Utjecaj obrade ugljikovih nanocjevčica na strukturu i svojstva polilaktida

master's thesis

• Title (english): Influence of carbon nanotubes modification on structure and properties of polylactide
• Author: Ana Kazalac
• Mentor: Sanja Lučić Blagojević (mentor)
• Committee member: Sanja Lučić Blagojević (predsjednik povjerenstva)
• Committee member: Domagoj Vrsaljko (član povjerenstva)
• Committee member: Zrinka Buhin Šturlić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Chemical Engineering and Technology; Zagreb
• Defense date and country: 2015-07-16, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Chemical Engineering; Chemical Engineering in Material Development

Abstract

Novi trendovi u istraživanjima su pronalazak materijala koji bi konkurirali na tržištu svojim dobrim svojstvima, biodegradabilnosti i proizvodnji iz obnovljivih izvora energije. Polilaktid je jedan od takvih materijala, koji s dodatkom ugljikovih nanocjevčica može konkurirati na tržištu. U ovom radu provedena su istraživanja utjecaja dodatka različitih masenih udjela funkcionaliziranih ugljikovih nanocjevčica (MWCNT-COOH; MWCNT-COOC12H25) u polilaktid. Uzorci su zamiješani na Brabender gnjetilici postupkom u talini. Potom je ispitivana morfologija, mehanička svojstva i mehanizam loma pomoću mehaničke kidalice i pretražnog elektronskog mikroskopa. Toplinska svojstva ispitivana su metodom diferencijalne pretražne kalorimetrije, te toplinska stabilnost termogravimetrijskom analizom. Električna svojstva određivana su mjerenjem otpora metodom četiri probe. Rezultati su pokazali da se mehanička svojstva PLA sustava s MWCNT-COOH i MWCNT-COOC12H25 nanopunilima poboljšavaju najznačajnije do 2 % mas. PLA nanokompoziti (do 2 % mas.) s ugljikovim nanocjevčicama funkcionaliziranim dugim alkilnim lancima (MWCNT-COOC12H25) imaju nešto bolja svojstva od sustava s MWCNT-COOH zbog bolje raspodijeljenosti MWCNT-COOC12H25 punila, što je potvrđeno analizom površine kidanja. Rezultati DSC analize pokazali su da dodatak oba punila ubrzava neizotermnu kristalizaciju PLA matrice i to najznačajnije do 2 % mas. Dodatak MWCNT-COOC12H25 punila zbog dugog alkilnog lanca koji ulazi u matricu znatnije ometa slaganje polimernih lanaca u kristalne forme. Neovisno o vrsti funkcionalnih skupina graftiranih na površini MWCNT tijekom procesa hladne kristalizacije u PLA nanokompozitima stvara se veći udio slabije uređenih struktura nego u čistoj PLA matrici. Toplinska stabilnost najznatnije se poboljšava dodatkom do 2 % mas. punila. Ovakvi rezultati se pripisuju učinku barijere koju stvaraju ugljikove nanocjevčice i dobroj toplinskoj vodljivosti MWCNT. Nije vidljiva znatna razlika u poboljšanju toplinske stabilnosti ovisno o funkcionalnoj skupini graftiranoj na ugljikovu nanocjevčicu. Rezultati ispitivanja električne vodljivosti pokazuju značajno poboljšanje vodljivosti već dodatkom malih količina funkcionaliziranih MWCNT do 0,5 % mas. zbog nastajanja trodimenzionalne vodljive mreže u matrici te istraživani nanokompoziti imaju potencijalnu primjenu za elektrostatsko bojanje i odvođenje elektrostatskog naboja.

Abstract (english)

New trends in research are finding materials who would compete in open market with it's properties, biodegradability and production from renewable sources of energy. Polylactide is one of those materials, and with addition of carbon nanotubes it can compete in the open market. In this study the addition of different quantities of modified carbon nanotubes (MWCNT-COOH; MWCNT-COOC12H25) in PLA was investigated. Samples were prepared by melt mixing in a Brabender plasticoder. Within this study morphology, mechanical properties and mechanism of failure with scanning electron microscopy (SEM) and universal mechanical testing machine were investigated. Thermal properties were investigated by differential scanning analysis and thermal stability was determined by thermogravimetric analysis. Electrical properties were investigated by measuring resistance using four probe method. Results showed the most significant increase of mechanical properties for PLA systems with MWCNT-COOH and MWCNT-COOC12H25 nanofillers up to 2 % wt. PLA nanocomposites (up to 2 % wt) with carbon nanotubes functionalized with long alkyl chains (PLA/MWCNT-COOC12H25) have slightly better properties than systems with MWCNT-COOH due to better distribution of MWCNT-COOC12H25 in PLA matrix, which is confirmed also by fracture surface analysis. DSC results indicate that addition of both fillers accelerates nonisothermal crystallization of PLA matrix and this effect is more pronounced up to 2 % wt. Addition of MWCNT-COOC12H25 nanofiller, due to long alkyl chains that entrance in a matrix, more significantly hinders ordering of polymer chains in the crystalline form. Regardless of the type of grafted functional groups on the surface of MWCNTs, during the cold crystallization a higher proportion of lower-ordered structures than in a pure PLA matrix were created. The most prominent improvement of thermal stability is obtained by the addition of 2% wt of fillers. These results can be attributed to formation of barrier that carbon nanotubes formed and to the very high thermal conductivity of MWCNTs. Depending on the type of functional groups on the carbon nanotubes difference in the improvement of the thermal stability were not observed. The results of electrical conductivity show significant improvement of conductivity with addition of small amounts of functionalized MWCNTs up to 0.5% wt due to the formation of three-dimensional conductive network in the PLA matrix. The investigated nanocomposites have potential use for electrostatic painting and dissipation of electrostatic charge.

• Keywords: nanokompozitni sustav; PLA(polilaktid); MWCNT-COOH; MWCNT-COOC12H25; PLA/f-MWCNT; morfologija; mehanizam popuštanja; mehanička svojstva; toplinska svojstva; toplinska stabilnost; električna svojstva
• Keywords (english): nanocomposite; PLA (polylactide); MWCNT-COOH; MWCNT-COOC12H25; PLA/m-MWCNT; morphology; mechanism of failure; mechanical properties; thermal properties; thermal stability; electrical properties
• Language: croatian
• URN:NBN: urn:nbn:hr:149:524521
• Study programme: Title: Materials Science and Engineering - Graduate study; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka kemijskog inženjerstva (magistar/magistra inženjer/inženjerka kemijskog inženjerstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2016-12-21 09:59:47