Uporaba hemiceluloz za funkcionalizacijo površin sintetičnih polimerov

doktorska disertacija

Nena Velkova (Author), Simona Strnad (Mentor), Bodo Saake (Co-mentor), Lidija Fras Zemljič (Co-mentor)

Abstract

The main aim of this thesis was development of thin functional layers from hemicelluloses xylans on the polyethylene terephthalate (PET) surfaces. Hemicelluloses, xylans, as renewable polymers, were chemically modified in order to introduce anionic and cationic functional groups. Two types of chemical modifications were performed: carboxymethylation in order to increase anionic nature of xylans and improve their hydrophilic character and cationization for introducing of amino groups and antimicrobial characteristics. Both types of modifications were successful, which was proved by ATR FTIR and raman techniques, elemental analysis, total bound nitrogen determination, size exclusion chromatography and polyelectrolyte titrations. Polyelectrolyte titration results showed increased amounts of deprotonated carboxyl groups in carboxymethylated xylans as well as increased amounts of protonated groups in cationized xylans. Antimicrobial activity of xylans was investigated by the determination of minimal inhibitory concentration (MIC) against S. aureus, E. coli, and C. albicans and it was found out that the samples with higher amounts of active amino groups showed lower MIC. Cationised glucuronoxylan showed significantly higher antimicrobial activities against S. aureus in comparison to cationised arabinoxylan and nonmodified xylan samples. However, none of xylan samples was active against fungi. In order to analyze surface properties of solid surfaces, films from xylan (nonmodified and modified) water solution was formed by casting method. The surface chemical composition of films were investigated by x-ray photoelectron spectroscopy (XPS), and the results showed that films made from carboxymethylated xylans had significantly higher amounts of carbon fraction involved in O=C-O bonds, compared to nonmodified xylans. Such surface chemical structure caused higher surface free energy with higher electron-donor contribution and thus high hydrophilicity of these films. Films made by cationized xylans had higher amount of carbon involved in C-C and C-H bonds compared to nonmodified and lower surface free energy with increase of dispersive Lifshitz Van der Waals contribution. In order to thoroughly investigate the adsorption of xylans onto synthetic surfaces Quartz crystal microbalance with dissipation unit (QCM-D) was used. For these measurements model films were prepared from PET by spin coating technique. Adsorption studies were performed at different conditions, such as pH, concentration and ionic strength of xylan solutions. For all the chemically modified xylans the adsorption was improved at pH 5 and with increased ionic strength with divalent ions. The adsorption increased as well with increasing of xylan solution concentration. In order to improve binding of adsorbed xylans so-called anchoring polymers were applied. When anchoring polymers were applied, better adsorption and fixation of adsorbed layer was confirmed, thus the adsorbed masses of xylans after rinsing with water were significantly higher in comparison to the adsorption without immediate anchoring layer. On the basis of these results, real PET fabric surfaces were treated using chemically modified xylans. The xylan solutions were applied onto PET fabric samples using spray coating technique, which is the best approximate to the large-scale procedures. In the first step, PET fabric was activated by alkaline hydrolysis and after that, anchoring agents and carboxymethylated and/or cationized xylans were adsorbed. The success of these treatments was evaluated by the determination of negative and positive charge of the treated PET fabric samples by titration techniques, methylene blue and acid orange 7 adsorption methods, water contact angles and wettability determination. From the potentiometric titrations results it was clearly seen that each new adsorbed layer onto PET fabric totally screened the charge of the former one. FESEM images showed rather thick layers covering the

Keywords

hemicellulose;polyetylene terephthalate;glucuronoxylan;arabinoxylan;carboxymethylation;cationization;PET model films;quartz crystal microbalance;PET fabric;surface free energy;wettability;antimicrobial properties;

Data

Language:	English
Year of publishing:	2016
Typology:	2.08 - Doctoral Dissertation
Organization:	UM FS - Faculty of Mechanical Engineering
Publisher:	N. Velkova]
UDC:	677.794.742.017.86:547.458.87.013.2(043.3)
COBISS:	19417878
Views:	1477
Downloads:	104
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Other data

Secondary language:	Slovenian
Secondary title:	Hemicelluloses application for synthetic polymer surfaces functionalisation
Secondary abstract:	Glavni namen doktorske naloge je bil študij uporabe hemiceluloz ksilanov, kot obnovljivih biopolimerov (stranski produkti papirne in prehrambene industrije) za razvoj postopkov in tehnik za izdelavo tankih funkcionalnih slojev na površinah sintetičnih polimerov, kot je npr. polietilentereftalat, ki ga najdemo v najrazličnejših tehničnih in medicinskih aplikacijah. Pri teh aplikacijah so najpogosteje iskani lastnosti sintetičnih površin hidrofilnost in protimikrobnost. Na področjih, kjer se materiali uporabljajo v stiku s človeškim telesom, je potrebno zadostiti številnim specifičnim zahtevam, od katerih je najpomembnejše fiziološko udobje. Glavni parametri, ki določajo fiziološko udobje so predvsem: prepustnost za vodno paro, hidrofilnost in termična prevodnost. Za medicinske namene je večkrat zelo zaželena odpornost na različne bakterije. Uporaba sintetičnih polimerov se je v zadnjih desetletjih močno uveljavila predvsem zaradi nizkih cen in dobrih mehanskih lastnosti kot so elastičnost, trdnost, odpornost na drgnjenje [1, 2]. Vendar pa je v glavnem osnovna značilnost teh materialov, da imajo nizko površinsko energijo in visoko inertnost, kar pomeni hidrofobnost in zato slabe fiziološke lastnosti [2, 3]. V smislu preseganja teh težav se najpogosteje poslužujejo različnih površinskih obdelav, ki ob spreminjanju površinskih lastnosti ohranjajo mehanske lastnosti polimera. Za izboljšanje hidrofilnosti poliestrov se zelo pogosto uporablja alkalna hidroliza [1, 4, 5] ali obdelava s plinsko plazmo, ki ji je bilo v zadnjih desetletjih posvečeno veliko pozornosti [6, 7]. Slabost teh obdelav je predvsem ugašanje učinkov s časom (staranje). Poleg navedenih se za površinsko funkcionalizacijo uporabljajo encimatske obdelave, površinska kopolimerizacija ali adsorpcija polimerov in izdelava tankih slojev. Nadomeščanje izdelkov, ki temeljijo na petrokemičnih virih s tistimi, ki so izdelani iz obnovljivih materialov je eden od najpomembnejših inovacijskih in raziskovalnih ciljev zadnjih desetletij. Takšni obnovljivi materiali vključujejo filme, embalažo in celo vrsto drugih materialov, izdelanih iz biopolimerov [8, 9]. Ekonomski potenciali biopolimerov so ogromni, saj je to najpomembnejše področje za razvoj in doseganje vseh komponent obnovljive industrije. Realizacija je v tem trenutku še relativno slaba, saj trenutno le manj kot 1 % vse proizvodnje polimerov temelji na biopolimerih, vendar pa ti, okoljsko neškodljivi polimeri kažejo potencialno visoko rast. Zadnje študije kažejo, da bo globalno povpraševanje po obnovljivih polimerih naraščalo, in sicer od 180 Mio Ton v letu 2007 na 258 Mio Ton v letu 2010, do leta 2020 pa bi naj biopolimeri nadomestili 5 % celotnega povpraševanja po petrokemičnih polimerih. Pomembna pomanjkljivost naštetih obnovljivih polimerov je, da vsi temeljijo na surovinah, katerih pridobivanje zahteva uporabo kmetijskih zemljišč, ki bi lahko sicer bila uporabljena za pridelavo hrane. To dejstvo predstavlja enega glavnih motivov za poglobljene raziskave drugih potencialnih virov, predvsem stranskih produktov industrijskih procesov. Med takšnimi je vsekakor proizvodnja celuloze in papirja kot vir hemiceluloz in lignina. Hemiceluloze so polisaharidi, ki so v rastlinah tesno povezani s celulozo in predstavljajo tretjo največjo skupino biomaterialov. Hemiceluloze so izjemno heterogena skupina snovi, med katerimi so najpomembnejši ksilani, arabinoksilani, manani, galaktoglukomanani, glukomanani, arabinogalaktan II, ß-1,3-glukan in ß-1,3-ß-1,4-glukani [10, 11]. Hemiceluloze se nahajajo v glavnem v sekundarnih celičnih stenah in skupaj s celulozo in ligninom oblikujejo rastline na način, ki omogoča optimalno mehansko oporo in transport vode in hranilnih snovi. Ksilani predstavljajo 10 do 35 % vseh hemiceluloz, prisotnih v trdem lesu, medtem ko galaktoglukomanani predstavljajo okrog 15 do 20 % hemiceluloz mehkega lesa [12].
Secondary keywords:	hemiceluloze;poletilentereftalat;glukuronoksilan;arabinoksilan;karboksimetilacija;kationizacija;PET modelni filmi;kremenova mikrotehtnica;PET tkanina;površinska prosta energija;omakanje;protimikrobne lastnosti;doktorske disertacije;
URN:	URN:SI:UM:
Type (COBISS):	Dissertation
Thesis comment:	Univ. Maribor, Fak. za strojništvo
Pages:	XIII, 145 f.
ID:	9122815