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Title:Optimizacija tvorbe filma premazov na vodni osnovi z uporabo elektrokemijske impedančne spektroskopije
Authors:Berce, Peter (Author)
Slemnik, Mojca (Mentor) More about this mentor... New window
Files:.pdf DOK_Berce_Peter_2017.pdf (3,63 MB)
MD5: B1BC0E3B7CD1E6B00C7748ECF4E16095
 
Language:Slovenian
Work type:Doctoral dissertation (mb31)
Typology:2.08 - Doctoral Dissertation
Organization:FKKT - Faculty of Chemistry and Chemical Engineering
Abstract:Premazi na vodni osnovi predstavljajo pomemben segment v tehnologiji premazov in se uporabljajo kot okolju prijaznejša alternativa tradicionalnim premazom na osnovi organskih topil. Velika večina polimerov, ki služijo kot veziva v premazih so praktično netopna v vodi, zato se v premazih na vodni osnovi nahajajo v obliki termodinamsko nestabilne koloidne disperzije, ki je kinetično stabilizirana preko površinskega naboja in neionskih polarnih skupin. Zaradi te oblike je sušenje premazov na vodni osnovi bistveno bolj kompleksno kot sušenje tradicionalnih premazov na osnovi organskih topil. Najfleksibilnejši način optimizacije tvorbe filma iz premazov na vodni osnovi je z dodatkom koalescentov, t.j. organskih topil, ki nekaj časa zastajajo v suhem filmu in olajšajo deformacijo ter zlivanje oziroma koalescenco koloidnih delcev v homogeno polimerno plast. V doktorski disertaciji je predstavljen razvoj metodologije na osnovi uporabe elektrokemijske impedančne spektroskopije za študij tvorbe filma in optimizacijo koalescentov pri formuliranju premazov na vodni osnovi, hkrati pa so predstavljeni tudi rezultati vpliva koalescentov na lastnosti in stabilnost disperzije veziva. Naši rezultati kažejo, da koalescenti povzročajo nabrekanje in solvatacijo delcev veziva, obseg teh dveh pojavov pa je pogojen s hidrofilnostjo koalescentov, oziroma z njihovo sposobnostjo tvorjenja vodikovih vezi z vodo. Izkaže se, da je porast viskoznosti posledica povečanja volumskega dela delcev zaradi nabrekanja s topilom in zaradi znižane mobilnosti, ki jo prinese solvatacija. Koalescenti zaradi povečane solvatacije in sprememb lastnosti medija poslabšajo elektrostatično stabilnost, vendar hkrati izboljšajo sterično stabilizacijo, obseg obeh pojavov pa je zopet pogojen s hidrofilnostjo koalescenta. Razvili smo novo metodo na osnovi elektrokemijske impedančne spektroskopije, ki smo jo verificirali s pomočjo mikroskopije na atomsko silo. Preko spremembe obsega Warburgove difuzije testnega elektrolita tekom sušenja, smo kvantitativno spremljali proces tvorbe oziroma homogenizacije filma. S to novo metodo smo nato proučili vpliv hidrofilnosti, hlapnosti in količine koalescenta na tvorbo filma. Rezultati študije kažejo, da se hidrofilni koalescenti zadržujejo bližje površini delcev in tako omogočajo učinkovitejšo tvorbo filma. Ugotovili smo tudi, da do določene mere večja količina in nižja hlapnost koalescentov izboljšata tvorbo filma, vendar pa prevelika količina in uporaba prepočasnih koalescentov povzroča zastajanje topila in s tem dolgoročno mehčanje filma, ki ne doseže optimalne mehanske in kemijske obstojnosti. V disertaciji je tudi predstavljen primer optimizacije realnega zaščitenega premaza na vodni osnovi, kjer smo s pomočjo nove metode poiskali optimalno kombinacijo koalescentov in rezultate dobili desetkrat hitreje kot z uporabo klasičnih razvojnih postopkov. V doktorskem delu sta zajeta dva ključna znanstvena prispevka, in sicer nova metodologija za opazovanje in optimizacijo tvorbe filma pri premazih na vodni osnovi ter opredelitev in razlaga vplivov različnih koalescentov na stabilnost in lastnosti vodnih disperzij polimernih veziv.
Keywords:elektrokemijska impedančna spektroskopija, koalescent, premazi na vodni osnovi, stabilnost disperzije, tvorba filma
Year of publishing:2017
Publisher:[P. Berce]
Source:Maribor
UDC:543.42:667.633.22(043.3)
COBISS_ID:20939798 New window
NUK URN:URN:SI:UM:DK:WK1ALJB3
Views:843
Downloads:111
Metadata:XML RDF-CHPDL DC-XML DC-RDF
Categories:KTFMB - FKKT
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Secondary language

Language:English
Title:Optimisation of film formation of waterborne coatings using electrochemical impedance spectroscopy
Abstract:Waterborne coatings represent an important segment in coatings technology and serve as an environmentally friendlier alternative to traditional organic solvent-based coatings. The vast majority of polymers that function as binders in coatings are practically insoluble in water which is why water-based resins predominately exist in the form of thermodynamically unstable colloid dispersions which are kinetically stabilised through existence of surface charge and non-ionic polar groups. This structure is the reason why film formation from waterborne coatings is much more complex than film formation from traditional solvent-based coatings. The most flexible way to optimise film formation from waterborne coatings is by addition of coalescing aids which are organic solvents that temporarily soften the nascent film and thus facilitate deformation and coalescence of colloid particles into a homogenous polymer film. In this thesis we present development of a new method based on electrochemical impedance spectroscopy which was then used for studying film formation and optimisation of coalescent composition in waterborne coatings. In addition we also present results of coalescing aids' influence on properties and stability of water-based polymer dispersions. Our results show that coalescing aids cause swelling and solvating of polymer particles and that the extent of these two phenomena is dependent on hydrophilicity of coalescing aids or in other words on their ability to form hydrogen bonds with water. We have shown that an increase in viscosity is the result of increased volume fraction of particles due to swelling and reduced mobility brought about by solvation. Solvation with coalescents, and modified properties of the liquid medium, have an adverse effect on electrostatic stability but simultaneously improve steric stability, the extent of both phenomena again being dependent on coalescent hydrophilicity. We have developed a new method based on electrochemical impedance spectroscopy and verified it with atomic force microscopy. We quantified the process of film formation through changes in the extent of Warburg diffusion of the test electrolyte during drying. This new method was used to study the effects of hydrophilicity, volatility and quantity of coalescing aids on film formation. Results show that hydrophilic coalescents reside closer to the particles' surface, which improves the film formation process. Higher concentrations and lower volatility are beneficial to film formation to some extent, but extremes cause solvent retention which results in a film with suboptimal mechanical and chemical resistance. We also present the use of the new method to optimise a real-world waterborne protective coating, where we successfully optimised the coalescing aid combination, and more importantly got the results significantly faster than using traditional development procedures. Two key scientific contributions are identified in this thesis, the first being development of a new method for studying and optimising film formation from waterborne coatings and the second being identification with explanation of different coalescing aids on properties and stability of water-based binders.
Keywords:Coalescing aid, Dispersion stability, Electrochemical impedance spectroscopy, Film formation, Waterborne coatings


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