| Abstract | Kao i brojne druge svjetske industrije, kemijska industrija u novije doba napušta uporabu fosilnih sirovina kako zbog saznanja o njihovoj ograničenosti tako i zbog povećane svijesti o njihovom štetnom utjecaju na okoliš. Zbog toga je jedna od glavnih zadaća ,,zelene kemije'' pronalazak ,,zelenih alternativa'', no one moraju zadovoljavati svojstva koja su do tada imali materijali dobiveni iz fosilnih sirovina te pritom trebaju biti ekonomski isplativi kako bi se mogli koristiti u široj upotrebi. Također, trebaju se pronaći i povoljna zelena otapala koja će zamijenti štetna organska otapala. Općeniti cilj priprave ekološki prihvatljivih polimera i kompozita je zamijeniti udio fosilnog sintetskog dijela nanokompozita s obnovljivom sastavnicom koja je povoljnija za okoliš, a u ovom radu pokušat će se zamijeniti čak
50 mas. % fosilnog sintetskog polimera obnovljivim biopunilom - celulozom. Celulozni nanokristali osim svojeg bio-podrijetla, imaju veliku specifičnu površinu i udio kristalnosti, male su mase te su nanometarskih veličina što ih čini vrlo poželjnim u primjeni prilikom pripreme polimernih nanokompozita.
U radu su ispitana svojstva čistih kopolimera metil-metakrilata (MMA) s 2-(diizopropil-amino)etil metakrilatom (DPA) ili 2-(dimetilamino)etil metakrilatom (DMAEMA) ili 2-N-morfolinoetil metakrilatom (NMPEM) u udjelima od 10 mol. % kao i njihovih nanokompozita s celuloznim nanokristalima u udjelima od 1, 5, 10, 15, 20 i 50 mas.%. Kopolimerizacije su provedene u zelenom otapalu, dihidrolevoglukozenonu poznatijem pod nazivom Cyrene™. Obzirom da je Cyrene™ dobiven pirolizom iz biomase celuloze, kao punilo odabrala se upravo celuloza zbog očekivane dobre disperzije u matrici. Ispitana su toplinska i mehanička svojstva polimernih nanokompozita te raspodjela molekulskih masa kopolimera. Sinteze kopolimera i kompozita uspješno su provedene do visokih konverzija monomera, te su dobiveni uzorci velike molekulske mase kopolimera, osobito za kopolimere s DPA i NMPEM. Za ove sustave rezultirale su i široke raspodjele molekulskih masa koje nisu potpuno unimodalne, vjerojatno zbog izraženog gel efekta tijekom polimerizacije. Utvrđeno je da se temperature staklastog prijelaza povećavaju s udjelom celuloznih nanokristala kod kompozita s DMAEMA, dok se kod drugih smanjuju, vjerojatno zbog nepovoljnih molekulskih međudjelovanja, osim za najveće udjele nanoceluloze od 20 i 50 mas. %. Dodatkom celuloznih nanokristala kopolimeru s NMPEM mehanička svojstva se blago poboljšavaju, dok za one s DPA i DMAEMA vrijedi suprotno, osim za najmanje udjele nanoceluloze. |
| Abstract (english) | Like many other global industries, the chemical industry in recent times is moving away from the use of fossil resources due to their limited availability and the increased awareness of their harmful impact on the environment. Therefore, one of the main tasks of "green chemistry" is to find "green alternatives," but these alternatives must meet the properties that materials obtained from fossil resouces had so far and must also be economically viable for broader use. Additionally, it is necessary to find favorable green solvents to replace harmful organic solvents. The general goal of preparing environmentally friendly polymers and composites is to replace the portion of fossil synthetic components in nanocomposites with a more environmentally friendly renewable component. In this work, an attempt will be made to replace as much as 50% by weight of fossil synthetic polymer with renewable bioreinforcement - cellulose. Cellulose nanocrystals, in addition to their bio-origin, have a large specific surface area and crystallinity, low weight, and nanometer-sized dimensions, making them highly desirable for use in the preparation of polymeric nanocomposites.
The properties of pure copolymers of methyl methacrylate (MMA) with 2-(diisopropylamino)ethyl methacrylate (DPA) or 2-(dimethylamino)ethyl methacrylate (DMAEMA) or 2-N-morpholinoethyl methacrylate (NMPEM) at 10 mol.% were investigated, as well as their nanocomposites with cellulose nanocrystals at 1, 5, 10, 15, 20, and 50 wt.%. The copolymerizations were carried out in a green solvent, dihydrolevoglucosenone, better known as Cyrene™. Since Cyrene™ is derived from biomass cellulose through pyrolysis, cellulose was chosen as the filler due to the expected good dispersion in the matrix.
The thermal and mechanical properties of polymeric nanocomposites were examined, as well as the molecular weight distribution of the copolymers. The synthesis of copolymers and composites was successfully carried out to high monomer conversions, and samples of high molecular weight copolymers were obtained, especially for copolymers with DPA and NMPEM. For these systems, broad molecular weight distributions that were not entirely unimodal were observed, likely due to the pronounced gel effect during polymerization. It was found that the glass transition temperatures increase with the cellulose nanocrystal content in the DMAEMA composites, while they decrease in other cases, probably due to unfavorable molecular interactions, except for the highest cellulose nanocrystal content of 20 and 50 wt.%.
The addition of cellulose nanocrystals to the NMPEM copolymer slightly improves the mechanical properties, while the opposite is true for DPA and DMAEMA, except for the lowest cellulose nanocrystal content. |
