Browse Articles

The influence of the painting process on a biocompostable waste is studied. Disintegration degree (D %) of a 100% biocompostable plastic made from potato almidon is calculated for both painted and non -painted samples. Solid matrix is also characterized by means of a laboratory scaled composting process following UNE-EN norms [2, 3]. It can be concluded that painting has a negative influence on biocomposting process decreasing 4.48% disintegration degree. Average D% for painted samples is 84.56 %, and 89.04 for non- painted ones. Regarding to solid matrix, dry mass after composting is double (91.12 %) as before process (43.63 %) for painted samples and 91 % and 45.41 % after and before composting for non-painted samples. Volatile solids are reduced 5.17 % after composting for painted samples, and 8.78 % for non-painted. Organic nitrogen is reduced 0.34 % and 0.16% for painted and non-painted samples respectively. The negative effect of painting is mainly due to the barrier effect of the paint that prevents microorganisms from converting organic components of the biopolymer into water, CO2 and compost. Keywords: biodisintegration; composting; painted; bioplastic; waste

In order to investigate the pyrolysis characteristics and mechanism of moso bamboo, its pyrolysis behaviour has been investigated by thermo-gravimetric analysis (TGA), which can be described as four steps: dehydration, hemicellulose pyrolysis, pyrolysis of cellulose and lignin, and residue decomposition. The decomposition of hemicellulose, cellulose and lignin are the main contributions for pyrolysis weight loss. Furthermore, the pyrolysis mechanism has been clarified based on pyrolysis kinetics model fitting. Detailedly, the pyrolysis kinetics of hemicellulose agrees with first order chemical reaction, whereas the pyrolysis kinetic equation of cellulose and lignin accords with the 1D-diffusion parabolic curve. And the apparent activation energy of them is 124.62 and 232.64 KJ/mol, respectively. Keywords: Moso bamboo, pyrolysis characteristics, pyrolysis kinetics, thermo-gravimetric analysis

The paper presents the results of compressive tests performed on Biomet® orthopedic bone cement currently used in arthroplasty. By direct molding of the cement, cylindrical test specimens were manufactured with cross section diameter of 6 mm and height of 12 mm. The stress–strain curves of all specimens tested exhibited similar linear elastic regime with a local maximum followed by yielding. The average compressive strength of the samples is 91.55 MPa, while the average modulus of elasticity was calculated at 1483 MPa. The obtained results can be used in order to asses the fatigue life-time of this type of bone cement. Keywords: total hip replacement, bone cement, PMMA, compression, elastic modulus, Poisson’s ratio

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