ESTUDO DA ADESÃO ENTRE PAPEL CARTÃO E POLIETILENO EM EMBALAGENS LONGA VIDA: INFLUÊNCIA DE ASPECTOS QUÍMICOS E FÍSICOS

Abstract

The objective of this work was to study the surface adhesion of polyethylene on the liquid paper board. By using surface characterization, the chemical and physical interactions between the paper board and polyethylene were studied. Paper board samples were laminated with low density polyethylene with an extruder, in order to evaluate the adhesion forces of the following samples: 1) Paper board coating with different latex composition; 2) paper board bottom layer (brown side) with surface sizing (starch) and, 3) paper board bottom layer (brown side) without surface sizing (starch). It was also evaluated in the extruded samples treated with flame the polyethylene adhesion. The following analyses were used in other to characterize the paper board surface: 1) Contact angle analysis for surface energy determination, 2) Confocal laser scanning microscopy for surface roughness analysis and, 3) FTIR spectroscopy Attenuated Total Reflectance (ATR) to evaluate differences in the functional groups. The characterization results were correlated with the increase of polyethylene adhesion forces on the paper board surface. It was observed that flame treatment on the paper board surface increased the surface tension, thus increasing the adhesion forces of the polyethylene. In comparison to the styrene-butadiene latex, the styrene acrylic latex, which contains polar groups in its composition, improved the adhesion forces of the polyethylene with the paper board top layer (white side). For the paper board bottom layer (brown side) with no surface sizing, the polyethylene adhesion was superior when compared to the sized paper board. It can be explained by the increase on the surface smoothness of the paper which may interfere on the polyethylene adhesion. The flame treatment may have caused the oxidation of functional groups on the surface of the paper board, resulting in the surface tension increase and, consequently, increasing the polyethylene adhesion. The surface tension has shown to be an excellent indicator for polyethylene adhesion due to its linear correlation with polyethylene adhesion forces. On the other hand, it has not been observed difference on surface roughness on the studied samples. The FTIR-ATR technique has not been sensitive for the detection of chemical differences among the samples treated with and without flame. However, this technique can be used to verify the latex composition in the paper board coating. The Peel Test Method (180º) which is used to evaluate the adhesion force, presents more reliable results than the manual delamination test that depends on the analyst.