abid boubakri - Academia.edu (original) (raw)

Papers by abid boubakri

Materials & Design, 2009

In this investigation, the absorption and diffusion of water in thermoplastic polyurethane (TPU) ... more In this investigation, the absorption and diffusion of water in thermoplastic polyurethane (TPU) was studied. Water-sorption experiments, physical and mechanical property tests were performed after immersion in water at a set temperature of 70°C for up to 6 months. Emphasis was given to the effect of immersion aging on thermal, mechanical and tribological properties. Fickian diffusion behaviour was found during the initial immersion time followed by saturation stage as time progressed. The use of differential scanning calorimetry (DSC) analysis showed that the glass transition temperature (Tg) was sensitive to the effect of hygrothermal aging and it decreased with increasing water uptake. More significantly, the mechanical properties in bulk material, obtained from tensile test, were affected by aging. Elastic modulus and stress at 200% of strain of the studied TPU were decreased after sufficient exposure to moisture. On the other hand, the mechanical properties of the material surface were equally investigated with the help of an abrasive wear test. A decrease in wear resistance of the aged TPU was discerned. The reversibility of mechanical and physical properties after moisture exposure was also assessed in this study. The polymer degradation was found as irreversible phenomenon. Finally, the evolution of the mechanical properties seems to be well correlated to structural modifications obtained from Fourier transform infrared spectroscopy (FTIR) characterization.

Materials Science and Engineering: A, 2010

In the present work, the characteristics of thermoplastic polyurethane (TPU) material exposed to ... more In the present work, the characteristics of thermoplastic polyurethane (TPU) material exposed to artificial weathering environment for different durations were studied. The influence on (i) appearance and morphology, (ii) thermal properties and (iii) mechanical properties evolution of the material were investigated during aging. For this purpose, ultraviolet (UV) chamber was used as accelerated aging technique. Optical and scanning electron microscopy (SEM) observations revealed changes in appearance and morphology of TPU material after UV-exposure. From differential scanning calorimetry (DSC) analysis, it was mainly found that thermal properties, in terms of glass transition temperature (T g), were affected. Changes in mechanical behaviour were equally discerned using both computer-controlled tensile testing and abrasive wear tester. The mechanical properties in bulk of the studied material displayed tow steps. The elastic modulus and the stress at 200% of strain initially decreased and then increased progressively revealing an increase in crosslink density. The tribological properties, in terms of wear resistance, were affected and this degradation became more important with UV-exposure. Furthermore, our experimental results displayed prominently that there was a competition between chain scission and crosslinking mechanisms.

Comptes Rendus Mécanique, 2011

Changes in mechanical and physical properties of polyurethane thermoplastic during aging at 70 • ... more Changes in mechanical and physical properties of polyurethane thermoplastic during aging at 70 • C and 90 • C were investigated. The loss weight response was analyzed by gravimetric measurements under these temperatures. Changes in appearance and morphology of TPU after thermal aging were revealed by optical microscopy. The prolongation of the thermal exposure time, up to 270 days, leads to a progressive increase in tensile strength. In fact, elastic modulus and stress at 200% of strain were increased with thermal exposure time. These results can be explained by the increase of thermal stability due to the increase of material rigidity and the decrease in chain mobility. The evolution of the mechanical properties from tensile tests seems to be well correlated to the creep behavior. Finally, Scanning Electron Microscopy (SEM) revealed the modification of TPU morphology fracture surface after thermal aging.

Materials & Design, 2010

In this study, impact of environmental aging conditions on the mechanical properties of thermopla... more In this study, impact of environmental aging conditions on the mechanical properties of thermoplastic polyurethane (TPU) was investigated. Especially, effect of temperature on water diffusion has been studied. Water-sorption experiments, tensile test and dynamic mechanical thermal analysis (DMTA) were performed after immersion in distilled water at different temperatures (25, 70 and 90°C). The sorption process was analyzed by gravimetric measurements at different temperatures. Also, diffusion coefficients of solvent molecules in the TPU samples were identified. Therefore the activation energy and the mixing enthalpy were deduced. The aging impact on some mechanical properties of this material has been investigated after various aging cycles. Degradation of mechanical properties was observed. In fact, elastic modulus and stress at 200% of strain were decreased. It was also shown that such degradation largely depends on both aging temperature and aging immersion duration. The storage modulus (E 0) was also affected by the hygrothermal (HT) environment. The modification of mechanical properties seems to be well correlated to structural observations obtained from scanning electron microscopy (SEM) photographs. Finally, through thermal aging experiments, it was deduced that the combination of temperature with water seems to be a major factor of TPU degradation.

Journal of Thermoplastic Composite Materials, 2020

In this paper, an experimental study was conducted to characterize industrial PVC pipes and to in... more In this paper, an experimental study was conducted to characterize industrial PVC pipes and to investigate the effect of hydrothermal aging on their physico-chemical, thermal, and mechanical behavior. Three temperature (25°C, 60°C and 90°C) and full immersion in distilled water were retained as accelerated hydrothermal conditions. Kinetic of water absorption was examined and Fickian behavior was observed. The aging temperature was found to influence the water uptake behavior of PVC samples. Thermogravimetric analysis (TGA) has proved that the pipe material is not pure, while it consists of PVC reinforced with calcium carbonate (CaCO3). After exposure to accelerated aging, TGA and FTIR analysis exhibit preliminary signs of degradation of PVC samples under the retained conditions. Changes affecting the shape and the color of aged samples were examined. Mechanical properties have been characterized, after immersion of 30 days, with an improvement of strength and stiffness of the aged s...

Tribology International, 2021