| Abstract | Nanošenje polimernih premaza na drvne materijale jednostavan je i ekonomski prihvatljiv način očuvanja i zaštite površina od vanjskih utjecaja. Međutim, polimerni premazi ne osiguravaju dovoljnu UV-zaštitu pa je dodatak anorganskih nanopunila kao što je titanijev dioksid (TiO2), koji apsorbiraju UV-zračenje, u polimer od velike važnosti. Emulzijskom polmerizacijom sintetizirane su vodene emulzije poliakrilat (PAK)/titanijev dioksid iz kojih su pripremljeni filmovi premaza. Istraživanja u ovom radu podjeljena su u 3 faze. U 1. fazi istraživan je učinak dodatka različite vrste TiO2 (vodene disperzije, praškasti oblik) i pripreme ex situ i in situ načinom na svojstva PAK-a prije i nakon UV-izlaganja. Iz 1. faze odabrano je najbolje punilo odnosno punilo u vodenoj disperziji (DW) te se u 2. fazi istraživanja pratilo kako koncentracija tog punila te način pripreme utječu na svojstva PAK-a prije i nakon UV-izlaganja. U 3. fazi istraživanja ispitivao se učinak modifikacije površine TiO2 sa (3-aminopropil)trimetoksi silanom (AMPTS), poliedarnim oligomernim silseskvioksanom (POSS), inicijatorom 2,2'-azobis(2-metilpropionamid) dihidrokloridom (AIBA) te neionskim emulgatorom dietil-fenol-etilen-oksidom (TX-100) na svojstva PAK-a prije i nakon UV-izlaganja. Karakterizacija emulzija usmjerena je na određivanje raspodjele veličina čestica i reoloških svojstva, dok je karakterizacija filmova prije UV-izlaganja uključivala istraživanje morfologije, transparentnosti, toplinske stabilnosti i mehaničkih svojstava. Nakon UV-izlaganja određivane su strukturne promjene, promjene u temperaturi staklastog prijelaza i promjene raspodjele molekulskih masa premaza. Provedena istraživanja ukazala su da se dodatkom vodene disperzije punila TiO2 postižu bolja svojstva nanokompozitnog premaza u odnosu na premaze s praškastim punilima. Rezultati raspodjele veličina čestica ukazuju da se dodatkom punila mijenja raspodjela veličina čestica PAK-a. In situ pripremom premaza s dodatkom nanočestica u obliku vodene disperzije DW postiže se bimodalana raspodjela veličina čestica u kojoj nema prisutnih aglomeriranih čestica dok ex situ priprema ukazuje na znatnu količinu aglomeriranih čestica posebno u sustavima s većom koncentracijm punila. Modifikacijom TiO2 nanočestica povećava se hidrodinamički promjer čestica te je kod emulzije s TiO2 modificiranim s neionskim emulgatorom TX-100 prisutna znatna količina aglomerata. Emulzije pripremljene in situ pokazuju povećanje viskoznosti PAK-a dodatkom punila TiO2 što se može pripisati uspostavljanju značajnih interakcija između punila i PAK-a dok kod ex situ emulzija naknadni dodatak punila ne utječe na viskoznost PAK-a. U odnosu na nemodificirane nanočestice, dodatkom modificiranih TiO2 nanočestica znatno se povećava viskoznost PAK-a. Bolja raspodjela i dispergiranost punila u PAK-u postiže se in situ načinom pripreme, a time i bolja prozirnost i UV-zaštitna svojstva. In situ načinom pripreme dolazi do polimerizacije PAKa oko površine TiO2 nanočestica te se stoga smanjuje mogućnost aglomeracije punila. Modifikacija punila TiO2 narušava raspodjelu i dispergiranost punila u PAK-u. Znatno lošija dispergiranosti i raspodjela punila u polimeru vidljiva je dodatkom TiO2 modificiranog s neionskim emulgatorom TX-100, dok modifikacija površine TiO2 s AMPTS silanom ne narušava raspodjelu i dispergiranost TiO2 u PAK-u. Rezultati mjerenja transmitancije premaza ukazali su da se in situ načinom pripreme te dodatkom punila u vodenoj disperziji poboljšavaju UV-zaštitna svojstva PAK filma, a ne narušava se znatno prozirnost premaza. Dodatak modificiranih punila ne utječe značajno na prozirnost premaza, a neznatno povećava UV-zaštitna svojstva. Dodatak modificiranog punila TiO2 znatno poboljšava toplinsku stabilnost PAK-a, što se može pripisati povećanju međufaznih interakcija između TiO2 i PAK-a uslijed modifikacije te se time znatno ograničava toplinski inducirana pokretljivost polimernih lanca i cijepanje lanaca uslijed toplinske razgradnje. Temperatura staklastog prijelaza premaza povećava se uslijed UV-zračenja zbog nastanka umreženih struktura koje ograničavaju pokretljivost polimernih lanaca. In situ pripremljen premaz s dodatkom DW punila ima najmanju promjenu temperature staklastog prijelaza nakon 144 h UV-izlaganja što ukazuje da usporava strukturne promjene u poliakrilatu uslijed UV-izlaganja. U ex situ premazima izraženo je fotokatalitičko djelovanje TiO2 nanočestica. Razlog tome može biti zbog prisutnosti aglomerata punila TiO2 u ex situ premazima koji onemogućuju učinkovito isparavanje vode iz filma prilikom sušenja i jedan dio vode zaostaje u premaza te se tako stvaraju područja bogata vodom koja kataliziraju proces UV-razgradnje. Strukturne promjene na FTIR spektru te promjene u raspodjeli molekulskih masa premaza uslijed UV-izlaganja su manje izražene kod in situ premaza pripremljenih s dodatkom nanočestica u vodenoj disperziji u odnosu na ostale premaze. Modifikacija površine TiO2 može imati i pozitivan i negativan učinak na UV-apsorpcijsku moć TiO2, pa tako modifikacija TiO2 s AMPTS-om povećava UV-apsorbirajući učinak TiO2 dok modifikacija s ostalim modifikatorima povećava fotokatalitički učinak TiO2. Premaz s TiO2 modificiran s AMPTS-om pokazuje najbolju toplinsku stabilnost, te najbolja mehanička svojstva, nisku transmitanciju u UV-dijelu spektra, najmanju promjenu temperature staklastog prijelaza te najmanje strukturne promjene tijekom UV-izlaganja. Prema tome modifikacijom površine s AMPTS-om te dodatkom takvog punila u PAK polimer postiže se znatno poboljšanje svojstava premaza. |
| Abstract (english) | Applying polymer coatings to wood-based materials is a simple and economically acceptable way to preserve surfaces and protect them from external influences. However, polymer coatings do not provide adequate UV protection. Therefore, the addition of inorganic nanofillers such as titanium dioxide (TiO2), which absorb UV radiation in the polymer, is of great importance. Emulsion polymerization was used to synthesize aqueous polyacrylate (PA)/titanium dioxide emulsions from which coating films were prepared. The research in this work is divided into 3 phases. In phase 1, the effect of adding different types of TiO2 (aqueous dispersions, powder form) and the method of ex situ and in situ preparation on the properties of PA before and after UV exposure was investigated. In phase 1, the best nanofiller or DW filler was selected and in the phase 2 of the study, it was observed how the concentration of that filler and the preparation method affected the properties of PA before and after UV exposure. In phase 3 of the study, the effect of surface modification of TiO2 with (3-Aminopropyl)trimethoxysilane (AMPTS), polyhedral oligomeric silsesquioxane (POSS), initiator 2,2´-Azobis(2-methylpropionamidine) dihydrochloride (AIBA) and nonionic emulsifier diethyl-phenol-ethylene-oxide TX-100 on the properties of PA before and after UV exposure was investigated. The nanofiller concentration of 0.75% used in the phase 3 of the study was obtained from the 2nd phase of the study. Characterization of the emulsions was aimed at determining particle size distribution and rheological properties, while characterization of the coating films before UV exposure was aimed at determining morphology, transparency, thermal stability and mechanical properties. After UV exposure structural changes, changes in glass transition temperature and changes in molecular weight distribution of coating were determined. Research showed that the addition of TiO2 nanofiller in the form of an aqueous dispersion achieved better properties of the nanocomposite compared to coatings with powder nanofillers. The method of preparation of the coating has a significant effect on the properties of the coating and ultimately on its application. The results of particle size distribution showed that the addition of nanofiller TiO2 changed the particle size distribution of PA. The in situ preparation of the coating with the addition of nanoparticles in the form of an aqueous dispersion DW obtained a bimodal particle size distribution in which no agglomerated particles were present, while the emulsion prepared ex situ showed a significant amount of agglomerated particles, especially when higher concentrations of DW were added. The particle size distribution of emulsions with the addition of modified DW nanoparticles indicates that the modification increases the hydrodynamic particle diameter and emulsion with TiO2 modified with non-ionic emulsifier TX-100 shows a significant amount of agglomerates. Emulsions prepared in situ show an increase in the viscosity of PA due to the addition of TiO2 filler, which can be attributed to the establishment of significant interactions between nanofillers and PA, whereas in ex situ emulsions the subsequent addition of filler has no effect on the viscosity of PA. The viscosity of PA is significantly increased by the addition of modified TiO2 nanoparticles. In situ preparation method achieves better distribution and dispersion of the nanofillers in PA, resulting in better transparency and UV protection. The in situ polymerization of PA is carried out from the surface of TiO2, which reduces the possibility of agglomeration of fillers. The modification of TiO2 filler impairs the distribution and dispersion of filler in PA, significantly worse dispersion and distribution of nanofiller is visible by the addition of TiO2 modified with non-ionic emulsifier TX -100, while surface modification of TiO2 with silane AMPTS does not impair the distribution and dispersion of TiO2 in PA. The results of the measurement of the light transmittance of the coating show that the in situ method of preparation and the addition of fillers in the aqueous dispersion improve the UV protective properties of the PA film and do not significantly affect the transparency of the coating. The addition of modified fillers does not affect the transparency of the coating and slightly increases the UV protection properties. The addition of modified TiO2 nanofiller significantly improves the thermal stability of PA, which can be attributed to the increase in the interfacial interactions between TiO2 and PA due to the modification, thus significantly limiting the thermally-induced mobility of polymer chains and chain scission due to thermal degradation. The glass transition temperature of the coating increases during UV radiation due to the formation of crosslinked structures that limit the mobility of polymer chains. In situ prepared coating with DW filler has the smallest change in glass transition temperature after 144 h of UV exposure indicating that it slows down structural changes in polyacrylate. In ex situ coatings, the photocatalytic effect of TiO2 nanoparticles was more pronounced. This may be due to the presence of agglomerates of TiO2 nanoparticles in ex situ coatings that prevent efficient evaporation of water from the coating during drying time and part of the water remains in the coating creating water-rich regions that catalyze the process of UV degradation. Structural changes of coating and changes in the distribution of molecular weight due to UV exposure are less pronounced in in situ prepared coatings with the addition of fillers in an aqueous dispersion compared to other coatings. TiO2 surface modification can have positive and negative effects on the UV absorbance of TiO2. For example, the modification of TiO2 with AMPTS increases the UV absorbing ability of TiO2, while the modification with other modifiers increases the photocatalytic ability of TiO2. The coating with TiO2 modified with AMPTS shows the best thermal stability and mechanical properties, low transmittance in the UV part of the spectrum, the smallest change in glass transition temperature, and the least structural changes during UV exposure. Thus, by modifying the surface of TiO2 with AMPTS and adding such a filler to the PA polymer, a significant improvement in properties is achieved. |
