Colloidal stability of tannin particles milled in a planetary micromill

Abstract

Tanini so polifenolne spojine, katere uvrščamo med naravne antioksidante in jih pridobivamo iz različnih delov rastlin. Od tega je odvisna tudi sama struktura molekule. Na podlagi strukture ločimo dve vrsti, kondenzirane in hidrolizirane. Tanini so, zaradi svojih lastnosti, zelo aplikativne spojine, katerih uporaba je razširjena na številnih področjih. Pomembni so tako za rastline kot pri ljudeh, saj zavirajo delovanje in razmnoževanje mikroorganizmov, ki povzročajo bolezenska stanja. Za njihovo učinkovito delovanje je stabilnost raztopine koloidov zelo pomemben dejavnik. Da dosežemo koloidno stabilnost, moramo zagotoviti ozko porazdelitev velikosti delcev in nižjo vrednost polidisperznega indeksa (PDI). Ena izmed metod, s katero vplivamo na ozko porazdelitev delcev je mletje. Z mletjem namreč povzročimo nastanek delcev manjšega hidrodinamskega premera mlevnega materiala, v primerjavi z izhodnim. Diplomsko delo zajema študijo vpliva zmanjšanja velikosti delcev s pomočjo mletja, na koloidno stabilnost delcev tanina v vodnih suspenzijah. Delce smo mleli z uporabo planetarnega mikromlina in planetarnega krogličnega mlina, pri tem pa smo spreminjali procesne parametre, kot so razmerje med mlevnim materialom in mlevnimi kroglicami (1:15 in 1:20), čas mletja in število obratov. Pred izvedbo dela smo referenčni vzorec ovrednotili z uporabo metode dinamičnega sipanja svetlobe (DLS) in zeta potenciala, s termogravimetrično analizo (TGA) ter Fourierjevo transformacijsko infrardečo spektroskopijo (FTIR). Za določanje (končnega) premera zmletih delcev smo ponovno uporabili DLS, merjenje antioksidativnosti pa smo spremljali z UV-Vis spektrofotometrom.Tannins are polyphenolic compounds classified as natural antioxidants and are obtained from various parts of plants. Their moleculare structure also depends on the plant source. Based on the structure, tannins are divided into two main types, condensed and hydrolyzed tannins. Due to their diverse properties, tannins are highly applicable and widely used in many fields. They are important for both plants and humans, as they inhibir the activity and reproduction of microorganisms that cause disease. For their effective function, the colloidal stability of the suspension is very important factor. To achieve this, it is necessary to ensure a narrow particle size distribution and a low polydispersity index (PDI). This can be influenced in several ways, including grinding. Grinding reduces the hydrodynamic diameter of the particles compared to their original one. The thesis investigates how particle size reduction through milling affects the colloidal stability of tannins particles in aqueous suspension. The particles were milled using a planetary micromill and a planetary ball mill, with variations in process parameters such as ratio, milling time and rotation speed. Before the experimental work, the reference sample was characterized using dynamic light scattering (DLS) and zeta potential measurments, thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). DLS was again used to determine the final diameter of the milled particles, while antioxidant activity was measured using a UV-Vis spectophotometry