Influence of additives on color stability of polyethylene

Polietilen z aditivi je polimerni material, ki je primeren za aplikacije v različnih industrijah. Najpogosteje ga uporabljamo v pakirni industriji. Zaradi cenovne dostopnosti in raznovrstnosti uporabe narašča povpraševanje po polietilenskih izdelkih. Magistrsko delo je potekalo v sodelovanju s podjetjem Makoter d.o.o. Namen magistrske naloge je bil raziskati vpliv aditivov na barvno stabilnost polietilena. Tekom proizvodnje polietilenskih filmov prihaja, zaradi različnih razlogov, do prezgodnjega razbarvanja polietilena. Zgodnja sprememba v barvi je pokazatelj degradacije materiala. Cilj magistrske naloge je bil ugotoviti razloge za prezgodnjo razbarvanje in predpostaviti izboljšave za boljšo barvno stabilnost. V sklopu eksperimentalnega dela smo izvedli Soxhletovo ekstrakcijo vzorcev polietilenskih filmov in analizirali ostanek v destilacijski bučki. Vzorce smo analizirali s tekočinsko kromatografijo visoke ločljivosti z UV detekcijo (HPLC-UV), termogravimetrično analizo (TGA), Fourierjevo transformacijsko spektroskopijo (FTIR) in nuklearno magnetno resonanco (NMR). Vpliv UV svetlobe na barvno stabilnost polietilena smo testirali v UV komori. Z analizo HPLC-UV smo v polietilenskem filmu potrdili prisotnost fenolnega antioksidanta butilhidroksitoluena (BHT). Testiranja vzorcev v UV komori so pokazala, da UV svetloba ne vpliva na takojšnje razbarvanje polietilenskih filmov. Rezultati TGA in FTIR so pokazali, da metodi nista primerni za kvalitativno določanje aditivov v naših vzorcih. Z analizo NMR smo podkrepili rezultate HPLC analize, da je v polietilenskem filmu prisoten BHT. Rezultati so pokazali prisotnost fenolnih antioksidantov, ki ob prekomerni oksidaciji vodijo v razbarvanje polietilenskih filmov. Na razbarvanje vplivajo tudi okolje, migracije fenolov ter interakcije med različnimi aditivi. Z omejevanjem vplivov lahko do določene mere preprečimo razbarvanje.Polyethylene with additives is a polymer material suitable for various industrial applications. It is most commonly used in the packaging industry. The demand for polyethylene products is increasing due to its cost efficiency and widespread application options. This master’s thesis was based on the cooperation with the Makoter d.o.o. company. The aim of this master’s thesis was to investigate the influence of additives on the color stability of polyethylene. Premature polyethylene discoloration often occurs due to various reasons during the production of polyethylene films. Premature discoloration is a sign of material degradation. The goal of the master’s thesis was to determine the causes of premature discoloration and to present possible improvements for increased color stability. In the experimental part of the master’s thesis we performed the Soxhlet method of extraction of polyethylene film sample and analyzed the residue in a distillation flask. The samples were analyzed using high-performance liquid chromatography with UV detection (HPLC-UV), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The impact of UV light on polyethylene color stability was tested in a UV chamber. We determined the presence of phenolic antioxidant butylated hydroxytoluene (BHT) in polyethylene film by HPLC analysis. Tests in the UV chamber showed that UV light has no impact on the immediate discoloration of polyethylene film. TGA and FTIR results showed that these methods are not suitable for qualitative determination of additives in our samples. Using NMR analysis we were able to confirm results of the HPLC analysis which showed the presence of BHT in the polyethylene film. The results showed that excessive oxidation of phenolic antioxidants leads to discoloration of polyethylene film. Discoloration is also affected by the environment, migration of phenolic compounds and interactions between various additives. Discoloration may be minimized by limiting the exposure to these factors