDPE on the rheological, thermal and mechanical properties of m-LLDPE/ HDPE blends of low and high branch content (BC) was studied. Melt rheology of m-LLDPE blended with linear HDPE revealed strong influence of M w on melt miscibility at both branching levels. Low M w m-LLDPE/HDPE blends are suggested to be miscible at all compositions, while viscosity of high M w m-LLDPE/HDPE blends showed negative deviation from log additivity suggesting layered morphology of these blends. The DSC results suggest that compatibility in the solid state is independent of M w and BC. For all blends studied, the HDPE-rich blends were found to contain single crystal populations suggesting high degree of cocrystallization, whereas, m-LLDPE rich phase showed separate crystallization. The melt miscibility and the crystallization of high BC m-LLDPE blends with HDPE are suggested to be controlled by different factors. Small strain mechanical properties of these blends were found to be a strong function of blend compatibility and the specific properties of the blend components.[doi:10.1295/polymj.PJ2005254] KEY WORDS LLDPE/HDPE Blends / Miscibility / Rheology / Mechanical Properties / DSC / Molecular Weight / Polyethylene blends are widely used to improve processing and tailor properties.1-7 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. These techniques include transmission electron spectroscopy, [8][9][10][11] small angle neutron scattering, 11-13 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. 2,[5][6][7][20][21][22][23][30][31][32] Molecular parameters like branch content (BC), branch type, composition distribution, molecular weight (M w ) and molecular weight distribution (MWD) were found to be the key factors affecting the miscibility of polyolefin blends. Hill 9 using transmission electron spectroscopy (TEM) found that M w of linear HDPE had little influence on its miscibility with branched PEs. Alamo et al.12 observed that BC of the branched polyethylene (PE) is the most important parameter controlling the phase behavior of branched and linear PE blends. They reported no effect of M w of branched PE on its miscibility with linear polyethylene for M w $ 100 kg/mol. On the other hand, Tanem and Stori 10 reported strong influence of M w on miscibility of linear and branched PEs. They observed that low M w of m-LLDPE enhanced its miscibility with linear HDPE. Recently, the authors have extensively studied the influence of molecular parameters on the miscibility of different polyethylenes [21][2...

Rheological behavior and mechanical properties of high‐density polyethylene blends with different molecular weights

“…A gradual increase in g* was observed with increasing HMW content, which suggested the miscibility of the components in the blends. 32 In this study, the additivity rule was used to calculate M w of the blends with M w values of the parent components. The calculated results are collected in Table I.…”

“…The influence of the molecular parameters on the miscibility of LLDPE/low-density polyethylene (LDPE) blends and LLDPE/high-density polyethylene (HDPE) blends were extensively studied by Hussein, Williams, and coworkers [23][24][25][26][27][28][29][30][31][32] using rheological techniques. The M w of LLDPE was observed to have a strong influence on its miscibility with LDPE.…”

“…Low-M w m-LLDPE/HDPE blends were observed to be miscible at all compositions, whereas the viscosity of high-M w m-LLDPE/HDPE blends showed negative deviation from the logarithm of additivity; this suggested a layered morphology for these blends. 32 For binary blends of HDPE, LLDPE, and LDPE, it was reported that in the solid state, the LLDPE/ LDPE and HDPE/LDPE blends were not miscible, but the LLDPE/HDPE blend was miscible, 34 and they were all miscible in the melt state. 7 The m-LLDPE/HDPE blend was also found to be miscible by rheological and morphological investigations.…”

Effect of Metallocene-Catalyzed Polyethylene on the Physicomechanical Properties of Blends with High-Density Polyethylene or Low-Density Polyethylene

“…Moreover, the addition of small amounts of HDPE can improve the optical properties of LLDPE in film blends [14] . The reported compatibility of HDPE=LLDPE blends determined by thermal analysis is often confirmed by invariable or superior physicomechanical properties [15,16] . The tensile properties of HDPE=LLDPE blends are shown to vary significantly from the rule of mixtures, particularly when the ratio of levels of HDPE to LLDPE approaches unity [17] .…”

Optimization of polyethylene binder for heterogeneous ion exchange membrane manufacture to improve its mechanical stability

“…Melted, they can be immiscible even if they have similar crystalline structure . Characterization of metallocene‐linear low‐density PE (mLLDPE) and high‐density PE (HDPE) mixtures with an emphasis on mLLDPE molecular weight and branching was presented by Hameed and Hussein . Mixtures with high content of HDPE showed high degree of co‐crystallization and conversely, in mLLDPE‐rich mixtures components tended to crystallize separately.…”