The role of acetic acid in degradation of polymers for photovoltaic modules

master's thesis

• Title (croatian): Uloga octene kiseline u razgradnji polimera za fotonaponske (PV) module
• Author: Antonia Mihaljević
• Mentor: Emi Govorčin Bajsić (mentor)
• Committee member: Emi Govorčin Bajsić (predsjednik povjerenstva)
• Committee member: Zlata Hrnjak-Murgić (član povjerenstva)
• Committee member: Marijana Kraljić Roković (član povjerenstva)
• Granter: University of Zagreb; Faculty of Chemical Engineering and Technology; Zagreb
• Defense date and country: 2015-09-25, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Basic Technical Sciences; Materials

Abstract

The main aim of this thesis was to measure the acetic acid permeation rates of various backsheet films at different temperature levels. At the moment, the dominating encapsulation material for PV modules is chemically cross-linked ethylene vinyl acetate copolymer (EVA). Besides the time and energy consuming module lamination process, the major drawback of EVA is the formation of corrosive degradation products like acetic acid. Acetic acid, which is formed during oxidation of ethylene vinyl acetate (EVA), leads to corrosion of the metal parts in a PV module, PID effect and to loss of adhesion and subsequent delamination of the PV module components. Furthermore, the formed acetic acid accelerates the oxidation process of EVA. Additionally, the degradation of the cell and the cell interconnections can be accelerated by degradation co-products of the encapsulant or by molecules and substances which diffused through the encapsulant. In this thesis the influence of temperature was investigated and permeation rates were measured by gravimetry. The samples were cut to size in order to fit in an open screw cup. Vials were filled with acetic acid and closed with the previously prepared screw cup containing the sample, which now functions as a membrane. The weight loss over 30 days was followed gravimetrically at 25 °C, 65 °C and 85 °C. Gravimetric analysis showed significant differences in the permeation behavior. The lowest permeation rates were found for laminates containing a polyester (PET) core layer and fluorpolymers. Co-extruded backsheets based on polyamides and polyolefines exhibited values which were up to 110 times higher than for laminates containing PET. According to the Arrhenius equation, an increase in temperature resulted in higher permeation rates. Higher concentration of acetic acid was found in minimodules with backsheets with lower AATR due to autocatalytic effect of retained acetic acid on the interface EVA/backsheet. Degradation of EVA due to acetic acid was investigated via spectroscopic methods (UV/Vis/NIR and Raman spectroscopy). Results showed that lower degradation was observed in minimodules combined with backsheets with high AATR.

Abstract (croatian)

Cilj ovog rada bio je izmjeriti stupanj prijenosa octene kiseline kroz različite polimerne filmove koji se koriste kao stražnji zaštitni sloj pri različitim temperaturama. Etilen vinil - acetat (EVA) trenutno je najdominantniji materijal koji se koristi kao prednji zaštitni sloj (omotač) u fotonaponskim modulima. Jedan od većih nedostatak EVA je formiranje produkata s korozivnim djelovanjem poput octene kiseline. Octena kiselina, koja nastaje tijekom oksidacije etilen vinil - acetata (EVA) dovodi do korozije metalnih dijelova fotonaponskog modula, PID efektu te smanjenju adhezije što uzrokuje delaminiciju komponenata fotonaposnkog modula. Dobivena octena kiselina ima autokatalitičko djelovanje te ubrzava oksidacijske procese EVA. Degradacija solarne ćelije i spojnih dijelova može biti ubrzana razgradnim produktima koji difundiraju kroz prednji zaštitni sloj. U radu je termogravimetrijskom tehnikom istražen utjecaj temperature na stupanj prijenosa octene kiseline. Uzorci polimernih filmova izrezani su te umetnuti u prethodno pripremljene čepove kojima su zatvorene bočice s octenom kiselinom. Na taj način čepovi su funkcionirali kao membrana. Bočice su smještene na sobnu temperaturu te u peći na 65 i 85 °C. Tijekom 30 dana praćen je gubitak mase bočica s octenom kiselinom. Termogravimetrijska analiza pokazala je značajnu razliku u permeaciji octene kiseline kroz različite materijale. Najniži stupanj prijenosa octene kiseline zabilježen je kod laminata s poliesterskim slojem (PET) kao središnjim slojem te kod fluoropolimera. Stražnji zaštitni slojevi od poliamida (PA) i poliolefina pokazali su vrijednosti čak 110 puta veće nego laminati s poliesterskim (PET) slojem. Prema Arrheniusovoj jednadžbi, povećanjem temperature došlo je i do povećanja prijenosa octene kiseline. Veća koncentracija octene kiseline uočena je kod minimodula koji imaju niži stupanj prijenosa octene kiseline (AATR) kao posljedica autokatalitičkog djelovanja octene kiseline koja se zadržala na međupovršini EVA/stražnji zaštitni sloj. Razgradnja etilen vinil - acetata (EVA) istražena je spektroskopskim metodama (UV/Vis/NIR i Raman). Rezultati su pokazali kako se minimoduli kombinirani sa stražnjim slojem koji ima visoki AATR manje razgrađuju u odnosu na one s niskim AATR vrijednostima.

• Keywords: PV module; EVA; acetic acid; permeation; degradation
• Keywords (croatian): fotonaponski moduli; EVA; octena kiselina; permeacija; razgradnja
• Language: english
• URN:NBN: urn:nbn:hr:149:493437
• Study programme: Title: Materials Science and Engineering - Graduate study; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka kemijskog inženjerstva (magistar/magistra inženjer/inženjerka kemijskog inženjerstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-03-14 09:48:27