Zahi Khalil - Academia.edu (original) (raw)

Papers by Zahi Khalil

Research paper thumbnail of Photolysis and photo-oxidation of unsaturated polyesters

Die makromolekulare Chemie, 1989

The photolytic and photo-oxidative evolution of unsaturated polyesters, crosslinked or not, expos... more The photolytic and photo-oxidative evolution of unsaturated polyesters, crosslinked or not, exposed to polychromatic light is studied using IR, FTIR, W spectrometries. The influence of each elaboration parameter (nature and concentration of diacids like maleic anhydride, fumaric acid or phthalic acids, nature of glycols, nature and concentrations of crosslinking agents, mode of crosslinking) is determined. The mechanism involving primary excitation of the maleate-fumarate or of phthalateunits and radical reactions accounts for the appearance of hydroxylated and carbonylated groups. Photoyellowing of unsaturated polyesters is related either to the styrene oligomers or to the phthalateunits. Through parallel studies of photochemistries in polystyrene (PS) and ply(buty1ene terephthalate) (PBT) at long wavelengths, the different sources of photoyellowing are precised. Unsaturated polyesters often used as thermoset matrices in composite materials are obtained by polycondensation of unsaturated and saturated acids with aliphatic glycols. The crosslinking agent which reacts with unsaturated groups along the polyester chain is usually styrene or methyl methacrylate. The detailed structure of crosslinked polyesters are, generally, not well known, this is mainly due to the insolubility of the cured products. The photochemical behaviour of these polymers (a) was anticipated to depend on the polymer composition : nature of diacids (phthalic, maleic, fumaric), nature of glycols, and nature of crosslinking comonomer and of crosslinking mode. Note a. The unsaturated polyesters studied, elaborated by CdF Chimie, are commercialized under the trademark I1NORSODYNE1'.

Research paper thumbnail of Oxydations photothermique et photocatalysee de polyesters insatures reticules utilises dans les materiaux composites

Comportement photochimique du polymaleophtalate reticule par le styrene. Perturbations de l'e... more Comportement photochimique du polymaleophtalate reticule par le styrene. Perturbations de l'evolution chimique du polyester, provoquees par l'addition de charges minerales absorbantes ou non. Mecanisme

Research paper thumbnail of Photolysis and photo‐oxidation of unsaturated polyesters

Makromolekulare Chemie. Macromolecular Symposia, 1989

The photolytic and photo‐oxidative evolution of unsaturated polyesters, crosslinked or not, expos... more The photolytic and photo‐oxidative evolution of unsaturated polyesters, crosslinked or not, exposed to polychromatic light is studied using IR, FTIR, UV spectrometries. The influence of each elaboration parameter (nature and concentration of diacids like maleic anhydride, fumaric acid or phthalic acids, nature of glycols, nature and concentrations of crosslinking agents, mode of crosslinking) is determined. The mechanism involving primary excitation of the maleate‐fumarate or of phthalate units and radical reactions accounts for the appearance of hydroxylated and carbonylated groups. Photoyellowing of unsaturated polyesters is related either to the styrene oligomers or to the phthalate units. Through parallel studies of photochemistries in polystyrene (PS) and poly(butylene terephthalate) (PBT) at long wavelengths, the different sources of photo‐yellowing are precised.

Research paper thumbnail of Oxydations photothermique et photocatalysee de polyesters insatures reticules utilises dans les materiaux composites

Comportement photochimique du polymaleophtalate reticule par le styrene. Perturbations de l'e... more Comportement photochimique du polymaleophtalate reticule par le styrene. Perturbations de l'evolution chimique du polyester, provoquees par l'addition de charges minerales absorbantes ou non. Mecanisme

Research paper thumbnail of Characterization Of Biocoal From Hydrothermal Carbonization Of Pine Needles And Palm Leaves

This work describes preparation of biocoal Pn-HTC and Pl-HTC by hydrothermal carbonization HTC of... more This work describes preparation of biocoal Pn-HTC and Pl-HTC by hydrothermal carbonization HTC of pine needles and palm leaves respectively. The biomass samples were treated with hot deionized water at a temperature range 180-250 °Cunder saturated pressure and inert atmosphere for six hours.The obtained coallike residues was well-characterized. They had a porous structure and showed very interesting energetic properties comparedto many biomass with derived energy such as bamboo, paper and food. The recovery of high energy conversion efficiency for Pn-HTC and Pl-HTC are78.4% and 88.7 respectively are recorded at the maximum reactor temperature 225oC. Calorific values were evaluated at 25.2 and 24.8 Mj/Kg for Pn-HTC and Pl-HTC respectively and showed 21 % increase in energy content compared to that of raw biomass. Palm leaves presented higher coal and fixed carbon yields and lower mass of volatile matter. The analysis of processed water showed good fertilizing property rich of nutrien...

Research paper thumbnail of Photo-oxydation du polystyrène à grandes longueurs d'onde (λ > 300 nm) et à 60°c

Die makromolekulare Chemie, Jul 1, 1987

An analytical and kinetic study of the photo-oxidation of polystyrene in the solid state carried ... more An analytical and kinetic study of the photo-oxidation of polystyrene in the solid state carried out at long wavelengths (λ > 300 nm) is reported. The concentration of the primary hydroperoxides has been determined throughout photo-oxidation using chemical titrations. IR and FTIR spectrometry were used to analyze the hydroxylated and carbonylated intermediate groups formed. Hydrogen-bonded alcohols (3540 cm−1), aromatic ketones (1690 cm−1), and unsaturated esters (1725 cm−1) were observed. The UV-absorbing products formed in the photo-oxidation enter a photothermal equilibrium; this allows to select only two structures to account for the yellowing of photooxidized polystyrene.

Research paper thumbnail of Photolysis and photo-oxidation of unsaturated polyesters

Die makromolekulare Chemie, 1989

The photolytic and photo-oxidative evolution of unsaturated polyesters, crosslinked or not, expos... more The photolytic and photo-oxidative evolution of unsaturated polyesters, crosslinked or not, exposed to polychromatic light is studied using IR, FTIR, W spectrometries. The influence of each elaboration parameter (nature and concentration of diacids like maleic anhydride, fumaric acid or phthalic acids, nature of glycols, nature and concentrations of crosslinking agents, mode of crosslinking) is determined. The mechanism involving primary excitation of the maleate-fumarate or of phthalateunits and radical reactions accounts for the appearance of hydroxylated and carbonylated groups. Photoyellowing of unsaturated polyesters is related either to the styrene oligomers or to the phthalateunits. Through parallel studies of photochemistries in polystyrene (PS) and ply(buty1ene terephthalate) (PBT) at long wavelengths, the different sources of photoyellowing are precised. Unsaturated polyesters often used as thermoset matrices in composite materials are obtained by polycondensation of unsaturated and saturated acids with aliphatic glycols. The crosslinking agent which reacts with unsaturated groups along the polyester chain is usually styrene or methyl methacrylate. The detailed structure of crosslinked polyesters are, generally, not well known, this is mainly due to the insolubility of the cured products. The photochemical behaviour of these polymers (a) was anticipated to depend on the polymer composition : nature of diacids (phthalic, maleic, fumaric), nature of glycols, and nature of crosslinking comonomer and of crosslinking mode. Note a. The unsaturated polyesters studied, elaborated by CdF Chimie, are commercialized under the trademark I1NORSODYNE1'.

Research paper thumbnail of Oxydations photothermique et photocatalysee de polyesters insatures reticules utilises dans les materiaux composites

Comportement photochimique du polymaleophtalate reticule par le styrene. Perturbations de l'e... more Comportement photochimique du polymaleophtalate reticule par le styrene. Perturbations de l'evolution chimique du polyester, provoquees par l'addition de charges minerales absorbantes ou non. Mecanisme

Research paper thumbnail of Photolysis and photo‐oxidation of unsaturated polyesters

Makromolekulare Chemie. Macromolecular Symposia, 1989

The photolytic and photo‐oxidative evolution of unsaturated polyesters, crosslinked or not, expos... more The photolytic and photo‐oxidative evolution of unsaturated polyesters, crosslinked or not, exposed to polychromatic light is studied using IR, FTIR, UV spectrometries. The influence of each elaboration parameter (nature and concentration of diacids like maleic anhydride, fumaric acid or phthalic acids, nature of glycols, nature and concentrations of crosslinking agents, mode of crosslinking) is determined. The mechanism involving primary excitation of the maleate‐fumarate or of phthalate units and radical reactions accounts for the appearance of hydroxylated and carbonylated groups. Photoyellowing of unsaturated polyesters is related either to the styrene oligomers or to the phthalate units. Through parallel studies of photochemistries in polystyrene (PS) and poly(butylene terephthalate) (PBT) at long wavelengths, the different sources of photo‐yellowing are precised.

Research paper thumbnail of Oxydations photothermique et photocatalysee de polyesters insatures reticules utilises dans les materiaux composites

Comportement photochimique du polymaleophtalate reticule par le styrene. Perturbations de l'e... more Comportement photochimique du polymaleophtalate reticule par le styrene. Perturbations de l'evolution chimique du polyester, provoquees par l'addition de charges minerales absorbantes ou non. Mecanisme

Research paper thumbnail of Characterization Of Biocoal From Hydrothermal Carbonization Of Pine Needles And Palm Leaves

This work describes preparation of biocoal Pn-HTC and Pl-HTC by hydrothermal carbonization HTC of... more This work describes preparation of biocoal Pn-HTC and Pl-HTC by hydrothermal carbonization HTC of pine needles and palm leaves respectively. The biomass samples were treated with hot deionized water at a temperature range 180-250 °Cunder saturated pressure and inert atmosphere for six hours.The obtained coallike residues was well-characterized. They had a porous structure and showed very interesting energetic properties comparedto many biomass with derived energy such as bamboo, paper and food. The recovery of high energy conversion efficiency for Pn-HTC and Pl-HTC are78.4% and 88.7 respectively are recorded at the maximum reactor temperature 225oC. Calorific values were evaluated at 25.2 and 24.8 Mj/Kg for Pn-HTC and Pl-HTC respectively and showed 21 % increase in energy content compared to that of raw biomass. Palm leaves presented higher coal and fixed carbon yields and lower mass of volatile matter. The analysis of processed water showed good fertilizing property rich of nutrien...

Research paper thumbnail of Photo-oxydation du polystyrène à grandes longueurs d'onde (λ > 300 nm) et à 60°c

Die makromolekulare Chemie, Jul 1, 1987

An analytical and kinetic study of the photo-oxidation of polystyrene in the solid state carried ... more An analytical and kinetic study of the photo-oxidation of polystyrene in the solid state carried out at long wavelengths (λ > 300 nm) is reported. The concentration of the primary hydroperoxides has been determined throughout photo-oxidation using chemical titrations. IR and FTIR spectrometry were used to analyze the hydroxylated and carbonylated intermediate groups formed. Hydrogen-bonded alcohols (3540 cm−1), aromatic ketones (1690 cm−1), and unsaturated esters (1725 cm−1) were observed. The UV-absorbing products formed in the photo-oxidation enter a photothermal equilibrium; this allows to select only two structures to account for the yellowing of photooxidized polystyrene.