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2018
Aziz, M. S. A., M. G. Elsoholy, and G. R. Saad, "Preparation and characterization of bio-based polyurethanes obtained from castor oil and poly (3-hydroxybutyrate) and their nanocomposites", Polymer Composites, vol. 39, pp. E489 - E499, 2018. AbstractWebsite

Bio-based polyurethanes (PUs) were synthesized from castor oil (CO) and poly(3-hydroxybutyrate)-diol (PHB-diol) using 1,6-hexamethylene diisocyanate, as nontoxic connecting agent. The PHB content in the obtained PUs was adjusted from 0 to 60.0 wt%. The synthesis was carried out by one pot solution polymerization. PUs nanocomposites loaded with different contents of cloisite®25A (C25A) were prepared by means of in situ solution polymerization. The molecular structure of the obtained PUs was confirmed by FT-IR. The thermal properties of the neat PUs and the resulting nanocomposites were investigated using DSC and TGA. It was found that the cold crystallization of the PHB component was enhanced, while its melt crystallization was retarded with increasing its own content in the PUs. The incorporated C25A in the PU matrix shifted the cold crystallization peak to higher temperature. TGA studies reveal that neat PUs and nanocomposites exhibited three main decompositions steps. The thermal stability of the neat PUs decreased with increasing the PHB content and increased with increasing the C25A content. Tensile mechanical testing revealed that increasing the content of the PHB and C25A made the PUs rigid and strong. The elastic modulus and ultimate tensile strength of the neat PUs were found to increase with increasing the PHB content and enhanced with incorporation of C25A, while the elongation decreased with increasing the PHB and C25A content. The equilibrium swelling in 1,2-dichloroethane decreased with increasing both the PHB and C25A content in PU matrix. POLYM. COMPOS., 39:E489–E499, 2018. © 2017 Society of Plastics Engineers. © 2017 Society of Plastics Engineers

Abudonia, K. S., G. R. Saad, H. F. Naguib, M. Eweis, D. Zahran, and M. Z. Elsabee, "Surface modification of polypropylene film by grafting with vinyl monomers for the attachment of chitosan", Journal of Polymer Research, vol. 25, issue 5, 2018. AbstractWebsite

Polypropylene (PP) film activated by corona discharge treatment was grafted with methyl methacrylate (MMA) and acrylic acid (AA). The grafted PP was characterized by spectral, thermal analysis and swelling behavior which confirmed the occurrence of the grafting. The water vapor and oxygen permeability (OTR and WVTR) as well as the mechanical properties have been enhanced by grafting with both AA and MMA. The grafted PP was further immobilized with chitosan (CS) using ceric ammonium nitrate (CAN) as an initiator under ultraviolet radiation. The chitosan immobilized grafted film was characterized by FTIR, mechanical properties, thermal properties and swelling measurements. Scanning electron microscope (SEM) confirmed that the CS is bonded to the grafted PP film. The CS modified PP film has acquired enhanced antibacterial and antifungal properties. © 2018, Springer Science+Business Media B.V., part of Springer Nature.

Ezz, A. A., M. M. Kamel, and G. R. Saad, "Synthesis and characterization of nanocarbon having different morphological structures by chemical vapor deposition over Fe-Ni-Co-Mo/MgO catalyst", Journal of Saudi Chemical Society, 2018. Abstract

Catalytic chemical vapor deposition (CCVD) is one of the most promising synthesis methods for economically producing large quantities of different nanocarbon structures. Here we report a systematic study of the synthesis conditions for the preparation of different nanocarbon morphological structures via acetylene decomposition over the surface of quaternary-metallic catalyst (Fe-Ni-Co-Mo) supported on MgO (Fe-Ni-Co-Mo/MgO). In particular, the effect of temperature, and the reaction time were investigated to optimize the yield, quality, size and graphitic crystallinity of the deposited carbon. The study showed a successful synthesis of: (i) a high-yield and quality bamboo-like multiwalled carbon nanotubes (b-CNT), (ii) hybrid graphene/carbon nanotubes (G/CNT), and (iii) multilayer graphene (MLG). The structures of the obtained products were characterized by HR-TEM, TGA, Raman spectroscopy, FTIR and X-ray diffraction. The results found seem essential for realizing the role of different synthesis parameters on the yield, quality, and morphology of the synthesized product. © 2018 King Saud University

Mohamed, R. R., M. H. Abu Elella, M. W. Sabaa, and G. R. Saad, "Synthesis of an efficient adsorbent hydrogel based on biodegradable polymers for removing crystal violet dye from aqueous solution", Cellulose, vol. 25, issue 11, pp. 6513 - 6529, 2018. AbstractWebsite

Water pollution with toxic dyes threatens human health world-wide. Herein, we prepared an effective adsorbent hydrogel for removing toxic cationic crystal violet (CV) dye from its aqueous solutions using biodegradable polymers such as; xanthan gum (XG) and poly (N-vinyl imidazole) (PVI). The structure and morphology of the prepared XG/PVI hydrogel and CV loaded hydrogel were characterized by FTIR, FE-SEM and XRD, while thermal stability of investigated hydrogel was characterized by TGA. Adsorption experiments were carried out as functions of initial concentration of CV dye, the adsorbent dose, pH of solution, temperature, and contact time. Results were analyzed using Langmuir and Freundlich isotherm models. It is found that the data were well fitted by Langmuir model. The maximum adsorption capacity achieved was found to be 453 mg g−1 due to electrostatic, H-bonding and dipole–dipole interactions between adsorbent surface and CV molecules. The adsorption kinetic studies showed that the adsorption followed pseudo-first order and intraparticle diffusion kinetic models. Regeneration (desorption) studies showed that XG/PVI hydrogel is an interesting adsorbent for removing toxic dyes from waste water. © 2018, Springer Nature B.V.

Salama, H. E., M. S. A. Aziz, and G. R. Saad, "Thermal properties, crystallization and antimicrobial activity of chitosan biguanidine grafted poly(3-hydroxybutyrate) containing silver nanoparticles", International Journal of Biological Macromolecules, vol. 111, pp. 19 - 27, 2018. AbstractWebsite

Green synthesis of novel nanocomposites series based on chitosan biguanidine grafted poly(3-hydroxybutyrate) copolymer (ChG-g-PHB) and silver nanoparticles (AgNPs) was successfully done via in situ reduction of AgNO3 in the copolymer matrix. Transmission electron microscopy verified the homogeneous dispersion of spherical shape of the AgNPs with an average particle size 12.3 to 19.2 nm. X-ray diffraction pattern revealed face centered cubic structure of AgNPs. The thermal stability was improved upon increasing the AgNPs content up to 2.0%, then declined upon loading with 3.0%. Coats-Redfern model showed that the sample with 2.0% AgNPs has the highest activation energy of the thermal degradation with values of 264 and 270 kJ mol− 1 for the 1st and 2nd degradation steps, respectively. Differential scanning calorimetry indicated that AgNPs acts as a nucleating agent for the nonisothermal melt crystallization of PHB component. Avrami equation described well the crystallization of PHB segments, with average Avrami exponent of 3.10 and 3.36 for ChG-g-PHB and its 2.0% nanocomposite, respectively. Regardless of the content of AgNPs, the antimicrobial activity of the nanocomposites is better than the neat copolymer. The sample loaded with 3.0% AgNPs showed the best antimicrobial activity with MIC value range of 0.98–1.95 μg mL− 1. © 2017 Elsevier B.V.

2017
Saad, G. R., M. A. Elsawy, and M. S. A. Aziz, "Nonisothermal crystallization behavior and molecular dynamics of poly(lactic acid) plasticized with jojoba oil", Journal of Thermal Analysis and Calorimetry, vol. 128, issue 1, pp. 211 - 223, 2017. AbstractWebsite

Poly(lactic acid) (PLA) containing different contents of jojoba oil (3 and 7 mass%; namely PLA-3JO and PLA-7JO), as natural plasticizer, was prepared via melt compounding. The nonisothermal crystallization behavior of PLA in the presence of jojoba oil was investigated from the glassy state. The obtained results revealed that the rate of crystallization and degree of crystallinity increased with increasing the content of jojoba. The nonisothermal crystallization kinetics was analyzed by the Avrami–Jeziorny model. Avrami exponent (n) of the PLA, PLA-3JO and PLA-7JO was found to be 4.08, 3.28 and 3.09, respectively, suggesting that the nonisothermal cold crystallizations of the plasticized PLA follow a heterogeneous nucleation and three-dimensional spherulitic growth, as occurring in the neat PLA. Furthermore, the activation energy of nonisothermal crystallization process (ΔEa) was calculated as a function of blend composition based on the Kissinger equation. It was found that the ΔEa of PLA insignificantly changed in the presence of jojoba oil. The dielectric properties of totally amorphous and crystallized plasticized PLA were also investigated for the α-relaxation process as a function of the temperature and frequency. The α-relaxation process was analyzed with Havriliak–Negami and Vogel–Fulcher–Tammann models, and fitting parameters with their evolution were discussed. © 2016, Akadémiai Kiadó, Budapest, Hungary.

Naoum, M. M., A. A. Fahmi, G. R. Saad, and M. H. Ali, "Polarity and steric effect of di-lateral substitution on the mesophase behaviour of some azo/ester compounds", Liquid Crystals, vol. 44, issue 11, pp. 1664 - 1677, 2017. AbstractWebsite

Eight homologous series of 2-(or 3-)substituted phenyl 4ʹ-(4″-alkoxy (2ʹ-, or 3″-substituted phenylazo) benzoates (InXY) were prepared in which the suffix ‘X’ refers to the lateral substituent X attached to the terminal benzene ring that carries the alkoxy group, and the suffix ‘Y’ refers to the substituent attached to the other terminal phenyl group. Within each homologous series, the length of the terminal alkoxy group varies from 8 to 16 carbons, while the lateral polar substituents, X and Y, alternatively varies between CH3 and F. The mesophase behaviour was investigated by differential scanning calorimetry and identified by polarised optical microscopy. The results were discussed in terms of the polarity and steric effects of the two lateral substituents. Comparative correlations were made to investigate the effect of the second lateral substituent on the mesophase behaviour of the previously investigated mono-laterally substituted analogues. UV–vis spectroscopic study revealed that the compounds I8XY exhibited two absorption bands: low intense bands at 254–263 and a broad band at 364–376 nm. These bands are attributed to the π–π∗ transition of the phenyl rings and the whole mesogenic portion. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

Hamed, A. A., G. R. Saad, and M. Z. Elsabee, "Synthesis and characterization of modified epoxy resins and novel E-glass-/spectra-reinforced composites", High Performance Polymers, vol. 29, issue 3, pp. 328 - 340, 2017. AbstractWebsite

Siliconized epoxy matrix systems have been developed using diglycidyl ether bisphenol A LY556 epoxy resin as a base, hydroxyl-terminated polydimethylsiloxane as modifier, and Î3-aminopropyltriethoxysilane as cross-linking agent together with dibutyltin dilaurate as a catalyst. Triethylene tetramine was used as a curing agent. Electrical-resistant glass (E-glass) and ultra-high-molecular-weight polyethylene (spectra)-reinforced composites are fabricated by hand-layup technique using the siliconized epoxy matrix systems. The effect of siloxane and the two fibers on the thermal and morphological characteristics of the siliconized epoxy polymer composites were studied using thermogravimetric analysis, differential scanning calorimetry, and scanning electron microscopy. The study reveals that the thermal stability of the epoxy systems is enhanced when siloxane is incorporated in them. Morphological studies show that the E-glass fiber reinforcement has better intermolecular adhesion to the epoxy resin than spectra reinforcement due to the presence of ionic sites. © 2016 The Author(s).

Salama, H. E., G. R. Saad, and M. W. Sabaa, "Synthesis, characterization and antimicrobial activity of biguanidinylated chitosan-g-poly[(R)-3-hydroxybutyrate]", International Journal of Biological Macromolecules, vol. 101, pp. 438 - 447, 2017. AbstractWebsite

Chitosan biguanidine hydrochloride (ChG) and low molecular weight poly[(R)-3-hydroxybutyrate] (PHB) were successfully prepared to overcome the solubility problem of chitosan and PHB and also to enhance antimicrobial activity of chitosan. The graft copolymers based on ChG and PHB (ChG-grafted PHB) were then prepared via condensation reaction of the carboxylic groups of PHB with the amino groups of ChG. These graft copolymers swell in water. The prepared graft copolymers were characterized by FTIR, 1H NMR, X-ray diffraction (XRD) and thermal analyses (TGA and DSC). TGA and DSC results revealed that the thermal stability and crystallinity of the graft copolymers were found to increase as the content of PHB increased. The antimicrobial activity of both ChG and ChG-grafted PHB, against Streptococcus pneumoniae, Bacillus subtilis, Escherichia coli (as examples of bacteria) and Aspergillus fumigatus, Geotricum candidum and Syncephalastrum recemosum (as examples of fungi), were tested. Among them, ChG and ChG-grafted PHB with the highest grafting percent investigated showed to possess relatively higher antimicrobial activity with low MIC values in the range of 0.49–3.90 μg mL−1. © 2017 Elsevier B.V.

2016
Omer, A. M., T. M. Tamer, A. El Monem, S. A. Elmoaty, M. A. El Fatah, and G. R. Saad, "Development of PVC membranes with clove oil as plasticizer for blood bag applications", Journal of Applied Pharmaceutical Science, vol. 6, issue 7, pp. 85 - 93, 2016. AbstractWebsite

In the present study, Antimicrobial PVC films containing different amounts of clove oil as a plasticizer were prepared using traditional casting method. The physical and mechanical properties of the plasticized PVC membranes e.g. surface wettability were investigated. The increase of clove oil content demonstrated an increase in surface hydrophilicity and elongation to break the film. The thermogravimetric analysis revealed a decrease of polymer thermal stability by increasing clove oil concentration. The antibacterial activities against four different bacterial strains (two-gram positive: Staphylococcus aureus and Bacillus cereus & two-gram negative: Pseudomonas aeruginosa and Escherichia coli) were promoted by addition of clove oil. Although the natural source of clove oil, the bio-evaluation of plasticized membranes showed an increase in hemolysis percent (%) and thrombus weight. It can be concluded that the addition of clove to PVC need to further studies for applying in blood bags. © 2016 Ahmed M. Omer et al.

Naoum, M. M., A. A. Fahmi, A. H. Abaza, and G. R. Saad, "The effect of orientation of the lateral methyl substituent on the mesophase behaviour of 4-alkoxyphenylazo aryl benzoates", Liquid Crystals, vol. 43, issue 12, pp. 1831 - 1845, 2016. AbstractWebsite

Two homologous series of 4-alkoxyphenylazo 4ʹ-(2ʺ- (and 3ʺ-) methyl-) 4ʹ-substituted benzoates (IIna–f and IIIna–f, six series each) were prepared and investigated. Within each series, the length of the terminal alkoxy group varies among 6, 8, 10 and 12 carbons, while the other terminal substituent, X, is a polar group that alternatively changes between the electron-donating CH3O, CH3, and the electron-withdrawing Br, NO2 and CN groups, in addition to the un-substituted analogue, X = H, aiming to investigate the effect of the different orientations of the methyl groups substituted on the central benzene ring, on the mesophase behaviour. The mesomorphic properties were discussed in terms of steric and polarisability effects. The mesophase stability was correlated with the polarisability anisotropy of bonds to the terminal substituent X. Comparative studies were made between the prepared isomers with each other and with the previously investigated laterally neat analogues 4-(4ʹ-alkoxyphenylazo) phenyl 4ʺ-substituted benzoates (Ina–f). © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Marei, N. H., E. A. El-Samie, T. Salah, G. R. Saad, and A. H. M. Elwahy, "Isolation and characterization of chitosan from different local insects in Egypt", International Journal of Biological Macromolecules, vol. 82, pp. 871 - 877, 2016. AbstractWebsite

Chitin was extracted from four different local sources: the shrimp (Penaeus monodon), the desert locust (Schistocerca gregaria), the honey bee (Apis mellifera) and the beetles (Calosoma rugosa). Chitosan was then obtained by deacetylation of chitin and physicochemically characterized using the Fourier transform infrared (FTIR) and X-ray diffraction. The moisture content, water binding capacity, fats binding capacity, ash content were determined and chitosans morphology was visualized using the scanning electron microscope (SEM). The difference between the obtained chitosans from three insect sources and α-chitosan from shrimp in terms of crystallinity, fibrous structure was discussed. © 2015 Elsevier B.V.

Elsawy, M. A., G. R. Saad, and A. M. Sayed, "Mechanical, thermal, and dielectric properties of poly(lactic acid)/chitosan nanocomposites", Polymer Engineering and Science, vol. 56, issue 9, pp. 987 - 994, 2016. AbstractWebsite

Poly(lactic acid) (PLA) loaded with various levels of chitosan nanoparticles (CsNP) (0–5.0%) were prepared by twin-screw extrusion. The nanocomposites were investigated based on their morphology, thermal, mechanical and dielectric properties. The SEM morphology showed that CsNP was dispersed uniformly in the PLA matrix. Thermal analysis through DSC revealed that the cold crystallization temperature of PLA in the case of nanocomposites slightly decreased with increasing content of CsNP; indicating a limit nucleating effect of CsNP. TGA analysis revealed that the incorporation CsNP slightly decreased the thermal stability of the PLA matrix. The mechanical analysis indicated that the incorporation of the CsNP in the PLA matrix improved the elongation and the impact strength, but decreased the tensile strength. The dielectric properties of these materials have been investigated for the α-relaxation process as a function of the temperature and frequency. The α-relaxation process was analyzed with Vogel–Fulcher–Tamman and Havriliak–Negami models and fitting parameters and their evolution were obtained. POLYM. ENG. SCI. 56:987–994, 2016. © 2016 Society of Plastics Engineers. © 2016 Society of Plastics Engineers

Ahmed, H. A., M. M. Naoum, and G. R. Saad, "Mesophase behaviour of 1:1 mixtures of 4-n-alkoxyphenylazo benzoic acids bearing terminal alkoxy groups of different chain lengths", Liquid Crystals, vol. 43, issue 9, pp. 1259 - 1267, 2016. AbstractWebsite

The thermal and mesophase behaviour of all possible 1:1 mixtures (In/Im) formed from any two homologues of 4-n-alkoxyphenylazo benzoic acids bearing different alkoxy chain lengths (n and m vary between 6 and 16 carbons), were investigated by differential scanning calorimetry (DSC) and phases identified by polarised light microscopy (PLM). Phase transitions were investigated as a function of the average alkoxy chain length (Formula presented) of the mixed acids. A comparison, made between the present series and previously investigated simpler analogues, 4-n-alkoxy benzoic acids, revealed that increasing the length of the mesogenic core increased the stabilities of both the smectic C and nematic phases. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Mohamed, N. A., H. E. Salama, M. W. Sabaa, and G. R. Saad, "Synthesis and characterization of biodegradable copoly(ether-ester-urethane)s and their chitin whisker nanocomposites", Journal of Thermal Analysis and Calorimetry, vol. 125, issue 1, pp. 163 - 173, 2016. AbstractWebsite

A series of copoly(ether-ester-urethane)s have been synthesized from poly(3-hydroxybutyrate) (PHB) diol prepolymer, as hard segments, and copoly(ε-caprolactone-ethylene glycol-ε-caprolactone) (PCL-PEG-PCL) diols with different PEG block lengths, as soft segments, with/without chitin whiskers (ChW) using hexamethylene diisocyanate, as a coupling agent, in one-step polymerization. The PHB content in the resulting copolymers was 0 and 40 %, and the content of ChW was varied from 0 to 5 %. The chemical structure of the resulting copolymers was characterized by FTIR, 1H-NMR and 13C-NMR spectra. The effect of chemical structure and ChW content on the thermal properties was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The DSC data revealed that the ΔHm of both PHB and PCL-PEG-PCL slightly increases with increasing the ChW content. The cold and melt crystallization of PHB enhanced with increasing ChW content. The TG data revealed that the thermal stability of copolymers slightly enhanced at high content of ChW. The swelling behavior of the copolymers was also investigated. © 2016, Akadémiai Kiadó, Budapest, Hungary.

Salama, H. E., G. R. Saad, and M. W. Sabaa, "Synthesis, characterization, and biological activity of cross-linked chitosan biguanidine loaded with silver nanoparticles", Journal of Biomaterials Science, Polymer Edition, vol. 27, issue 18, pp. 1880 - 1898, 2016. AbstractWebsite

Chitosan biguanidine hydrochloride (ChG) and glutaraldehyde cross-linked chitosan biguanidine (CChG) were synthesized and characterized by Fourier transform infrared spectroscopy, 1H NMR and 13C NMR, X-ray diffraction, scanning electron microscopy (SEM) and thermal analyses (TGA and DTA). The results showed that ChG and CChG had a more amorphous structure than that of chitosan, and their thermal stability were slightly lower than that of chitosan. Colloidal silver nanoparticles (AgNPs) were prepared using borohydride reduction method and then investigated as fillers in partially cross-linked chitosan biguanidine. The obtained nanoparticles were uniform and spherical with average size of 9.6 ± 0.5 nm. The prepared CChG/AgNPs composites were characterized for their morphology, thermal properties, cytotoxicity and antimicrobial activity. The SEM images showed that the AgNPs are well imbedded in the CChG matrix. The thermal stability of CChG was improved with incorporation of AgNPs. The CChG and CChG/AgNPs showed less cytotoxicity to breast cancer cells (MCF-7). Compared with chitosan and CChG, the ChG and CChG/AgNPs showed better antimicrobial activity against Streptococcus pneumoniae and Bacillus subtilis as Gram-positive bacteria, Escherichia coli as Gram-negative bacteria and Aspergillus fumigatus, Geotricum candidum and Syncephalastrum recemosum as fungi. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

2015
Saad, G. R., H. M. Abdallah, M. S. A. Aziz, N. A. Mohamed, and M. W. Sabaa, "Cure kinetics and thermal stability of maleimide modified epoxy TGIC/CPE powder coating system", Thermochimica Acta, vol. 617, pp. 191 - 199, 2015. AbstractWebsite

The curing kinetics of the modified triglycidyl isocyanurate (TGIC) with various content of N-phenylmaleimido group and carboxylated polyester (CPE) was investigated using dynamic differential scanning calorimetry (DSC). The curing kinetic behavior was well described by Šesták-Berggren (SB (m, n)) model. The m order of the curing reaction was varied from 0.229 to 0.356 and n order varied from 1.278 to 2.035, depending on the PMI content. In addition, the isoconversional method of Kissinger-Akahira-Sunose (KAS) was applied to correlate the activation energy (Ea) with the extent of cure. The obtained Ea increased with increasing phenyl maleimide content. As α increases, Ea declined up to α 0.3, then remained almost constant for α 0.3-0.8, and finally increased until completion of reaction, indicating complex reaction mechanism. The thermal stability of the cured modified TGIC/CPE was enhanced with incorporation of phenyl maleimide. © 2015 Elsevier B.V. All rights reserved.

Saad, G. R., A. A. Ezz, and H. A. Ahmed, "Cure kinetics, thermal stability, and dielectric properties of epoxy/barium ferrite/polyaniline composites", Thermochimica Acta, vol. 599, pp. 84 - 94, 2015. AbstractWebsite

Barium ferrite/polyaniline composites (Ba ferrite/PANI) were synthesized using in situ polymerization of different BaFe12O19/aniline weight ratios and dispersed in diglycidyl ether bisphenol-A/carboxylated polyester (DGEBA/CPE) hybrid powder coating system. The effects of heating rate, Ba ferrite/PANI compositions and their loading level on the curing process was investigated by differential scanning calorimetry (DSC) in the dynamic mode. The activation energy of the cure reaction was examined utilizing Kissinger-Akahira-Sunose (KAS) method. It was found that the activation energy of the cure reaction of the epoxy increases with increasing the content of the filler. The dielectric properties were studied using dielectric relaxation analysis over a range of frequency (0.2-100 kHz) at 30 °C. The obtained dielectric data were analyzed using complex permittivity and modulus formalisms, depending on the concentration of filler in the epoxy matrix. ©2014 Elsevier B.V. All rights reserved.

Naoum, M. M., A. A. Fahmi, N. H. S. Ahmed, and G. R. Saad, "The effect of inversion of the ester group on the mesophase behaviour of some azo/ester compounds", Liquid Crystals, vol. 42, issue 9, pp. 1298 - 1308, 2015. AbstractWebsite

Five homologous series of 4-substituted phenyl 4′-(4″-alkoxy phenylazo) benzoates (Ina – −e) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 8, 10, 12, 14 and 16 carbons, while the other terminal substituent, X, is a polar group that alternatively changed from CH3O, CH3, H, Br, and CN groups. Compounds prepared were characterised by infrared, mass, and H1-NMR spectroscopy and their mesophase behaviour investigated by differential scanning calorimetry (DSC) and polarised light microscopy (PLM). The results were discussed in terms of mesomeric and polarisability effects. Only for the lower group of compounds, I8a-e, that showed a nematic phase, the nematic-to-isotropic transition temperatures (TN–I) were successfully correlated to the polarisability anisotropy of bonds to the substituent X. A comparative study was made between the investigated compounds and two previously prepared isomeric groups. In the first group of isomers, 4-(4′alkoxy phenylazo) phenyl 4″-substituted benzoates (IIna – e), the ester groups are inverted. While in the second, 4-(4′-substituted phenylazo) phenyl 4″-alkoxy benzoates (IIIna – e), two modifications were made, inversion of the COO group, and exchange of the two wing substituents © 2015 Taylor & Francis.

Naoum, M. M., A. A. Fahmi, N. H. S. Ahmed, and G. R. Saad, "The effect of lateral methyl substitution on the mesophase behaviour of aryl 4-alkoxyphenylazo benzoates", Liquid Crystals, vol. 42, issue 11, pp. 1627 - 1637, 2015. AbstractWebsite

In order to investigate the effect of lateral methyl substitution on the mesophase behaviour of the previously investigated laterally neat 4-substituted phenyl 4ʹ-(4ʺ-alkoxyphenylazo) benzoates (Ina–e), five homologous series of 4-substituted phenyl 4ʹ-(3ʺ-methyl-4ʺ-alkoxyphenylazo) benzoates (IIna–e) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 8, 10, 12, 14, and 16 carbons, while the other terminal substituent, X, is a polar group that alternatively changed between the electron-donating CH3O and CH3 groups, and the electron-withdrawing Br and CN groups, in addition to the unsubstituted analogue. Two other isomeric series (IIIna–e) were also prepared in which the methyl group is laterally attached, this time, to position 2 of the same ring, aiming to investigate the effect of the different orientation of the methyl groups on the mesophase behaviour of the produced isomers. The results were discussed in terms of steric, mesomeric, and polarisability effects. © 2015 Taylor & Francis.

Ahmed, H. A., and G. R. Saad, "Mesophase behaviour of laterally di-fluoro-substituted four-ring compounds", Liquid Crystals, vol. 42, issue 12, pp. 1765 - 1772, 2015. AbstractWebsite

Four new groups of the di-fluoro-substituted 4-(2′-(or 3′)-fluoro phenylazo)-2-(or 3-) fluoro phenyl-4″-alkoxyphenylazo benzoates (In–IVn) were prepared and investigated for their mesophase behaviour. An alkoxy group of variable chain length (n = 6, 10 and 14 carbons) is attached to the terminal phenylazo benzoate moiety, and two lateral fluoro substituents are attached individually with different orientations to the other two adjacent rings. The molecular structures of the prepared compounds were confirmed by Fourier transform infrared spectroscopy and 1H NMR spectroscopy. The study aims to investigate the steric effect of the spatial orientation and relative positions of the two lateral fluorine atoms on the mesomorphic properties in their pure states. The mesophase behaviour was investigated via differential scanning calorimetry and mesophases were identified by polarised light microscopy. The investigation shows that these compounds exhibit high enantiotropic mesophases (SmC and N) and broad mesophase temperature range. The type and stability of the mesophase depends on the length of the terminal alkoxy chain and the position the two fluoro substituents. A comparison between these investigated compounds with their corresponding three-ring analogues was discussed. © 2015 Taylor & Francis.

Aziz, M. S. A., H. F. Naguib, and G. R. Saad, "Nanocomposites based on chitosan-graft-poly(N-Vinyl-2-Pyrrolidone): Synthesis, characterization, and biological activity", International Journal of Polymeric Materials and Polymeric Biomaterials, vol. 64, issue 11, pp. 578 - 586, 2015. AbstractWebsite

Organophilic montmorillonite (OMMT) was synthesized by cationic exchange between Na+-MMT and N-octyl-N-vinyl-2-pyrrolidonium bromide. Chitosan graft copolymer nanocomposites were synthesized by grafting N-vinyl-2-pyrrolidone onto chitosan in aqueous acetic acid in the presence of OMMT using free radical polymerization. The chemical structures were verified by FTIR. Scanning electron microscopy showed a surface roughness for chitosan graft nanocomposites. Wide-angle X-ray diffraction confirmed the intercalation of grafted chitosan chains between OMMT galleries. Thermogravimetric analysis indicated that the thermal stability of grafted chitosan was enhanced by OMMT incorporation. Preliminary studies showed that the nanocomposites exhibited antimicrobial activity compared with chitosan graft copolymer. © 2015 Taylor and Francis Group, LLC.

Aziz, M. S. A., G. R. Saad, and H. F. Naguib, "Non-isothermal crystallization kinetics of poly(3-hydroxybutyrate) in copoly(ester-urethane) nanocomposites based on poly(3-hydroxybutyrate) and cloisite 30B", Thermochimica Acta, vol. 605, pp. 52 - 62, 2015. AbstractWebsite

The non-isothermal melt crystallization kinetics of PHB segment in copoly(ester-urethane)s based on poly(3-hydroxybutyrate) and poly(butylene adipate) and their nanocomposites with cloisite 30B (C30B) were investigated at different cooling rates (5, 10, 15, and 20 °C min-1) using DSC. Ozawa, Avrami, and the combined Avrami-Ozawa (Mo) methods were used for analyzing the non-isothermal crystallization behavior. The results showed that Avrami and Ozawa models provide a fair description of the non-isothermal crystallization process while Mo model was successful in describing it. The results indicated that C30B not only served as heterogeneous nucleating agents for PHB crystallization, at lower content (5 wt%), but also restricted the mobility and diffusion of PHB chains at higher content (10 wt%). Polarized optical microscope (POM) showed that the nucleation density of PHB segment was increased significantly in the case of nanocomposites. The isoconversional method of Friedman was used to determine the effective activation energy of crystallization of the PUs and the Lauritzen-Hoffman parameters (Kg and U∗) were calculated by applying the Vyazovkin method. © 2015 Published by Elsevier B.V.

Salama, H. E., G. R. Saad, and M. W. Sabaa, "Synthesis, characterization and biological activity of Schiff bases based on chitosan and arylpyrazole moiety", International Journal of Biological Macromolecules, vol. 79, pp. 996 - 1003, 2015. AbstractWebsite

The Schiff bases of chitosan were synthesized by the reaction of chitosan with 3-(4-substituted-phenyl)-1-phenyl-1H-pyrazole-4-carbaldehyde. The structure of the prepared chitosan derivatives was characterized by FT-IR spectroscopy, elemental analysis, and X-ray diffraction studies and thermogravimetric analysis (TG). The results show that the specific properties of Schiff bases of chitosan can be altered by modifying the molecular structures with proper substituent groups.TG results reveal that the thermal stability of the prepared chitosan Schiff bases was lower than chitosan. The activation energy of decomposition was calculated using Coats-Redfern model. The antimicrobial activity of chitosan and Schiff bases of chitosan were investigated against Streptococcus pneumonia, Bacillis subtilis, Escherichia coli (as examples of bacteria) and Aspergillus fumigatus, Geotricum candidum and Syncephalastrum recemosum (as examples of fungi). The results indicated that the antimicrobial activity of the Schiff bases was stronger than that of chitosan and was dependent on the substituent group. The activity of un-substituted arylpyrazole chitosan derivative toward the investigated bacteria and fungi species was better than the other derivatives. © 2015 Elsevier B.V.

Naguib, H. F., M. S. A. Aziz, and G. R. Saad, "Synthesis, Characterization, and Microbial Activity of Nanocomposites of Chitosan-Graft-Poly(4-vinyl pyridine) Copolymer/Organophilic Montmorillonite", Polymer - Plastics Technology and Engineering, vol. 54, issue 12, pp. 1270 - 1279, 2015. AbstractWebsite

Organophilic montmorillonite was synthesized by cationic exchange between Na+-MMT and N-octyl-N-vinyl-2-pyrrolidonium bromide. Nanocomposites of chitosan grafted with 4-vinyl pyridine and organophilic montmorillonite were prepared in acetic acid using ammonium persulfate as initiator. The molecular structure of the grafted copolymer was confirmed by FTIR. The degree of dispersion and the intercalation spacing of these nanocomposites were investigated using X-ray diffraction. The enhanced thermal stability of nanocomposites was verified by differential scanning calorimetry and thermogravimetric analysis. Preliminary results of the antibacterial and antifungal activities of the prepared nanocomposites have demonstrated significant antimicrobial activity of the nanocomposites compared with pure and grafted chitosan. © 2015, Copyright © Taylor & Francis Group, LLC.