Expanding of polylactide

Polilaktid (PLA) je termoplastični biorazgradivi polimer, pri čemu se proizvodnja PLA temelji na prirodnim izvorima kao što su kukuruz ili šećerna trska. Zbog dobrih mehaničkih i drugih svojstava (gustoća, prozirnost, barijerna svojstva) PLA je našao primjenu u industriji pakiranja (boce, kruta plastika, folije). Osim toga, znatan broj radova posvećen je istraživanju ekspandiranog PLA kao alternative za zamjenu ekspandiranog poli(stirena) (PS-E). Ekspandiranje PLA se najčešće provodi pomoću fizikalnih ekspandirajućih agensa kao što su CO2, N2 ili i–butan. Upotreba navedenih fizikalnih agensa za ekspandiranje PLA ograničena je zbog loših reoloških svojstava taline PLA. U ovom radu kao ekspandirajući agens korištene su mikrosfere komercijalnog Expancela. Granule PLA usitnjene su pomoću mlina, a zatim su priređene njihove smjese sa 3, 5 i 7 mas % Expancela te dodatno homogenizrane uz pomoć tresilice. Homogena smjesa prešana je u hidrauličkoj preši na temperaturi od 190 °C u vremenu 8 minuta. Nakon optimizacije uvjeta prešanja, prešanje je provođeno na 180 °C u vremenu 6 minuta. Nadalje, optimiranjem temperature i vremena prešanja smanjena je degradacija uzoraka prilikom prešanja. Kod pripreme ekspandiranih uzoraka ispitivan je i utjecaj punjenja kalupa na strukturu i svojstva ekspandiranog materijala. Jednoliko popunjavanje kalupa postignuto je za uzorke sa 16 g i 18 g PLA, dok uzorci s 12 g PLA nisu u potpunosti popunili kalup.Polylactide (PLA) is a biodegradable thermoplastic polyester, wherein the production of PLA is based on natural sources such as corn or sugarcane. PLA has found application in the packaging industry (bottles, rigid plastic, foil) due to mechanical and other properties (density, transparency, barrier properties). In addition, a considerable number of papers is devoted to the study of expanded PLA which is an alternative for replacement of the expanded poly(styrene) (E-PS). Expanding of PLA is most commonly achieved by physical blowing agents such as CO2, N2 or i-butane. The use of those physical blowing agents for expanding PLA is limited due to poor rheological properties of PLA melt. Expancel microspheres were used as an expanding agent in this work. PLA granules were grinded with mill and then the mixtures were prepared by adding 3, 5 or 7 wt % of Expancel to grinded PLA granules. Mixtures were additionally homogenized with vortex. The homogeneous mixtures were compressed in a hydraulic press at a temperature of 190 °C for 8 minutes. After optimization of the molding conditions, molding was conducted at 180 °C for 6 minutes. Furthermore, by optimizing the temperature and the pressing time during the pressing process, degradation of samples is reduced. During the preparation of expanded test samples, impact of mold filling on the structure and properties of the expanded material was investigated. Uniform filling of mold was achieved for samples with 16 and 18 g of PLA, while the samples with 12 g of PLA did not completely fill the mold

Preparation of Cellulose Hydrogels Modified with (2-Dimethylaminoethyl) Methacrylate and Silver Nanoparticles

Hidrogelovi su materijali koji se odlikuju mogućnošću upijanja velike količine vode. Celuloza je vrlo rasprostranjen biokompatibilan i biorazgradljiv polisaharid s hidrofilnim OH skupinama u strukturi koje omogućuju raznovrsne modifikacije. Uvođenjem novih funkcijskih skupina na osnovni polisaharidni lanac moguće je mijenjati svojstva hidrogela kako bi se pripremili hidrogelovi željenih svojstava: antibakterijska svojstva, osjetljivost na vanjske podražaje i slično. U ovom radu provedeno je graftiranje dimetilaminoetil-metakrilata (DMAEMA) na celulozu. Polimerizacija DMAEMA na celulozu provedena je u otapalu N,N-dimetil acetamid/LiCl uz peroksidni inicijator pri temperaturi od 90 °C te N,N-metilen-bis-akrilamid (MBA) kao umreživačem. U pripravljene hidrogelove unesene su i nanočestice srebra, dobro poznate po antibakterijskim svojstvima. Relativni udio PDMAEMA u hidrogelovima određen je pomoću infracrvene spektroskopije. Morfologija osušenih uzorka i prisutnost srebra određene su pretražnom elektronskom mikroskopijom koja je pokazala da je dodatkom PDMAEMA i sušenjem hidrogelova ekstrakcijom zamrzavanjem dobivena vrlo porozna struktura. Na taj način pospješeno je i vezanje nanočestica srebra na hidrogelove. Uzorci kopolimera priređeni sušenjem u sušioniku pokazuju veći stupanj bubrenja u deioniziranoj vodi (~ 109 %) u odnosu na čistu celulozu (80 %). Isti materijali sušeni ekstrakcijom zamrzavanjem i tako oblikovani u porozne hidrogelove pokazuju znatno veće vrijednosti stupnja bubrenja (256 % i 505 %) naspram čiste celuloze (80 %). Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.Hydrogels are materials displaying the ability to absorb large amounts of water. Cellulose is a widespread, biocompatible, and biodegradable polysaccharide with hydrophilic OH groups in a structure that allows various modifications. By introducing new functional groups to the repeating units of the polysaccharide chain, it is possible to modify properties of the material in order to prepare hydrogels of desired properties such as antibacterial properties or response to external stimuli. In this work, 2-dimethylaminoethyl methacrylate (DMAEMA) grafting on cellulose was performed. The polymerization of DMAEMA on cellulose was carried out in solvent N,N-dimethyl acetamide / LiCl with a peroxide initiator at 90 °C and N,N-methylene-bis-acrylamide (MBA) as a crosslinker. Nanoparticles of silver, well known for their antibacterial properties, were also introduced into the prepared hydrogels. The relative proportion of PDMAEMA in hydrogels was determined by infrared spectroscopy. The morphology of the dried samples and the presence of silver were determined by scanning electron microscopy, which showed that the addition of PDMAEMA and drying of the hydrogels by freeze-extraction resulted with a very porous structure. In this way, the binding of silver nanoparticles to hydrogels was also facilitated. Samples of copolymers prepared by drying in a dryer showed a higher degree of swelling in water (~ 109 %) than pure cellulose (80 %). The same materials prepared by freeze-drying formed into porous hydrogels showed much higher swelling rates (256 % and 505 %) compared to pure cellulose (80 %). This work is licensed under a Creative Commons Attribution 4.0 International License

Nanofluids as Heat Transfer Media

U posljednjih 20 godina nanofluidi su privukli pažnju znanstvene zajednice te se broj radova na temu nanofluida tijekom godina znatno povećao. Povećana toplinska vodljivost fluida uslijed dodatka nanočestica osnovno je svojstvo koje je potaknulo intenzivno istraživanje nanofluida. S obzirom na to da u industriji uvijek postoji težnja poboljšanju učinkovitosti proizvodnih procesa, pa tako i procesa hlađenja procesnih struja, povećana toplinska vodljivost rashladnih fluida otvara mogućnosti za postizanje navedenog cilja. U ovom radu dan je pregled metoda priprave nanofluida te opis parametara koji utječu na njihovu toplinsku vodljivost. Dan je i osvrt na modele kojima se opisuje toplinska vodljivost nanofluida te pregled mogućih mehanizama koji doprinose povećanju njihove toplinske vodljivosti. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.Nanofluids have attracted the attention of the scientific community during last twenty years and the number of papers on nanofluids has increased significantly as a result. The increased thermal conductivity of the fluid due to the addition of nanoparticles is a basic feature that has raised intensive research on nanofluids. Considering a permanent urge in the industry to improve efficiency of production processes, including the cooling streams of processes, the increased thermal conductivity of cooling fluids opens the possibility of achieving that goal. This paper provides an overview of nanofluid preparation methods and a description of parameters that affect the thermal conductivity of nanofluids. Also, the overviews of few models that describe the thermal conductivity of nanofluids as well as of possible mechanisms that contribute to the increase in thermal conductivity of nanofluids are given. This work is licensed under a Creative Commons Attribution 4.0 International License

Synthesis of Poly(3,4-ethylenedioxythiophene) Based ATRP Macroinitiator

Poli(3,4-etilendioksitiofen) (PEDOT) je elektrovodljivi polimer koji se primjenjuje u baterijama, superkondenzatorima, solarnim ćelijama i različitim biosenzorima u nosivoj elektronici. Kontroliranom radikalskom polimerizacijom prijenosom atoma (ATRP) moguće je cijepljenjem bočnih grana modificirati svojstava PEDOT-a za specifičnu primjenu. U ovom radu sintetizirani su ATRP makroinicijatori na osnovi PEDOT-a, funkcionalizirani reaktivnim bromom, koji omogućuje cijepljenje različitih polimera kao bočnih grana. Karakterizacija dobivenih uzoraka provedena je pomoću NMR-a, FTIR-a, GPC-a, TGA-a i mjerenjem elektrokemijskih svojstava. Pokazalo se da uzorak s manjim udjelom broma ima bolja kemijska svojstva i kao takav je prikladniji za daljnju sintezu i modifikaciju PEDOT-a.Poly(3,4-ethylenedioxythiophene) (PEDOT) is a conductive polymer used in batteries, supercapacitors, solar cells, and various biosensors in wearable electronics. Through controlled atom transfer radical polymerisation (ATRP), it is possible to modify the properties of PEDOT for specific applications by grafting the side branches. In this work, PEDOT-based ATRP macroinitiators, functionalised with reactive bromine allowing the grafting of different polymers as side branches, were synthesised. Characterisation of the obtained samples was carried out by NMR, FTIR, GPC, TGA and measurement of electrochemical properties. Results showed that the sample with lower bromine content had better chemical properties; hence it was more suitable for further synthesis and modification of PEDOT

Expanding of polylactide

Polilaktid (PLA) je termoplastični biorazgradivi polimer, pri čemu se proizvodnja PLA temelji na prirodnim izvorima kao što su kukuruz ili šećerna trska. Zbog dobrih mehaničkih i drugih svojstava (gustoća, prozirnost, barijerna svojstva) PLA je našao primjenu u industriji pakiranja (boce, kruta plastika, folije). Osim toga, znatan broj radova posvećen je istraživanju ekspandiranog PLA kao alternative za zamjenu ekspandiranog poli(stirena) (PS-E). Ekspandiranje PLA se najčešće provodi pomoću fizikalnih ekspandirajućih agensa kao što su CO2, N2 ili i–butan. Upotreba navedenih fizikalnih agensa za ekspandiranje PLA ograničena je zbog loših reoloških svojstava taline PLA. U ovom radu kao ekspandirajući agens korištene su mikrosfere komercijalnog Expancela. Granule PLA usitnjene su pomoću mlina, a zatim su priređene njihove smjese sa 3, 5 i 7 mas % Expancela te dodatno homogenizrane uz pomoć tresilice. Homogena smjesa prešana je u hidrauličkoj preši na temperaturi od 190 °C u vremenu 8 minuta. Nakon optimizacije uvjeta prešanja, prešanje je provođeno na 180 °C u vremenu 6 minuta. Nadalje, optimiranjem temperature i vremena prešanja smanjena je degradacija uzoraka prilikom prešanja. Kod pripreme ekspandiranih uzoraka ispitivan je i utjecaj punjenja kalupa na strukturu i svojstva ekspandiranog materijala. Jednoliko popunjavanje kalupa postignuto je za uzorke sa 16 g i 18 g PLA, dok uzorci s 12 g PLA nisu u potpunosti popunili kalup.Polylactide (PLA) is a biodegradable thermoplastic polyester, wherein the production of PLA is based on natural sources such as corn or sugarcane. PLA has found application in the packaging industry (bottles, rigid plastic, foil) due to mechanical and other properties (density, transparency, barrier properties). In addition, a considerable number of papers is devoted to the study of expanded PLA which is an alternative for replacement of the expanded poly(styrene) (E-PS). Expanding of PLA is most commonly achieved by physical blowing agents such as CO2, N2 or i-butane. The use of those physical blowing agents for expanding PLA is limited due to poor rheological properties of PLA melt. Expancel microspheres were used as an expanding agent in this work. PLA granules were grinded with mill and then the mixtures were prepared by adding 3, 5 or 7 wt % of Expancel to grinded PLA granules. Mixtures were additionally homogenized with vortex. The homogeneous mixtures were compressed in a hydraulic press at a temperature of 190 °C for 8 minutes. After optimization of the molding conditions, molding was conducted at 180 °C for 6 minutes. Furthermore, by optimizing the temperature and the pressing time during the pressing process, degradation of samples is reduced. During the preparation of expanded test samples, impact of mold filling on the structure and properties of the expanded material was investigated. Uniform filling of mold was achieved for samples with 16 and 18 g of PLA, while the samples with 12 g of PLA did not completely fill the mold

Swelling and Viscoelastic Properties of Cellulose-Based Hydrogels Prepared by Free Radical Polymerization of Dimethylaminoethyl Methacrylate in Cellulose Solution

The grafting of a stimuli-responsive polymer (poly(dimethylaminoethyl methacrylate)) onto cellulose was achieved by performing free radical polymerization of a vinyl/divinyl monomer in cellulose solution. The grafting and crosslinking efficiency in the material have been increased by subsequent irradiation of the samples with ionizing radiation (doses of 10, 30, or 100 kGy). The relative amount of poly(dimethylaminoethyl methacrylate) in the prepared hydrogels was determined by infrared spectroscopy. The swelling behavior of the hydrogels was studied thoroughly, including microgelation extent, equilibrium swelling, and reswelling degree, as well as the dependence on the gelation procedure. The dynamic viscoelastic behavior of prepared hydrogels was also studied. The tan δ values indicate a solid-like behavior while the obtained hydrogels have a complex modulus in the range of 14–39 kPa, which is suitable for hydrogels used in biomedical applications. In addition, the incorporation of Ag particles and the adsorption of Fe3+ ions were tested to evaluate the additional functionalities of the prepared hydrogels. It was found that the introduction of PDMAEMA to the hydrogels enhanced their ability to synthesize Ag particles and absorb Fe3+ ions, providing a platform for the potential preparation of hydrogels for the treatment of wounds

Swelling and Viscoelastic Properties of Cellulose-Based Hydrogels Prepared by Free Radical Polymerization of Dimethylaminoethyl Methacrylate in Cellulose Solution

The grafting of a stimuli-responsive polymer (poly(dimethylaminoethyl methacrylate)) onto cellulose was achieved by performing free radical polymerization of a vinyl/divinyl monomer in cellulose solution. The grafting and crosslinking efficiency in the material have been increased by subsequent irradiation of the samples with ionizing radiation (doses of 10, 30, or 100 kGy). The relative amount of poly(dimethylaminoethyl methacrylate) in the prepared hydrogels was determined by infrared spectroscopy. The swelling behavior of the hydrogels was studied thoroughly, including microgelation extent, equilibrium swelling, and reswelling degree, as well as the dependence on the gelation procedure. The dynamic viscoelastic behavior of prepared hydrogels was also studied. The tan δ values indicate a solid-like behavior while the obtained hydrogels have a complex modulus in the range of 14–39 kPa, which is suitable for hydrogels used in biomedical applications. In addition, the incorporation of Ag particles and the adsorption of Fe3+ ions were tested to evaluate the additional functionalities of the prepared hydrogels. It was found that the introduction of PDMAEMA to the hydrogels enhanced their ability to synthesize Ag particles and absorb Fe3+ ions, providing a platform for the potential preparation of hydrogels for the treatment of wounds

Cellulose-g-poly(2-(dimethylamino)ethylmethacrylate) Hydrogels: Synthesis, Characterization, Antibacterial Testing and Polymer Electrolyte Application

Hydrogels have been investigated due to their unique properties. These include high water content and biocompatibility. Here, hydrogels with different ratios of poly(2-(dimethylamino)ethylmethacrylate) (PDMAEMA) were grafted onto cellulose (Cel-g-PDMAEMA) by the free radical polymerization method and gamma-ray radiation was applied in order to increase crosslinking and content of PDMAEMA. Gamma irradiation enabled an increase of PDMAEMA content in hydrogels in case of higher ratio of 2-(dimethylamino)ethyl methacrylate in the initial reaction mixture. The swelling of synthesized hydrogels was monitored in dependence of pH (3, 5.5 and 10) during up to 60 days. The swelling increased from 270% to 900%. Testing of antimicrobial activity of selected hydrogel films showed weak inhibitory activity against Escherichia coli, Pseudomonas aeruginosa, and Bacillus subtilis. The results obtained by the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) indicate that chemically synthesized hydrogels have good characteristics for the supercapacitor application

Investigation of the Conditions for the Synthesis of Poly(3,4-ethylenedioxythiophene) ATRP Macroinitiator

One of the most widely used conductive polymers in the growing conductive polymer industry is poly(3,4-ethylenedioxythiophene) (PEDOT), whose main advantages are good thermal and chemical stability, a conjugated backbone, and ease of functionalization. The main drawback of PEDOT for use as wearable electronics is the lack of stretchable and self-healing properties. This can be overcome by grafting PEDOT with flexible side branches. As pure PEDOT is highly stable and grafting would not be possible, a new bromine-functionalized thiophene derivative, 2-(tiophen-3-yl) ethyl 2-bromo-2-methylpropanoate (ThBr), was synthesized and copolymerized with EDOT for the synthesis of a poly(EDOT-co-ThBr) ATRP macroinitiator. After the synthesis of the macroinitiator, flexible polymers could be introduced as side branches by atom-transfer radical polymerization (ATRP) to modify mechanical properties. Before this last synthesis step, the conditions for the synthesis of the ATRP macroinitiator should be investigated, as only functionalized units can function as grafting sites. In this study, nine new copolymers with different monomer ratios were synthesized to investigate the reactivity of each monomer. The ratios used in the different syntheses were ThBr:EDOT = 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, 0.8:1, 0.6:1, 0.4:1, and 0.2:1. In order to determine the effect of reaction time on the final properties of the polymer, macroinitiator synthesis at a 1:1 ratio was carried out at different time periods: 8 h, 16 h, 24 h, and 48 h. The obtained products were characterized by different techniques, and it was found that polymerizations longer than 24 h yielded practically insoluble macroinitiators, thus limiting its further application. Reactivity ratios of both monomers were found to be similar and close to 1, making the copolymerization reaction symmetrical and the obtained macroinitiators almost random copolymers

Ružička days : International conference 18th Ružička Days “Today Science – Tomorrow Industry” : Proceedings

Proceedings contains articles presented at Conference divided into sections: chemical analysis and synthesis, chemical and biochemical engineering, food technology and biotechnology, medical chemistry and pharmacy, environmental protection and meeting of young chemists