Browse Articles

Shape Memory Polymer Composites (SMPCs) are a class of smart materials in which the structural properties of long-fiber polymer-matrix composites and the functional behavior of Shape Memory Polymers (SMP) are combined together. In this study, the frozen stresses resulting from fixing a deformed shape have been investigated. Two different samples were manufactured, with and without significant shape memory properties, and a three point flexural test equipment was used in order to fix a deformed shape. The forces and the resulting stresses were measured during the samples deformation and after the shape freezing. The experimental tests have shown that the shape memory sample has a better ability to fix a deformed shape, since its frozen stress is higher in all the tests.

Biodegradable polymers became one of the most important materials with large applicability, as they do not generate wastes after life cycle. An important application is food packaging fabricated by injection molding processing. In this paper, we present the investigation of the mechanical properties of some biodegradable polymers based on PLA composites obtained by melting processing and their morphology studied by SEM analyses, in comparison to polypropylene and neat PLA. We found out that tensile strength, elongation at break and Young modulus exhibit values appropriate to injection molding processing and they are very close related to crystalline or amorphous character of the materials.

Surface chemistry and micro-nanoscale topography of biomaterials can significantly influence tissue engineering and cell biology. In this study, polystyrene (PS) Petri dishes were subjected to microtexturing by compression molding process, which resulted in three-dimensional (3D) microscale surface topographies. Three different micropatterned surfaces were fabricated using bronze sintered molds with different mean pore pitch sizes. The surface changes and the morphological aspects were analyzed by 3D surface analyzer. The dishes were then used to investigate the cell behavior of Mouse Embryonic Fibroblasts (MEF) P4 cells. The surface micropatterning have affected in different ways the MEF cell adhesion and proliferation, related to the morphological changes in comparison with unmodified PS. At the increasing of the sintered particle dimensions of the mold, the cavities dimensions on the molded Petri increase and also the cells adhesion in the cavities seems to increase independently from the roughness inside them.

Polypropylene (PP) and polyamide (PA) polymers are used in different situations where they provide a flame retarding effect to meet safety standards. The expandable graphite as an additive for polymer materials has a good flame retardant effect and it does not harm the environment. The processing of this additive is presented for those two different polymers. Compounds with proportions of 10, 20, 30% of this additive were prepared in order to investigate the processability and flame retarding effect of PP and PA samples. The results show that the process conditions differ greatly between the polymers used in higher proportions. The improvement of the flame retarding effect was observed for both polymer compounds with expandable graphite. The plastics flammability standard UL 94 V0 could be achieved for the PP compound in all additive proportions and for the PA compounds only above 20%. The processing of the PP compound with co-rotating twin-screw extruder and an injection moulding machine takes place works well and provides a good homogenous mixture. The PA compound could not be processed at a higher additive content by the extruder. Special screw configuration is necessary to process this polymer compound. Also the flame retardant effect was inferior to the PP compound. The mechanical properties of the compounds decrease with the increasing additive content, particularly the impact strength of the samples.

In the present paper the authors study the pertraction of the nitrophenols through the immobilization using chemical reaction in receiving phase, using a laboratory installation conceived by the Group of Membranes, Materials and Membrane Processes within University Politehnica of Bucharest. This installation was developed using liquid synthetically solutions, through composite membranes having a matrix of capillary polypropylene and inclusions of ethylene propylene diene terpolymer sulfonic acid (S-EPDM) or sulfonated ethylene-propylene-diene terpolymer (S-EPDM). The results were follow: The permeation through the compartments of the system with composite S-EPDM membranes is limited, in the aqueous phases, by the solubility of the compound about to be separated, namely the membrane itself, and subsequently by its diffusion from the feed compartment to the collection compartment. The chemical reaction of immobilization, in the receiving phase, can be achieved in several variants (neutralization, esterification, complexation, oxidation, coupling, oxidative degradation); The biggest flows are obtained in compensation of the o-nitrophenol with ferric ions and then, in acetylation of the o-nitrophenol with acetic anhydride. However, we can emphasize that the derivatization of the o-nitrophenol through complexation and acetylation reactions requires its use as such in later processes, unlike the neutralization, for which the nitrophenolate ion easily frees the nitrophenol for future applications;For the neutralization reaction, the removing coefficient grows with decreasing of pKa value of the nitrophenols. For complexation reaction, the most favorable results were obtained for o-nitrophenol - over 66%;The coupling reaction of the o-nitrophenol, in the receiving phase, with the diazonium chloride of the p-nitroaniline and hydrogen peroxide 3% in sulfuric acid 20%, respectively, concludes with the exhaustion of the source phase, after 24 hours of operation.

Various applications in industry and medicine require the transmission of movement using systems that do not influence magnetic or electromagnetic fields. These components include systems which transmit linear or rotational motion, change position (switches), attach or detach to objects (latches), grip objects, etc. This paper looks into the possibility of producing such mechanisms using FDM 3D-printed parts from thermoplastic materials with embedded moving parts, which can be pneumatically actuated. In order to make the parts suitable for use in pressurized air systems, different sets of printing parameters have been investigated. PLA annealing is used in the attempt to minimize play and increase air-tightness of 3D-printed parts.

While over the past century fairly extensive work has been carried out on explosively-driven metallic envelope fragmentation, as the development of explosive materials and warhead configurations continued, the issue under consideration is still topical. The current paper aims to investigate the fragmentation characteristics of explosively-driven steel cylinders when double layer envelopes are used. Mott’s approach was modified in order to account for such particular configuration (layered envelope). Several tests in a simplified type procedure were performed aiming to confirm the theoretical approach.

This study presents research regarding the calculation of the mechanical characteristics of composite polymeric materials. By using LabVIEW’ software a virtual instrument was created used for monitoring in real time the process of cross-linking the composite polymeric materials. The experiments were realized based on composite materials containing epoxy/fiberglass resin of different topologies. By means of the virtual instrument and of a sensor created based on the mechanical impedance analysis, implanted in the composite material, it was determined the G shearing module of the composite material at different temperatures.

In order to identify the premature biodegradation causes of paint applied in 2013 on a railway bridge, top coat layers applied have been investigated by XRF and SEM-EDAX techniques after 32 years, corresponding to periods of operation under identical climatic conditions of 4.5 years and 3.5 years respectively. By analysis of the experimental results obtained, it has been found that by using suitable painting materials (titanium content of about 7.5 % - TiO2 for UV protection) an exploitation period of more than 30 years could be obtained. Low-carbon (low polymer) and titanium dyeing materials with significant content of soluble salts have a low durability and anticorrosive protection capability. They degrade relatively fast both by top coat degradation and by intense increases of biofouling.

The paper deals with some aspects regarding the behavior of modern and efficient solutions - for rehabilitation of reinforced concrete framed structures. The paper is devoted to experimental studies on carbon fiber reinforced polymer (CFRP) systems used as strengthening solution for reinforced concrete (RC) frames assumed as existing structures, which were tested as un-strengthened and as (CFRP) strengthened structures. Single span and single story frames (scale 1:2) were designed and detailed according to the Romanian design codes from 1970s under which seismic design was inadequate. The RC design and the magnitude of applied forces were ensuring the failure mechanism, of non-strengthened RC frames, by plastic hinges at columns ends. Then the columns were strengthened by using CFRP materials. The experimental program emphasized some important aspects regarding the behavior and failure by debonding of CFRP strengthening materials applied to RC frames. The analysis of experimental data and theoretical values showed up an increase of resistance and stiffness achieved by strengthening.