Materials Science and Applied Chemistry

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Authors: Jevgenijs Jaunslavietis, Galia Shulga, Jurijs Ozolins, Brigita Neiberte, Anrijs Verovkins, Sanita Vitolina, Talrits Betkers
Abstract: In this study, hydrophobic-hydrophilic characteristics, including contact angle and moisture sorption of a modified wood filler and the wood-polymer composites (WPC) containing it was investigated. The wood filler obtained from aspen sawdust was modified by mild acid hydrolysis and by ammoxidation. Contact angles of the wood particles and the WPC samples were measured with Kruss K100M using the Washburn and Wilhelmy methods, respectively. Work of adhesion was calculated using Young-Dupre equation. Surface free energy as well as its dispersive and polar parts were found using Owens-Wendt-Rabel-Kaelble approach. It was found that the hydrolysis and the ammoxidation led to decrease of the hemicelluloses content in the lignocellulosic matrix. Beside this, the ammoxidation favours the formation of amide bonds in the ammoxidised particles. These changes enhanced the contact angles, decreased the work of adhesion, and decreased surface free energy of the WPC samples filled with the modified particles in comparison with the WPC sample that contained the unmodified ones. The treatment of the wood particles decreased the wettability towards water, but increased it towards recycled polypropylene. This positively effects mechanical properties of the samples.
Authors: Laimonis Malers, Renate Kurme
Abstract: Composite materials based on scrap tires and polyurethane type polymer binder with defined reactivity were investigated to underline the influence of water (varying air humidity, special treatment of rubber crumb with water) during the production on selected mechanical properties. Compressive stress and modulus of elasticity E at 10% deformation, Shore C hardness and apparent density were investigated. Strong correlation between the above-mentioned mechanical properties of the composite materials and the crosslinking conditions of the polymer (presence of water during the production of composite materials) were observed. It has been confirmed previously that the crosslinking degree of polyurethane type binder separately and, therefore, at the same time mechanical properties of binder was strongly dependent on water as a significant factor during the hardening of the polymer.
Authors: Anna Trubača-Boginska, Rūta Ādiņa, Guntars Vaivars, Janis Švirksts
Abstract: The acidification and intercalation of illite containing clays were studied for potential use as fillers for sulphonated poly (ether ether ketone) (SPEEK) composite membrane preparation and future proton exchange membrane fuel cells application. The acidification and dimethyl sulfoxide (DMSO) intercalation of illite clays have been studied by powder X-ray diffractometry, X-ray fluorescence spectrometry, and thermogravimetric analysis. SPEEK composite membranes were made with 1, 3 and 5% purified, acidified, DMSO intercalated clay fillers. SPEEK/clay composite membranes were characterized by proton conductivity, water uptake, and mechanical strength.
Authors: Walid Fermas, Remo Merijs Meri, Mustapha Kaci, Janis Zicans
Abstract: This paper deals with the characterization of the physico-mechanical properties of starch-grafted-polyethylene (Starch-g-PE)/unmodified Algerian halloysite nanotubes (HNT) nanocomposites prepared by melt compounding. The nanoclay was incorporated at various filler contents, i.e., 1.5, 3 and 5 wt%. Rheological and tensile properties of the nanocomposites were evaluated by different techniques and the results obtained are compared with those of virgin Starch-g-PE matrix. The study shows a decrease in melt flow index (MFI) values upon increasing the HNT content, which indicates a restriction in the polymer chains mobility due to the confinement effect of HNT. Further, a tensile strength is also improved.
Authors: Laima Vevere, Sarmīte Janceva, Alexandr Arshanitsa, Galina Telysheva
Abstract: A condensed tannin enriched extract from Grey alder bark was completely liquefied using the batch solvent free oxypropylation process in a high pressure reactor. The obtained polyols were characterized in terms of their composition, functionality, viscosity, and reactivity towards isocyanate. The main constituents of the obtained polyols included high functional polyphenolics based copolymers and low functional constituents – carbohydrate derived products based copolymers and polypropylene glycols. This structure is important for governing the balance between the rigidity and elasticity of polyurethane networks. The polyols were successfully tested in rigid polyurethane foam compositions. Closed cell foams with a density of about 45 kg·m-3 were produced.
Authors: Guna Vugule, Ingars Reinholds, Janis Zicans, Remo Merijs Meri, Kaspars Ozols
Abstract: In the present study, an approach for the graft polymerization of multi-walled carbon nanotubes (MWCNTs) with 3,4-ethylenedioxythiophene (EDOT) has been evaluated. The surface of the MWCNTs was activated with thiophene groups through the amide linker followed by oxidative polymerization of EDOT monomer resulted in the development of PEDOT-g-MWCNTs. The methods of thermal gravimetric analysis (TGA), X-ray fluorescence, and Raman spectroscopy were used for characterization of functionalization efficiency. The TGA data indicated of 21% functionalization attached to MWCNTs. X-ray fluorescence confirmed the presence of Cl, and S atoms in functionalized fillers. The study of Raman spectra confirmed the presence of PEDOT groups attributed to most characteristic signal at 1400-1500 cm-1 region. The electrical conductivity for both pristine MWCNT and PEDOT-g-MWCNT powder materials was compared.
Authors: Aleksandra Jurkane, Sergejs Gaidukov
Abstract: Novel and highly effective polyethylene oxide (PEO) based composite electrolytes were prepared by combining the graphene nanoplatelets (GR) and multiwall carbon nanotubes (MWCNT) for the application as solid polymer electrolyte. MWCNT and GR were used as reinforcing filler and as electrical conductivity enhancement agent. Dispersions in N,N-dimethylformamide (DMF) of MWCNT and GR within the PEO matrix were prepared. DMF are featured by high electron-pair donor number and low hydrogen-bonding parameters, therefore DMF is considered a standard for liquid-phase exfoliation of MWCNT and GR. In our study, the MWCNT and GR solutions were tip sonicated using an ultrasonic processor, operated at 80% amplitude. A pulse-mode (cycle of 0.5 s) sonication was used because of the system relaxation role for the off phase, allowing a higher cavitation intensity and lower heat generation to be reached. Subsequent heat pressing was applied to obtain thin solid PEO composite electrolytes. Analyses of the experimental and theoretical density of prepared solid PEO composite electrolytes are calculated and discussed. GR and MWCNT functionalization effect on void content of polymer composites is evaluated. FTIR analysis was carried out to further investigate the effect of fillers content. The SEM results showed that surface of electrolyte film became rougher after the addition of MWCNT and GR. It is concluded, that the higher is filler fraction, the lower is void content and greater is composite density.
Authors: Ritvars Berzins, Remo Merijs Meri, Janis Zicans
Abstract: Thiokol is one of the oldest and the most expensive prepolymers which also is used for insulating glass application. One of potential alternatives is modified polyether polyol, but it has poor ultraviolet light stability. This work is dedicated to synthesized alternative prepolymers and development of two component systems for insulating glass sealant application. By subjecting these particular systems to temperature, water and ultraviolet light resistance tests, it is concluded that in respect to water and UV-light resistance the systems of modified prepolymers are even better than the system with thiokol prepolymer.
Authors: Kaspars Veldre, Elīna Sala, Elīna Āboltiņa, Guntars Vaivars
Abstract: Polymer electrolyte membranes (PEM) have a potential to become power sources in automotive industry and other household applications. PEM such as sulfonated polyetheretherketone (SPEEK) have acceptable operating temperature range but proton conductivity is dependent on amount of sulfonic groups attached to the polymer backbone (degree of sulfonation). At the same time, the sulfonic groups cause sorption of water from surrounding vapour or liquid. This factor may lead to mechanical failure if membrane absorbs too much water. Modification of PEM by adding ionic liquids (IL) may provide good proton conductivity but presence of water could also be critical factor of membrane stability as in high humidity conditions IL are washed out of membrane and replaced by water molecules. PEM with IL inclusions could be potentially used at temperatures close to water boiling point and higher as IL used in this research are thermally stable in temperatures up to 200°C.
Authors: Janis Kajaks, Karlis Kalnins, Juris Matvejs
Abstract: Article summarizes investigation results of rheological and thermal stability properties of industrially prepared wood plastic composites, based on virgin polypropylene and birch wood plywood production residues-plywood sanding dust (PSD). WPCs PP+40 wt. % PSD contain different modifiers, such as lubricant Struktol TWP (blend of an aliphatic carboxylic acid salts and mono and diamides), sterically hindered phenolic antioxidant 1010, thermal stabilizer 168 (hydrolytically stable phosphite), UV stabilizer 770-low molecular weight hindered amine light stabilizer (HALS) and pigments based on LDPE. According to our studies, we could conclude that rheological properties studied by capillary rheometer method, strongly depends on WPCs composition. MFI values fluctuate in limits from 0.212 up to 0.724 g/10min. that is changes 3.4 times. Thermal and antioxidant stabilizers promote increase of thermal stability of WPCs noted by TGA. Curves of fluidity indicates character of typical pseudo-plastic liquids for which viscosity not only depends on temperature and shear stress and deformation rate, but also decrease with increase of shear rate. That confirms fluidity index n values which are smaller than 1.

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