Branka Pilic

Poly(methyl-methacrylate) nanocomposites with low silica addition

STATEMENT OF PROBLEM Poly(methyl-methacrylate) (PMMA) represents the most popular current denture material. However, its major drawbacks are insufficient ductility and strength. PURPOSE The purpose of this study was to improve the mechanical properties of PMMA in denture base application by adding small quantities of nanosilica. MATERIAL AND METHOD Silica nanoparticles were added to the liquid component of the tested materials. The standard heat polymerizing procedure was followed to obtain 6 PMMA--silicon dioxide (/SiO2) concentrations (0.023%, 0.046%, 0.091%, 0.23%, 0.46%, and 0.91% by volume). Microhardness and fracture toughness of each set of specimens was compared with the unmodified specimens. Furthermore, differential scanning calorimetry and scanning electron microscopy analyses were conducted, and the results obtained were correlated with the results of mechanical properties. RESULTS It was found that the maximum microhardness and fracture toughness values of the materials tested were obtained for the lowest nanosilica content. A nanosilica content of 0.023% resulted in an almost unchanged glass transition temperature (Tg), whereas the maximum amount of nanosilica induced a considerable increase in Tg. A higher Tg indicated the possible existence of a thicker interfacial layer caused by the chain immobility due to the presence of the particles. However, scanning electron microscopy results demonstrated extensive agglomeration at 0.91% nanosilica, which may have prevented the formation of a homogenous reinforced field. At a nanosilica content of 0.023%, no agglomeration was observed, which probably influenced a more homogenous distribution of nanoparticles as well as uniform reinforcing fields. CONCLUSIONS Low nanoparticle content yields superior mechanical properties along with the lower cost of nanocomposite synthesis.

Modification of cellulose and rutile welding electrode coating by infiltrated TiO2 nanoparticles

In this paper, a novel method of infiltration of TiO2 nanoparticles into the coating of the cellulose and rutile shielded metal arc welding electrode is shown. Tensile properties and strength of weld metals were correlated to the chemical composition of the weld metals, ferrite type, and non-metallic inclusion type, size and composition. As infiltration time is increased in the cellulose electrodes, the non-metallic inclusion count increases and their size decreases. They act as inoculants and lead to the replacement of Widmanstaetten with the finegrained acicular ferrite which increases the mechanical properties of the welds. The modification of rutile electrodes with low and medium infiltration time also refines the microstructure and increases the mechanical properties. Specimens welded with rutile electrodes infiltrated at maximum duration exhibited the lowest mechanical properties due to the relatively large non-metallic inclusions that act as void nucleation sites and the appearance of large grain allotriomorphic ferrite in the weld metal.

Antimicrobial nanomaterials for food packaging applications

Food packaging industry presents one of the fastest growing industries nowadays. New trends in this industry, which include reducing food as well as packaging waste, improved preservation of food and prolonged shelf-life together with substitution of petrochemical sources with renewable ones are leading to development of this industrial area in diverse directions. This multidisciplinary challenge is set up both in front of food and material scientists. Nanotechnology is recently answering to these challenges, with different solutions-from improvements in materials properties to active packaging solutions, or both at the same time. Incorporation of nanoparticles into polymer matrix and preparation of hybrid materials is one of the methods of modification of polymer properties. Nano scaled materials with antimicrobial properties can act as active components when added into polymer, thereby leading to prolonged protective function of pristine food packaging material. This paper presents a review in the field of antimicrobial nanomaterials for food packaging in turn of technology, application and regulatory issues.

Primena veštačkih neuronskih mreža za matematičko modelovanje uticaja sastava i uslova proizvodnje na svojstva PVC podnih obloga

The application of PVC floor coverings is strongly connected with their end-use properties, which depend on the composition and processing conditions. It is very difficult to estimate the proper influence of the production parameters on the characteristics of PVC floor coverings due to their complex composition and various preparation procedures. The effect of different processing variables (such as time of bowling, temperature of bowling and composition of PVC plastisol) on the mechanical properties of PVC floor coverings was investigated. The influence of different input parameters on the mechanical properties was successfully determined using an artificial neural network with an optimized number of hidden neurons. The Garson and Yoon models were applied to calculate and describe the variable contributions in the artificial neural networks. [Projekat Ministarstva nauke Republike Srbije, br. III 45022]

The investigation reaction kinetic for polyurethanes based on different types of diisocyanate and castor oil

The formation of polyurethanes based on vegetable oils is very complex and thus for industrial production of this materials it is important to determine the optimal temperature for polymerisation and finally to obtain materials with the proper mechanical properties. The goal of this work was to assess the kinetic of catalysed and noncatalysed reactions for polyurethanes based on castor oil as the polyol component and different types of diisocyanates. Due to the presences of hydroxyl groups on ricinoleic acid, castor oil is suitable for polyurethane preparation. The differential scanning calorimetry has been employed to study the polyurethane formation reaction using Ozawa isoconversion method. It was estimated that the catalyst addition decreases the activation energy. The highest reduction of activation energy was observed for the reactive systems with hexamethylene diisocyanate. Validity of obtained kinetic model was examined by FTIR spectroscopy following the apsorption of reactive groups. Obtained results of mechanical characteristics of the polyuretahane networks (with different NCO/OH ratio) confirmed that applied method could be used for prediction of optimal reaction condition in polyurethane networks synthesis.