10 research outputs found
Expanding of polylactide
Polilaktid (PLA) je termoplastiÄni biorazgradivi polimer, pri Äemu se proizvodnja PLA temelji na prirodnim izvorima kao Å”to su kukuruz ili Å”eÄerna trska. Zbog dobrih mehaniÄkih i drugih svojstava (gustoÄa, prozirnost, barijerna svojstva) PLA je naÅ”ao primjenu u industriji pakiranja (boce, kruta plastika, folije). Osim toga, znatan broj radova posveÄen je istraživanju ekspandiranog PLA kao alternative za zamjenu ekspandiranog poli(stirena) (PS-E). Ekspandiranje PLA se najÄeÅ”Äe provodi pomoÄu fizikalnih ekspandirajuÄih agensa kao Å”to su CO2, N2 ili iābutan. Upotreba navedenih fizikalnih agensa za ekspandiranje PLA ograniÄena je zbog loÅ”ih reoloÅ”kih svojstava taline PLA. U ovom radu kao ekspandirajuÄi agens koriÅ”tene su mikrosfere komercijalnog Expancela. Granule PLA usitnjene su pomoÄu mlina, a zatim su prireÄene njihove smjese sa 3, 5 i 7 mas % Expancela te dodatno homogenizrane uz pomoÄ tresilice. Homogena smjesa preÅ”ana je u hidrauliÄkoj preÅ”i na temperaturi od 190 Ā°C u vremenu 8 minuta. Nakon optimizacije uvjeta preÅ”anja, preÅ”anje je provoÄeno na 180 Ā°C u vremenu 6 minuta. Nadalje, optimiranjem temperature i vremena preÅ”anja smanjena je degradacija uzoraka prilikom preÅ”anja. 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 Ā°C for 8 minutes. After optimization of the molding conditions, molding was conducted at 180 Ā°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 moguÄnoÅ”Äu upijanja velike koliÄine vode. Celuloza je vrlo rasprostranjen biokompatibilan i biorazgradljiv polisaharid s hidrofilnim OH skupinama u strukturi koje omoguÄuju raznovrsne modifikacije. UvoÄenjem novih funkcijskih skupina na osnovni polisaharidni lanac moguÄe je mijenjati svojstva hidrogela kako bi se pripremili hidrogelovi željenih svojstava: antibakterijska svojstva, osjetljivost na vanjske podražaje i sliÄno. 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 Ā°C te N,N-metilen-bis-akrilamid (MBA) kao umreživaÄem. U pripravljene hidrogelove unesene su i nanoÄestice srebra, dobro poznate po antibakterijskim svojstvima. Relativni udio PDMAEMA u hidrogelovima odreÄen je pomoÄu infracrvene spektroskopije. Morfologija osuÅ”enih uzorka i prisutnost srebra odreÄene su pretražnom elektronskom mikroskopijom koja je pokazala da je dodatkom PDMAEMA i suÅ”enjem hidrogelova ekstrakcijom zamrzavanjem dobivena vrlo porozna struktura. Na taj naÄin pospjeÅ”eno je i vezanje nanoÄestica srebra na hidrogelove. Uzorci kopolimera prireÄeni suÅ”enjem u suÅ”ioniku pokazuju veÄi stupanj bubrenja u deioniziranoj vodi (~ 109 %) u odnosu na Äistu celulozu (80 %). Isti materijali suÅ”eni ekstrakcijom zamrzavanjem i tako oblikovani u porozne hidrogelove pokazuju znatno veÄe vrijednosti stupnja bubrenja (256 % i 505 %) naspram Äiste celuloze (80 %).
Ovo djelo je dano na koriÅ”tenje pod licencom Creative Commons Imenovanje 4.0 meÄunarodna.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 Ā°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 poveÄao. PoveÄana toplinska vodljivost fluida uslijed dodatka nanoÄestica osnovno je svojstvo koje je potaknulo intenzivno istraživanje nanofluida. S obzirom na to da u industriji uvijek postoji težnja poboljÅ”anju uÄinkovitosti proizvodnih procesa, pa tako i procesa hlaÄenja procesnih struja, poveÄana toplinska vodljivost rashladnih fluida otvara moguÄnosti za postizanje navedenog cilja. U ovom radu dan je pregled metoda priprave nanofluida te opis parametara koji utjeÄu na njihovu toplinsku vodljivost. Dan je i osvrt na modele kojima se opisuje toplinska vodljivost nanofluida te pregled moguÄih mehanizama koji doprinose poveÄanju njihove toplinske vodljivosti.
Ovo djelo je dano na koriÅ”tenje pod licencom Creative Commons Imenovanje 4.0 meÄunarodna.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 Äelijama i razliÄitim biosenzorima u nosivoj elektronici. Kontroliranom radikalskom polimerizacijom prijenosom atoma (ATRP) moguÄe je cijepljenjem boÄnih grana modificirati svojstava PEDOT-a za specifiÄnu primjenu.
U ovom radu sintetizirani su ATRP makroinicijatori na osnovi PEDOT-a, funkcionalizirani reaktivnim bromom, koji omoguÄuje cijepljenje razliÄitih polimera kao boÄnih grana. Karakterizacija dobivenih uzoraka provedena je pomoÄu 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 termoplastiÄni biorazgradivi polimer, pri Äemu se proizvodnja PLA temelji na prirodnim izvorima kao Å”to su kukuruz ili Å”eÄerna trska. Zbog dobrih mehaniÄkih i drugih svojstava (gustoÄa, prozirnost, barijerna svojstva) PLA je naÅ”ao primjenu u industriji pakiranja (boce, kruta plastika, folije). Osim toga, znatan broj radova posveÄen je istraživanju ekspandiranog PLA kao alternative za zamjenu ekspandiranog poli(stirena) (PS-E). Ekspandiranje PLA se najÄeÅ”Äe provodi pomoÄu fizikalnih ekspandirajuÄih agensa kao Å”to su CO2, N2 ili iābutan. Upotreba navedenih fizikalnih agensa za ekspandiranje PLA ograniÄena je zbog loÅ”ih reoloÅ”kih svojstava taline PLA. U ovom radu kao ekspandirajuÄi agens koriÅ”tene su mikrosfere komercijalnog Expancela. Granule PLA usitnjene su pomoÄu mlina, a zatim su prireÄene njihove smjese sa 3, 5 i 7 mas % Expancela te dodatno homogenizrane uz pomoÄ tresilice. Homogena smjesa preÅ”ana je u hidrauliÄkoj preÅ”i na temperaturi od 190 Ā°C u vremenu 8 minuta. Nakon optimizacije uvjeta preÅ”anja, preÅ”anje je provoÄeno na 180 Ā°C u vremenu 6 minuta. Nadalje, optimiranjem temperature i vremena preÅ”anja smanjena je degradacija uzoraka prilikom preÅ”anja. 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 Ā°C for 8 minutes. After optimization of the molding conditions, molding was conducted at 180 Ā°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 Ī“ values indicate a solid-like behavior while the obtained hydrogels have a complex modulus in the range of 14ā39 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
RužiÄka days : International conference 18th RužiÄka Days āToday Science ā Tomorrow Industryā : 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