Volume 48, Issue 3

Abstract: This study focuses on possible applications of polystyrene in the medical field. Nonwoven fiber mats were produced through electrospinning, using limonene or, as control, the conventionally used ethyl acetate. Subsequently, different types of dilutions were tested. Electrospinning (ES) was performed with different parameters to study the effect upon the fibrous materials resulted, in view of obtaining structures with high porosity and a specific desired morphology. Thin fibers were obtained using both solvents, with fibers average diameter of 1.98-2.58 mm for limonene and 8.87-13.81 mm for ethyl acetate. The obtained various materials are a result of the different solvent densities, surface tensions and polymer concentrations. Best quality fibers, when using limonene, were obtained for 35 % polystyrene, while when using ethyl acetate the high quality fibers were obtained for 60 % polystyrene in solution. The mats morphology and structure were compared and analyzed through optical microscopy, scanning electron microscopy and Fourier Transform Infrared Spectroscopy. This study proposes the fabrication of nonwoven fibrous mats from polystyrene using a natural, economical, biocompatible and environmentally friendly solvent that can successfully replace the common and toxic solvents in medical applications involving wound dressing or tissue reconstruction. Keywords: electrospinning, limonene, polystyrene, ethyl acetate, wound dressings

Abstract: In this study interpenetrating polymer networks (IPNs) based on bisphenol A diglycidyl dimethacrylate (BisGMA) and diglycidyl ether of bisphenol A (DGEBA) with or without native fumed silica nanoparticles were prepared by in situ polymerization. The properties of the IPNs and hybrid IPNs were evaluated using different thermal techniques as differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermogravimetrical analysis (TGA). The mechanical properties were also determined. Keywords: dimethacrylate, epoxy resin, interpenetrating polymer network, fumed silica

Abstract: The work presents a study on a possible solution of metal replacement for pneumatic drives rods working in dry friction condition. If the total absence of lubricant and others contaminating agents is required, due to specific working environment, the pneumatic drives use is recommended. The rod sealing system is elastomeric lip seal based and works, in this case, in linear sliding dry condition. The authors tried to establish the way that polymeric material replacing the metallic rod behaves, taking into account the working conditions. Considering that the sealing system failure is due to wear, a closer investigation is performed at surfaces level by optical and 3D reconstruction methods. The observations allowed an optimization of polymeric rod rubber lip seal system in dry sliding conditions from the materials choosing point of view. Keywords: dry friction, elastomer-plastomer couple, linear sliding motion

Abstract: Working on high structures is one of the jobs in the cities vertically developed. The abilities of climbing workers are used for the purpose of mounting publicity banners, cleaning building face, mounting objects on buildings etc. The use of fall arrester equipment is made under strict surveillance and training of the workers because of imminence of the accidents. Before sailing, the fall arrester equipment is tested and certified. Keywords: polyethylene, shock absorber, fall arrester, climbing, HBM MGC

Abstract: Conventional methods for processing and shaping plastics parts (mold injection, thermoforming, extrusion etc) require heating (melting) process in which plastics material is soften or liquefied firstly and then imparted by using different dies and techniques. However, plastics material could be formed without any heating and for that purpose a few non-conventional procedures have been developed. An alternative to conventional shaping of plastic parts offers metal forming processes and cold forming technique.In this paper results of theoretical, numerical and experimental investigation of cold forming of plastics are present. Traditional metal forming processes such as upsetting and backward extrusion were applied for shaping billets made from HDPE and PA. Both processes are simulated by FEM and Simufact.Forging 8.1 program package. Numerically predicted load-stroke diagrams are compared to those experimentally recorded. All necessary material data and process parameters were determined according to the methodology which is used in metal forming processes. Keywords: thermoplastics, cold forming, FEM

Abstract: The main characteristics of pressure sensitive adhesives are: peel resistance, shear and tensile strength. This work presents the tensile tests and related phenomena of pressure sensitive adhesives based on polychloroprene rubber with wood and steel substrates. The tensile breaking mechanism for the adhesive assembly is proposed and discussed within this article. Keywords: pressure sensitive adhesives, elastomers, tensile strength, wood, steel

Abstract: In this paper were investigated influences of various types and concentrations of crosslinking agents on the properties of thermoplastic vulcanizates based on ethylene-propylene terpolymer rubber (EPDM) and plasticized poly (vinyl chloride) (PVC). Three different crosslinking systems were used: (a) common method with sulphur and vulcanization accelerators (tetramethylthiuram disulfide and mercaptobenzothiazole); (b) crosslinking with di(tert-buthyl peroxi-isopropyl) benzene Perkadox 14-40B-GR and co-agent trimethylol-propane trimethacrylate TMPT DL 75 (c) vulcanization with phenol resin Ribetak 75-30E and tin chloride dehydrate. The influence of each crosslinking systems on cross-link density, mechanical properties and DSC analysis of samples were investigated. The hardness shows a slight decrease as a result of dynamic vulcanization, because this is a way to disperse large amounts of elastomer in the thermoplastic matrix, resulting in a refined morphology. It was observed that the highest values of crosslinking density and 100% modulus were obtained by using the classic cross-linking with sulphur and accelerators, and that for a reduced amount of crosslinking agents used, there was a decrease in crosslinking density. Elastomer crosslinking led to an increased Tg and decreased Tm. These blends can be used in the manufacture of hoses, gaskets, footwear constituents etc. Keywords: TPV, EPDM, PVC, cross-link density, differential scanning calorimetry

Abstract: 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

Abstract: When great damages occur on gas-pipes, a quick intervention is often needed, as close to the place of damage as it can be. That is the reason why recently it has more and more been used a procedure of squeezing the pipe using a squeeze-off tool and thus stopping the flow. After the damage has been removed, the deformed pipe returns to the original shape by using re-rounding clam and the flow is established yet again. After the above-described process, the pipe is permanently deformed, as far as shape and thickness are concerned. The size of the deformation is important for the assessment of further use of the existing pipes or for determining the parameters for the newly-projected pipes. So far, the researches have been dealing with the hydrostatic and stress states after the squeezing of the pipe. The subject of this research is the decrease of the pipe thickness after the squeezing, and the goal is to help the designers of distributive plastic gas-pipes to determine the pipe wall thickness, as well as to help the managers of distributive networks so that they would know what happens to the existing gas-pipes after the intervention on the pipe. Keywords: sqeeze – off tool, polyethilene gas pipe

Abstract: The present paper aims to present a method for redesigning plastic products using the Reverse Engineering technique. The originality of this paper stems from its integration of modern scanning techniques and reverse engineering with traditional manufacturing techniques. The paper presents a case study about the redesign of an existing product for which no technical documentation is available, using three distinct phases: reverse engineering, modeling analysis and redesign, manufacturing and testing.. Keywords: redesign, reverse engineering, mould, polymeric material

Abstract: This study presents new findings of the water/ethanol (ratio) influence on the aniline hydrochloride polymerization process in presence of ammonium persulfate. Water/ethanol mixtures in presence of monomer hydrochloride, as proved by the conductometric, spectrophotometric and refractometric investigations, are far from ideal solutions and promote a partitioned environment , for the polymerization process. By controlling this key parameter (water/ethanol ratio) the polymerization can be shifted from a initial dispersion process to a solution one, followed by precipitation. The associated phenomena revealed modification in terms of conversion, structure (FTIR, UV-VIS), morphology (SEM), thermal stability and doping agent retention (TGA-DTG). Keywords: conductive polymers, aniline hydrochloride, water/ethanol system, polyaniline