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Production and characterization of nanocomposite materials from recycled thermoplastics

Karabulut, Metin
Nanocomposites are a new class of mineral-field plastics that contain relatively small amounts (<10%) of nanometer-sized clay particles. The particles, due to their extremely high aspect ratios (about 100-15000), and high surface area (in excess of 750-800 m2/g) promise to improve structural, mechanical, flame retardant, thermal and barrier properties without substantially increasing the density or reducing the light transmission properties of the base polymer. Production of thermoplastic based nanocomposites involves melt mixing the base polymer and layered silicate powders that have been modified with hydroxyl terminated quaternary ammonium salt. During mixing, polymer chains diffuse from the bulk polymer into the van der Waals galleries between the silicate layers. In this study, new nanocomposite materials were produced from the components of recycled thermoplastic as the matrix and montmorillonite as the filler by using a co-rotating twin screw extruder. During the study, recycled poly(ethylene terepthalate), R-PET, was mixed with organically modified quaternary alkylammonium montmorillonite in the contents of 1, 2, and 5 weight %. Three types of clays were evaluated during the studies. For comparison, 2 weight % clay containing samples were prepared with three different clay types, Cloisite 15A, 25A, 30B. The nanocomposites were prepared at three different screw speeds, 150, 350, 500 rpm, in order to observe the property changes with the screw speed. Mechanical tests, scanning electron microscopy and melt flow index measurements were used to characterize the nanocomposites. The clay type of 25A having long alkyl sidegroups gave the best results in general. Owing to its branched nature, in nanocomposites with 25A mixing characteristics were enhanced leading to better dispersion of clay platelets. This effect was observed in the SEM micrographs as higher degrees