Browse Articles

In this article we present a new thermostat – theory and simulation results – obtained by combining two thermostats – Berendsen and DPD types. The new thermostat provides a predictable behavior with temperatures that do not deviate from the reference and with thermal rate constant agreement between simulations and theory. The presented work can be used for the study of polymer properties. Keywords: molecular dynamics, polymers, thermostats

The chemical recycling of poly(ethylene terephtalate) PET using a unconventional method employing microwave radiation was studied. The reaction parameters were varied in order to study their influence. The reactivity of several glycols was compared and results showed consistency with conventional solvolysis methods. The dissolution of PET polymer into the glycol solution is one of the key parameters in determining the reaction time. The modification of the microwave field power afforded a 50% reduction of the reaction time. This method presents certain advantages compared to conventional glycolysis methods such as: energy and time saving through a rapid and a more uniform heating capacity, leading to a complete depolymerization in the presence of the catalyst. Keywords: PET waste, glycolysis, microwave, oligomers, viscosity

A number of epidemiological, clinical and experimental studies show that cholinergic stimulation induced by the contact between human body and several plastic materials plays an important role in the pathogenesis of diseases. Extraneuronal acetylcholine mediates the reduction of cytokines synthesis, the increased synthesis and release of histamine from dermal mast cells or basophils, and the suppression of the inflammation. Based on these considerations, the authors proposed to verify the importance of acetylcholine in the mechanism of generation of the inflammatory response, using Helicobacter pylori infection as an experimental model for systemic inflammation. We also studied the impact of antihistamines/anti-Helicobacter pyori treatment on acetylcholine levels in chronic idiopathic diseases. Determination of the inflammation tests and the cholinesterase activity, as the level of non-neuronal acetylcholine, showed a significant association between cholinesterase activity, inflammatory response and therapeutic efficacy. In conclusion, evaluation of the inflammation tests and the cholinesterase activity could be an adjuvant factor for therapeutic management in chronic idiopathic diseases subjects. Keywords: plastic materials, inflammatory response, non-neuronal acetylcholine, cholinesterase activity

Polymer composites from polypropylene (PP) and treated and untreated hemp fibers (HF) were prepared using a twin screw extruder and separated feeding ports. Both treated and untreated HF show reinforcing effect in PP composites but the treatments applied to HF accentuate this effect. An increase with 78 % of tensile strength and with 61 % of Young’s modulus was obtained with untreated fibers and double tensile strength and modulus when using treated HF. Aminosilane treatment of HF was the most efficient, leading to simultaneous improvement of tensile properties and impact strength of PP composites. Keywords: hemp fibers, mechanical properties, twin screw extruder, polymer composites

The bonding materials used in orthodontics must resist to masticatory and active orthodontic forces. The aim of this study is to evaluate and compare the tensile bond strength of three orthodontic bonding procedures: acid etching and chemically cured macrofilled composite (Evicrol, SpofaDental, Jièin, Cehia), glass ionomer cement Ketac Cem (3M ESPE AG, Seefeld, Germany) and self-etching primer with light cure adhesive bond material (Transbond Plus Self Etching Primer + Transbond Plus Color Changer Adhesive, 3M Unitek, Monrovia, California). Moreover, after removing the brackets, the Adhesive Remnant Index (ARI) has also been measured. For this purpose 30 recently extracted human premolars were used, grouped randomly in three groups, 10 teeth for each tested material. After bonding the brackets, these were torn off from the teeth surfaces with a tensile testing machine (Instron 1195). The ultimate tensile strenght (UTS) and the ARI has been measured. Our conclusion was that glass ionomer cement fails first to the tractioning forces, while light cured composite has proven to resist best to streching and traction. Although light-cured composite has failed to lower forces than the chemically cured one, the frequency of ARI score 3 has been the highest, which means that its adhesion is the best. Key words: tensile bond strength, bonding material, adhesive remnant index

The paper presents our results with polymethylmethacrylate cement augmentation osteosynthesis around the knee joint and to discuss the advantages and complications encountered. We presented the benefits and limitations of cement augmented fixation constructs around the knee because of the lack of such studies that focus on this particular anatomical location. We consider that the cases described can contribute to a greater understanding when searching for solutions targeted on the knee defects. In conclusion, we find polymethylmethacrylate cement augmentation of implants to provide excellent fixation around the knee both for tumoral resections as well as for managing complex trauma cases. Keywords: polymethylmethacrylate spacers, osteosynthesis, knee joint

The purpose of this paper is a radiological evaluation of the prosthetic polyethylene component wear in time (years), a quantification of this wear depending on the different types of prostheses and a correlation between the degree of wear and the radiological signs of deterioration of the periprosthetic bone structures, resulting in mobilization of the prosthetic components (loosening). Keywords: polyethylene, hip prosthesis, particle disease, loosening

This paper presents the study of sorption kinetics and thermodynamic equilibrium of chloroform and methanol sorption in thin polyvinyl acetate (PVAc) films. Experiments were conducted on a laboratory set-up using a pressure-decay technique. The obtained data were compared with other literature data obtained using other experimental method and are in good agreement. Comparison between the actual experimental and other literature data obtained using different investigation techniques are in good agreement. Keywords: polymer films, solvent sorption, pressure-decay technique

In this paper are presented structural parameters that influenced the metachromatic phenomenon induced by two maleic acid copolymers in form of sodium salts, as anionic partners. One is hydrophilic, namely the copolymer sodium maleate-vinyl acetate, (NaM-VA), and the other is a hydrophobic one, namely sodium maleate-styrene copolymer (NaM-S). The cationic dye was Methylene Blue. The correlations between UV-Vis spectrum data and those of spectral remission are also discussed. Keywords: maleic acid copolymers, Methylene Blue, metachromasy, Melana fiber, spectral remission, K/S values

Asphalt nanocomposites were prepared by mixing nanoparticles of calcium carbonate with a solution of bitumen in xylene in the presence of a solution of polymer in xylene. Calcium carbonate nanoparticles were obtained by wet milling and their characterization was performed by dynamic light scattering (DLS). The polymers used were either polyacrylate type and polystyrene homopolymers or copolymer of polyacrylate-polystyrene type synthesized by solution process. Asphalt nanocomposites prepared were characterized by dynamic mechanical analysis (DMA). The results indicate a close behaviour of nanocomposite based on polyacrylate and polystyrene homopolymers and polyacrylate-polystyrene copolymer. Keywords: asphalt nanocomposites, calcium carbonate, dynamic mechanical analysis