Papers by Author: R. Perera

Abstract: The need for solid-waste management has pushed the development of alternative systems for recycling and revalue used plastic containers. Poly(ethylene terephthalate) (PET) is being widely used as raw material for beverage bottles. However, as has been widely reported, PET undergoes degradation and hydrolysis when reprocessed. On the other hand, poly(butylene terephthalate) (PBT) is another thermoplastic polyester with easy processability but high brittleness and cost. Hence, it has been blended with other polymers such as polypropylene to overcome its disadvantages. In this work, bentonite was incorporated into recycled PET and PBT/polypropylene blends by extrusion. Rheological and tensile properties and processability of the composites thus prepared were studied. Results showed a strong newtonean character of extrudates of recycled PET and higher viscosities and a more pseudoplastic behavior and improved reprocessability when bentonite was added to PET. Furthermore, inclusion of the filler increased its initial degradation temperature, as observed during rheological testing. All composites displayed a brittle behavior. However, the tensile properties of PET composites were not strongly deteriorated. There was a slight increase in the Young’s modulus values and in the tensile strength, with unnoticeable effects on the elongation at break. The Young’s modulus values of PBT/PP composites were not significantly affected.

Abstract: Polypropylene/polyamide-6 and polypropylene/metallocene polyethylene blends containing 2.5 phr of organophilic modified montmorillonite were prepared in a twin-screw extruder followed by injection molding. In order to compare, blends without layered clay were also made. Styreneethylene- butylene-styrene copolymer and polypropylene grafted with anhydride maleic were used as compatibilizers in the ternary blends and in the PP nanocomposite preparation, respectively. The presence of tactoids, intercalated and exfoliated structures was observed by TEM in some of the samples containing layered clay and modified PP materials. Results showed that the compatibilized blends prepared without clay are tougher than those prepared with the nanocomposite of PP as the matrix phase and no significant changes in tensile moduli were observed between them. However, the binary blend with a nanocomposite of PP as matrix and metallocene polyethylene exhibited better tensile toughness and lower tensile modulus, than those prepared with a nanocomposite of PP and polyamide-6 as dispersed phase. These results are related to the degree of clay dispersion in the PP and to the type of morphology developed in the different blends. Differential scanning calorimetry (DSC) showed that blends with a finer and homogeneously dispersed morphology determined by SEM, the PA component exhibited fractionated crystallization exotherms in the temperature range of 159-185°C. Also, nucleation of the PP component by PA phase and/or the layered clay was observed in the blends with PA as dispersed phase.