Mustapha Raihane

Effect of Palm Tree Fiber Orientation on Electrical Properties of Palm Tree Fiber-reinforced Polyester Composites

The dynamic dielectrical analysis of short palm tree lignocellulosic fiber-reinforced polyester composites was carried out with special reference to the effect of fiber orientation, frequency, and temperature. Measurements were performed in the temperature range 40—200°C and in the frequency range 1—100 kHz. Three relaxations processes were identified, namely the orientation polarization imputed to the presence of polar water molecules in palm fiber, the relaxation process associated with conductivity occurring as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies, and the interfacial or Maxwell—Wagner—Sillars relaxation that is attributable to the accumulation of charges at the palm fibers/polyester interfaces. The orientation of the fiber can strongly influence the dielectrical properties and interfacial polarization processes in composites.

Electric field alignment of nanofibrillated cellulose (NFC) in silicone oil: impact on electrical properties.

This work aims to study how the magnitude, frequency, and duration of an AC electric field affect the orientation of two kinds of nanofibrillated cellulose (NFC) dispersed in silicone oil that differ by their surface charge density and aspect ratio. In both cases, the electric field alignment occurs in two steps: first, the NFC makes a gyratory motion oriented by the electric field; second, NFC interacts with itself to form chains parallel to the electric field lines. It was also observed that NFC chains become thicker and longer when the duration of application of the electric field is increased. In-situ dielectric properties have shown that the dielectric constant of the medium increases in comparison to the randomly dispersed NFC (when no electric field is applied). The optimal parameters of alignment were found to be 5000 Vpp/mm and 10 kHz for a duration of 20 min for both kinds of NFC. The highest increase in dielectric constant was achieved with NFC oxidized for 5 min (NFC-O-5 min) at the optimum conditions mentioned above.

Copolymers of Cyano Compounds with Captodative Monomers. Studies of Their Microstructures

Abstract Copolymers of vinylidene cyanide, methacrylonitrile, and acrylonitrile with various captodative monomers such as cyanovinyl acetate, methyl α-acetoxyacrylate or methyl 1-(methoxy carbonyl) vinyl carbonate were synthesized by radical copolymerization. The microstructures of these copolymers were studied by means of 13C NMR. The copolymers of vinylidene cyanide are rich in alternating structure, and the copolymers of methacrylonitrile and acrylonitrile are rather statistical than alternating. The measurements of reactivity ratios for three copolymerization reactions, vinylidene cyanide, methacrylonitrile, and acrylonitrile with methyl α-acetoxyacrylate, confirm these conclusions.

Kinetics of thermal degradation of an alternating copolymer: poly(methylvinylidene cyanide-co-vinyl acetate). Thermogravimetric and gas chromatography—mass spectroscopy studies

Abstract The thermal behaviour of poly(methylvinylidene cyanide-co-vinyl acetate), an alternating copolymer, has been studied by means of dynamic and isothermal thermogravimetric analysis in the range 280–350°C, and gas chromatographymass spectrometry. The main volatile products are acetic acid, acetonitrile and hydrogen cyanide which indicates that the thermal degradation is mainly an elimination reaction. A kinetic model including, simultaneously, a random and an autocatalytic process, leads to good agreement between experimental and theoretical curves. Kinetic parameters have been calculated. The activation energies are found to be, respectively, 144·1 and 178·6 kJ mol −1 for the random and the autocatalytic process; consequently, the autocatalytic process is slightly predominant at high temperature.

Novel Copolymers of 2-Phenyl-1,1-dicyanoethylene with 4-Fluoro- and Pentafluorostyrene

Copolymerization of 2-phenyl-1,1-dicyanoethylene (PDE) with 4-fluorostyrene and pentafluorostyrene in solution with radical initiation (ABCN) at 70°C yielded random copolymers with PDE alternating units. The composition of the copolymers was calculated from nitrogen analysis and the structure was analyzed by IR, 1H and 13C-NMR. The order of relative reactivity (1/r1) and the tendency toward alternation of monomer units in the copolymer for these two monomers, is 4-fluorostyrene (1.96) > pentafluorostyrene (0.51). Higher glass transition temperature of the copolymers in comparison with that of homopolymers indicates a decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit.

Microstructure of copolymers of vinylidene cyanide, methacrylonitrile and acrylonitrile with methyl α acetoxyacrylate, a captodative monomer

SummaryCopolymers of vinylidene cyanide (1a) methacrylonitrile (1b) and acrylonitrile (1c) with a captodative monomer, methyl α acetoxyacrylate were synthesized by radical copolymerization and their microstructures were studied by 13C NMR spectroscopy.The copolymer of 1a with methyl α-acetoxyacrylate (2) has mostly an alternating structure but the copolymers of 1b and 1c with 2 are rather statistical. The measurement of their reactivity ratios for these two reactions is in agreement with the proposed structures.

Thermal degradation of two copolymers of vinylidene cyanide and methyl α acetoxyacrylate. Thermogravimetric and gas chromatography-mass spectrometry studies

Abstract The thermal behaviour of two copolymers of poly(vinylidene cyanide-co-methyl α acetoxyacrylate) has been studied by means of dynamic and isothermal thermogravimetric analysis in the range 246–316 °C, and gas chromatography-mass spectrometry. The main volatile product is acetic acid, which indicates that the thermal degradation is mainly an elimination reaction. A kinetic model described by a kinetic law of order 1 for the copolymer P(VCN-co-MAA)25 leads to good agreement between experimental and theoretical curves. Kinetic parameters have been calculated. The activation energy is 170.7 kJ mol −1 . For the copolymer P(VCN-co-MAA)50, the depolymerization process is more important while the elimination is still present. No kinetic model can be proposed for this case.

Kinetics of thermal degradation of copolymers of methylvinylidene cyanide with substituted styrenes. Thermogravimetric and gas chromatography-mass spectroscopy studies

Abstract The thermal degradation behaviour of poly(methylvinylidene cyanide cosubstituted styrenes) has been studied by means of dynamic and isothermal thermogravimetry, in the range 324–395°C, and gas chromatography-mass spectroscopy analysis. The main volatile products are the substituted styrenes and the methylvinylidene cyanide. This indicates that the thermal degradation is mainly a depolymerisation reaction. A kinetic model including initiation by random chain scission, depropagation and termination leads to good agreement between experimental and theoretical curves. Kinetic parameters have been calculated. The activation energies are found to be more than those of polysubstituted styrenes.

Novel Copolymers of Difluoro Ring-substituted 2-Phenyl-1,1-dicyanoethylenes with 4-Fluorostyrene: Synthesis, Structure and Dielectric Study

Copolymerization of fluorine ring-substituted 2-phenyl-1,1-dicyanoethenes, RC6H3CH˭C(CN)2 (R is 2,3-F,F, 2,4-F,F, 2,5-F,F, 2,6-F,F, and 4-CF3) with 4-fluorostyrene were prepared in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the copolymers were characterized by IR, 1H and 13C-NMR, GPC, DSC, and TGA. The monomer reactivity ratios for 4-fluorostyrene (M1), r1 = 0.6 and 2-(2,4-difluorophenyl)-1,1-dicyanoethene (M2), r2 = 0 were determined from Fineman-Ross plot. The order of relative reactivity (1/r1) for difluoro-substituted monomers is 2,4-F,F (0.31) > 2,3-F,F (0.25) > 2,5-F,F (0.22) > 2,6-F,F (0.10). DSC curves showed that the copolymers were amorphous with high T g in comparison with that poly(4-fluorostyrene) indicating a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer units. From the thermogravimetric analysis, the copolymers began to degrade in the range 214–260°C. The copolymer of 4-fluorostyrene and 2-(2,4-difluorophenyl)-1,1-dicyanoethene and poly(4-fluorostyrene) were dielectrically characterized in the range 25–200°C. The dominating relaxation process detected in both materials was the α-relaxation, associated with the dynamic glass transition. The relationship polarity-permittivity was discussed.

Radical Copolymerization of Fluorine Ring-Substituted 2-Phenyl-1,1-dicyanoethylenes with 4-Fluorostyrene: Synthesis and Characterization

Novel copolymers of trisubstituted ethylene monomers, fluorine ring-substituted 2-phenyl-1,1-dicyanoethenes, RC6H4CH˭C(CN)2 (where R is 2-F, 3-F, and 4-F) and 4-fluorostyrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and 13C-NMR. High T g of the copolymers, in comparison with that of poly(4-fluorostyrene) indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. The gravimetric analysis indicated that the copolymers decomposed in two stages in the range 210–600°C.