Effects of melt blended poss nanofillers on pom and ABS thermal stability

Resumen

This PhD thesis investigated the incorporation of Polyhedral Oligomeric Silsesquioxanes (POSS) in thermoplastic base materials via melt-blending procedures. Particularly, a focus is taken on the enhancement of the thermal resistance through the addition of different types of POSS on two popular engineering plastics known by their low thermal stability, one being a semi-crystalline copolymer i.e. polyoxymethylene (POM) and the other an amorphous copolymer i.e. acrylonitrile butadiene styrene grafted with maleic anhydride (ABS-g-Ma). Different nanocomposites have been produced, from which its morphology, miscibility, structure, thermal properties and appearance behaviour before and during the thermoxidative degradation is herein quantified and discussed together with the resulting benefits and drawbacks. All the nanocomposites have been produced via melt-blending, using the nanofillers Glycidyl, Glycidyl-Isobutyl, Aminopropyl-isobutyl and Poly(ethylene-glycol) for the POM matrix, and Amino-Propyl Isobutyl, Glycidyl, and Trisilanol for the ABS-g-Ma matrix. The incorporation adequacy of the nanofillers into the matrix has been pre-assessed with the Hoy¿s solubility calculation method and later on corroborated with scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The quantification of the thermal degradation behaviour of each sample at different temperatures and exposure times was carried out through Fourier transform infrared spectrography (FTIR), thermogravimetric analysis (TGA) including the degradation kinetics and, ultimately, the sample appearance progress has been assessed in terms of yellowing by means of colour spectrophotometry (Cielab). The results showed that the presence of different POSS's used with the POM matrix improves dramatically the thermal stability of the base material and that such improvement is proportionate to the solubility compatibility between matrix and the nanofiller. The best performance was found with Aminopropyl-isobutyl, whereby the temperature of maximum rate of degradation (TMAX) increased by 22ºC. Said improvement is also seen in the conditions at which the nanocomposite developed only 2% of carbonyl yield and 8% of yellowing compared to the standard POM copolymer, which is taken as the base reference with 100% deterioration suffered in the above two indicators. However, the performance of the different nanocomposites produced in this work with ABS-g-Ma has not been as encouraging as the POM-based nanocomposites described above. Although the SEM morphological analysis show adequate incorporation and miscibility of the nanofillers into the matrix, the GPOSS and the TPOSS nanocomposites provided no relevant improvements in thermal stability when compared to the base ABS-g-Ma, and the APOSS blend exhibits a very slight decay in almost all the quantitative analysis carried out in this work.