Browse Articles

This paper outlines the results of a series of experiments designed and conducted by the authors in order to determine the mechanical properties of a new composite material used for manufacturing the sleeves for the consolidation or reinforcement of the zones with local surface defects (flaws) in transport pipelines. The analysis and interpretation of the results allowed the authors to: assess the effectiveness of the new composite in repairing pipelines with local metal loss defects; establish the most effective way of preparing the pipeline surface for the application of the new composite sleeve; and to emphasize the correlation between the elastic properties of composites and the consolidation or reinforcement effect on the corroded or damaged pipelines following the application of composite sleeves. Keywords: pipeline maintenance, composite sleeve or wrap, mechanical properties of composites

The paper proposes a way of using of the recycled rubber for the manufacturing of a hybrid composite material based on epoxy resin, reinforced both with glass woven fabrics and with recycled rubber. One presents the mechanical characteristics of this composite material, measured in: flexural test by using the method of the three points and impact testing with Charpy pendulum. The work also describes some aspects concerning to the effects of the water absorption on the mechanical behaviour in flexural testing after 2980 h (124 days) of immersion in water, at room temperature. Finally, the experimental results obtained were comparatively analysed for both the dried and wet specimens. One could remark a degradation of the mechanical characteristics (elastic modulus E, flexural strength s, mechanical work W until the maximum force). Concerning the impact behaviour, it was measured the failure energy U and then computed the resilience K (impact strength). It was observed that additionally reinforcing with rubber particles leads to the increasing of the resilience K. Keywords: hybrid composite; recycled rubber; absorption; bending; impact

The plastics components of a random sample of waste electrical and electronic equipment (WEEE) from small household appliances were identified and sorted. Moreover, by taking into account the practical needs for applications demanding medium to less severe restrictions from the standpoint of end-use characteristics, the mechanical and thermal properties are investigated for the four most used plastics in the EU, including acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile (SAN), polystyrene (PS) and polypropylene (PP), as well as for a mixture resulting on the basis of corresponding EEE market evaluations. The obtained results show that in the case of these materials, separated prior to processing, even if a minor decrease arises from the standpoint of thermal properties due to inherent degradation induced by processing, the problem is the decline of different mechanical properties. In fact, this appears to be the net result of different morphologies of components – the essentially amorphous-like nature of ABS, SAN and PS, and the semi-crystalline component (PP). Accordingly, the loss in mechanical properties was lower for the elastic modulus, higher in case of impact strength and intermediate for the tensile strength, when the components and the resulting blend properties are compared. Keywords: WEEE, plastics, recycling, thermal properties, mechanical properties

This study followed the value of thermographic investigation in interrelation of polymeric materials with oral mucosa in patients with complete dentures, respectively thermal surface changes at completely edentulous patients, with and without stomatitis, using ThermaCAM PM 350. Thermograms revealed an elevated temperature under the denture, thermal values corresponding to mucosal aspects (edentulous without dentures, dentures wearer, normal or congested mucosa, flabby ridge) and prosthetics (suction degree), with asymmetrical color distribution of the thermal field in oral mucosa, respectively denture surface. Polymeric material shows a similar temperature rise to the mucosa (thermal impression) and residual heat. Thus, thermography may be a method of polymer-oral status interrelation assessment in denture wearers, providing important information in prevention, diagnosis and treatment of oral diseases, acquired in relation to polymer dentures. Keywords: polymeric material, oral mucosa, complete denture, thermography

The paper presents, some experimental results obtained with different types and amounts of reinforcement in composite materials based on polypropylene matrix for automotive applications. There were characterized fourteen experimental samples. The reinforcing agents utilized were: particulate reinforcement (organic and biodegradable – powder wood and inorganic and non-biodegradable – talc powder) and fibrous reinforcement (organic biodegradable-short flax fibers). Key words: composite, polypropylene, flax fibers

A biodegradable blend based on low-density polyethylene (LDPE) and 36 % starch that can be used for horticultural application was studied. The mechanical properties and the processing by molding injection were also studied. It is found that the starch helps to increase surface area on which the microorganism can attack the polymer matrix. The increase in the carboxyl index, which indicates the concentration of carboxyl blend, with time, also indicates the progress of biodegradation. Although this type of blend is not completely biodegradable it is preferred to those completely biodegradable which are expensive and with many processing problems. Keywords: biodegradation, starch, polyethylene, blend, application

The main characteristics of pressure sensitive adhesives are: peel, shear and tensile strength. This paperwork presents the shear tests and related phenomena of pressure sensitive adhesives based on polychloroprene rubber using both metallic and polymeric substrates. The influence of the main parameters which control the shear strength of the adhesive assemblies was studied: nature of the substrates, contact time and pressure. Keywords: pressure sensitive adhesives, elastomers, polychloroprene rubber

Polyacrylonitryle (PAN) fibers are used on a large scale in textile industry but, some sorts of PAN fibers are valuable precursors for specific carbon fiber (CF) due to their best fitness to the purpose e.g. for high strength CF or for active CF. The application of PAN as precursors of CF is based on its specific structure and texture. Thus, the properties of PAN base CF strongly depend on PAN structure, texture and fiber morphology. In this respect, the paper addresses the modeling of PAN fiber structure and texture and, subsequently, estimation of structure and texture parameters based mainly on Wide Angle X-ray Diffraction (WAXD) technique but, on SEM and other data. The PAN fiber structure and texture parameters were calculated on the basis of classical X-ray diffraction theory applied to paracrystals. The preferred orientation parameters were calculated on a wide accepted model. The main structural parameter of PAN paracrystal d200, d201, and L200 and preferred orientation/texture parameters Z, [cos2 u], P (cos2 u) of the PAN fibers were determinated. Based on WAXD data it was calculated the PAN fiber crystallinity. As it results from the paper the WAXD technique seems to be the best from the efficiency-cost point of view for PAN structure and preferred orientation characterization. Keywords: WAXD, SEM, structure, preffered orientation, polyacrylonitryle fibers

The aim of this study was to test the hypothesis that microwave post-polymerization treatment influences the rise of hardness, flexural strength, impact strength and fracture toughness of autopolimerizing poly(methyl-methacrylate) by the decrease in residual monomer content. Specimens produced from a commercial acrylic denture reline resin were polymerized according to manufacturers instructions. Control group was left untreated, while other five were post irradiated in a microwave oven with different power and time settings, keeping the irradiation energy constant. Each group of samples was tested for mentioned mechanical properties. Enthalpies of polymerization were tested by differential scanning calorimetry (DSC), while the amount of residual monomer was determined using fourier transform infra-red spectroscopy (FTIR). Microwave post-irradiation resulted in increase of all tested mechanical properties. The highest mecanical properties were obtained with maximum irradiation power, which was confirmed by the results of ANOVA statistical analysis. It has been found that residual monomer content strongly influences the benefits in all tested mechanical properties, increasing biocompatibility. These results have been confirmed by the results of Scanning electron microscope (SEM) fracture surface analisys. Keywords: PMMA biopolymer, microwave post – irradiation, mechanical properties, residual monomer

In this paper we present a new multiscale method for coupling molecular dynamics simulations (MD) with Monte Carlo (MC) simulations. The method is relevant for heat transfer phenomena at the molecular level with applicability in many domains such as polymer processing, crystallization process in moving polymer melt, complex flows near the interfaces, e.g. wetting, colloids near surfaces, drop formation, etc. First the theoretical background is described and after that simulation results between multiscale MD-MC and pure MD simulation are presented. At the end, comparisons between accuracy and computational costs of MD, MC and multiscale MD-MC simulations are outlined. Keywords: heat transfer techniques, polymers, Monte Carlo simulations, molecular dynamics,multiscale modeling