Desenvolvimento de um filamento de polietileno com propriedade termocrômica para aplicações têxteis

Abstract

The objective of this work was to develop a continuous filament of high density polyethylene (HDPE) with thermochromic property, for application in textile materials. For this purpose, two thermochromic pigments, in orange and purple, both with a color change at a temperature of 31 °C, were mixed with HDPE during extrusion processing to obtain a filament through fusion spinning, with the proportions used of 0.5, 1.0 and 2.0 wt% of pigment. The micrographs obtained from the pigment powders showed that the materials showed a spherical morphology. To identify the activation of the pigments, the powders were subjected to heating, where the thermochromic transition temperature could be identified and, through images taken with a digital camera, the difference in color at 21 and 45 °C was shown. After the mixing process by extrusion and granulation of all samples, part of the granulates was used for injection molding, which were used in the preliminary characterizations to evaluate the incorporation of pigments in HDPE before the production of filaments. The rest of the granules were used for the production of continuous filaments, keeping the screw rotation speed and the filament pulling speed constant in all samples. Melt flow index (MFI) measurements were performed on pure HDPE granules and on mixtures of HDPE with pigments for the three proportions used. Shore D hardness that decreased, such behavior is an indication that the proportions of thermochromic pigments used promoted an increase in the mobility of HDPE polymer chains. The photomicrographs obtained by scanning electron microscopy (SEM) of the injected specimens showed that the pigments kept the spherical structure preserved within the polymer, maintaining its protected function. The images obtained from the specimens by digital camera showed the color change of pure HDPE from beige to orange and purple, as well as the color change to yellow and blue, respectively, when the samples were submitted to thermochromic activation temperature, the color change is reversible. The yarns obtained from the granules also acquired the thermochromic property and, through images taken with a digital camera, it was possible to identify the difference in color when the samples were exposed to 21 and 45 °C. The UV-vis analysis showed the change in the reflectance spectra when these materials were exposed to these two temperatures, evidencing the color alteration caused by the structural alterations of the pigments. The atomic force microscopy test showed that despite a slight difference in the surface roughness of the HDPE additives, the thermochromic pigment particles were incorporated into the matrix and the additive filaments showed greater roughness in relation to the pure HDPE filament, when the microcapsules were found in the matrix. filament surface. The uniaxial tensile results showed that the addition of thermochromic pigments, at the concentrations used, interfered in the mechanical properties of the HDPE polymer matrix, as a function of the difference in size of the microcapsules of the two pigments used. It was concluded in this work that the optimal composition of thermochromic addition in filaments is less than 0.5% wt% of pigment, as this proportion already gives the material thermochromic characteristics that are not lost during the melt spinning process.