Gamal R. Saad

Biodegradable copolymers based on bacterial Poly((R)-3-hydroxybutyrate): thermal and mechanical properties and biodegradation behaviour

Abstract 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.

Miscibility, crystallization and phase structure of poly(3-hydroxybutyrate)/cellulose acetate butyrate blends

Abstract Blends of poly(3-hydroxybutyrate) (PHB) with cellulose acetate butyrate (CAB) were prepared by solution casting from chloroform solutions at different compositions. The miscibility, crystallization behavior and phase structure were investigated using differential scanning calorimetry, optical microscopy and small-angle X-ray scattering (SAXS). CAB/PHB blends were found to be miscible in the melt state as evidenced by the deduction of a single glass transition ( T g ) for each composition, a depression in the equilibrium melting point of PHB, and a marked reduction in the spherulites growth rate of PHB in the PHB/CAB blends. The Flory–Huggins interaction parameter ( χ 12 ), obtained from melting point depression data, is composition dependent, and its value is always negative. The nucleation factor, K g , was determined using Lauritzen–Hoffman model. The K g values for the PHB in the blends are considerably lower than the K g value in the pure homopolymer. The phase structure of the blend in the solid state as revealed by SAXS is characterized by the presence of a homogeneous amorphous phase situated mainly in the interlamellar regions of crystalline PHB and consisting of CAB molecules and uncrystalline PHB chains.

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures II. 4-Hexadecyloxyphenyl arylates and aryl 4-hexadecyloxy benzoates

4-Hexadecyloxyphenyl-4-substituted benzoates, Ia-d, and 4-substituted phenyl-4- hexadecyloxy benzoates, IIa-d, with the substituents CH3O, Cl, CN, and NO2, respectively, were prepared and characterized by infrared spectroscopy and the apparent solution dipole moment measured using cyclohexane as a solvent. Smectic A mesophase stability was investigated by differential scanning calorimetry and polarized light microscopy. The effects of structural changes on phase transitions in these two series of compounds are discussed in terms of dipole and mesomeric effects.

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures IV. Dependence of Tc on the anisotropy of the aryl-X of polarizability bond

Transition temperatures of binary mixtures of the two series, 4-hexadecyloxyphenyl-4- substituted benzoates (Ia-d) and 4-substituted phenyl-4-hexadecyloxybenzoates (IIa-d), have been determined on cooling and the phase diagrams compared with those previously obtained on heating. Tc values for the monotropes and the non-LC analogues have been evaluated by extrapolation. Examination of both series revealed that the square root of Tc is related to the polarizability anisotropy, Delta alphaX, of the CAr-X bond, except for the methoxy derivatives.

Synthesis, characterization and biological activity of Schiff bases based on chitosan and arylpyrazole moiety.

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.

Dielectric investigation of cold crystallization of poly(3-hydroxybutyrate)

Abstract The dielectric behaviour of poly(3-hydroxybutyrate) (PHB) has been investigated for the glass (α) relaxation in the temperature and frequency ranges of −60 to 100°C and 103–105 Hz, respectively. Also, the crystallization kinetics of PHB has been studied dielectrically as a function of heating rate, time and temperature. Crystallinity has a marked influence on the glass relaxation characteristics owing to the relative constraint imposed on the amorphous phase by the crystallites. Furthermore, the results obtained showed that: (1) the optimum crystallization temperature is about 25°C; (2) the time at which crystallization starts is a function of the working temperatures and apparently is reduced to just a few minutes at 40°C; and (3) the crystallization process is completed within a period of less than 1 h in the temperature range 20–40°C. The bulk crystallization phenomena could be also described by the Avrami equation with an exponent ∼ 3.8.

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures III. Binary mixtures of alkoxyphenyl arylates and arylalkoxybenzoates

4-Substituted phenyl-4-hexadecyloxybenzoates and 4-hexadecyloxyphenyl-4-substituted benzoates were prepared and thermally characterized by differential scanning calorimetry. Transition temperatures were identified by polarized-light microscopy. Substituents were chosen to cover a wide range of electronic and dipolar characteristics. Binary mixtures of different components were prepared and similarly characterized to construct their phase diagrams. In mixtures of the 4-CN and 4-NO2 analogues, enhanced SmA mesophases were found when either of these esters was mixed with one of the methoxy analogues. A weak molecular complex is proposed to account for this non-ideal solution behaviour. Linear or slightly enhanced mixture behaviours were found for the nitro or cyano derivatives when mixed with each other. The results are interpreted in terms of electronic, dipolar, and molecular interactions.

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures VI[1]. The effect of molecular length

The apparent solution dipole moments of compounds based on 4,4-di-substituted phenyl benzoate (ROC6H4COOC6H4X), I, where X is a cyano group and R a terminal linear alkyl chain ranging from C12 to C20, were determined in cyclohexane at 30 C. The compounds were also thermally characterized by polarized light microscopy and differential scanning calorimetry. Phase diagrams were constructed for various binary mixtures prepared from any two homologues of series I as well as for every one of them with the nitro analogue II, where X is a nitro group and R C16H33. The study was undertaken in order to investigate the effect of the alkyl chain length on the mesophase behaviour. In order to assess the influence of structural variation in the central mesogenic group on the mesophase stability of pure and mixed compounds, the investigation was extended to cover binary mixtures of any two of the three compounds: analogue II (X=OC16H33), and the symmetric dialkoxy substituted phenyl esters (C16H33OC6H4COO)2 A, where A i...

Preparation, Characterization and Antimicrobial Activity of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-g-Poly(N-vinylpyrrolidone) Copolymers

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.

Potentiometric determination of some 1,4-benzodiazepines in pharmaceutical preparations and biological samples

Abstract New, simple, low cost and sensitive ion-selective electrodes are described for the determination of some 1,4-benzodiazepines in their pharmaceutical preparations as well as in biological fluids. Drug-tetraphenylborate and drug-phosphotungstate ion pairs have been prepared and used as electroactive materials. Poly(vinyl chloride) (PVC), and poly(esterurethane)s (UPCLs, UPBA, and UPDEGA) are used as the matrix. The proposed sensors give rapid Nernstian responses for 10−4–10−6 M of the abovementioned drugs in a pH range of 3–7. The membranes developed have potential stability for up to 4 weeks and show high selectivity for the investigated drugs over many interfering ions. The electrodes are used for determining trace amounts of bromazepam, clonazepam and diazepam in their pharmaceutical preparations as well as in biological fluids. For pharmaceutical preparations, the relative standard deviation (RSD) values were in the range, 1.37–4.1, 0.7–2.52 and 0.3–1.2% for bromazepam, clonazepam and diazepam, respectively using the PVC based electrodes, while for the UPBA based electrodes, the (RSD) values were in the range 0.6–3.35, 0.7–2.45 and 0.6–2.41%. For biological samples, the RSD values were 0.64–1.88, 0.37–1.8 and 1.36–3.57% for bromazepam, clonazepam and diazepam, respectively. Comparison of the results obtained using the proposed electrodes with those found using a (HPLC) reference method showed that the ion-selective electrode technique is sensitive, reliable and can be used with very good accuracy and high % recovery without pretreatment procedures of the samples to minimize interfering matrix effects.