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U ovom radu istraživan je učinak dodatka višestjenih ugljikovih nanocjevčica (MWCNT) te MWCNT-a modificiranog skupinama COOH (MWCNT-COOH) u rasponu masenih udjela od 0 do 4 % na svojstva poliuretana. Uzorci nanokompozita pripravljani su dispergiranjem nanopunila u otopini poliuretana u acetonu te polaganim isparavanjem otapala pri sobnoj temperaturi. Utjecaj punila na mehanička svojstva kompozita ispitan je testom jednoosnog istezanja, a električna provodnost uzoraka određivana je metodom četiri kontakta. Toplinska postojanost istražena je termogravimetrijskom analizom (TGA). Obje vrste punila MWCNT povećavaju modul, ali snižavaju prekidnu čvrstoću i prekidno istezanje kompozita. Rezultati ispitivanja električne provodnosti pokazali su da se, u odnosu na čisti PU koji ima provodnost reda veličine 10–13 S cm–1, provodnost nanokompozita s masenim udjelom punila MWCNT 0,2 % znatno povećava na vrijednost reda veličine 10–6 S cm–1. Daljnjim povećanjem do masenog udjela obje vrste MWCNT-a 4 %, provodnost se dalje povećava do vrijednosti većih od 10–2 S cm–1. Taj učinak povećanja provodnosti neznatno je jače izražen u sustavima s MWCNT-COOH-om. Rezultati termogravimetrijske analize upućuju na to da se dodatkom obje vrste MWCNT-a znatno poboljšava toplinsku postojanost u istraživanom rasponu udjela nanopunila, pri čemu je ovaj učinak nešto izraženiji za sustave s punilom MWCNT. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna., In this paper, the influence of multiwalled carbon nanotubes (MWCNT) and carbon nanotubes modified with COOH groups (MWCNT-COOH) on the mechanical and electrical properties as well as on thermal stability of polyurethane (PU) were investigated. The samples of nanocomposite were prepared by dispersion of the nanofiller in a solution of polyurethane in acetone, followed by slow evaporation of the solvent at room temperature. The effect of the fillers on the mechanical properties of PU nanocomposites was examined by the uniaxial deformation test, and electrical properties of the samples were determined by the four probe method. Thermal stability was investigated by thermogravimetric analysis (TGA). The addition of both types of MWCNTs fillers increases modulus (Fig. 1), due to higher modulus of the nanofillers. Due to the better distribution in PU matrix and stronger interactions between COOH groups and carbonyl group in PU matrix, nanocomposites with MWCNT-COOH have higher modulus than nanocomposites with MWCNT filler. Most of the composites have lower strength and elongation at break than PU (Figs. 2 and 3). Smaller MWCNT-COOH aggregates and stronger interactions between this filler and the PU matrix cause less pronounced decreasing of strength at break. Compared to the pure PU, with conductivity of the order of 10–13 S cm–1, the conductivity of the nanocomposite with mass fraction of MWCNT nanofiller 0.2 % substantially increases up to the value of the order 10–6 S cm–1 (Fig. 4). A further increase up to 4 % for both types of MWCNTs, resulted in a further increase in conductivity up to values exceeding 10–2 S cm–1. Due to the better distribution in PU matrix and stronger interactions between COOH groups and carbonyl groups in PU matrix, the conductivity increase effect in systems with MWCNTs-COOH is slightly more pronounced. All investigated nanocomposites have potential applications as electric discharge materials and for electrostatic painting. The results of the thermogravimetric analysis indicate that the addition of both types of MWCNTs significantly improves the thermal stability (Figs. 6 and 7). The maximal degradation rate temperature of polyurethane increased by about 45 °C, thereby this effect is slightly more pronounced for systems with MWCNTs (Fig. 7). This work is licensed under a Creative Commons Attribution 4.0 International License.

U ovom radu istraživan je učinak dodatka višestjenih ugljikovih nanocjevčica (MWCNT) te MWCNT-a modificiranog skupinama COOH (MWCNT-COOH) u rasponu masenih udjela od 0 do 4 % na svojstva termoplastičnog poliuretana (PU). Uzorci nanokompozita pripravljani su postupkom polaganog sušenja iz smjese poliuretana i nanopunila u acetonu pri sobnoj temperaturi. Učinak dodatka nanopunila na sferolitnu morfologiju poliuretana te raspodijeljenost nanopunila u matrici PU analizirana je optičkom polarizacijskom mikroskopijom. Toplinska svojstva u neizotermnim i izotermnim uvjetima istraživana su diferencijalnom pretražnom kalorimetrijom (DSC). Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna., In this work, the influence of multiwalled carbon nanotubes (MWCNT) and carbon nanotubes modified with COOH groups (MWCNT-COOH) on the structure and properties of thermoplastic polyurethane (PU) were investigated. The samples of nanocomposite were prepared from a mixture of polyurethane and MWCNT in acetone by slow drying at room temperature. The effect of the addition of nanofillers on the spherulite structure of polyurethane and the distribution of the nanofillers in the PU matrix were analysed with optical polarization microscopy. Thermal properties in non-isothermal and isothermal conditions were investigated by differential scanning calorimetry (DSC). The results of contact angle measurement imply that modification of MWCNT surface with COOH groups changes its surface from hydrophobic to hydrophilic (Fig. 2 and Table 1). Optical polarization microscopy showed that the addition of both nanofillers disrupts the coarse spherulite morphology of the polyurethane matrix (Fig. 4 and Fig. 5). It was observed that, at the macro level, the modified MWCNT-COOH filler is better distributed in the PU matrix than is the MWCNT filler (Fig. 5). The DSC results showed that, in non-isothermal conditions, up to a certain amount, both nanofillers accelerate the crystallization of the soft segments of polyurethane. This effect is more pronounced in systems with MWCNT filler (Fig. 9). The results of the crystallization enthalpy during cooling showed that MWCNT filler, despite its worse distribution in the PU matrix, more significantly enhances crystallization of PU’s soft segment than does the MWCNT-COOH filler (Fig. 10). This conclusion can be ascribed to better compatibility between the nonpolar MWCNT filler and the nonpolar soft phase of the PU matrix, as well as to the previous scientific finding that functional groups at MWCNT surface decrease the nucleation effect of MWCNT. By analysing the melting peaks, it can be concluded that the PU systems with MWCNT compared to systems with MWCNT-COOH contain a higher proportion of less ordered crystalline soft phase (Fig. 11). In isothermal conditions, the MWCNT filler accelerates crystallization more significantly than does the MWCNT-COOH filler (Fig. 16). This work is licensed under a Creative Commons Attribution 4.0 International License.

U ovom radu ispitivan je utjecaj nanopunila silicijeva dioksida (SiO2) kao i kompatibilizatora etilen/ propilen kopolimera (EPR) te etilen/vinil-acetata (EVA) na svojstva polimerne mješavine polietilen/polipropilen (PE/PP). Morfološke promjene pripremljenih uzoraka praćene su skenirajućom elektronskom mikroskopijom (SEM) i rendgenskom difrakcijom (XRD) te su određena fizikalno-mehanička svojstva i granični indeks kisika (LOI). Uspostavom privlačnih međudjelovanja poboljšava se adhezija između faza PE i PP, što ima za posljedicu finiju dispergiranost čestica u polimernim mješavinama. Što je dispergiranost nanopunila bolja povećava se postojanost polimerne mješavine i smanjuje gorivost polimernog materijala. Iz rezultata je vidljivo da je dodatkom kompatibilizatora i punila morfologija pripremljenih polimernih mješavina finija u usporedbi s čistim mješavinama. Dodatkom punila i kompatibilizatora povećava se elastičnost, što je posebno vidljivo kod uzoraka pripremljenih dvostupanjskim procesom ekstrudiranja gdje je prvo ekstrudirano punilo s matricom PE, a zatim su u drugom stupnju dodane preostale komponente mješavine. Rezultati određivanja graničnog indeksa kisika pokazali su da sastav ispitivanih polimernih mješavina ima neznatan učinak na gorivost., During the last decade, the use of polyolephinic polymers has been growing in a wide range of fields of applicability and the most widely used polymers are polyethylene and polypropylene. They can be processed separately to produce items with certain properties as well as in the form of blends, where special combinations of properties and price are intended. As it is known, polyethylene (PE) and polypropylene (PP) are incompatible and the weak interfacial bond strength between the phases directly linked to the blend morphology and results in poor mechanical properties. The properties of many polymer blends arise from the fine-scale structural arrangements or blend morphologies obtained during processing in addition to the proportion of each polymer type present. Compounding PE/PP blends with a single compatibilizer or their combination or some other additives as nanofiller, results in multi-component composites of great interest to research as they enable simultaneous improvement in the final properties of the blend. In addition, it is well known that the extrusion process has a significant effect on the dispersion of the filler in the blends. In this work, the mutual effect of the nanofiller silicium-dioxide (SiO2) and the compatibilizers ethylene-propylene copolymer (EPR) and ethylene-vinyl acetate copolymer (EVA) on the properties of blends based on polyethylene and polypropylene were studied. The morphology of the samples prepared with nanofiller and compatibilizers is much finer in comparison to the virgin blend. Better dispersion of nanofiller will result in better stability of the polymer blend and decrease in polymer flammability. The addition of the nanofiller and compatibilizers produced an increase in the elasticity especially for the samples prepared in the two-stage extrusion process where the nanofiller was first extruded with PE matrix and then with other polymers of the blends. SEM micrographs confirm finer morphology of samples prepared with compatibilizer and filler, which is the result of improved interactions between polymer components. The morphology also showed finer dispersion when EPR was used as compatibilizer, meaning that it has more effect in the investigated blends than EVA. Further, a slight increase in the limiting oxygen index was found in the blend prepared with EVA and nanofiller, which means that this blend has higher flame resistance, and it can be concluded that the nanofiller in combination with different amounts of the components in the formulations affects flammability.

Opisana je priprava i karakterizacija polimernih nanokompozita na osnovi slojevitih dvostrukih hidroksida (LDH). Pripravljen je novi razred punila na osnovi tetrakalcijeva aluminata hidrata, modificiranog benzoatnim (LDH-B) ili undecenoatnim (LDH-U) anionima. Punila su karakterizirana metodama rendgenske difrakcije (XRD) i infracrvene spektroskopije (FTIR) i potvrđena je ugradnja organskih aniona kao modifikatora i povećanje međuslojnog razmaka u odnosu na izvorno punilo. Punila su umješavana u polistirensku (PS), poli(metil-metakrilat)nu (PMMA) ili kopolimernu (SMMA) matricu metodom dvostupanjske in-situ radikalske polimerizacije u masi. Dobiveni prozirni kompozitni filmovi PS/LDH-B, odnosno SMMA/LDH-B karakterizirani su metodama XRD i FTIR, koje uz transmisijsku elektronsku mikroskopiju upućuju na to da kod PS/LDH-B nastaju potpuno raslojeni, a kod SMMA/LDH-B interkalirani nanokompoziti. Rezultati toplinske analize ukazuju na povišenje staklišta kod PS/LDH-B te poboljšanje toplinske postojanosti kod uzoraka PS/LDH-B i SMMA/LDH-B, u usporedbi s čistim polimerima., Polymeric nanocomposites are commonly considered as systems composed of a polymeric matrix and - usually inorganic - filler. The types of nanofillers are indicated in Fig. 1. Beside wellknown layered silicate fillers, recent attention is attracted to layered double hydroxide fillers (LDH), mainly of synthetic origin. The structure of LDH is based on brucite, or magnesium hydroxide, Mg(OH)2 and is illustrated in Fig. 2. The modification of LDHs is commonly done by organic anions, to increase the original interlayer distance and to improve the organophilicity of the filler, keeping in mind their final application as fillers for, usually hydrophobic, polymer matrices. We have used the modified rehydration procedure for preparing organically modified LDH. The stoichiometric quantities of Ca33Al2O6, CaO and benzoic (B) (or undecenoic (U)) acid were mixed with water and some acetone. After long and vigorous shaking, the precipitated fillers were washed, dried and characterized. X-ray diffraction method (XRD) has shown the increase of the original interlayer distance for unmodified LDH (OH–-saturated) of 0.76 nm to the 1.6 nm in LDH-B or LDH-U fillers (Fig. 3). Infrared spectroscopy method (FTIR) has confirmed the incorporation of benzoic anion within the filler layers (Fig. 4). For the preparation of LDH-B and LDH-U composites with polystyrene (PS), poly(methyl methacrylate) (PMMA) and copolymer (SMMA) matrices, a two-step in situ bulk radical polymerization was selected (Table 1 for recipes, azobisisobutyronitrile as initiator), using conventional stirred tank reactor in the first step, and heated mold with the movable wall (Fig. 6) in the second step of polymerization. All the prepared composites with LDH-U fillers were macroscopically phase-separated, as was the PMMA/LDH-B composite. PS/LDH-B and SMMA/LDH-B samples were found to be transparent and were further examined for deduction of their structure (Fig. 5) and thermal properties. FTIR measurements showed that there is some filler present in the nanocomposites (Fig. 7). XRD measurements pointed to the disturbance of the characteristic layered structure of the filler in the obtained composites (Fig. 8). Transmission electron microscopy (TEM) images showed that the filler was not homogeneously dispersed within the matrix (Fig. 9). However, the dispersion was quite good, and a high degree of exfoliation was obtained for PS/LDH-B composites (Fig. 10); the predominantly intercalated structure was found for SMMA/LDH-B composites (Fig. 11). Thus, in both cases nanocomposites were prepared. The thermal characterization by the differential scanning calorimetry (DSC) showed the increase of glass transition point of 10 °C for PS/LDH-B nanocomposite with intermediate (w = 2.5 or 5.0 %) filler content (in comparison with neat PS), a feature that is characteristic for exfoliated nanocomposites. No such increase was obtained for SMMA/LDH-B nanocomposites. The thermal degradation in the inert nitrogen atmosphere was studied by thermal gravimetric analysis (TGA) method. The improvement of thermal stability of PS/LDH-B in comparison with neat PS was found only for the nanocomposites with intermediate (w = 2.5 or 5.0 %) filler content (Fig. 12), again proving the exfoliated structure. The half-weight loss temperature of SMMA/LDH-B nanocomposites continuously increases with the increase of filler content (Fig. 13), a feature that is characteristic for intercalated nanocomposites. In conclusion, the described methods were found satisfactory for preparing the exfoliated nanocomposites of LDH-B and PS. New organic modifiers are to be sought, if exfoliated nanocomposites of SMMA and PMMA matrices are to be prepared. Further investigation will include the deduction of mechanical properties of prepared materials.