Influence of Multiwalled Carbon Nanotube Modification on Polyurethane Properties: I. Morphology and Thermal Properties

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). Optička polarizacijska mikroskopija pokazala je da dodatak oba punila razrušava krupnu sferolitnu morfologiju poliuretana. Utvrđeno je da je modificirani MWCNT-COOH bolje dispergiran u masi uzorka nego čisti MWCNT. Rezultati DSC-a pokazali su da u neizotermnim uvjetima do određenog udjela dodatak obje vrste MWCNT-a ubrzava kristalizaciju mekog segmenta poliuretana, pri čemu je ubrzanje kristalizacije izraženije u sustavima s punilom MWCNT. Vrijednosti entalpija kristalizacije pokazuju da punilo MWCNT, unatoč lošijoj raspodijeljenosti u masi uzorka, znatnije ometa kristalizaciju mekog segmenta PU-a nego MWCNT-COOH. U uvjetima izotermne kristalizacije punilo MWCNT također znatnije ubrzava kristalizaciju poliuretana nego MWCNT-COOH

Influence of Multiwalled Carbon Nanotube Modification on Polyurethane Properties: II. Mechanical Properties, Electrical Conductivity and Thermal Stability

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

Properties of Waste Polyamide Powder and Titanium Dioxide Nanocomposites

Selektivno lasersko sinteriranje (SLS) jedan je od važnijih postupaka 3D ispisa koji se u današnje vrijeme sve više primjenjuju za dobivanje različitih modela. Najvažniji polimerni materijali koji se upotrebljavaju u tom procesu su poliamidi. Značajan nedostatak tog procesa je velika količina otpadnog polimernog praha. Stoga je cilj ovoga rada bio istražiti utjecaj dodatka nanočestica titanijeva dioksida (TiO2) na toplinska i mehanička svojstva otpadnog poliamidnog praha (PA 2200). U ovom radu pripremljeni su nanokompoziti PA/TiO2 u rasponu masenog udjela punila 1 – 5 %, postupkom zamješavanja punila u talinu polimera u gnjetilici Brabender. Aglomerati nanopunila vidljivi su na SEM mikrografiji 5 %-tnog PA/TiO2 nanokompozita. Rezultati diferencijalne pretražne kalorimetrije (DSC) ukazuju na djelovanje nanočestica TiO2 kao heterogenih nukleacijskih centara. Također, dodatak nanopunila pospješuje stvaranje stabilnijih i uređenijih kristalnih struktura poliamidne matrice. Termogravimetrijskom analizom (TGA) dokazano je da dodatak TiO2 nanopunila povećava temperaturu početka razgradnje PA matrice, to jest poboljšava toplinsku postojanost PA matrice i neznatno povećava vrijednosti toplinske vodljivosti nanokompozita u odnosu na čistu polimernu matricu. Ispitivanjem mehaničkih svojstava uzoraka uočeno je smanjenje vrijednosti sekantnog modula te neznatne promjene naprezanja i istezanja u točki popuštanja s povećanjem udjela punila u nanokompozitu. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.The PA 2200 waste powder generated during selective laser sintering (SLS) process is an important environmental and economic problem. In order to test and modify the properties of the waste powder, nanocomposites based on polyamide matrix and TiO2 nanoparticles were prepared in this work. Agglomerates of the TiO2 nanofiller are visible on the SEM micrographs for the nanocomposite with 5 wt. % of the nanofiller (Fig. 1). The DSC analysis indicates an increase in crystallization temperature (Tc) by the addition of filler to the polymer matrix and it can be concluded that the TiO2 nanoparticles represent the nucleation centres in the PA matrix (Fig. 2, Table 1). In systems with 4 and 5 wt. % TiO2 crystallization enthalpy (ΔHc) and melting enthalpy (ΔHm) are higher than the values for the polyamide matrix (Table 1), indicating that the nanoparticles promote crystallization of the PA matrix. The results of TG analysis imply a positive effect of the TiO2 nanoparticles on the onset of thermal decomposition, which is most pronounced in the system with 3 wt. % TiO2 (Fig. 3, Table 2). As thermal degradation progresses further, the positive effect of the addition of TiO2 nanoparticles becomes less pronounced and finally becomes negative in the final stages, i.e. TiO2 nanoparticles accelerate the degradation. The thermal conductivity values (λ) are slightly higher for the nanocomposites relative to the pure PA matrix (Fig. 4) due to the formation of a more ordered structure of the polymer matrix by the addition of TiO2 and/or the formation of so-called conductive pathway. The results of the mechanical test indicate that the addition of TiO2 nanofiller decreases the values of the secant modulus (E), while the values of the yield stress (σ2>y2>y2 nanoparticles to the PA 2200 waste powder represents a useful approach for its reuse, thus improving the economic and environmental sustainability of the SLS process. The main disadvantage of the studied systems is the inconsistent mechanical properties at break. In future studies, this problem will be solved with adequate surface modification of TiO2 nanoparticles. This work is licensed under a Creative Commons Attribution 4.0 International License

Influence of Thermoplastic Polyolefins Flame Treatment on Coating Adhesion in Industrial Conditions of Robotic Dyeing

U ovom radu istražen je utjecaj obrade plamenom polipropilena (PP) i termoplastičnih poliolefina s talkom i čađom (TPO) na površinska svojstva i adheziju nanesenog premaza u uvjetima industrijskog procesa robotskog bojenja. Obrada plamenom provedena je na dvije udaljenosti plamena od površine (7,5 cm i 12,5 cm) pri konstantnom protoku zraka i metana te brzini kretanja plamenika. Toplinska postojanost netretiranih uzoraka ispitana je primjenom termogravimetrijske analize (TGA). Promjena toplinskih svojstava prije i nakon obrade plamenom praćena je primjenom diferencijalne pretražne kalorimetrije (DSC). Metodom kontaktnog kuta određena je površinska energija uzoraka prije obrade plamenom te 1 h i 24 h nakon obrade plamenom. Promjene uzrokovane obradom plamenom istražene su ATR – FTIR analizom, a morfološke promjene pretražnim elektronskim mikroskopom (SEM). Nakon nanošenja temeljnog sloja, sloja boje i sloja laka na površinu obrađenih uzoraka određena je adhezija standardnim metodama ISO 2409 i ISO 16925/D25 2018-B. Rezultati su pokazali da TPO uzorci koji sadrže punilo talk i čađu imaju bolju toplinsku postojanost u odnosu na PP. Obrada plamenom utječe na promjenu površinskih karakteristika uzoraka, povećanje slobodne površinske energije i na izgled/strukturu površine. ATR – FTIR analizom utvrđeno je postojanje polarnih skupina na površini nakon obrade plamenom. Svi obojeni uzorci prema zahtjevima normi zadovoljavaju uvjete izvrsne adhezije na međupovršini supstrat/premaz. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.In this paper, the influence of flame treatment on the surface properties of polypropylene (PP) and thermoplastic polyolefins with talc and carbon black filler (TPO), and adhesion of the applied coating in the conditions of industrial robotic dyeing process were investigated. The flame treatment was carried out at two distances from the flame (7.5 cm and 12.5 cm) at constant air and methane flows as well as speed of the burner. The thermal stability of untreated samples was investigated using thermogravimetric analysis (TGA). The change in thermal properties before and after flame treatment was investigated using differential scanning calorimetry (DSC). Changes of the samples’ surface energy were examined before flame treatment, 1 h and 24 h after flame treatment, by the contact angle method. Qualitative analysis of the surface chemical composition, before and after flame treatment, was performed by ATR – FTIR analysis, and morphological changes by scanning electron microscopy (SEM). After applying the base layer, dye and topcoat on the surface of the treated samples, the adhesion was determined by standard methods ISO 2409 and ISO 16925/D25 2018-B. The results showed that TPO containing talc and carbon black filler have better thermal stability compared to PP. Flame treatment influenced the surface characteristics of the samples, namely the increase in surface free energy and the appearance/structure of the surface. With ATR – FTIR, the existence of polar groups on the surface after flame treatment were determined. According to the standards, all dyed samples met the requirements of excellent adhesion on the substrate/coating interface. This work is licensed under a Creative Commons Attribution 4.0 International License

The Effect of Polyacrylate Emulsion Coating with Unmodified and Modified Nano-TiO₂ on Weathering Resistance of Untreated and Heat-Treated Wood

In this research, the influence of titanium dioxide (TiO2) nanoparticles and their modifications on the weathering resistance of untreated and heat-treated wood was studied. The wood samples were coated with polyacrylate waterborne emulsion coatings that contain nano-TiO2 in the amount of 0.75 wt.%. Two types of modifiers were used to modify the nano-TiO2 surface: 2,2′-azobis(2-methylpropionamide) dihydrochloride (AIBA) and 3-aminopropyltrimethoxy silane (AMPTS). Coated and uncoated wood samples were exposed to accelerated weathering by application of sunlight, water and moisture for 360 h. During the research, the dry film thickness, color, gloss and hardness of the surface of the samples were measured. The obtained results showed that the effect of the addition and surface modification of nano-TiO2 on the color and gloss stability was different on untreated and heat-treated ash wood, and that accelerated weathering causes an increase in surface hardness and a decrease in thickness of the dry coating

Environmentally Friendly UV-Protective Polyacrylate/TiO2 Nanocoatings

The development of coatings that maintain the attractive natural appearance of wood while providing ultraviolet (UV) protection is extremely important for the widespread use of wood products. In this study, the influence of different types (powder form and aqueous dispersions) of TiO2 in an amount of 1.0 wt% by monomer weight on the properties of environmentally friendly polyacrylate (PA)/TiO2 emulsions prepared by ex situ and in situ polymerization, as well as on the UV-protective properties of the coating films, was investigated. The results showed that the addition of TiO2 significantly affected the particle size distribution of PA and the viscosity of PA varied according to the preparation method. Compared with the ex situ preparation method, in situ polymerization provides better dispersibility of TiO2 nanoparticles in PA coating film, as well as a better UV protection effect and greater transparency of the coating films. Better morphology and transparency of nanocoating films were achieved by adding TiO2 nanofillers in aqueous dispersion as compared to the addition of TiO2 in powder form. An increase in the glass transition temperature during UV exposure associated with cross-linking in the polymer was less pronounced in the in situ-prepared coating films, confirming better UV protection, while the photocatalytic effect of TiO2 was more pronounced in the ex situ-prepared coating films. The results indicate that the method of preparation has a significant influence on the properties of the coating films