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The paper presents a brief overview of the polymeric materials recycling problems and especially those connected with polypropylene reprocessing. It is pointed out the manner in which reprocessing of polymeric materials determines the change of the polymeric melts viscous-elastic properties and, as a consequence, the change of rheological behaviour during the recycling process. It was chosen to do the study of the extrusion reprocessing, so, it was determined, after a significantly number of recycling, the modifying of the process parameters needed in order to obtain the best performances and the highest quality of the product. There were compared the screw extruder performances in the case of the first processing and after ten times recycling of the PP. Keywords: recycling, rheological behavior, polymeric materials, polypropylene, screw extruder

This paper presents the tribological behaviour of four polymeric materials, polybutylene terephthalate (PBT), PBT + 10% micro glass beads, PBT + 10% polytetrafluoroethylene (PTFE) and PBT + 10% aramid fibers, in order to rank them in dry sliding regime. Tests were done using a block-on-ring module. The test parameters were: the sliding speed was set for 0.25 m/s, 0.50 m/s and 0.75 m/s, respectively, the load and the sliding distance being kept constant (5 N and 5000 m, respectively). There were analyzed the dependence of friction coefficient and linear wear rate on the adding material. Particular wear mechanisms were identified with the help of SEM images. Keywords: PBT-based materials, PTFE, glass beads, aramid fibers, friction coefficient, linear wear rate

In this paper we study the influences on mechanical behavior of nonuniformity that appear in bars reinforced with carbon fibers fabric, and respectively carbon-kevlar fibers fabric. We studied the manner in which nonuniformity produced by interruption of a layer or two layers of reinforcement affects the modulus of elasticity, tensile strength and elongation at rupture. In addition to these mechanical properties, we have experimentally determined the coefficient of uniformity for samples with matrix of epoxy resin, reinforced by carbon and carbon-kevlar fibers fabric and which having one and two layers with interruptions. By changing the dimensions of interruptions from layers we analyzed the effect of these nonuniformity on the mechanical properties studied. Keywords: composite materials, uniformity coefficient, elasticity modulus, tensile strength

In this study the results of the dry wear tests of composite material used to repair brass made parts are presented. The material belongs to Multimetall Messing category. It has a polymer matrix reinforced with Cu, Zn, Sn particles, and various allotropic forms of silicon dioxide (SiO2). This composite material was tribologically tested in dry friction reciprocating conditions, in ball-on-flat configuration, using the tribometer CETR-UMT-2. The counterpiece was a steel ball. The tests were performed at normal loads of 20, 30, 40 and 50N, over a distance of 100 m, at an average sliding speed of 3.5 mm/s, at room temperature and relative humidity of 50-60% . The results of the analysis were compared with the similar ones obtained under the same conditions for brass. Keywords: composite material, brass, wear track, profilometer, tribometer, reciprocating, ball-on-flat

Polymer-bonded explosives (PBXs) are widely used in various engineering applications. Thus, the safety of PBXs has received much attention. In this study, dynamic experiments on a typical PBX were conducted and the mechanical behaviour was studied. Based on the statistical crack mechanics (SCRAM) model, two constitutive models, the Visco-SCRAM model and the Elastic-Plastic-SCRAM model, were developed. Finite element simulations have also been carried out by applying the Visco-SCRAM model and the Elastic-Plastic-SCRAM model in the simulations and good agreement was found between the simulation results and the experimental results. It is suggested that the Elastic-Plastic-SCRAM model can be used for simulating the dynamic behaviour of PBXs under high strain rate conditions. Keywords: PBXs; Elastic-Plastic-SCRAM model; Visco-SCRAM model

An experimental study was conducted to investigate the flexural behaviour of the pre-damaged reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP). 25 beams with the size of 2200mm×150mm×200mm (length, width and height) were tested to bending loads. The parameters of the investigation included two pre-damage levels of RC beam, four shear span-depth ratios and two CFRP thicknesses. The effects of these parameters were analyzed on the failure modes, load carrying capacity, flexural stiffness and midspan CFRP strain of the strengthened beams. The results show that CFRP can significantly improve the flexural load carrying capacity of load-damaged RC beams. The pre-damage level has no obvious effects on the flexural behaviour of the strengthened RC beams with CFRP. With the decrease of the shear span-depth ratio, the failure mode of the strengthened beams may transform from debonding induced by intermediate crack (IC) to cover separation near CFRP end. For the strengthened beams failed by IC debonding, more CFRP can provide the higher load carrying capacity and flexural stiffness, but it is not the case for the beams failed by cover separation near CFRP end. Keywords: Carbon Fiber reinforced polymer (CFRP), StrengtheningÿPre-damage, Reinforced Concrete (RC), Shear span-depth ratio, Debonding

Rapid Heat Cycle Molding is a new environmental-friendly technology to access high surface quality of plastic products. In this paper, the influence of processing parameters of this technology on weld line of High density polyethylene (HDPE) plastics has been investigated using the orthogonal experiment method. Weld line is evaluated by dE(Euclidean distance). All the parameters influencing weld line have been respectively discussed, while the result shows that heating temperature is the most important factor in the process of forming weld line. From this point of view, the influence of heating temperature on weld line is then further studied from a micro prospective. Keywords: weld line, Rapid Heat Cycle Molding, processing parameters, orthogonal experiment, heating temperature

Consolidation of old frail wood by impregnation with polymers is a key step in wooden cultural heritage conservation. Paraloid B72 is an acrylic polymer widely used for this purpose. FTIR spectroscopy, though microdestructive, was found to be a versatile method able to reveal the presence / penetration of Paraloid B72 into the wood structure. A semiquantitative method of investigation was developed with the aim of correlating FTIR data with gravimetric analysis. Relative consolidant retention indexes were calculated based on the integrated areas of relevant absorption bands and compared with gravimetric data of consolidant retention, resulting a fairly good correlation. The method developed on laboratory treated samples made of new sound wood (poplar Populus tremula) was further applied on three case studies, representing heavily degraded wooden artefacts from cultural heritage. Keywords: Paraloid B72, wood consolidation, FTIR, cultural heritage

Dental restorative materials due to their composition and structure relatively easily reacts in oral environment, subject to a chemical, electrochemical and biological degradation process. Effects vary from material discoloration and pigmentation, leading to cracks or fractures of fillings. Saliva as oral biotope is a continuous environment favouring these changes. In this saliva are dissolved chemicals coming from the external environment (food, beverages), which modifies the composition and the pH of the saliva, elements which are playing a main role inside the degradation processes, and in particular in electrochemical process. The intensity and its effects are heavily determined both by the composition, structure and quality of materials used and the composition and pH of saliva. Keywords: composite materials, restorative dentistry, artifcial saliva

This is a study between ultra-high molecular weight polyethylene (UHMWPE) reinforced with zinc oxide (ZnO) under various filler loadings. These composites were then incorporated with chitosan for hybridization purposes. All composite specimens were prepared by using a hot compression mold through dry ball milling process. Wear and tensile tests were carried out using specific experimental techniques namely pin on disc method as well as universal testing machine, respectively. Results indicated that the addition of ZnO filler up to optimum percentage (12 wt%) has significantly increase the wear resistance of tested composites, in accordance with the minimal weight loss. Contrary, the incorporation of chitosan (1, 2, 3 wt%) in the optimum percentage (12 wt%) of UHMWPE/ZnO composites has slightly reduced the wear resistance of the hybrid composites. For the tensile properties point of view, the results indicated that the yield strength, tensile strength and Young modulus were perpendicularly increased with increasing of ZnO filler loading, up to 12 wt%. Meanwhile, the elongation at break show contradict trend where it was gradually decreased with an increasing ZnO particle loadings. Interestingly, the incorporation of 2 wt% of chitosan in the optimum percentage (12 wt%) of UHMWPE/ZnO composites has further increased the yield strength as well as the elongation at break values of tested hybrid composites. Ultimately, the morphology analysis was also carried out in order to visually justify the state of hybridization and dispersion of fillers within UHMWPE matrix. Keywords: ultra-high molecular weight polyethylene (UHMWPE), hybrid filler, wear resistance, tensile properties, morphology analysis