magistrsko delo
Luka Skubic (Author), Urška Šebenik (Mentor), Marjan Marinšek (Thesis defence commission member), Aleš Ručigaj (Thesis defence commission member)

Abstract

Hidrogeli so pametni materiali, ki so v zadnji letih dobili veliko pozornosti zaradi svojih lastnosti, kot so odzivanje na zunanje dražljaje, obstojnost, sposobnosti absorpcije, relativno visok elastični modul. Dandanes so izrednega pomena predvsem biorazgradljivi hidrogeli s širokim področjem uporabe. Tak primer so hidrogeli iz nanoceluloze. Hidrogele iz celuloznih nanovlaken ali nanokristalov se uporablja v senzoriki, kot sisteme za dostavo zdravil, dodatke v higienski in prehrambni industriji. Pomembni področji uporabe sta predvsem farmacija in medicina. Dodatki, kot so ogljikove nanocevke ali grafen se uporabljajo za izboljšanje lastnosti hidrogelov za specifično uporabo. Reološke lastnosti hidrogelov določujemo s pomočjo reometra, naprave, s katero merimo reološke parametre preiskovanega vzorca, kot so viskoznost, elastični modul in viskozni modul. V magistrski nalogi sem preučeval hidrogele iz TEMPO modificiranih celuloznih nanovlaken (CNF). Raziskoval sem reološke lastnosti hidrogelov TEMPO CNF z dodanimi tremi različnimi vrstami grafenskih nanoploščic. Uporabil sem nemodificiran grafen, grafen modificiran z amino skupinami in grafen modificiran s karboksilnimi skupinami. Določil sem vpliv staranja in vpliv deleža posameznega grafena na reološke lastnosti TEMPO CNF hidrogelov. Ugotovil sem, da se hidrogelom TEMPO CNF s časom povečuje viskoznost in narašča elastični modul kot posledica spreminjanja mikrostrukture hidrogelov, urejanja celuloznih verig s časom in tvorba vodikovih in van der Waalsovih vezi v hidrogelu. Zelo majhno razliko sem opazil pri rezultatih reoloških meritev pri preučevanju vpliva deleža grafena. S konduktometrično titracijo sem pokazal, da je bila koncentracija amino in karboksilnih skupin na modificiranih grafenih nizka, grafen modificiran s karboksilno skupino je vseboval 0,042-0,045 mmol/g -COOH skupine, grafen modificiran z amino skupino pa 0,979 mmol/g -NH_2 skupine. Opazil sem povišanje viskoznosti z višjo vsebnostjo posameznega grafena kot posledica višjega deleža nezvezne faze v suspenzijah. Dodatno sem preučil še vpliv pH vrednosti na reološke lastnosti hidrogelov TEMPO CNF. Ugotovil sem opazno višje vrednosti viskoznosti in elastičnega ter viskoznega modula pri hidrogelih s pH = 3. Možen razlog za to je izločanje vode, zmanjšanja odboja med polimernimi verigami in aglomeracija le teh zaradi prevladovanja van der Waalsovih vezi med verigami. Pri suspenzijah TEMPO CNF s pH = 11 sprememb v reoloških lastnosti nisem opazil. Reološke meritve so pokazale podobne rezultate kot pri pH = 7. Pri raziskovanju sem tako uspel določiti vpliv staranja, vpliv različno modificiranih grafenov in pH vrednosti na reološke lastnosti TEMPO CNF hidrogelov. Upam, da bo moje delo pripomoglo k nadaljnemu raziskovanju kompozitnih hidrogelov na osnovi TEMPO CNF in uporabi le-teh v novih aplikacijah.

Keywords

polimeri;hidrogeli;TEMPO oksidirana nanoceluloza;modificiran grafen;reologija;magistrska dela;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FKKT - Faculty of Chemistry and Chemical Technology
Publisher: [L. Skubic]
UDC: 678(043.2)
COBISS: 71149827 Link will open in a new window
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Other data

Secondary language: English
Secondary title: TEMPO-oxidized nanofibrillated cellulose composite hydrogels with graphene
Secondary abstract: Hydrogels are smart materials, which in recent years received plenty of attention due to their excellent properties, such as response to stimuli, durability, capability of adsorption and relatively high storage modulus. Nowadays, great emphasis is put on biodegradable hydrogels with wide aspect of applications. Such examples are nanocellulose hydrogels, which are made from cellulose nanofibrils or nanocrystals, and can be used in various fields such as sensors, drug delivery systems and additives in food and health industry. Two of the most important fields for hydrogel applications are medicine and pharmacy. Nanofillers such as carbon nanotubes and graphene are used to improve hydrogel properties, so they can be used in specific applications. Rheological properties of hydrogels are measured by rheometers, which are used to measure rheological parameters such as viscosity, storage and loss moduli. In my master’s thesis hydrogels made of TEMPO modified nanocellulose are investigated. Three different graphene nanoparticles were added to TEMPO CNF suspensions; graphene, graphene modified with amino groups and graphene modified with carboxyl groups. Firstly, I investigated the effect of aging of TEMPO CNF suspensions with specific additive and the influence of the amount of specific additive on rheological properties. The results showed higher viscosity and storage modulus of TEMPO CNF hydrogels over time. The reason for such behaviour is the microstructural change in suspensions, the arranging of nanocellulose chains over time and the creation of hydrogen and van der Waals bonds inside the hydrogel. Results from rheological measurements did not show major differences when comparing the effect of concentration of specific graphene on rheological behaviour of hydrogels. Later on, I was able to explain these results with conductometric titration. The amount of amino and carboxyl groups was low, there was between 0,042 – 0,045 mmol/g of -COOH groups in graphene modified with carboxyl groups and 0,979 mmol/g of -NH_2 groups in graphene modified with amino groups. I was able to obtain an increase in viscosity with higher amount of each graphene, which was the consequence of increase of dispersed phase in hydrogels. In addition, I researched the effect of pH value on TEMPO CNF hydrogels. Rheological results showed the increase in viscosity, elastic and storage moduli in acidic environment pH = 3. The reason for such behaviour could be water elimination from hydrogels as well as weaker repulsion between polymer chains. Nanocellulose chains also started to agglomerate due to the van der Waals interactions. Rheological behaviour of hydrogels at pH = 11 was similar to hydrogels with pH = 7. Furthermore, I concluded that higher pH does not affect the rheological behaviour of TEMPO CNF hydrogels. In my research, I managed to determine the effect of aging, the effect of modified graphene nanoplatelets addition, and the effect of pH value on the rheological properties of TEMPO CNF hydrogels. I hope my work will help with further research of TEMPO CNF composite hydrogels and the use of these smart materials in various new applications.
Secondary keywords: hydrogels;TEMPO oxidized nanocellulose;modified graphene;rheology;
Type (COBISS): Master's thesis/paper
Study programme: 1000376
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za kemijo in kemijsko tehnologijo, smer Kemijsko inženirstvo
Pages: 77 str.
ID: 13103398