Poli(tereftalato de etileno) : reprocessamento por extrusão e metodologias de caracterização
Marcia Aparecida da Silva Spinace
DATA DE PUBLICAÇÃO
Pellets of virgin PET were reprocessed by extrusion to evaluate the number of recycles that these materiaIs can suffer without changes their properties. After each reprocessing cycle the thermal, mechanical, optics properties, the carboxylic end groups concentration (CEG), intrinsic viscosity [h] and non-isothermal crystallization kinetics by Ozawa and Avrami s theory were measured. The tensile strength at break for the virgin PET was 25 MPa and this value was also observed for the second cycle, then its increases to 55 MPa. After the third cycle the elongation at break decreases from 112 ( 23) to 6,0 ( 0,3) and the material became hard and fragile. The melt flow index and CEG increases from 23 to 80 g/10 min and from 36 to 100 eqw/ 10 g, respectively. The melting and glass transition temperatures did not change, however, the crystallinity degree and crystallization temperature increase from 24 to 38 % and from 160 to 200 °C, respectively. An increase of six times in the index of yellowness was observed. The Avrami s theory shows that occurs two regime behavior. In the first regime Avrami exponent (n) changes with the cooling rate from 2.3 to 4.0 as a function of reprocessing cycles. The non integer values of n are attributed to homogeneous and heterogeneous nucleation generated simultaneously. The Ozawa parameters did not present the same tendency of Avrami. The Ea was calculated by Ozawa s theory and the estimated value for the first cycle was -229,8 kJ mol which was similar to the virgin PET. This value decreases to ca. -400 kJ mol after the second cycle. These results show that after the second cycle of reprocessing PET properties change drastically . The addition of stabilizers and virgin PET in the reprocessed PET to preserve its characteristics during and after the processing was evaluated. The Reciclostab®441 act as process and thermal oxidative stabilizer. However, we did observe an improvement of the mechanical properties of virgin and post consumed PET mixtures with Reciclostab ®441. A simple method was developed to estimate the CEG and [h] through the association of infrared spectroscopy and multivariate analysis. Spectral regions were selected by subtraction yielding 13 significant regions. The set of spectral regions was optimized to obtain highly consistent PLS models. The best model was adjusted and calibration curves were made. The correlation between the estimated and measured values were 0.9875 for CEG and 0.975 for [h]. Therefore we could estimate the CEG and [h] with this method and it is a fast and non destructive technique to evaluate the degradation degree of PET. Besides, it generates no chemical residues.
ACESSO AO ARTIGOhttp://libdigi.unicamp.br/document/?code=vtls000214849
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