الفهرس 
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Abstract
This work aims at exploring modified reduced graphene oxide (RGO) for active packaging or energy storage applications. To fulfill this aim, sur-face modification of RGO with two types of modifiers, hyperbranched poly-ester (PES) for the first application and silver/copper oxide nanoparticles, has been carried out. The purpose of surface functionalization of RGO with PES, is not only to improve the dispersion of graphene nanosheets and hence their properties but also to impart new characteristics to a hosting biodegradable matrix (we choose polycaprolactone (PCL)). Meanwhile, the surface decoration of RGO with metal/metal oxide nanoparticles goes to enhance the electrochemical properties of supercapacitor electrodes.
In more details, RGO was firstly prepared by Hummer method and then functionalized with PES using in-situ and ex-situ approaches, in order to determine the best technique that provides improved properties. The suc-cessful preparation of graphene and its modified forms was confirmed with different characterization techniques such as X-ray diffraction, X-ray photo-electron spectroscopy, infrared spectroscopy, Raman spectroscopy, trans-mission electron microscope, and atomic force microscope. The biological activity against deleterious pathogens was also discussed and the results showed improved biocidal activity in presence of PES. Moreover, the impact of RGO during the in-situ polymerization step was investigated using proton magnetic resonance and gel permeation chromatography for structural analysis of unattached PES obtained in presence of RGO compared with pure PES that prepared in absence of RGO. The results confirmed that, in presence of RGO, the polymerization was occurred and the PES was formed with its well-known chemical structure. Nevertheless, the degree of branch-ing was found lower than in case of pure PES. Finally, the prepared RGO and its in-situ and ex-situ modified forms were added with different ratios to the PCL films utilizing two comparable techniques; casting and melting. In the latter process, the filler or its modified form was blended with the commer-cial PCL under thermal conditions in the Barbender and then thermal press-ing to obtain free standing films. Moreover, these nanocomposite films were also obtained using casting technique. The thermal and mechanical properties were studied for all produced films. The results obtained were different and depending on the method of film fabrication. Particularly, the films prepared with casting technique exhibited improvement in the degra-dation and crystallization temperatures of PCL film, with the incorporation of fillers, without significant changing in the Tg. On contrast, inclusion of such fillers under melting conditions showed increasing in the decomposi-tion and glass transition temperatures without changing in the crystallinity of the PCL matrix. Mechanically, addition of the prepared fillers to melt PCL matrix led to enhancement of stiffness, mechanical strength, tensile strength, and elongation at break. Nevertheless, the surface modification of RGO with PES could be an effective approach to fine tune the stiffness and elasticity of the PCL matrix prepared with casting method. The improve-ment of surface wettability was checked with contact angle measurements. The results emphasized that the inclusion of modified fillers decreased the values of contact angle whatever the method of film fabrication. The rate of water permeability decreased to ~ one third of PCL film after the rein-forcement with modified filler either with casting or with melting process. However, further improvement ~ 20 % against the permeability of CO2 and H2O was observed for the nanocomposite blends prepared with melting process. Meanwhile, the casted films did not exhibit a significant enhance-ment either in water or gas permeability. The antimicrobial performance against Gram-positive and Gram-negative bacteria was debated in details. Specifically, the PCL films incorporated with the prepared fillers are selec-tive to Gram-positive bacteria regardless the way of film preparation. Last-ly, the biodegradation test indicated to the successful decay of the PCL and its nanocomposite films in soil. However, utilizing fungal based method, blends reinforced with modified graphene showed a weight loss three-fold higher than the neat matrix. Generally, the results indicate the strong workability of the modified RGO incorporated in the PCL matrix particularly under melting process which simulates the industrial conditions.
On the other hand, surface decoration of RGO with silver and copper oxide nanoparticles was achieved via in-situ reduction process of graphene oxide in presence of metallic precursors in order to improve the electro-chemical properties of RGO. The successful preparation of metal/metal ox-ide doped RGO was confirmed with transmission and scanning electron mi-croscopes, X-ray diffraction, and Energy-dispersive X-ray spectroscopy. Par-ticularly, TEM images confirmed that the obtained copper oxide nanoparti-cles have a lower particle size than silver nanoparticles. The prepared elec-trodes based RGO and RGO hybrid materials were check in different elec-trolyte medium. The effect of nanoparticle loading percentages, scan rates, and cycling were also intensively investigated in order to determine the op-timized conditions at which the modified electrode exhibit superior perfor-mance. The results showed that the specific capacitance of RGO was found two fold greater (200 F g-1) in presence of 5 Wt. % CuO nanoparticles at 50 mVs-1 in the acidic medium. Interestingly, these results emphasize that the copper oxide nanoparticles doped RGO is a promising electrode material for supercapacitor applications.
Finally, it could be claimed that the findings presented in this thesis have provided not only fundamental understanding of graphene nanocom-posites impacts in the polymeric matrix but also applications in different potential fields.