Domagoj Vrsaljko

Global parameter of ultrasound exploitation (GPUE) in the reactors for wastewater treatment by sono-Fenton oxidation

Modeling of the sonochemical reactors presents a great challenge due to issues related to the experimental investigation and description of the primary effects of the ultrasound. The main idea proposed in this work was to establish an algorithm consisting of the viable laboratory analyses and basic elements of chemical reaction engineering. In this paper, a novel modeling approach is presented. Proposed approach is characterized by the following; ultrasound was investigated as an auxiliary source of energy and the kinetic constants determined for the basic oxidation reactions, i.e. Fenton type oxidation were treated as independent of the ultrasound. Sonochemical effectiveness factor is expressed as a global parameter of the ultrasound exploitation (GPUE) that was introduced in the kinetic model as the e(US) factor. Factor e(US) is modeled as a function of employed frequency, actual power of the transducer, portion of the cavitationally active zone, i.e. dimensionless active volume and the average temperature in the reactor. Lumped system has been assumed. In order to obtain all the necessary data, the experimental study included different sets of experiments. The kinetics of the sonochemical processes, e.g. US/Fe(2+)/H(2)O(2), US/Fe(2+)/S(2)O(8)(2-), US/Fe(2+)/HSO(5)(-) was investigated in the term of mineralization of model wastewaters containing different types of organic pollutants. The Weissler dosimetry and peroxodisulfate decomposition upon sonication, were used to facilitate the determination of e(US). They follow zero order kinetics, thus can be used as a model reaction to reflect all the primary effects of ultrasound and to establish the empirical correlation for e(US) calculation. Finally, GPUE has been introduced in the adequate kinetic models and the overall model was validated.

Effect of calcium carbonate particle size and surface pretreatment on polyurethane composite Part I: interface and mechanical properties

Abstract In the present paper, the changes at interface between calcium carbonate (CaCO3) and polyurethane (PU) matrix in correlation to the mechanical and morphological properties were investigated. The effect of the untreated CaCO3 microfillers versus nanofillers and/or selected silane pretreatment of nanofiller surface were followed. Correlation between the calculated adhesion parameters i.e. interfacial free energy, thermodynamic reversible work of adhesion and coefficient of wetting, based on the measured surface free energies of pure components using the contact angle method, and composite properties was made. The lower surface free energy of the micro CaCO3 filler than the surface energy of the unmodified and silane modified nanofillers resulted in lower work of adhesion for PU/micro CaCO3 than for the PU/nano CaCO3 composites. These results implied weaker interactions in PU/micro CaCO3 than in the PU/nano CaCO3 composites followed by the lower tensile strength and failure at the interface.

Hybrid sol–gel thin films doped with a pH indicator: effect of organic modification on optical pH response and film surface hydrophilicity

Optical sensors for application in innovative wearable sensing systems such as textile-integrated systems and wireless sensor platforms rely on the development of low-cost multifunctional materials compatible with standard fabrication technologies. We are developing optically responsive pH sensitive sol–gel coatings for integration with a mobile wireless smart tag sensing system. For this application, we have fabricated a range of thin pH sensitive films using bromocresol green (BCG) indicator immobilised in inorganic–organic silica hybrid matrices prepared by a sol–gel method and deposited by spin-coating onto glass substrates. The surface hydrophilicity of the films were varied by using the inorganic sol–gel precursor tetraethoxysilane together with either methyltriethoxysilane, ethyltriethoxysilane, phenyltrimethoxysilane or glycidoxypropyltrimethoxysilane as organically modified sol–gel precursors, co-polymerised in different ratios. Spectral characterisation of the films was performed using visible absorption spectroscopy. The shift in absorption maxima and other spectral changes of the different matrices have been identified, and the apparent pKapp values of the immobilised BCG pH indicator determined. The surface wettability properties of the films have been studied by measuring the contact angle of water, formamide and diiodomethane which has allowed the estimation of the surface free energy (SFE) using three different models: Owens–Wendt, Wu and van Oss-Chaudhury-Good. It is shown that the SFE of the hybrid films is directly related to the type and the degree of organic modification, which in turn has a significant effect on the pH response-time of these sensing films.

Silane pre-treatment of calcium carbonate nanofillers for polyurethane composites

Abstract In this work we have investigated the effects of CaCO3 nanofiller pretreatment on the properties of polyurethane (PU) composites prepared by a mixing procedure. The aim was to enhance interactions at the matrix/filler interface and to improve the distribution of the filler in the polyurethane matrix. CaCO3 nanofiller was treated with two different functional trialkoxysilanes, viz. γ-aminopropyltriethoxysilane (AMPTES) and γ-glycidoxypropyltrimethoxysilane (GPTMS). Fourier transform IR spectroscopy of the pre-treated CaCO3 surface indicates that AMPTES formed a high-molecular-weight ladder-type structure on the CaCO3 surface, while GPTMS was adsorbed in the form of a lower-molecular-weight oligomeric structure. Increased ultimate tensile strength and elongation were obtained for PU + CaCO3 nanocomposites with silane pre-treated filler. This can be explained as the consequence of better stress transfer through the composite, observed on scanning electron micrographs, due to an improved adhesion between PU matrix and silane-treated fillers. The reinforcement effect is more pronounced for PU composites with aminosilane-treated CaCO3 filler in comparison to filler treated with glycidoxysilane.

Effect of preparation on morphology-properties relationships in SAN/EPDM/PCC composites

Mechanical and morphological properties of composites containing styrene—acrylonitrile (SAN) copolymer, ethylene— propylene—diene (EPDM) polymer, and different types of precipitated calcium carbonate (PCC) were investigated and their properties were analyzed in regard to PCC surface properties and the way of sample preparation (with or without use of a masterbatch (MB)). Contact angles of test liquids on PCC samples were measured in order to determine surface free energies of filler and to predict strength of filler—polymer interactions. Filler—polymer interactions play a significant role in determining preferential localization of the filler in the composite. The tensile and impact strength results of the composites without the MB show much higher values than composites prepared with the MB. Significant decrease of tensile strength is observed for the samples prepared with the MB due to change in morphology, which is elongated dispersed EPDM particles in SAN matrix, compared to the samples prepared without the MB that have droplet morphology.

Effect of calcium carbonate particle size and surface pretreatment on polyurethane composite Part 2 – phase behaviour

Abstract Effects of untreated calcium carbonate (CaCO3) of different sizes, and silane pretreated CaCO3 fillers on properties of polyurethane (PU) composites (PU/CaCO3) were investigated. Small angle X-ray scattering research of phase structure and morphology has shown significantly stronger influence of the CaCO3 nanofillers than the CaCO3 microfiller on a crystallisation process (domain/grain restructurisation) of the PU matrix. This influence also increased with higher filler loading. Wide angle X-ray diffractograms investigations proved that the presence of nanofiller in the PU composites affects the nucleation and crystal growth of polyester segment domains. The conclusion is that the nanoparticles of CaCO3 filler are situated preferably in the polyurethane soft segment domains and decrease the crystallite size of polyester domains.

Materijali za izradu mikroreaktora

Mikroreaktori su reaktorski sustavi izvedeni u mikroskopskom mjerilu, a zbog svoje velike međufazne povrsine imaju prednosti u odnosu na klasicne – makroreaktorske sustave. Odabir materijala za izradu mikroreaktora ovisi o vrsti reakcije koja se provodi u sustavu, kompatibilnosti otapala i materijala, mehanickim zahtjevima te o cijeni i dostupnosti na tržistu. Materijali koji se najcesce upotrebljavaju za izradu su razlicite vrste stakla, keramike, metali te polimerni materijali. Ovisno o materijalu odabiru se postupci izrade, a najcesci postupci su jetkanje, litografija, pjeskarenje, strojna obrada, injekcijsko presanje te aditivni postupci izrade. Cilj ovog rada je predstaviti najcesce materijale i postupke izrade mikroreaktora.

Pre-treatment of CaCO3 nanofiller by irradiation in the presence of vinyl monomers for the preparation of poly(vinyl acetate) composites

Abstract Poly(vinyl acetate) (PVAc) composites were prepared by different approaches, namely (i) by mechanical mixing of untreated CaCO3 and PVAc, (ii) by mechanical mixing of CaCO3 pre-treated by irradiation polymerization in the presence of vinyl acetate, and (iii) by in situ emulsion polymerization of VAc in the presence of untreated CaCO3 nanofiller. The effects of nanoparticle pre-treatment and different approaches of preparation were correlated with changes in morphology and mechanical properties of PVAc composites using scanning electron microscopy and tensile tests. Untreated CaCO3 nanoparticles in the composite prepared by mechanical mixing provided strong interactions with the PVAc matrix. On the other hand, CaCO3 pre-treated nanoparticles decreased the interfacial interactions. For composites prepared by in situ polymerization a better dispersion of encapsulated nanoparticles was achieved and, as a result, a significant improvement of composite strength was observed. Interfacial interactions in nanocomposites can be changed by filler pre-treatment or by a suitable way of nanocomposite preparation.