14 research outputs found
Hydrophobic silica nanoparticles as reinforcing filler for poly (lactic acid) polymer matrix
Properties of poly (lactic acid) (PLA) and its nanocomposites, with silica
nanoparticles (SiO2), as filler were investigated. Neat PLA films and PLA
films with different percentage of hydrophobic fumed silica nanoparticles
(0.2, 0.5, 1, 2, 3 and 5 wt. %) were prepared by solution casting method.
Several tools were used to characterize the influence of different silica
content on crystalline behavior, and thermal, mechanical and barrier
properties of PLA/SiO2 nanocomposites. Results from scanning electron
microscope (SEM) showed that the nanocomposite preparation and selection of
specific hydrophobic spherical nano filler provide a good dispersion of the
silica nanoparticles in the PLA matrix. Addition of silica nanoparticles
improved mechanical properties, the most significant improvement being
observed for lowest silica content (0.2wt.%). Barrier properties were
improved for all measured gases at all loadings of silica nanoparticles. The
degree of crystallinity for PLA slightly increased by adding 0.2 and 0.5 wt.
% of nano filler
Suppressing the use of critical raw materials in joining of AISI 304 stainless steel using activated tungsten inert gas welding
The aim of this study was to study the influence of TiO2 coating for its efficacy during the activated-tungsten inert gas (TIG) welding and to suppress the use of consumables that are rich in critical raw materials. Post-welding penetration depth, particle size distribution, microstructure, and microhardness of welded samples were assessed. Based on these results, it was found that there is no direct correlation between the weld metal surface area and the coating. The particle size in the coating, although, seemed to have played an important role, e.g., nanoparticles resulted in an increased penetration depth and depth/width (D/W) ratio as opposed to the submicron-sized particles. The most optimal welding condition resulted when a mixture of submicron-sized and nanometric-sized particles were used. It was demonstrated by the Zeta analyser results that the micron particles rub the nanoparticles due to mechanical friction resulting in smaller oxide particle formation in the coating. Finally, the presence of Marangoni convection in TIG and reversed Marangoni convection in the activated TIG (A-TIG) process were proven by means of the microstructure analysis and measurement, which were found to be positively correlated
Microstructure, Microhardness, and Wear Properties of Cobalt Alloy Electrodes Coated with TiO2 Nanoparticles
In this paper, the influence of TiO2 nanoparticle coating on cobalt-based electrodes was studied. Different coating treatment times were applied, and the results were compared to the hard-faced layer obtained with unmodified electrodes. The hard facing was done in three layers, the first being a Ni-based interlayer, followed by two layers of corrosion and wear-resistant Co-based Stellite 6 alloy. Pin-on-disc wear testing was applied, along with the metallographic study and hardness measurements of the hard-faced layers. Furthermore, energy-dispersive X-ray spectroscopy (EDS) analysis was conducted. It was found that the microstructural properties, as well as microhardness profiles, are modified in hard-faced layers obtained with modified electrodes. Interdendritic distances are altered, as are the dendrite growth directions. Titanium oxides are formed, which, along with the present complex carbides, increase the wear resistance of the hard-faced layers compared to layers obtained with untreated electrodes
Proučavanje mogućnosti mikrotalasne polimerizacije monomera na osnovu obnovljivih sirovina
Polylactide belongs to the biodegradable and biocompatible polymers, and degrade
to harmless component, lactic acid, which allows their use in various areas. The
development of new methods for the synthesis of polylactide can further extend the
application of this polymer and makes its use more economical. The use of microwaves
in the synthesis of the polymer can reduce the polymerization time of only 10 to 30
minutes and save a large amount of energy. In this paper, polylactide is synthesized in a
microwave reactor, using a frequency of 2,45 GHz and a power of 150 W. FITR
analysis confirmed the structure of the resulting polylactide and the thermal properties
were studied using differential scanning calorimetry.Polilaktid spada u grupu biorazgradivih i biokompatibilnih polimera i može se
razložiti na neškodljivu komponentu, mlečnu kiselinu, što omogućava njegovu primenu u
najrazličitijim oblastima. Razvoj novih metoda sinteze polilaktida može proširiti područje
primene ovog polimera i učiniti njegovu upotrebu ekonomičnijom. Upotreba mikrotalasa
u sintezi polimera može skratiti vreme polimerizacije na svega 10 do 30 minuta štedeći
veliku količinu energiju. U ovom radu polilaktid je sintetisan u mikrotalasnom reaktoru,
koristeći frekvenciju od 2.45 GHz i snagu od 150 W. FTIC analiza je potvrdila strukturu
dobijenog polilaktida, a toplotna svojstva su proučavana metodom diferencijalne
skenirajuće kalorimetrije.Vrednost temperatura prelaska u staklasto stanje i temperatura
kristalizacije dobijenog polimera zavise od molskog odnosa monomera (L-laktida) i
katalizatora (kalaj-oktoata)
Ispitivanje toplotnih svojstava nanokompozitnih polimernih materijala na osnovu biljnih sirovina
Environmental friendliness and functionality have made biopolymers one of the
most interesting materials today. In order to broadening their application, there is need
for improving their poor mechanical and thermal properties by using reinforce effect of
inorganic nanoparticles. In this paper, thermal properties of nanocomposites based on
poly(lactide) (PLA) and silicon dioxide were investigated using the differential scanning
calorimetry (DSC). The obtained results showed that the addition of nanoparticles
causes a change in the values of melting and crystallization temperatures of
nanocomposites. Significant influence on the glass transition temperature was not
observed.Ekološka prihvatljivost i funkcionalnost biopolimera učinila ih je jednima od
najtraženijih materijala današnjice. Njihovu veću primenu ograničavaju slaba mehanička i
toplotna svojstva. Kako bi se poboljšala primenska svojstva biopolimera oni se kombinuju
sa neorganskim česticama gradeći nanokompozite. U ovom radu ispitivana su toplotna
svojstva nanokompozita na osnovu poli(laktida) (PLA) i silicijum(IV)oksida. Dobijeni
rezultati su pokazali da dodatak nanočestica dovodi do promene temperature topljenja,
porasta temperature kristalizacije, pri čemu nije uočen značajan uticaj nanočestica na
temperaturu prelaska u staklasto stanje nanokompozita poli(laktida)
The charge percolation mechanism and simulation of Ziegler–Natta polymerizations. Part VII. Effects of the distribution of chromium active centers on silica on the polymerization of ethylene
The charge percolation mechanism (CPM) of olefin polymerization in the presence of transition metal compounds has been applied to explain the polymerization of ethylene by silica supported chromium oxide. In the previous work of this series, the fundamental issues and mechanism of this polymerization were presented. In this work the compatibility of the CPM with the empirical findings is confirmed. The CPM has been applied to explain: the appearanceof an induction period; the deactivation of active centers and the formation of oligomers; the effects of chromium concentration on the silica surface, the silica surface discontinuity and the pore size of silica on polymerization and the formation of the structure of polyethylene. A mathematical model has been derived to explain the effects of the CrOx/SiO2 ratio on the productivity of Phillips catalysts in the polymerization of ethylene. The empirical findings have also been confirmed by computer simulations