Development, characterisation and properties of nanophases, nanofluids and nanomaterials

Abstract

The accumulation of domestic plastics derived from fossil fuels is a major global environmental problem. One of the strategies being pursued to confront this problem is the use of bioplastics. Although bioplastics have many interesting properties, they generally have poorer mechanical properties than conventional polymers. Hence, they are commonly modified with nanofillers, nanofluids and nanomaterials. This thesis focuses on the development, characterization and study of the properties of different nanomaterials, ionic liquids, and nanofluids to be included into bioplastic matrices. The biopolymer selected as polymeric matrix is polylactic acid (PLA). The nanomaterials used are graphene oxide (GO) and zinc oxide (ZnO). The ionic liquids used are the aprotic ionic liquids 1-butyl-1-methylpyrrolidinium hexafluorophosphate (LPI104), 1-hexyl-3-methylimidazolium hexafluorophosphate (LP106), 1-butyl-3-methylimidazolium hexafluorophosphate (LP104), 1-hexyl-3-methylimidazolium tetrafluoroborate (L106) and 1-butyl-3-methylimidazolium tetrafluoroborate (L104), and the protic ionic liquid Bis(2-hydroxyethyl)ammonium salicylate (DSa). Two nanofluids were developed, the first one combines the ionic liquid 1-butyl-1-methylpyrrolidinium hexafluorophosphate (LPI104) with the nanomaterial graphene oxide (GO), and the second one combines the protic ionic liquid Bis(2-hydroxyethyl)ammonium salicylate (DSa) with the nanomaterial zinc oxide (ZnO). This second nanofluid was developed at Østfold University College (Fredrikstad, Norway), during a pre-doctoral stay. A characterization of the polymeric matrix, ionic liquids, nanomaterials, nanophases and the newly developed nanocomposites was carried out. Numerous materials characterization and testing techniques have been used such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), rheological testing, contact angle measurement, surface profilometry, ultraviolet-visible (UV) spectroscopy, hardness, dynamo-mechanical analysis (DMA) and tribological testing. Calibration and tuning of the extrusion system was performed. Prior to the processing of the materials, a study of the processability of the polymer matrix was carried out. Once the optimum extrusion conditions were known, the processing of each one of the nanocomposites that were studied in the thesis was carried out. The rheology of the new nanofluids was evaluated by studying the influence of the nanophase concentration with the test temperature and shear gradient. The viscoelastic behavior of PLA with different nanomaterials, ionic liquids and nanofluids was studied through oscillatory tests evaluating the influence of temperature. One of the limitations of bioplastics is their poor resistance to friction and wear. To solve this problem, lubricants can be applied to the surface of the polymer or the polymer can be modified to improve its tribological properties. Tribological tests can be used to determine the coefficient of friction of the dry polymer, the polymer with a lubricant on the surface and the modified polymer to analyze the effect of nanofluids and nanophases on the tribological properties. After the tribological tests, wear tracks were studied with the help of a microprofilometer, evaluating the surface damage generated after the test and measuring the different wear rates. It has been observed that all ionic liquids and all nanofluids used reduce the coefficient of friction and surface damage when used as external lubricants on the polymer. When used as internal lubricants, it is observed that aprotic ionic liquids containing hexafluorophosphate anion do not improve the tribological properties of the polymer or reduce surface damage. In contrast, both the aprotic ionic liquids containing the tetrafluoroborate anion, the protic ionic liquid and the nanofluid prepared from the protic ionic liquid and zinc oxide significantly reduce the coefficient of friction of the polymer matrix and the surface damage.