Title Priprava i karakterizacija polimernih kompozita s celulozom Title (english) Preparation and characterization of polymer composites with cellulose Author Kristijan Mrkalj Mentor Ante Jukić (mentor)Mentor Fabio Faraguna (komentor)Committee member Ante Jukić (predsjednik povjerenstva)Committee member Fabio Faraguna (član povjerenstva)Committee member Mirela Leskovac (član povjerenstva)Granter University of Zagreb Defense date and country 2019-09-16, Croatia Scientific / art field, TECHNICAL SCIENCES Abstract Zbog velike kristalne savršenosti, toplinske stabilnosti te poželjnih mehaničkih svojstava, ali i izražene polarnosti, nanoceluloza se postavila kao potencijalno ojačavalo polimetakrilatnih matrica. Svrha ovog rada bila je ispitati utjecaj nanoceluloznog punila (celuloznih nanokristala) na raspodjelu molekulskih masa pripadajućih matrica, njihove toplinske prijelaze (temperature staklastog prijelaza), toplinsku stabilnost, svojstva površine (kontaktni kut) te mehanička svojstva pripremljenih nanokompozita. U radu su ispitani ex situ priređeni kompoziti nanoceluloze, tj. celuloznih nanokristala (1, 2,5 i 5 mas.%; 10-20 nm × 300-900 nm s udjelom kristalnosti od 92 %) s poli(metil-metakrilatom) (PMMA) i MMA/dimetilaminoetil-metakrilatnim kopolimerom (90/10 mol.%), gdje aminoskupina dodatno doprinosi polarnosti matrice. Mikrografije skenirajućeg elektronskog mikroskopa poslužile su kako bi se ustanovilo tvori li nanoceluloza aglomerate u polimetakrilatnoj matrici. Pripremljeni kompoziti su karakterizirani kromatografijom isključenja po veličini kako bi se utvrdio utjecaj nanoceluloznog punila na molekulske mase i disperznost polimernih matrica i diferencijalnom pretražnom kalorimetrijom kako bi se utvrdio pomak staklišta. Termogravimetrijska analiza provedena je kako bi se odredio utjecaj nanoceluloze na toplinsku stabilnost pripremljenih kompozita. Provedeno je mjerenje kontaktnog kuta kako bi se ocijenilo utječe li nanoceluloza na kvašenje površine kompozita vodom. Pretraživanjem lomne površine uzoraka skenirajućom elektronskom mikroskopijom pretpostavljeno je kako je sva nanoceluloza homogeno raspodijeljena kroz uzorke. Prema rezultatima diferencijalne pretražne kalorimetrije mogao se uočiti trend povećanja temperature staklastog prijelaza s povećanim udjelom celuloznih nanokristala kod kompozita s oba tipa matrica. Rezultati kromatografije isključenjem po veličini ukazuju da je prešanje na povišenim temperaturama u određenoj mjeri dovelo do blage degradacije kompozita pripravljenih s PMMA. Kod kompozita pripravljenih s kopolimerom, pronađena su dva signala; pretpostavlja da signal manjih molekulskih masa pripada neumreženom polimeru, a signal većih molekulskih masa umreženom polimeru koji je nastao u procesu prešanja. Rezultati termogravimetrijske analize potvrđuju visoku toplinsku stabilnost nanoceluloze, međutim, dodatak nanoceluloznog punila nije utjecao na temperaturu početka toplinske razgradnje. Utjecaj njenog masenog udjela u kopolimeru na toplinsku stabilnost pripremljenih kompozita nije jednoznačan; u slučaju matrice poli(metil-metakrilata) povećanje udjela nanoceluloze pomiče krivulju razgradnje prema nižim temperaturnim vrijednostima, dok je kod matrice kopolimera učinak suprotan; kompoziti s većim udjelom nanoceluloze imaju termogravimetrijske krivulje pomaknute prema većim vrijednostima. Mjerenje kontaktnog kuta ukazuje na smanjenje kontaktnog kuta s povećanim udjelom celuloznih nanokristala.
Abstract (english) Because of its high crystallinity, thermal stability and desirable mechanical properties, but also expressed polarity, nanocellulose was set up as potential reinforcment for polymethacrylate matrices. The purpose of this study was to investigate the influence of nanocellulose (cellulose nanocrystal) fillers on the distribution of molecular weights of the respective matrices, their thermal transitions (glass transition temperatures), thermal stability, surface properties (contact angle) and mechanical properties of prepared nanocomposites. This thesis included ex situ preparation of composites with nanocellulose (1, 2.5 and 5 wt%, 10-20 nm × 300-900 nm with 92% crystallinity) with poly(methyl -methacrylate) (PMMA) and MMA/dimethylaminoethyl methacrylate copolymer (90/10 mol.%) matrices. Amino group in copolymer additionally contributes to the polarity of the matrix. Scanning electron microscope micrographs were used to determine whether nanocellulose forms agglomerates in the polymethacrylate matrix. Prepared composites were characterized by size exclusion chromatography to determine the influence of nanocellulose fillers on the molecular weight and the dispersion of polymer matrices. Differential scanning calorimetry was used to determine the nanocellullse influence on the glass transition temperature. Thermogravimetric analysis was performed to determine the influence of nanocellulose on the thermal stability of the prepared composites. Contact angle measurement with water droplets was performed to assess whether nanocellulose affects the surface wetting. By scanning the surface of the samples by scanning electron microscopy, it was assumed that all the nanocellulose was homogeneously distributed throughout samples. According to the results of differential scanning calorimetry, a trend of increased glass transition temperature with increased mass fraction of cellulose nanocrystals in composites with both matrices could be observed. Size-exclusion chromatography results indicate that hydraulic pressing at elevated temperatures led to a slight degradation of PMMA-prepared composites. For composites prepared with a copolymer, two signals were found; it is assumed that the smaller molecular weight signal belongs to the non-cross-linked molecules and the signal of higher molecular weight to the cross-linked polymer that had formed during hydraulic pressing. The results of thermogravimetric analysis confirm the high thermal stability of the nanocellulose, however, the addition of the nanocellulose filler did not affect thermal decomposition onset temperature of prepared composites. The influence of its mass fraction in the copolymer on the thermal stability of prepared composites is not equivocal; in the case of the PMMA matrix, an increase in the nanocellulose content shifts the degradation curve towards lower temperature values, whereas for the copolymer matrix the opposite is the effect; composites with a higher content of nanocellulose have thermogravimetric curves shifted to higher values. Measurement of the contact angle indicates a decrease in the contact angle with an increased mass fraction of cellulose nanocrystals.
Keywords
nanoceluloza
nanokompoziti
polimetakrilati
Keywords (english)
nanocellulose
nanocomposites
polymethacrylates
Language croatian URN:NBN urn:nbn:hr:149:422031 Study programme Title: Chemical Engineering - Graduate study Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2022-02-26 10:33:26
