Publications

Export 106 results:
Sort by: Author Title Type [ Year  (Desc)]
2014
Saad, G. R., H. E. Salama, N. A. Mohamed, and M. W. Sabaa, "Crystallization and thermal properties of biodegradable polyurethanes based on poly[(R)-3-hydroxybutyrate] and their composites with chitin whiskers", Journal of Applied Polymer Science, vol. 131, issue 18, pp. 9395 - 9407, 2014. AbstractWebsite

A series of biodegradable polyurethanes (PUs) were synthesized from hydroxylated bacterial poly[(R)-3-hydroxybutyrate], P[(R)-HB]-diol, as crystallizable hard segment and hydroxyl-terminated synthetic poly[(R,S)-3-hydroxybutyrate), P[(R,S)-HB]-diol, as an amorphous soft segment, using 1,6-hexamethylene diisocyanate, as non-toxic connecting agent. The P[(R)-HB] content was varied from 30 to 70 wt %. The resulting copolymers were characterized by FT-IR, 1H-NMR, DSC, and TGA. The DSC data revealed that the melting of P[(R)-HB] segment increases with increasing its own content in the PUs. The cold and melt crystallization are enhanced with increasing P[(R)-HB] content. The TGA data revealed that the thermal decomposition mainly occurred via a single degradation step and the thermal stability slightly increased with increasing P[(R)-HB] content. The non-isothermal crystallization behavior of PU sample containing 40 wt % PHB with and without α-Chitin whiskers was studied using DSC, and their kinetics data were investigated via the Avrami, Ozawa, and Z.S. Mo methods, respectively. Crystallization activation energy was estimated using Kissinger's method. Copyright © 2014 Wiley Periodicals, Inc.

Naoum, M. M., A. A. Fahmi, A. H. Abaza, and G. R. Saad, "Effect of exchange of terminal substituents on the mesophase behaviour of some azo/ester compounds", Liquid Crystals, vol. 41, issue 11, pp. 1559 - 1568, 2014. AbstractWebsite

Six homologous series of 4-(4′-alkoxy phenylazo) phenyl 4″-substituted benzoates (Ina-f) were prepared in which, within each homologous series, the length of the terminal alkoxy chain varies between 6, 8, 10, and 12 carbons, while the other terminal substituent, X, is a polar group that alternatively changed from CH3O, CH3, H, Br, NO2 and CN. Compounds prepared were characterised by spectroscopic methods, and their mesophase behaviour investigated by differential scanning calorimetry (DSC) and polarised optical microscopy (POM). The results were discussed in terms of mesomeric and polarisability effects. In each group of compounds, bearing the same alkoxy substituent, the nematic-to-isotropic transition temperatures (TC) were successfully correlated with the polarisability anisotropy of bonds to the substituent X. A comparative study was made between the investigated compounds and their previously prepared isomers, namely, 4-(4′-substituted phenylazo) phenyl 4″-alkoxybenzoates (IIna-f) in which the two terminal (alkoxy- and X) groups are exchanged. © 2014, © 2014 Taylor & Francis.

Naguib, H. F., M. S. A. Aziz, and G. R. Saad, "Effect of Organo-Modified Montmorillonite on Thermal Properties of Bacterial Poly(3-hydroxybutyrate)", Polymer - Plastics Technology and Engineering, vol. 53, issue 1, pp. 90 - 96, 2014. AbstractWebsite

Nanocomposites based on biodegradable poly(3-hydroxybutyrate) (PHB) and two types of organically modified layered silicates, cloisite 30B (C30B) and montmorillonite grafted-poly(ε{lunate}-caprolactone) (MPCL), were prepared through solution intercalation technique. The thermal properties of PHB/nanocomposites at different organoclay contents (5 and 10%) were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC results showed that the dispersed MPCL enhanced the rate of crystallization of PHB from glassy and molten states, whereas C30B retarded the crystallization of PHB from glassy state and enhanced its crystallization from molten state. Kinetics of thermal degradation was studied using Ozawa and Kissinger methods. © 2014 Copyright Taylor and Francis Group, LLC.

Aziz, M. S. A., H. F. Naguib, and G. R. Saad, "Non-isothermal crystallization kinetics of bacterial poly(3- hydroxybutyrate) in poly(3-hydroxybutyrate-co-butylene adipate) urethanes", Thermochimica Acta, vol. 591, pp. 130 - 139, 2014. AbstractWebsite

The non-isothermal melt crystallization kinetics of a series of copoly(ester-urethane)s, PUs, based on poly(3-hydroxybutyrate), PHB, and poly(butylene adipate), PBA, of different PHB content 20, 40, and 60 wt% were studied using DSC at different cooling rates. Various macrokinetic models, namely, Avrami, Tobin, Ozawa, and Mo models were applied to describe the crystallization process of PHB in the PU matrices. Avrami, Tobin, and Mo models could successfully describe the non-isothermal crystallization behavior of PHB segments in all samples, while Ozawa model provides a fair description of the non-isothermal crystallization process of PUs containing only 20 and 40 wt% PHB. The Avrami exponent was found to range from 3.6 to 4.0, while the Tobin exponent was found to range from 2.3 to 3.0. The spherulites shape and size were analyzed using polarized optical microscopy (POM). The results of kinetic parameters showed that the crystallization rate of PHB segments in the investigated PUs was increased with increasing the PHB content. 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. © 2014 Elsevier B.V. All rights reserved.

Aziz, M. S. A., H. F. Naguib, S. M. Sherif, and G. R. Saad, "Preparation and Characterization of Biodegradable Polyurethane Nanocomposites Based on Poly(3-hydroxybutyrate) and Poly(Butylene Adipate) Using Reactive Organoclay", Polymer - Plastics Technology and Engineering, vol. 53, issue 16, pp. 1671 - 1681, 2014. AbstractWebsite

Polyurethane nanocomposites were synthesized using one-step solution polymerization of poly(3-hydroxybutyrate)-diol, poly(butylene adipate)-diol using 1,6-hexamethylene diisocyanate. Nanocomposites were prepared using an in-situ polymerization method. The structure was verified using FTIR and 1HNMR. Morphology was examined by XRD and TEM methods. Thermal properties were examined using DSC and TG. DSC showed that all samples were semicrystalline. The Cloisite 30B enhanced the melt crystallization of PHB segments while hindering those of the PBA segments. Thermal stability was improved compared to the neat PUs samples. The Coats-Redfern model was used to calculate the activation energy. Mechanical properties were improved with incorporation of organoclays. © 2014, Copyright Taylor & Francis Group, LLC.

2013
Ahmed, H. A., M. M. Naoum, and G. R. Saad, "Effect of alkoxy-chain length proportionation on the mesophase behaviour of terminally di-substituted phenylazo phenyl benzoates", Liquid Crystals, vol. 40, issue 7, pp. 914 - 921, 2013. AbstractWebsite

A series of 4-alkoxyphenylazo-4′-phenyl-4′′-alkoxybenzoates bearing two terminal alkoxy groups (I m + n), where m and n denote the number of carbon atoms in the alkoxy groups attached to the phenylazo and benzoate moieties, respectively, was synthesised, and the molecular structures were established via elemental analyses, IR, NMR and mass spectroscopy. First, the thermal transitions and mesophase characteristics of any two isomeric molecules, having the same molecular length but with differently proportionated alkoxy groups, were investigated by differential scanning calorimetry and polarised-light microscopy. All compounds investigated proved to have a wide smectic C and nematic liquid crystalline ranges, except for the lower homologous (I 6 + 8 and I 8 + 6) where they are purely nematogenic. Mesophases were confirmed by the miscibility method, using dodecyloxybenzoic acid as the mesophase reference. Second, the mesophase behaviours of binary mixtures of isomeric compounds, bearing the same total alkoxy-chain length (m + n) but differ in the individual values of m and n, were studied and discussed. It was found that the smectic C and nematic phases behaved ideally in their binary mixture with the 4-alkoxy benzoic acid, independent of either n or m. © 2013 Copyright Taylor and Francis Group, LLC.

Saad, G. R., H. F. Naguib, and S. A. Elmenyawy, "Effect of organically modified montmorillonite filler on the dynamic cure kinetics, thermal stability, and mechanical properties of brominated epoxy/aniline formaldehyde condensates system", Journal of Thermal Analysis and Calorimetry, vol. 111, issue 2, pp. 1409 - 1417, 2013. AbstractWebsite

Nanocomposites, based on tetrabromo-bisphenol-A epoxy and aniline formaldehyde condensates, containing 5 and 10 % organically modified montmorillonite (O-MMT), were prepared. The morphologies of these nanocomposites were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of O-MMT on the dynamic cure kinetics, thermal stability, and mechanical properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and non-destructive ultrasonic testing techniques. The XRD and SEM results indicated a good dispersion of O-MMT within the epoxy matrix. The relation between the activation energy, E a, and the degree of cure, α, for the examined systems was obtained by applying model-free isoconversional Kissinger-Akahira-Sunose method. As α increases, E a increases gradually, almost independent of the amount of O-MMT. The dynamic cure kinetics of the neat epoxy system as well as its nanocomposites were described by Šestàk-Berggren, [SB (m, n)], autocatalytic model. The O-MMT enhances the thermal stability of the examined epoxy system. The results of the mechanical properties indicated that the addition of O-MMT enhances the Young's and shear elastic modulus and microhardness. The values of these parameters increase with increasing O-MMT loading. © 2012 Akadémiai Kiadó, Budapest, Hungary.

Naguib, H. F., M. S. A. Aziz, and G. R. Saad, "Synthesis, morphology and thermal properties of polyurethanes nanocomposites based on poly(3-hydroxybutyrate) and organoclay", Journal of Industrial and Engineering Chemistry, vol. 19, issue 1, pp. 56 - 62, 2013. AbstractWebsite

Segmented poly(ester-ether urethane)s/organoclay nanocomposites based on bacterial poly(3-hydroxybutyrate) (PHB) and poly(e{open}-caprolactone)-b-poly(ethylene glycol)-b-poly(e{open}-caprolactone) (PCL-PEG-PCL triblock copolymer) with Cloisite® 30B organoclay (C30B) were prepared by solution intercalation method. XRD, SEM and TEM results showed good dispersion of clay particles in polyurethane matrix. The presence of C30B increased Tg of PCL-PEG-PCL soft segments and the crystallization rate of PHB and PCL-PEG-PCL segments. C30B caused an enhancement in polyurethanes thermal stability and had an accelerating effect upon the main thermal decomposition of the polymer matrix as indicated by the lower activation energy (Ea) of decomposition compared to virgin materials, estimated using Kissinger-Akahira-Sunose isoconversional method. © 2012 The Korean Society of Industrial and Engineering Chemistry.

2012
Saad, G. R., and A. F. Serag Eldin, "Isothermal cure kinetics of uncatalyzed and catalyzed diglycidyl ether of bisphenol-A/carboxylated polyester hybrid powder coating", Journal of Thermal Analysis and Calorimetry, vol. 110, issue 3, pp. 1425 - 1430, 2012. AbstractWebsite

The thermal cure behavior of diglycidyl ether bisphenol-A/carboxylated polyester hybrid powder coating system in the absence and presence of catalyst was monitored using differential scanning calorimetry. Curing temperatures were between 160 and 200 °C. The experimental results showed an autocatalytic behavior of the reaction, which could be described by the model proposed by Kamal. This model includes two rate constants k1 and k2 and two reaction orders m and n. The activation energies Ea1 and Ea2 of these rate constants were 51.7 and 42.3 kJ/mol for uncatalyzed cure reaction and 40.6 and 35.0 kJ/mol for externally catalyzed reaction. The average order of the overall reaction was found to be 2.45 and 2.72 for uncatalyzed and catalyzed system, respectively. Except for the late stage of cure reaction, the model agreed well with the experimental data, especially at high temperatures and in externally catalyzed cure reaction. A diffusion factor was introduced into the model to account for the effect of diffusion on the cure rate. The modified model greatly improved the predicated data at the late stage of cure reaction. © Akadémiai Kiadó, Budapest, Hungary 2011.

Al-Sabagh, A. M., T. M. Khalil, M. W. Sabaa, T. T. Khidr, and G. R. Saad, "Poly(n-Alkyl Itaconate-Co-Vinyl Acetate) as Pour Point Depressants for Lube Oil in Relation to Rheological Flow Properties", Journal of Dispersion Science and Technology, vol. 33, issue 11, pp. 1649 - 1660, 2012. AbstractWebsite

In the present work, poly(n-alkyl itaconate-co-vinyl acetate) comb-like polymers were synthesized by radical copolymerization of n-alkyl itaconates of various alkyl chain length and vinyl acetate monomers for use as pour point depressants in lubricant oil. Initially four n-alkyl itaconate monomers were synthesized by esterification of itaconic acid with a series of n-alkyl alcohol, having different alkyl chain length C 16/C 18/NAFOL 20 + A (C av = 20)/NAFOL 1822 B (C av = 22). The copolymerization of these monomers with vinyl acetate was then performed using dibenzoyl peroxide in toluene at 120°C up to high conversion, with molar ratios of 0.25:0.75, 0.50:0.50, and 0.75:0.25 for alkyl itaconate: vinyl acetate. All products were characterized by FTIR, 1H NMR and gel permeation chromatography (GPC). These copolymers were tested in terms of their suitability as pour point depressants and flow improvers for lube oil. The obtained data revealed that the prepared compounds depress the pour point of the lube oil successfully and the additive efficiency on the pour point reduction of the lube oil increases by increasing the concentration of these additives and by decreasing the alkyl chain length of n-alkyl itaconate. The rheological properties of lube oil (with and without copolymer additive) were studied in term of shear rate, shear stress and viscosity. The results indicated that the performance of flow improver was dependent on the copolymer compositions and the size of alkyl chain length of n-alkyl itaconate monomers. Poly(hexadecyl itaconate-co-vinyl acetate) with high content of vinyl acetate showed the best flow improver properties of lube oil. Comparison of morphologies and structures of wax crystals or aggregates in untreated and treated lube oil was also done by micro photographic studies which showed the modification in wax crystal morphology due to additives. © 2012 Copyright Taylor and Francis Group, LLC.

Saad, G. R., M. A. Elsawy, and M. Z. Elsabee, "Preparation, Characterization and Antimicrobial Activity of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-g-Poly(N-vinylpyrrolidone) Copolymers", Polymer - Plastics Technology and Engineering, vol. 51, issue 11, pp. 1113 - 1121, 2012. AbstractWebsite

Graft polymerization of N-vinylpyrrolidone onto poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV was carried out in solution. The evidence of grafting was provided by FTIR, and 1H-NMR. The DSC results showed that the cold crystallization temperature from the glass state increased with increase of grafting %. TGA analysis revealed that the thermal stability of the host PHBV was improved remarkably with increasing extent of grafting. The swelling of the graft copolymer in water increases with increasing G%. The antibacterial activity of PHBV-g-PVP copolymers was improved dramatically with the extent of grafting. The biodegradability of PHBV and its graft copolymers was investigated in active soil. © 2012 Copyright Taylor and Francis Group, LLC.

Al-Sabagh, A. M., M. W. Sabaa, G. R. Saad, T. T. Khidr, and T. M. Khalil, "Synthesis of polymeric additives based on itaconic acid and their evaluation as pour point depressants for lube oil in relation to rheological flow properties", Egyptian Journal of Petroleum, vol. 21, issue 1, pp. 19 - 30, 2012. AbstractWebsite

Modification of the wax crystal habit practical interest during transportation processing of lube oil at low temperature. Various pour point depressant (PPD) additives can facilitate this modification by different mechanisms. Comb shaped polymer additives are known to depress the pour point of lube oil by providing different nucleation sites for the precipitation of wax. This paper describes performance based design, synthesis, characterization and evaluation of comb shaped polymeric additives. Alkyl itaconates were prepared by the esterification of itaconic acid with different saturated alcohols C16/C18/NAFOL 20+A (Cav = 20)/NAFOL 1822 B (Cav = 22). The four synthesized monomers were characterized and copolymerized with styrene in different molar ratios. All the products were characterized by infra-red (FTIR), Nuclear Magnetic Resonance (NMR) Spectroscopy and Gel permeation chromatography (GPC). Rheological properties of lube oil (with and without additives) were studied by Brookfield viscometer. In this study the additives based on itaconic acid were evaluated as good PPD and rheology modifiers. © 2012 Egyptian Petroleum Research Institute

Naguib, H. F., M. S. A. Aziz, S. M. Sherif, and G. R. Saad, "Thermal properties of biodegradable poly(PHB/PCL-PEG-PCL) urethanes nanocomposites using clay/poly(ε-caprolactone) nanohybrid based masterbatch", Applied Clay Science, vol. 57, pp. 55 - 63, 2012. AbstractWebsite

Organoclay/polyurethanes nanocomposites (CPNs) based on bacterial poly(3-hydroxybutyrate), PHB and poly(ε-caprolactone)-b-poly(ethylene glycol)-b-poly(ε-caprolactone), PCL-PEG-PCL triblock copolymer with poly(ε-caprolactone) grafted montmorillonite, Mt-PCL, were prepared by dispersion intercalation method. The microstructure of the CPNs with different content of Mt-PCL was investigated with wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) revealed good dispersion of Mt-PCL within the polyurethane matrix. The thermal properties of the prepared CPNs were investigated with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC data revealed the increase in T g and crystallization rate of both the PHB and PCL-PEG-PCL segments upon incorporation of Mt-PCL. The thermal stability of the nanocomposites was enhanced with increase of the Mt-PCL content. Activation energy (E a) was evaluated applying both Flynn-Wall-Ozawa and Kissinger methods. The CPNs were found to exhibit a lower activation energy compared with pure polyurethanes, indicating that the presence of Mt-PCL possesses an accelerating effect on the thermal decomposition of polyurethanes. © 2012 Elsevier B.V.

2011
Saad, G. R., E. E. Abd Elhamid, and S. A. Elmenyawy, "Dynamic cure kinetics and thermal degradation of brominated epoxy resin-organoclay based nanocomposites", Thermochimica Acta, vol. 524, issue 1-2, pp. 186 - 193, 2011. AbstractWebsite

The reaction kinetics of epoxy resin cured with stoichiometric amounts of amine-like structure and loaded with different levels of Cloisite 25A (C25A), has been studied by dynamic differential scanning calorimetry (DSC) to investigate the effect of the nano-organoclay particles on the kinetic parameters of the cure reaction. The kinetic analysis of non-isothermal cure showed that the Šesták-Berggren autocatalytic model is suitable to describe the kinetics of these reactions. Analysis of DSC data indicated that the presence of the C25A filler has a very small effect on the kinetics of cure. Thermogravimetric analyses showed higher thermal stability for the epoxy nanocomposites compared to pure epoxy. The activation energy of degradation process was estimated using both Kissinger and Ozawa methods. The epoxy nanocomposites loaded with 10 wt% C25A proved to exhibit high activation energy, indicating that C25A acquired a stabilizing effect upon the decomposition of polymer matrix. © 2011 Elsevier B.V.

Elsawy, M. A., G. R. Saad, and M. Z. Elsabee, "Grafting of N-isopropyl Acrylamide onto Bacterial Polyhydroxybutrate/Hydroxyvalerate Copolymers", Polymer - Plastics Technology and Engineering, vol. 50, issue 10, pp. 1055 - 1063, 2011. AbstractWebsite

This work deals with the grafting of N-isopropyl acrylamide (IPA) onto poly (3-hydroxybutyrate-3-hydroxyvalerate), (PHBV) (5.4 mole % 3-hydroxyvalerate), using benzoyl peroxide as free radical initiators. The effect of N-isopropyl acrylamide and initiator concentrations and reaction time on the degree of grafting has been investigated. The maximum degree of grafting was 82%. The grafted products were characterized by FTIR, 1HNMR, DSC, wide-angle X-ray diffraction and TGA analysis. The DSC results showed that the cold crystallization temperature from the glassy state increased with increasing the extent of grafting, while the Tg and Tm are not affected significantly. TGA analysis revealed that grafting of the host PHBV polymer did not affect much its onset decomposition temperature. The Grafted products swell in aqueous solution and the swelling is controlled by the extent of grafting, temperature, and pH. The biodegradability of PHBV and its graft copolymers solutioncast films was investigated in active soil. The results indicated that the introduction of the hydrophilic PVP and PIPA graft chains enhanced the biodegradability of PHBV. © Taylor & Francis Group, LLC.

Naguib, H. F., M. S. A. Aziz, S. M. Sherif, and G. R. Saad, "Synthesis and thermal characterization of poly(ester-ether urethane)s based on PHB and PCL-PEG-PCL blocks", Journal of Polymer Research, vol. 18, issue 5, pp. 1217 - 1227, 2011. AbstractWebsite

A series of block poly(ester-ether urethane)s, poly (PHB/PCL-PEG-PCL), based on poly(3-hydroxybutyrate) (PHB-diol), as hard segments, and poly(ε-caprolactone)-bpoly( ethylene glycol)-b-poly(ε-caprolactone), (PCL-PEGPCL) triblock copolydiol, as soft segments, were prepared using 1,6-hexamethylene diisocyanate (HDI), as non-toxic connecting agent. Polyurethanes block copolymer was synthesized from bacterial PHB and PCL-PEG-PCL blocks. The chemical structure and molecular weights of polymers prepared were characterized by FTIR, 1H NMR and GPC. The effect of chemical structure on the thermal and mechanical properties was studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile testing. The DSC results revealed that poly(PHB/ PCL-PEG-PCL) urethanes are semi-crystalline with two crystallizable PHB and PCL-PEG-PCL blocks. The thermal stability of the urethanes is less than neat PHB. The results of tensile testing showed that the extensibility of PHB is largely enhanced by the incorporation of PCL-PEG-PCL soft segments. Activation energy Ea, as a kinetic parameter of thermal decomposition, was estimated by each of the Ozawa and Kissinger methods. Close values of activation energy were obtained by both methods. The swelling behaviour of the copolymers was also investigated. © 2010 Springer Science+Business Media B.V.

2010
Saad, G. R., T. M. Khalil, and M. W. Sabaa, "Photo- and bio-degradation of poly(ester-urethane)s films based on poly[(R)-3-hydroxybutyrate] and poly(ℰ-caprolactone) blocks", Journal of Polymer Research, vol. 17, issue 1, pp. 33 - 42, 2010. AbstractWebsite

Biodegradable segmented poly(ester-urethane)s derived from telechelic dihydroxy-poly[(R)-3-hydroxybutyrate], acting as hard segments, and poly(ℰ-caprolactone)-diols, acting as soft segments, using 1,6-hexamethylene diisocyanate, as non toxic connecting agent, were synthesized. The copolymers were characterized with regard to their molecular weight by GPC and their main thermal transitions by DSC. These copolymers as well as PHB were exposed to UV-irradiation for different time intervals and the changes in the chemical structure were analyzed by FTIR spectroscopy. Under our experimental conditions, it was found that the increase of irradiation time was accompanied by increase of the proportion of the gel fraction and the decrease of the intrinsic viscosity of the soluble fraction of the investigated copolymers. The biodegradability of PHB and poly(ester-urethane) sample containing ∼40 wt% PHB before and after UV-irradiation was investigated under soil burial. The results showed that the photolysis in air prior to biodegradation increased the rate of degradation.

2009
El.shafee, E., M. Zaki, and G. R. Saad, "Annealing of poly(trimethylene terephthalate)/polycarbonate blends", Journal of Polymer Research, vol. 16, issue 4, pp. 317 - 327, 2009. AbstractWebsite

A blend of poly(trimethylene terephthalate) (PTT) and polycarbonate with a weight ratio of 50/50 was studied by means of differential scanning calorimetry (DSC) and dielectric spectroscopy (DS) after melt annealing that enables transesterification. The DSC results show that with increasing the residence time in the melt, the melting temperature and the heat of fusion of PTT crystals decrease. Prolonged thermal treatment at 300 °C gives rise to a copolymer that no longer reveals melting or crystallization. Additional annealing of such samples below the melting temperature of PTT results in restoration of the crystallization ability. The amorphous phase dynamics is studied by means of DS demonstrating that the glass transition relaxations are very sensitive to the crystallinity changes. The random copolymer is characterized by only one α-relaxation indicating a more or less homogeneous amorphous phase. In contrast to this, the physical blend and the block copolymers show two α-relaxation processes attributed to the existence of two amorphous fractions. Analysis of the relaxation process in terms of Vogel-Fucher-Tammann- Hesse model reveals a correlation between the fragility parameter and the extent of trans-reaction. The crystallization kinetics of the blocky copolymer determined from the changes of the dielectric constant with time are discussed and compared with pure PTT. © 2008 Springer Science+Business Media B.V.

2008
El Shafee, E., G. R. Saad, and M. Zaki, "Calorimetric and dielectric study on poly(trimethylene terephthalate)/ polycarbonate blends", Journal of Polymer Research, vol. 15, issue 1, pp. 47 - 58, 2008. AbstractWebsite

Poly(trimethylene terephthalate) (PTT)/polycarbonate (PC) blends with different compositions were prepared by melt blending. The miscibility and phase behavior of melt-quenched and cold-crystallized blends were studied using differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy. The blends of all compositions display only one glass transition (T g ) in both states. The melting temperature and the crystallinity of PTT in the blend decrease with increasing PC content. The dielectric results for the melt-quenched blends, for PC content up to 60 wt.%, exhibited two merged relaxation peaks during the heating scan; the lower temperature relaxation peak represent the normal glass-transition (α) relaxation of the mixed amorphous phase and the higher temperature relaxation due to the new-constrained mixed amorphous phase after crystallization. Cold-crystallized blends displayed only one glass transition α-relaxation whose temperatures varied with composition in manner similar to that observed by DSC. The dielectric α-relaxation of cold crystallized blends has been analyzed. Parameters relating to relaxation broadening, dielectric relaxation strength, and activation energy were quantified and were found to be composition dependent. The PTT/PC blends could be considered as two-phase system, a crystalline PTT phase and a mixed amorphous phase consisting of a miscible mixture of the two polymers. However, the crystallinity was only detected for blends containing greater than 40 wt.% PTT. © 2007 Springer Science+Business Media B.V.

Saad, G. R., R. E. Morsi, S. Z. Mohammady, and M. Z. Elsabee, "Dielectric relaxation of monoesters based poly(styrene-co-maleic anhydride) copolymer", Journal of Polymer Research, vol. 15, issue 2, pp. 115 - 123, 2008. AbstractWebsite

A series of alkyl-grafted copolymers based on styrene-maleic anhydride (SMA) copolymers were synthesized by esterification of SMA with several long chain normal aliphatic alcohols. The prepared copolymers were characterized by FT-IR and 1H NMR and DSC. The dielectric behavior of these copolymers was investigated in the frequency 20-105 Hz and temperature -40 to 180 °C ranges. Two relaxation processes were observed, α, and β-relaxation. The former is associated with the glass-rubber transition and is characterized by the Vogel-Fulcher-Tammann temperature dependence and the latter relaxation is related to the local motion of the ester side groups attached to the polymer backbone. The apparent activation energy for the β-relaxation was found to depend significantly on the alkyl chain length. The dielectric analysis of the β-relaxation process detected is discussed. © 2007 Springer Science+Business Media B.V.

2007
Saad, G. R., T. M. Khalil, and M. W. Sabaa, "Biodegradable poly(ester-urethane)s based on poly[(R)-3-hydroxybutyrate] and poly(ε-caprolactone) blocks: Thermal, mechanical and biodegradation behaviour", Eurasian Chemico-Technological Journal, vol. 9, issue 3, pp. 231 - 242, 2007. AbstractWebsite

α-ω-Dihydroxy-terminated poly[(R)-3-hydroxybutyrate] (PBB-diol) (Mn - 4800) was synthesized by transesterification of the corresponding PHB homopolymer with 1,4-butanediol in presence of p-toluenesulfanic acid. It was subsequently combined with poly(ε-caprolactone)-diols (PCL-diols) (Mn - 1260 and 2200) acting as soft segment via 1,6-hexamethylene diisocyanate to high molecular weight poly(esterurethane)s. The content of PHB acting as hard segments systematically varied from ∼20 to 60 wt.%. The synthesized materials were characterized by FTIR, 1H-NMF, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile properties. In the case of segmented poly(ester-urethane)s, those samples obtained from PCL (Mn - 1260) showed an increase in Tg's with increasing PHB content, indicating some extent of PCL/PHB segment phase mixing. All of the investigated copolymers were semicrystalline with Tm of PCL phase varying from 39-47°C and PHB phase varying from 141-150°C. The TGA analysis of the investigated copolymers showed three distinct weight loss steps assigned to the thermal degradation of PHB, PCL and urethane linkage with increasing temperature, respectively. As for mechanical tensile, it was found that the ultimate strength and elongation at the breakpoint decrease with increasing PHB content. The biodegradability was studied in active soil. The results showed that the biodegradation rate of the investigated copolymers increases with increasing PHB content. © 2007 al-Farabi Kazakh National University.

2004
Saad, G. R., and H. Seliger, "Biodegradable copolymers based on bacterial Poly((R)-3-hydroxybutyrate): Thermal and mechanical properties and biodegradation behaviour", Polymer Degradation and Stability, vol. 83, issue 1, pp. 101 - 110, 2004. AbstractWebsite

Two series of poly(ester-urethane) block copolymers were synthesized from bacterial telechelics, hydroxylated poly[(R)-3-hydroxybutyrate] (PHB-diol), as hard segments, and either poly(butylene glycol adipate)-diol (PBA-diol) or poly(diethylene glycol adipate)-diol (PDEGA-diol), as soft segments, using 1,6-hexamethylene diisocyanate as a non-toxic connecting agent. The content of PHB hard segments systematically varied from 10 to 60 wt.%. The synthesized materials were characterized by 1H NMR, GPC, differential scanning calorimetry, thermogravimetric analysis, wide angle X-ray diffraction, and tensile properties. The crystallization characteristics, reflecting the segmented properties of the synthesized copolymers, are discussed. For poly(ester-urethane)s, based on PHB-diol and PBA-diol, with PHB content less than 50 wt.%, both PBA and PHB crystalline phases, were detected. In contrast, in poly(ester-urethane)s, derived from PHB-diol and PDEGA-diol, only one crystalline phase, corresponding to the PHB hard segments, was observed. The thermogravimetric results of the prepared copolymers showed three-step decomposition assigned to the thermal degradation of PHB hard, PBA or PDEGA soft blocks, and urethane linkage, respectively. The tensile properties indicated that the tensile strength and elongation at the break points of poly(ester-urethane)s, derived from PHB and PBA, are greater than those prepared from PHB and PDEGA. The biodegradability was studied in compost-derived culture. The extent of mineralization was dependent on the copolymer composition. At a comparable incubation time, the copolymers containing 50 wt.% PHB were mineralized to an extent similar to that of the PHB homopolymer. © 2003 Elsevier Ltd. All rights reserved.

2003
Naguib, H. F., G. R. Saad, and M. Z. Elsabeé, "Copolymerization of bromophenylmaleimide with ethyl or butyl methacrylate", Polymer International, vol. 52, issue 7, pp. 1217 - 1221, 2003. AbstractWebsite

N-p-Bromophenylmaleimide (BrPMI) does not polymerize in solution by conventional free radical mechanism. However, it readily polymerized in bulk when mixed with a free radical initiator and heated in a microwave oven for 7-8 min. Copolymerization of ethyl methacrylate or butyl methacrylate with BrPMI was conducted in dioxane. The copolymers were characterized by IR and 1H NMR spectroscopy and gel permeation chromatography. The monomer reactivity ratios were calculated by a non-linear least-square analysis. Thermal analysis indicated a great improvement in thermal stability of the copolymers compared with the methacrylate homopolymers. BrPMI was also polymerized in bulk in the DSC pan, which allowed the calculation of the activation energy of its polymerization. © 2003 Society of Chemical Industry.

Naoum, M. M., R. I. Nessim, G. R. Saad, and T. Y. Labeeb, "Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures XII. Binary mixtures of homologues of unsymmetrical 1,4-phenylene bis(4-substituted benzoates)", Liquid Crystals, vol. 30, issue 2, pp. 165 - 172, 2003. AbstractWebsite

Twentyfour liquid crystalline esters of the type 4-(n-CnH2n+1O)C6H4 COOC6H4OOCC6H4-X-4 have been investigated for their phase behaviour. These compounds constitute six homologous series that differ from each other by the substituent X. The latter varies between CH3O, CH3, Cl, CN, NO2, and n-CnH2n+1O, and the number (n) of carbons varies, within a homologous series, between 6, 8, 14, and 16. All possible binary mixtures made from any two homologues were prepared and characterized for their mesophase behaviour by differential scanning calorimetry and polarizing optical microscopy.

2002
Saad, G. R., "Blends of bacterial poly[(R)-3-hydroxybutyrate] with oligo[(R,S)-3-hydroxybutyrate]-diol", Polymer International, vol. 51, issue 4, pp. 338 - 348, 2002. AbstractWebsite

The miscibility, melting and crystallization behaviour of poly[(R)-3-hydroxybutyrate], PHB, and oligo[(R,S)-3-hydroxybutyrate]-diol, oligo-HB, blends have been investigated by differential scanning calorimetry: thermograms of blends containing up to 60 wt% oligo-HB showed behaviour characteristic of single-phase amorphous glasses with a composition dependent glass transition, Tg, and a depression in the equilibrium melting temperature of PHB. The negative value of the interaction parameter, determined from the equilibrium melting depression, confirms miscibility between blend components. In parallel studies, glass transition relaxations of different meltcrystallized polymer blends containing 0-20 wt% oligo-HB were dielectrically investigated between -70°C and 120°C in the 100 Hz to 50 kHz range. The results revealed the existence of a single α-relaxation process for blends, indicating the miscibility between amorphous fractions of PHB and oligo-HB. © 2002 Society of Chemical Industry.

Tourism