Vpliv različnih koncentracij izbranih zgoščeval na reološke lastnosti hidrofilnih gelov

Podvratnik, Kaja (author), German Ilić, Ilija (mentor)

Hidrofilni geli so dvo- ali večkomponentni sistemi, sestavljeni iz tridimenzionalnega omrežja polimernih verig in vode, ki napolni prostor med makromolekulami. Makromolekule, ki tvorijo hidrofilne gele, imenujemo zgoščevala. To so snovi, ki jih uporabljamo za uravnavanje reoloških lastnosti sistemov, saj povečajo viskoznost in gelirajo vodo. V diplomski nalogi smo za izdelavo hidrofilnih gelov uporabili tri zgoščevala: sintetični karbomer (Carbopol 934), polsintezno natrijevo karboksimetilcelulozo (NaCMC) in ksantan, ki je naravnega izvora. Vsa tri zgoščevala so široko uporabljana v kozmetični industriji in so primerna za izdelavo različnih kozmetičnih izdelkov. Reološke lastnosti izdelanih hidrogelov smo ovrednotili s preskusi rotacijske in oscilacijske viskozimetrije. Ugotovili smo, da najvišje vrednosti viskoznosti dosega Carbopol 934, sledi mu NaCMC in nato ksantan. Sprememba koncentracije na obnašanje hidrofilnih gelov ni vplivala – vsi geli se pri vseh koncentracijah obnašajo psevdoplastično. V sklopu oscilacijskih meritev smo ugotovili, da se najbolj elastično obnašajo geli Carbopola 934, saj je bil delež elastičnega modula G' najvišji. Zaradi veliko nižjih deležev elastičnosti pri NaCMC smo ugotovili, da tvori bolj plastične gele, kot ostali dve zgoščevali. S frekvenčnimi oscilacijskimi preskusi smo skozi celotno frekvenčno območje opazovali vrednosti elastičnega (G') in viskoznega (G'') modula vseh hidrofilnih gelov in ugotovili, da je G' pri vseh koncentracijah višji od G'', kar pomeni, da so vsi hidrofilni geli bolj elastični kot plastični. Opazovali smo tudi razmerje med G' in G'' vseh hidrofilnih gelov pri frekvenci 2,51 rad/s in ugotovili, da se razmerje G'/G'' s povečevanjem koncentracije pri NaCMC in ksantanu povečuje, medtem ko pri Carbopolu 934 upada. Kljub temu se še vedno vsi geli obnašajo elastično. Proučevali smo tudi koncentracijo prehoda iz sol v gel stanje. Pri Carbopolu 934, kjer je razmerje G'/G'' največje, je ta prehod najhitrejši, saj teoretično gelira že pri 0,23-odstotni koncentraciji, sledi mu ksantan (0,47 %) in nato NaCMC (2,2 %). Zgoščevala močno vplivajo na pomembne lastnosti poltrdnih sistemov, kot so mazljivost, občutek na koži in fizikalna stabilnost, zato je zelo pomembno, katere snovi izberemo za izdelavo. Glede na to, da se vsi geli obnašajo psevdoplastično, so zelo primerni za izdelavo različnih kozmetičnih izdelkov, saj je to obnašanje najbolj zaželeno za izdelke, ki jih nanesemo na kožo.

• Language: Slovenian
• Keywords: carbopol 934, ksantan, natrijeva karboksimetilceluloza, rotacijska viskozimetrija, oscilacijske meritve
• Work type: Bachelor thesis/paper
• Organization: FFA - Faculty of Pharmacy
• Year: 2019
• PID: 20.500.12556/RUL-107389
• Publication date in RUL: 10.04.2019

Secondary language

• Language: English
• Title: Influence of different concentrations of selected thickeners on rheological

Abstract

Hydrophilic gels are two- or multi-component systems consisting of a three-dimensional network of polymeric chains and water that fills the space between macromolecules. Macromolecules that form hydrophilic gels are called thickeners. These are materials that are used to regulate the rheological properties of systems as they increase viscosity and are able to gel water. In the diploma thesis, three thickeners were used for the production of hydrophilic gels: synthetic carbomer (Carbopol 934), semi-synthetic sodium carboxymethylcellulose (NaCMC) and Xanthan gum, which is of natural origin. All three thickeners are widely used in the cosmetics industry and are suitable for making a wide range of cosmetic products. The rheological properties of our hydrogels were evaluated by rotational and oscillatory viscosimetry tests. We found that Carbopol 934 had the highest viscosity values, followed by NaCMC and then Xanthan gum. The change in concentration did not affect the behavior of hydrophilic gels – all gels behaved pseudoplastic at all concentrations. As part of the oscilatory measurements, it was found that Carbopol 934 gels are the most elastic, since the proportion of the elastic module G' was the highest. NaCMC was found to form more plastic gels than the other two thickeners, due to much lower share of elasticity. Using the frequency oscilatory tests, the values of the elastic (G') and viscous (G'') modules of all the hydrophilic gels were observed throughout the frequency range and found that G' is higher at all concentrations than G'', which means that all hydrophilic gels are more elastic than plastic. We also observed the G'/G'' ratio of all hydrophilic gels at a frequency of 2.51 rad/s and found that the ratio increased with concentration for NaCMC and Xanthan gum, while it decreased for Carbopol 934. Nevertheless, all gels still behave elastically. We also studied the concentration of the transition from sol to gel state. For Carbopol 934, where the ratio G'/G'' is the highest, this transition is the fastest, as it theoretically gels at a concentration of 0.23 %, followed by Xanthan gum (0.47 %) and then NaCMC (2.2 %). Thickeners have a strong influence on the important properties of semi-solid systems such as lubrication, skin sensation and physical stability so it is very important which substances are selected for the manufacture. Since all gels behave pseudoplastic, they are very suitable for the manufacture of various cosmetic products because this behavior is the most desirable for products that are applied to the skin.

• Keywords: carbopol 934, xanthan gum, sodium carboxymethylcellulose, rotational viscometry, oscillatory measurements