Papers by Author: Gabriela Botelho

Abstract: The present work evaluates the combination effect of hindered amine light stabilizers (HALS) and ultraviolet absorbers (UVA) on the ultraviolet (UV) stability of acrylonitrile-butadiene-styrene (ABS). Thus, two types of light stabilizers, Tinuvin P and Chimassorb 119 FL, were used to improve the ABS endurance against UV. Stabilized ABS samples were submitted to accelerated weathering in a Xenontest 150 S chamber, according to standard methods, in order to predict copolymer lifetime within a commercially acceptable time period. Infrared spectroscopy with attenuated total reflectance accessory (FTIR-ATR) was used to follow chemical modifications that occur on the material surface as a consequence of degradation process. While non-stabilized ABS samples loose the butadiene component in the first 22 h of exposure, in stabilized samples submitted to same accelerated conditions this component only disappears after 150 h of exposure. Non-stabilized and stabilized ABS samples present a similar yellowing behavior, a gradually increase with exposure time. Nevertheless, as expected, color modifications are less pronounced for stabilized ABS samples. The results obtained suggest that a better performance was achieved for stabilized ABS samples with Tinuvin P and Chimassorb 119 FL, which is very important to extend the copolymer lifetime.

Abstract: In this work, commercial poly(vinylidene fluoride) PVDF, in its β phase was analysed before and after the samples were exposed to UV radiation using a xenon lamp, for ten weeks. Changes in chemical structures, crystallinity, dielectric and piezoelectric response were investigated. From the present study it can be concluded that PVDF shows high stability towards photodegradation and can be used for outdoor applications without interference in its performance.

Abstract: The kinetics of the isothermal crystallization of the γ-phase Poly(vinylidene fluoride) has been investigated. Samples were prepared from the melt at different crystallisation temperatures and the variation of the microstructure of the samples was monitored with time by optical microscopy. Raman and Infrared transmission spectroscopies also show the appearance of the γ-phase for higher crystallisation temperatures. Two types of γ-phase spherulites have been identified. These spherulites represents different ways to obtain the γ-phase and show different thermal stability. The correlation between microstructure and kinetic parameters allows the tailoring of the microstructure by choosing the crystallisation conditions of the samples.

Abstract: This work aimed to prepare biodegradable polymeric materials based on blends of a synthetic high density polyethylene (HDPE) and biodegradable polymers such as polylactic acid (PCL) and poly(caprolactone) (PLA), in a co-rotating twin-screw extruder. A polyethylene modified with maleic anhydride was used as compatibiliser. The mechanical results showed that the addition of PLA improves the blends stiffness while the addition of PCL leads to materials with a greater elongation at break and a lower Young modulus. This feature is related with the mechanical properties of each material as well as the adhesion between them. Concerning the biodegradability tests, it was found that HDPE/PCL blend presents the highest degree of biodegradability.

Abstract: Commercial samples of high density polyethylene were decomposed over faujasites (FAU) type zeolites (Y-type) using thermal gravimetric analysis (TGA). The catalytic activity and behavior of the FAU-zeolites catalysts were determined. It was found that the degradation temperature of polymer strongly depends on the catalytic acidity of the zeolites. HY zeolite was identified as the most active catalyst due to its strong acidity. The results showed that the activation energy decrease with the amount of catalyst added.

Abstract: The photodegradation of EPDM based on dicyclopentadiene was followed by FTIR spectroscopy and the main photo-oxidation products were identified by derivatization reactions. It could be found that the photodegradation is initiated at the diene with formation of α,β–unsaturated carbonyl compounds and is then propagated to the ethylene-propylene segments. The propagation reactions are accelerated and, hence, the rate of photodegradation increases with the diene content.