Preparation of nanocomposites based on thermoplastic polymers and influence of titanium and iron oxides nanoparticles on their properties

U ovoj disertaciji prikazan je postupak dobijanja polimernih nanokompozita in situ polimerizacijom monomera u prisustvu čestica punila. Kao punilo korišćene su nanočestice TiO2 i α-Fe2O3. Polimerni nanokompoziti poli(metil metakrilata) i TiO2 dobijeni su polimerizacijom metil metakrilata preko slobodnih radikala u rastvoru, u masi i u suspenziji, dok su nanokompoziti poli(metil metakrilata) i α-Fe2O3 dobijeni polimerizacijom preko slobodnih radikala u masi. Nanokompoziti poli(stirena) i TiO2 su dobijeni polimerizacijom stirena preko slobodnih radikala u masi. Površinska modifikacija nanočestica TiO2, dobijenih kontrolisanom hidrolizom TiCl4, izvršena je sa pet različitih jedinjenja - palmitatom askorbinske kiseline, oktil galatom, decil galatom, lauril galatom i cetil galatom. Kao punilo su korišćene dve vrste α-Fe2O3 čestica, u obliku štapića i u obliku kocki, dobijene forsiranom hidrolizom FeCl3. Površinskom modifikacijom nanočestica TiO2 izvršena je njihova hidrofobizacija što je omogućilo njihovo prebacivanje iz vodene sredine u organsku fazu, odnosno monomere metil metakrilat i stiren. Palmitat askorbinske kiseline i estri galne kiseline su se preko OH grupa hemijski vezali za površinu TiO2 čestica, što je rezultiralo pomeranjem apsorpcionog spektra površinski modifikovanih čestica TiO2 ka većim talasnim dužinama u odnosu na spektar TiO2 koloida. Karakterizacija površinski modifikovanih čestica TiO2 izvršena je apsorpcionom UV i FTIR spektroskopijom. Kristalna struktura sintetisanih α-Fe2O3 čestica određena je na osnovu difrakcije rendgenskih zraka, a veličina i oblik čestica su određeni pomoću transmisione elektronske mikroskopije. Karakterizacija dobijenih polimernih kompozita izvršena je UV i NMR spektroskopijom i transmisionom elektronskom mikroskopijom. Molarne mase poli(metil metakrilata) i poli(stirena), čistih i ekstrahovanih iz kompozitnih uzoraka, određene su korišćenjem gel propusne hromatografije i viskozimetrijske metode. Termička svojstva dobijeni polimernih nanokompozita ispitivana su termogravimetrijskom analizom i diferencijalnom skenirajućom kalorimetrijom. Cilj ovog rada je bio da se ispita uticaj načina sinteze polimerne matrice, vrste, veličine, oblika, načina površinske modifikacije i koncentracije oksidnih čestica punila na svojstva dobijenih polimernih nanokompozita. Dobijeni rezultati su pokazali da su površinski modifikovane nanočestice TiO2 i nanočestice α-Fe2O3 u obliku štapića, prisutne u toku polimerizacije MMA, uticale na reakcije terminacije pa samim tim i na molarne mase dobijenog PMMA. Čestice α-Fe2O3 u obliku kocki, prisutne u toku polimerizacije MMA, nemaju uticaj na reakcije terminacije pa ni na molarne mase dobijenog PMMA. Nanočestice TiO2 i α-Fe2O3 nisu dovele do značajnije promene vrednosti temperature ostakljivanja PMMA, što je ukazalo na slabu interakciju između čestica punila i PMMA matrice. Površinski modifikovane nanočestice TiO2, prisutne u toku polimerizacije stirena, nisu uticale na molarne mase dobijenog PS. Dodatak nanočestica TiO2-PAA u PS matricu dovodi do povećanja temperature ostakljivanja, dok nanočestice TiO2 modifikovane estrima galne kiseline ne utiču na temperaturu ostakljivanja PS matrice. Dodavanje nanočestica TiO2 u PMMA i PS matricu je povećalo njihovu termičku i termooksidativnu stabilnost.The synthesis of polymer nanocomposites by in situ polymerization of monomers in the presence of filler particles is presented in this dissertation. Nanoparticles of TiO2 and α-Fe2O3 were used as fillers. Polymer nanocomposites of poly(methyl methacrylate) and TiO2 were obtained by radical polymerization of methyl methacrylate in solution, bulk and suspension, while nanocomposites of poly(methyl methacrylate) and α-Fe2O3 and poly(styrene) and TiO2 were prepared by radical polymerization in bulk. Surface modification of TiO2 nanoparticles, obtained by control hydrolysis of TiCl4, was performed using five different compounds- ascorbic acid palmitate, octyl gallate, decyl gallate, lauryl gallate and cetyl gallate. The α-Fe2O3 particles were obtained by forced hydrolysis of FeCl3 and depending on the conditions of the reaction they were in the shape of rods or cubes. Surface modification of TiO2 nanoparticles allows the extraction of the TiO2 nanoparticles from water into organic phase, methyl methacrylate and styrene, due to the increased hydrophobic character of the modified particles. Ascorbic acid palmitate and gallic acid esters were chemically bonded to the surface of TiO2 particles through –OH groups, which resulted in the red-shift of the absorption spectrum of the surface modified TiO2 particles compared to the non-modified ones. Characterization of surface modified TiO2 particles was performed using absorption UV and FTIR spectroscopy. Crystal structure of the synthesized α-Fe2O3 particles was determined from the X-ray diffraction measurements, while size and shape of the particles were determined using transmission electron microscopy. Characterization of the obtained polymer composites was done using UV and NMR spectroscopy and transmission electron microscopy. Molar masses of poly(methyl methacrylate) and poly(styrene) samples, pure and extracted from the composites, were determined by gel permeation chromatography and viscosimetry. Thermal properties of the synthesized polymer nanocomposites were investigated by thermogravimetric analysis and differential scanning calorimetry, The goal of this study was to examine the influence of methods of synthesis of polymer matrix, and the influence of nature, size, shape, surface modification method and concentration of filler particles on the properties of the obtained polymer nanocomposites. The obtained results showed that surface modified TiO2 nanoparticles and α-Fe2O3 nanorods, present during the polymerization of MMA, influenced the termination reactions and thus the molar masses of the obtained PMMA. Cubic α-Fe2O3 particles, present during the polymerization of MMA, did not have the influence on the termination reactions and molar masses of obtained PMMA. The presence of TiO2 and α-Fe2O3 nanoparticles did not lead to significant changes of glass transition temperature of PMMA, indicating weak interactions between filler particles and PMMA matrix. Surface modified TiO2 nanoparticles, present during the polymerization of styrene, did not influence molar masses of obtained PS. Incorporation of TiO2 nanopraticles modified with ascorbic acid palmitate in PS matrix led to an increase of glass transition temperature of PS, while the TiO2 nanoparticles, surface modified by gallic acid esters, did not influence the glass transition temperature of PS matrix. Incorporation of TiO2 nanoparticles in PMMA and PS matrix increased their thermal and thermo-oxidative stability