Papers by Keyword: Polymerization

Abstract: The aim of this work was to develop methods for the synthesis of organic aerogels based on epoxy resins and to investigate their properties. Aerogels based on DGEBA-epoxy resin were obtained by CO₂-supercritical drying of gel samples prepared from acetone solutions of epoxy resin with different amount of catalyst and solvents. As a result, aerogels of different density were obtained; the dependence of density on the solvent content in the samples was revealed. The aerogels were characterized by infrared spectroscopy to define the degree of conversion of the epoxy groups, by SEM to confirm nanoscale morphology of aerogels, as well as by the BET method to determine the specific surface area of the samples and its dependence on the catalyst content and curing conditions.

Abstract: The oxidative polymerization of 3-amino-3 ́-nitro-diphenylazomethine was carried out in various ways. In this case, the effect of the concentration of monomer and initiator, their ratio, temperature and reaction time, on the yield and molecular weight of the polymer was studied. The morphology is established, the size of the polymer particles and their distribution are determined. It is shown that the synthesized polymer has increased electrical conductivity and is active in redox processes.

Abstract: Smart polymers have been one of the most popularly studied materials owing to their capability to alter physio-chemical behaviour upon exposure to specific external stimuli. The biocompatible thermally responsive poly (N-isopropylacrylamide), PNIPAm shows reversible transition between hydrophilic-hydrophobic characteristics at the vicinity of human physiological temperature has great potential to propel the development of smart tissue engineering scaffold and drug delivery. However, the limited availability and its high cost have dampened the extent of research on this polymer. To address these challenges, the current work demonstrates an economical lab-scale polymerization of crosslinked PNIPAm and the optimised parameters to produce mono-dispersed polymer hydrogel particles were investigated. Characterisation of the synthesized PNIPAm polymer revealed particle size polydispersity index of 0.215, indicative of distribution within the mono-dispersed range, with average hydrodynamic diameter of 346.3 nm. Zeta-potential of the synthesized PNIPAm was found to be -20.6 mV, suggesting an incipient instability in terms of colloidal coagulation. Viscosity of the synthesized PNIPAm (4 wt% concentration in methanol) was 28.6 cP. Thermal gravimetric analysis (TGA) indicated the thermal degradation of main chain PNIPAm fell in the range of 340 to 480°C.

Abstract: In order to provide good adhesion for natural nail coatings and to avoid loss of adhesion between the substrate and the coating, the mechanical properties of the coating should be close to those of the substrate. Three different mono-functional monomers (HPMA, THFA, THFMA) and one bi-functional monomer (EGDMA) have been added to decrease the viscosity of un-polymerized composition. Optimal monomer concentration was found evaluating monomer concentration effect on viscosity. Polymerized coatings were tested with monomer concentrations of 30% and 40%. The tensile strength properties of the polymerized coatings were determined 24 hours after polymerization. Polymerization T and conversion rate of unsaturated links were also studied to find the best monomer for natural nail coatings.

Abstract: The kinetic and morphological peculiarities of polytetrafluoroethylene (PTFE) coating growth onset from the active gas phase on differently pretreated substrates are considered. The substrate surface energy was found to exert an effect on distribution of polymer micro-and nanoparticles both at the initial stage so during coating growth. The substrate surface activation was proved to result in the increasing growth rate and formation of a continuous coating with a thinner apparent thickness. The physicomathematical model of presented regularities was elaborated.

Abstract: Soft chemistry (chimie douce) processes allow the design of multifunctional composite coatings tailoring the interfaces between phases. Instrumented indentation has become routinely used to characterize thin systems and allows for getting insight into interface mechanics. The paper illustrates both experimental approaches allowing for the fabrication PMMA based nanocomposites and their characterization employing nanoindentation.

Abstract: A bio material is a inert and non-viable material with a natural or synthetic origin that comes in to contact with tissues, blood or biological fluids, being used in prosthetic, therapeutic and storage applications, without affecting in any way living organism or their components.Biological systems may produce the deterioration of materials, process known as bio-degradation. In case of oral environment this also includes the dissolution in saliva, chemical and physical degradation, abrasion and erosion caused by the diet components, mastication process and bacteria actions. Most of the materials used in dental therapy may be toxic or may produce allergies until they bind.We evaluated during our experiment the biological consequences (bio-compatibility) that subcutaneous implanting of small acrylic dental fragments have upon tissues in case of white lab mice, keeping an eye on the local tissues reactions. The evaluation of dental materials is made by testing the bio-compatibility. Biologically tests are performed in vivo and in vitro strictly in the lab and on animals.For our experiment we used 20 white mice Wistar line, 8-9 weeks old males, 40 grams, divided in 3 groups; all of them received an acrylic implant. The experiment was centered on the observation of some physiological or pathological effects, local or systemic, that implants may have produced effects that show a toxic answer or the rejection of the material.All experimens was performed in compliance with (European Communities Council Directive 1986 (86/609/EEC) and Ordinance No. 37 of Romanian Government from 2^nd February 2002.Materials bio-compatibility was highlighted by anatomic-pathological exams during which we noticed all the modifications at dermis level during the entire period. We observed the phenomenon that occurred around the implants at different time periods, than we collected samples.The data obtained at the end of our experiment allow us to sustain that acrylic materials used in dental implants have all the properties required to be considered as bio-compatible.

Abstract: In recent years, supercritical carbon dioxide, as a green chemical solvent, is widely used. The surfactants for polymerization in supercritical fluids have become one of the important issues. This paper mainly discusses the mechanism and influence of the surfactants in supercritical carbon dioxide system. The choice and design principle of surfactants and the recent development of surfactants were introduced in detail.

Abstract: The development of the cable industry is growing rapidly. Cable manufacturing process occurs at high energy intensive and require different materials in an amount sufficient. The question of marriage of the finished product is very serious. Moreover, the dwell time of cables with different types of coating materials at high temperatures cannot be identified because of possible burn. The purpose of the work was to determine the optimal time for the polymerization of various types of cable jacket. There is a numerical study of the polymerization of cable products. Also, there are set scales of influence of different types of cable sheaths at the time of full cure.

Abstract: A novel superplasticizer with a multi-arm structure, i.e., a “core” connected with multiple copolymer “arms”, was synthesized through two steps including an esterification reaction between polyhydric alcohols and acrylic acid and a copolymerization reaction in an aqueous solution among the esterification product, isobutenyl polyethylene glycol and acrylic acid. The reaction conditions were determined, and the results showed that the esterification rate can reach above 95% with a water-carrying agent of 70g, a catalyst/alcohol molar ratio of 0.07, an inhibitor/monomer molar ratio of 0.03, and a reaction time of 7 hrs. The reaction products were characterized by ¹H Nuclear Magnetic Resonance (¹H NMR) and Fourier Transform infrared spectroscopy (FTIR). It is confirmed to be the multi-arm structure, and the self-synthesized superplasticizer with a multi-arm structure exhibited higher energy efficiency, which was in accordance with its excellent paste fluidity performances and adsorption behavior in cement paste