Reduction efficiencies of natural substances for reduced graphene oxide synthesis

Journal of Materials Science - Synthesis of graphene by reducing graphene oxide is the most propitious route for bulk graphene production. Reduction using eco-friendly techniques is more feasible...     

Mild functionalization of carbon nanotubes filled epoxy composites: Effect on electromagnetic interferences shielding effectiveness

The effect of nitric acid mild functionalized multiwalled carbon nanotubes (MWCNTs) on electromagnetic interference (EMI) shielding effectiveness (SE) of epoxy composites was examined. MWCNTs were oxidized by concentrated nitric acid under reflux conditions, with different reaction times. The dispersion of MWCNTs after functionalization was improved due to the presence of oxygen functional groups on the nanotubes surface. Functionalization at 2 h exhibits the highest EMI SE and electrical conductivity of MWCNTs filled epoxy composites. However, EMI shielding performance of MWCNTs filled epoxy composite declined when the functionalization reaction time was prolonged. This was due to extensive damage on the MWCNT structure, as verified by a Raman spectroscope. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42557.     

Silane treatment of magnetite filler and its effect on the properties of magnetite-filled epoxy thin-film composites

Surface modification of magnetite by 3-aminopropyltriethoxysilane coupling agent (3APTES) at different percentages (5, 10, and 20 wt%) with variable treatment times (3, 5, and 7 h) was performed. The effects of these two variables on the properties of magnetite-filled epoxy thin-film composite were investigated. Treated composites exhibited higher saturation magnetization, storage modulus and T _g than untreated composites. Increasing 3APTES amount associated with increasing treatment time improved both the interfacial adhesion of magnetite filler matrix and the properties of treated composites. However, using a comparison system at a fixed treatment time, the system treated with a higher concentration of 3APTES exhibited lower saturation magnetization than that treated with a lower concentration. This result can be attributed to the thick coating on the filler surface that acted as a non-magnetic mass to the total sample volume and subsequently reduced the magnetization efficiency.     

Surface functionalization of multi-walled carbon nanotubes via electron reduction of benzophenone by potassium metal

The covalent sidewall functionalization of multi-walled carbon nanotubes (MWCNTs) via the electron reduction of benzophenone by potassium metal is reported. Fourier transform infrared spectroscopy (FTIR) results show that diphenylcarbinol (DPC) groups were successfully grafted to the MWCNTs sidewalls after 10 days of reaction time. Raman and UV–vis spectroscopies reveal the presence of covalent sidewall functionalization. The percentage of residues for DPC-MWCNTs was found to be lower than that for pristine MWCNTs, which indicates the existence of functional groups on the sidewalls of DPC-MWCNTs. It is shown that the sidewall of the DPC-MWCNTs was covered by non-uniform layer of DPC, as observed by transmission electron microscopy (TEM). Results from Raman spectroscopy, FTIR, TGA, UV–vis spectroscopy and TEM confirm that the functionalization of the covalent sidewalls of MWCNTs was successfully performed by this method.     

Properties of synthetic diamond and graphene nanoplatelet-filled epoxy thin film composites for electronic applications

Epoxy thin film composites filled with particulate nanofillers; synthetic diamond and graphene nanoplatelets were prepared and characterized based on tensile, thermal, and electrical properties. The influences of these two types of fillers, especially in terms of their loading, sizes and shapes, were discussed. It was found that the epoxy thin film composites incorporating synthetic diamond displayed optimum properties where the addition of synthetic diamond from 0 to 2 vol.% results in higher elastic modulus, tensile strength, elongation at break, thermal conductivity and storage modulus if compared to those of graphene nanoplatelets composites. Both thin film composites showed improvement in the glass transition temperature with increasing filler loadings. Results on the electrical conductivity of both systems showed that higher conductivity is observed in graphene nanoplatelets composites if compared to synthetic diamond composites.     

Transparent,electrically conductive,and flexible films made from multiwalled carbon nanotube/epoxy composites

Optically transparent, conductive, and mechanically flexible epoxy thin films are produced in the present study. Two types of multiwalled carbon nanotubes (MWCNTs) with different aspect ratios are dispersed in epoxy resin through an ultrasonication process. The MWCNT content is varied during the preparation of the thin films. The light transmittance and electrical conductivity of the thin films are characterized. Results show that composites containing MWCNTs with a lower aspect ratio exhibit enhanced electrical conductivity compared to those with a higher aspect ratio. A sheet resistance as low as 100 Ω/sq with nearly 60% optical transparency in 550 nm is achieved with the addition of MWCNTs in epoxy. In summary, transparent, conductive, and flexible MWCNT/epoxy thin films are successfully produced, and the properties of such films are governed by the aspect ratio and content of MWCNTs.     

Effect of filler surface treatment on mechanical properties and thermal properties of single and hybrid filler–filled PP composites

The influence of two types of surface treatments (aminosilane and Lica‐12) on the mechanical and thermal properties of polypropylene (PP) filled with single and hybrid filler (silica and mica) was studied. An improvement in tensile properties and impact strength was found for both treatments compared to those of untreated composites. However, the filler with silane coupling agent showed better improvement compared to the filler with Lica‐12 coupling agent. This was due to better adhesion between filler and matrix. Thermal analysis indicates that surface treatments increased the nucleating ability of filler, but decreased the coefficient of thermal expansion of PP composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A review on degradation mechanisms of polylactic acid: Hydrolytic,photodegradative, microbial,and enzymatic degradation

Recently, thoughtful disagreements between scientists concerning environmental issues including the use of renewable materials have enhanced universal awareness of the use of biodegradable materials. Polylactic acid (PLA) is one of the most promising biodegradable materials for commercially replacing nondegradable materials such as polyethylene terephthalate and polystyrene. The main advantages of PLA production over the conventional plastic materials is PLA can be produced from renewable resources such as corn or other carbohydrate sources. Besides, PLA provides adequate energy saving by consuming CO₂ during production. Thus, we aim to highlight recent research involving the investigation of properties of PLA, its applications and the four types of potential PLA degradation mechanisms. In the first part of the article, a brief discussion of the problems surrounding use of conventional plastic is provided and examples of biodegradable polymers currently used are provided. Next, properties of PLA, and (Poly[L-lactide]), (Poly[D-lactide]) (PDLA) and (Poly[DL-lactide]) and application of PLA in various industries such as in packaging, transportation, agriculture and the biomedical, textile and electronic industry are described. Behaviors of PLA subjected to hydrolytic, photodegradative, microbial and enzymatic degradation mechanisms are discussed in detail in the latter portion of the article.     

β-cyclodextrin as a Partial Replacement of Phosphorus Flame Retardant for Poly(Lactic Acid)/Poly(Methyl Methacrylate): A More Environmental Friendly Flame-Retarded Blends

β-Cyclodextrin was used together with isopropylated triaryl phosphate ester flame retardant to improve the flame resistance of poly(lactic acid)/poly(methyl methacrylate). Poly(lactic acid)/poly(methyl methacrylate)/flame-retardant blend (with and without β-cyclodextrin) was evaluated using limiting oxygen index, Underwriters Laboratories-94 vertical burning test, scanning electron microscopy, and thermogravimetric analysis (in O₂ and N₂). The addition of β-cyclodextrin was able to reduce the amount of flame retardant required for poly(lactic acid)/poly(methyl methacrylate) blends to achieve self-extinguishing properties. The poly(lactic acid)/poly(methyl methacrylate)20/flame-retardant/β-cyclodextrin blends achieved Underwriters Laboratories-94, V-0, and limiting oxygen index value of 29.3%. A compact and wide coverage of char layer was formed on the burning surface of poly(lactic acid)/poly(methyl methacrylate)20/flame-retardant/β-cyclodextrin blends.