Correlation between rheological and optical properties and the morphology of blown films of LLDPE/LDPE

ABSTRACT In this work, correlations between the rheological and optical properties and the morphology of blow films of blends of linear low density, LLDPE, and low density polyethylene, LDPE, were studied. The films were blown in an industrial film blowing line. Rheological properties of the blends, such as shear steady state viscosity, h(<img border=0 id="_x0000_i1031" src="../../../../../img/revistas/po/v14n1/19868x8.gif" align=absmiddle>) , first normal stress difference, N1(<img border=0 id="_x0000_i1032" src="../../../../../img/revistas/po/v14n1/19868x1.gif" align=texttop>), shear complex modulus, G* (omega) and recoverable strain, gammar (t) were analyzed. h(<img border=0 id="_x0000_i1033" src="../../../../../img/revistas/po/v14n1/19868x1.gif" align=texttop>) and N1 (<img border=0 id="_x0000_i1034" src="../../../../../img/revistas/po/v14n1/19868x1.gif" align=texttop>) were measured in a strain controlled rheometer with cone and plate geometry (low shear rates) and in a capillary rheometer (hig shear rates); on the other hand, G* (omega) and gammar (t) were measured in a tension controlled rheometer with parallel plates geometry. The optical properties (specular gloss and haze) were also measured in standard equipment. The surface morphology of the blown films was analyzed by scanning electron and atomic force microscopes. A correlation between recoverable strain, total haze and surface morphology of the blown films was obtained: the higher the recoverable strain, the lower the total haze and the smaller the crystallites. The addition of the LDPE to the LLDPE increased the recoverable strain of the films, decreasing their haze.

Blow films; rheological properties; optical properties; linear low density polyethylene; low density polyethylene


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