The cyclization index and toughness of gel spun polyacrylonitrile (PAN) proportionality with its heat of stabilization

The spun tapes of synthesized PAN, its copolymer with 1 wt% itaconic acid, and doped version with 1 wt% sodium dodecyl sulfate (SDS) all showed stripy, even, and compact cross-sections as the hallmark of gel forming products. PAN doping with SDS and acrylonitrile copolymerization with itaconic acid reduced its dimethylformamide (DMF) solution structural viscosity index (Δη) by 50% and 30%, respectively, at 675 s^??1. In addition, the modification of synthesized PAN through doping and acrylonitrile copolymerization with itaconic acid led to severe and mild gelation temperature decrease, respectively. The stabilization peak of the synthesized PAN tape was enhanced as much as 25 °C by 900% hot drawing, decreased by about 10 °C through copolymerization, while experienced small temperature changes through doping. The second derivative of Fourier transform infrared and Gaussian fitting was used to analyze the tapes cyclization due to stabilization treatment through introducing I_sd index. 10 min I_sd index was raised as much as 430% and 800% in comparison with the synthesized PAN through its doping or acrylonitrile copolymerization with itaconic acid, respectively. Further 180 min of I_sd index, however, showed the same proportional increase as toughness of the drawn tapes versus their heat of stabilization through their physical and chemical modifications.     

A high molecular weight acrylonitrile copolymer prepared by mixed solvents polymerization: II. effect of DMSO/water ratios on polymerization and stabilization

A bifunctional comonomer β-methylhydrogen itaconate was synthesized to prepare high molecular weight poly [acrylonitrile-co-(β-methylhydrogen itaconate)] [P (AN-co-MHI)] by mixed solvents polymerization, which was used as carbon fiber precursor instead of acrylonitrile terpolymers. The effect of dimethyl sulfoxide (DMSO)/deionized water ratios on the polymerization, structure and stabilization of P (AN-co-MHI) was studied by elemental analysis, UV-Visible Spectroscopy, fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The highest viscosity-average molecular weight (76.72 × 10⁴ g/mol) of P(AN-co-MHI) was obtained in the mixed solvents of DMSO/deionized water = 10/90 (wt/wt) due to the zero chain transfer constant of deionized water for radical ~ ~ ~AN·, which is 10 times larger than that of P(AN-co-MHI) copolymers prepared in DMSO solution polymerization under the same conditions and is beneficial to improving the tensile strength of resulting carbon fiber. The composition of P(AN-co-MHI) was controlled by the ratio of DMSO/deionized water in the mixed solvents, it is attributed to the changes of AN/MHI ratio taking part in the polymerization reactions, which is caused by the different solubility of AN in the mixed solvents. From elemental analysis and FTIR studies, it can be found out that the content of MHI in P(AN-co-MHI) copolymer becomes larger with the increase of DMSO content in the mixed solvents. The FTIR, XRD and DSC results show that the stabilization of P(AN-co-MHI) copolymer was significantly improved by MHI compared with PAN homopolymer and poly (acrlonitrile-methyl acrylate-acrylic acid) terpolymer, such as larger extent of stabilization, lower initiation temperature and smaller E _a of cyclization, which is beneficial to preparing high performance carbon fiber.     

Dielectric study of side-chain liquid crystalline polyazomethine/fullerene C<Subscript>60</Subscript> nanocomposite

For side-chain liquid crystalline polyazomethine/fullerene C₆₀ nanocomposite (C₆₀ loading is 0.25 wt%), both real and imaginary components of the dielectric permittivity were investigated in wide regions of temperature and frequency. Analysis of frequency dependent permittivity allowed finding three relaxations (α, β ₁ and β ₂) in the nanocomposite. They were attributed to specific modes of molecular mobility. β-relaxations were described with the Arrhenius equation, whereas α-relaxation was described with the Vogel-Fulcher-Tammann equation. Anti-plasticization effect of the C₆₀ doping was shown to be manifested as an increase of the glass transition temperature of the nanocomposite as compared with that of the neat polymer.     

In Vitro Biological Evaluations of Zn Doped CaSiO<Subscript>3</Subscript> Synthesized by Sol–Gel Combustion Technique

Wollastonite (CaSiO₃) is one of the calcium silicate based material and is widely applied in hard tissue engineering applications. Combustion based sol–gel method was adopted to prepare the phase pure CaSiO₃ with inclusion of Zn ions (1, 3 and 5 wt%) using glycine as a reducing agent. The synthesized pure and Zn doped CaSiO₃ powders were characterized by attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS), scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS), transmission electron microscopy (TEM) analyses to confirm their functional groups, phase composition, thermal stability, particle size, surface morphology and topography, respectively. In vitro biological examinations were carried out to evaluate the biological behaviour of pure and Zn doped CaSiO₃ powders. The antibacterial activity was tested for 1–5 wt% of Zn doped CaSiO₃ powders against E. coli and S. aureus by colony forming unit (CFU) which proved that with increase of Zn concentration, the microbial restriction was found to be enhanced for both pathogens than control and pure CaSiO₃. In vitro apatite layer formation was observed on the surface of Zn doped CaSiO₃ powders with existence of ball like crystals for 14 days. In vitro cytocompatible study revealed that 5 wt% of Zn doped CaSiO₃ powder exhibited good cellular interaction of MG-63 cells at concentrations of 200–1000 µg/ml for 24 h. Thus, these biological studies reveal that the developed Zn doped CaSiO₃ powders could be applied for better clinical applications.     

Synthesis and electrospinning of well-defined polymer brushes by modification of polyacrylonitrile

As one of the most important precursors, polyacrylonitrile (PAN) and its functionality gained extensive attention but faced challenges in the preparation of nanofiber by electrospinning technology. Herein, poly(acrylonitrile-g-ethylene alcohol) (PAN-g-PEG) were succussfuly synthesized by the modification of PAN, using the methods of Click Chemistry and Mitsunobu reaction sequentially. Firstly, well-defined PAN was prepared by Cu(0)-mediated controlled/living radical polymerization with a molar ratio of [AN]₀:[EBiB]₀:[Cu]₀:[TEMED]₀?=?500:1:1:2. Tetrazole-containing PAN was then successfully modified by nitrile-Click Chemistry, which sodium azide and ammonium chloride was used as substrate and catalyst, respectively. Using Mitsunobu reaction, PAN-g-PEG was obtained from tetrazole-containing PAN and poly(ethyl alcohol) with the catalyst of diethyl azodicarboxylate and triphenylphosphine. After typical characterization, PAN-g-PEG nanofiber with the average diameter around 90 nm, was successfully prepared by electrospinning. The obtained PAN-g-PEG nanofiber has a smoother surface than PAN nanofiber, which suggests that a new modification approach of PAN nanofiber is successfully achieved.     

Effect of epoxidized soybean oil grafted poly(12-hydroxy stearate) on mechanical and thermal properties of microcrystalline cellulose fibers/polypropylene composites

A new green compatibilizer named epoxidized soybean oil grafted poly(12-hydroxy stearate) (ESO-g-PHS) was successfully synthesized using 12-hydroxy stearic acid and epoxidized soybean oil (ESO). The chemical structure of ESO-g-PHS was investigated through Fourier transformed infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. ESO-g-PHS was used as a compatibilizer to enhance the interfacial compatibility between polypropylene (PP) and microcrystalline cellulose fibers (MCF). The results showed that the impact strength and tensile strength were 33.55 and 27.57 MPa when the content loading of MCF reached 10 wt% and ESO-g-PHS was 4 wt%, which enhanced by 75.4 and 30.04 %, respectively, compared to that of composites without ESO-g-PHS. In addition, the SEM images of the fracture surfaces display that PP was highly bonded to MCF with ESO-g-PHS treated. In addition, the wide angle X-ray diffraction measurement revealed that the addition of ESO-g-PHS did not change the crystal structure of PP. Moreover, there was a slight improvement in thermal properties for PP composites with the addition of ESO-g-PHS.     

The Effect of Aniline Hydrochloride Hydrotrope on the Phase Behavior of SDS/Water System

The aim of this work was to determine the detailed phase behavior of the sodium dodecyl sulfate/aniline hydrochloride/water system as a function of concentration of sodium dodecyl sulfate (SDS), aniline hydrochloride (AHC) to sodium dodecyl sulfate molar ratio (R = [AHC]/[SDS]) and temperature. Phase behavior information was obtained via polarizing microscopy, differential scanning calorimetry (DSC), cryo-scanning electron microscopy (Cryo-SEM) and oscillatory linear rheological measurements with good agreement among these techniques. It is well known that SDS in water forms spherical micelles at concentrations lower than 40 wt% and temperatures above its Krafft temperature (T _k = 16–21 °C). In this region, the SDS/water system exhibits Newtonian rheological behavior, which is characteristic of spherical micellar solutions. The addition of the hydrotrope, aniline hydrochloride, to SDS aqueous solutions produces a viscosity increase in this system as R augments, and a maximum of about five orders of magnitude was found at R = 0.47 for 5 wt% SDS at 20 °C. Moreover, the system shows a transition from viscous to strong viscoelastic behavior. These changes in the rheological behavior are produced by the transitions from sphere to rodlike micelles, which are induced by the hydrophobicity of AHC causing it to be absorbed into the core and the hydrophilic interface of the micelles, which screens the repulsions between the charged head groups.     

Selective Microbial Degradation of Saturated Methyl Branched-Chain Fatty Acid Isomers

Three strains of Pseudomonas (P.) bacteria were screened for their capabilities of degrading chemically synthesized saturated branched-chain fatty acids (sbc–FA). Mixtures of sbc–FA with the methyl-branch located at various locales along the fatty acid were used as a carbon feedstock in shake-flask culture. Utilization (and hence degradability) of the sbc–FA was monitored based on positive bacterial growth, fatty acid recovery rates and chromatographic (gas chromatography (GC) and GC-mass spectroscopy (MS)) analysis of the recovered carbon source. P. putida KT2442 and P. oleovorans NRRL B-14683 were both able to grow on sbc–FA utilizing 35 wt% and 27 wt% of the carbon source, respectively after 144 h. In contrast, P. resinovorans NRRL B-2649 exhibited the most efficient use of the carbon source by utilizing 89 % of the starting material after 96 h resulting in a cell dry weight (CDW) of 3.1 g/L. GC and GC–MS analysis of the recovered carbon source revealed that the bacterial strains selectively utilized the isostearic acid in the sbc–FA mixture, and a new group of C₁₀, C₁₂, C₁₄ and C₁₆-linear and/or branched-chain fatty acids (approximately 4–29 wt%) were formed during degradation.     

Laponite-graphene oxide hybrid particulate filler enhances mechanical properties of cross-linked epoxy

A new hybrid of Laponite and graphene oxide (LGO), prepared in aqueous media by ultrasonication followed by solvent evaporation was used to reinforce epoxy matrix. The hybrid system was dispersed in liquid epoxy using a two-step solvent-assisted process. The suspensions showed negligible enhancements in processing barrier as revealed by rheology. A combinatorial analysis of small-angle x-ray scattering (SAXS) and microscopy suggested uniform dispersion of nanofillers in the matrix. The fillers showed fractal dimensions in polymer matrix as inferred from SAXS studies. Below 0.5 wt% LGO, the structure showed surface fractal and above 0.5 wt% the composites showed mass fractal, indicating a transformation from well-dispersed to agglomerated composites as the filler content increases. The composites exhibited substantial improvements in various mechanical properties. Notably, the flexural strength and modulus increased by ~23% and ~29%, respectively, with only 0.5 wt% LGO and the fracture toughness showed an increment of ~23% with 0.3 wt% LGO in epoxy matrix. A bimodal distribution of glass transition temperature (T _g ) with improved T _g was obtained for the composites. The simultaneous strengthening and toughening effects of nanofillers are explained by means of fractography.     

Development of natural and synthetic polymer-based semi-interpenetrating polymer network for controlled drug delivery: optimization and in vitro evaluation studies

This research paper describes the development, optimization and in vitro characterization of chemically cross-linked pectin–polyvinyl alcohol-co-poly(2-Acrylamido-2-methylpropane sulfonic acid) semi-interpenetrating polymer network hydrogel [pectin–PVA-co-poly(AMPS) semi-IPN hydrogel] for controlled delivery of model drug tramadol HCl. Response surface methodology based on 3² factorial design was used for optimization and investigating the effect of independent factors: polymer-blend ratio (pectin:PVA = X ₁) and monomer (AMPS = X ₂) concentration on the dependent variables, swelling ratio (q _18th), percent drug release (R _18th, %), time required for 80 % drug release (t _{80 %}, h), drug encapsulation efficiency (DEE, %) and drug loaded contents (DLC, mg/g) in pectin-PVA-co-poly(AMPS) gels prepared by free radical polymerization. The optimized semi-IPN gel (FPP-10) showed controlled in vitro drug release (R _18th) of 56.34 % in 18 h, t _{80 %} of 30 h, and DEE of 23.40 %. These semi-IPN hydrogels were also characterized through SEM, FTIR, sol–gel analysis, swelling studies and drug release characteristics. Therefore, this newly synthesized polymeric network could be a potential polymeric system for controlled drug delivery of tramadol HCl for prolonged drug release.     

Leakage currents and self-discharge of ionic liquid-based supercapacitors

Ionic liquid (IL)-based supercapacitors have been widely demonstrated to outperform electrochemical double-layer capacitors (EDLCs) working with conventional organic electrolytes in terms of specific energy and operating voltage. Here, the results of a study on the leakage currents (I _leak) and self-discharge energy loss factors (SDLF) of IL-based EDLCs at different cell voltages up to 3.2 V and at 30° and 60 °C are reported. Cells assembled with the N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR₁₄TFSI) and N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide pure ILs and a mixture of PYR₁₄TFSI and propylene carbonate (PC) 1 to 1 molar were tested. The results are compared to those achieved with EDLCs featuring the conventional 1 M tetraethyl ammonium tetrafluoroborate (Et₄NBF₄)-PC electrolyte. The study demonstrates that ILs provide I _leak and SDLF that are lower than those obtained with the latter electrolyte, with PYR₁₄TFSI allowing the lowest values.     

Synthesis,Characterization and Surface Properties of Amidosulfobetaine Surfactants Bearing Odd-Number Hydrophobic Tail

Three amidosulfobetaine surfactants were synthesized namely: 3-(N-pentadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2a); 3-(N-heptadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2b), and 3-(N-nonadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2c). These surfactants were prepared by direct amidation of commercially available fatty acids with 3-(dimethylamino)-1-propylamine and subsequent reaction with 1,3-propanesultone to obtain quaternary ammonium salts. The synthesized surfactants were characterized by IR, NMR and mass spectrometry. Thermogravimetric analysis (TGA) results showed that the synthesized surfactants have excellent thermal stability with no major thermal degradation below 300 °C. The critical micelle concentration (CMC) values of the surfactants 2a and 2b were found to be 2.2 × 10^?4 and 1.04 × 10^?4 mol/L, and the corresponding surface tension (γ_CMC) values were 33.14 and 34.89 mN m^?1, respectively. The surfactants exhibit excellent surface properties, which are comparable with conventional surfactants. The intrinsic viscosity of surfactant (2b) was studied at various temperatures and concentrations of multi-component brine solution. The plot of natural logarithm of relative viscosity versus surfactant concentration obtained from Higiro et al. model best fit the surfactant behavior. Due to good salt resistance, excellent surface properties and thermal stability, the synthesized surfactant has potential to be used in various oil field applications such as enhanced oil recovery, fracturing, acid diversion, and well stimulation.     

Polysiloxanes with Quaternary Ammonium and Polyether Groups for Silyl-Terminated Polypropylene Oxide Waterborne Emulsions

In this paper, polysiloxanes with pendant quaternary ammonium and polyether segments (EQAPS, nonionic–cationic silicone surfactant) were synthesized through hydrosilylation of poly(dimethylhydro)siloxane with allyl poly(ethylene glycol) acetic ester (M _n  = 540) and allyl glycidyl ether, followed by a ring-opening reaction of epoxide groups with diethyl amine and quaternization with benzyl chloride. The chemical structures of EQAPS and intermediate products were characterized by ¹H-NMR and FT-IR spectra. The surface activity and thermal properties of EQAPS were studied with surface tension measurement and differential scanning calorimetry analysis, respectively. The results showed that the EQAPS had a much smaller critical micelle concentration value (118 mg/L) and lower glass-transition temperature (T _g: ?57 °C). The silyl-terminated polypropylene oxide waterborne emulsions, which were substantially free from organic solvent, were prepared via a phase-inversion emulsification technique using EQAPS as single emulsifier and/or poly(ethylene glycol) (\(\bar{M}\) _n  = 400) as cosolvent. The electrical properties of the system indicated that the phase inversion was completely accomplished. The viscosity of the emulsions with different solid contents was measured, and the results showed that the most suitable solid content was about 50 wt%. The emulsions with smaller particle size (12 μm) had better storage stability (48 days at 50 °C) and freeze–thaw stability.     

Ion conducting nano-composite polymer electrolytes: synthesis and ion transport characterization

Synthesis and ion transport characterization of a new K⁺-ion conducting nano-composite polymer electrolytes (NCPEs): (1?x) [70PEO:30KBr] + x SiO₂, where 0 < x < 20 wt%, are reported. The present NCPEs have been cast using a novel hot-press technique in place of the traditional solution cast method. The conventional solid polymer electrolyte (SPE) composition: (70PEO:30KBr), identified as the highest conducting composition at room temperature, has been used as first-phase host matrix and nano-size (~8 nm) particles of SiO₂ as second-phase dispersoid. As a consequence of dispersal of SiO₂ in SPE host, two orders of conductivity enhancement have been observed in NCPE composition: [95(70PEO:30KBr) + 5SiO₂] and this has been referred to as optimum conducting composition (OCC). The polymer-salt/nano-filler SiO₂ complexation and thermal properties characterization were done with the help of XRD, FTIR, SEM, DSC and TGA studies. The ion transport behavior in NCPEs have been discussed on the basis of experimental measurements on some basic ionic parameters, viz. conductivity (σ), ionic mobility (μ), mobile ion concentration (n), ionic transference number (t _ion), etc. The temperature-dependent conductivity studies of NCPE OCC have been done and activation energy (E _a) value was determined using log σ?1/T Arrhenius plot.     

Selective Enrichment of Conjugated Linoleic Acid Isomers in Their Mixtures Using Combined Chemical and Enzymatic Methods

The aim of this study was to selectively enrich t10,c12-conjugated linoleic acid (t10,c12-CLA) and c9,t11-CLA in commercial CLA mixtures using a combination of urea crystallization and lipase-catalyzed esterification. The objective of the urea fractionation is to remove saturated and monounsaturated fatty acids (FA) from the CLA mixtures. CLA-enriched free FA (FFA) mixtures containing 53.8 wt% t10,c12-CLA and 39.1 wt% c9,t11-CLA were produced from the CLA mixtures containing ~34 wt% each of the two CLA isomers by a urea crystallization using methanol and the urea-to-FA weight ratio of 2.5:1. The CLA-enriched FFA mixtures were partially esterified with dodecan-1-ol in a recirculating packed-bed reactor using an immobilized lipase from Candida rugosa to further enrich the t10,c12-CLA and c9,t11-CLA in an FFA fraction and an FA dodecyl ester fraction, respectively, under the optimal conditions, i.e., temperature, 20 °C; FA-to-dodecan-1-ol molar ratio, 1:1; water content, 2 wt% of total substrates; residence time, 5 min; and reaction time, 24 h (for t10,c12-CLA enrichment) and 12 h (for c9,t11-CLA enrichment). After the reaction, an FFA fraction with 72.6 wt% t10,c12-CLA was obtained. Another FFA fraction with 62.0 wt% c9,t11-CLA was recovered after the saponification of the FA dodecyl ester fraction. The yields of t10,c12-CLA and c9,t11-CLA in the FFA fractions were 43.6 and 21.5 wt%, respectively, based on their initial weights in the CLA mixtures.     

Glycerol Steam Reforming for Hydrogen Production over Nickel Supported on Alumina,Zirconia and Silica Catalysts

The aim of the work was to investigate the influence of support on the catalytic performance of Ni catalysts for the glycerol steam reforming reaction. Nickel catalysts (8 wt%) supported on Al₂O₃, ZrO₂, SiO₂ were prepared by the wet impregnation technique. The catalysts’ surface and bulk properties, at their calcined, reduced and used forms, were determined by ICP, BET, XRD, NH₃-TPD, CO₂-TPD, TPR, XPS, TEM, TPO, Raman, SEM techniques. The Ni/Si sample, even if it was less active for T?<600?°C, produces more gaseous products and reveals higher H₂ yield for the whole temperature range. Ni/Zr and Ni/Si catalysts facilitate the WGS reaction, producing a gas mixture with a high H₂/CO molar ratio. Ni/Si after stability tests exhibits highest values for total (70%) and gaseous products (45%) glycerol conversion, Y_H2 (2.5), S_H2 (80%), S_CO2 (65%), H₂/CO molar ratio (6.0) and lowest values for S_CO (31%), S_CH4 (3.1%), CO/CO₂ molar ratio (0.48) among all samples. The contribution of the graphitized carbon formed on the catalysts follows the trend Ni/Si (I _D /I _G ?=?1.34)?<?Ni/Zr (I _D /I _G = 1.08)?<?Ni/Al (I _D /I _G = 0.88) and indicates that the fraction of different carbon types depends on the catalyst’s support nature. It is suggested that the type of carbon is rather more important than the amount of carbon deposited in determining stability. It is confirmed that the nature of the support affects mainly the catalytic performance of the active phase and that Ni/SiO₂ can be considered as a promising catalyst for the glycerol steam reforming reaction.     

Magnetic and Phase Behavior of Magnetic Water-in-Oil Microemulsions

Magnetic water-in-oil microemulsions with anisotropic morphology have been generated by mixing single-chain magnetic surfactants (dodecyltrimethylammonium trichloromonobromoferrate, DTAF) with non-magnetic di-chain analogues (didodecyldimethylammonium bromide, DDAB). Full phase diagrams have been mapped as a function of surfactant composition, water content, and temperature. It was shown that for all surfactant concentrations [Surfactant_total], on replacing 30 wt% DDAB with DTAF optimum (i.e. wt% of the total surfactant) w ratios (w = [water]/[surfactant]) could be achieved; up to w = 120 for [Surfactant_total] = 0.050 M. Small-angle neutron scattering (SANS) indicated that microemulsion droplets have a rod-like morphology with a radius commensurate with the surfactant tail length and an aspect ratio between 6 and 35. In the presence of a large magnetic field (6.7 T) no reorientation of the droplets was observed by SANS.     

Tuning the interlaminar shear strength and thermo-mechanical properties of glass fiber composites by incorporation of (3-mercaptopropyl) trimethoxysilane-functionalized carbon black

The incorporation of functionalized nanoscale fillers into traditional glass fiber/unsaturated polyester (GF/UPE) composites provides a more robust mechanical attributes. The current study demonstrates the potential of 3-mercaptopropyl trimethoxysilane (MPTS)-functionalized carbon black (f-CB) for enhancing the thermo-mechanical properties of GF composites. The composites infused with 1, 3 and 5 wt% of pristine and MPTS-functionalized CB were fabricated by hand lay-up and hot press processing. Tensile testing, interlaminar shear strength (ILSS) testing and dynamic mechanical analysis were used to evaluate the performance of nanocomposites. Fourier transform infrared spectroscopy validated the MPTS functionalization of CB. Pristine CB-loaded nanocomposites exhibited marginal improvement in ultimate tensile strength (UTS), ILSS and thermo-mechanical properties. However, with the addition of f-CB, the improvement in all the studied properties was more substantial. The inclusion of 5 wt% f-CB increased the elastic modulus and UTS by 16 and 22%, respectively, whereas the ILSS was enhanced by 36%, in comparison to the neat GF composite. The scanning electron microscope analysis of fractured ILSS samples revealed better fiber-matrix adhesion and compatibility in f-CB-loaded nanocomposites. At the same filler weight percentage, the storage modulus at 25 °C was ~ 19% higher than that of neat composite. The f-CB inclusion resulted in increment of T _g by ~ 13 °C over the T _g of neat GF/UPE composite (~ 109 °C). These improvements were due to the chemical connection of f-CB to the UPE matrix and GF surface. With such improvements in thermal and mechanical properties, these nanocomposites can replace the conventional GF composites with prominent improvements in performance.     

Optimization of controlled ring-opening polymerization of <Emphasis Type="SmallCaps">l</Emphasis>-lactide to hydroxyl terminated polylactides using zinc acetate catalyst

Hydroxyl terminated polylactide polymers with number of average molecular weights (M _n ) varying from 1625 to 3459 g mol^?1 were synthesized by ring opening bulk polymerization of lactide in the presence of zinc acetate being a potent catalyst. The use of 1,4 butanediol (BDO) initiator leads to hydroxyl terminated polylactides, thus excellent precursors for shape-memory biodegradable polyurethanes. Different reaction conditions employed for the synthesis of hydroxyl terminated polylactide polymers via activated monomer mechanism may result in differences in M _n , percentage mass conversion and percentage degree of crystallinity (%χ _c ) of the product. Influence of process parameters, i.e. catalyst concentration, initiator concentration, reaction temperature and time on characteristics of hydroxyl terminated polylactides was studied. These polymers were characterized by Nuclear Magnetic Resonance (¹H-NMR) spectroscopy, Fourier transforms infrared (FTIR) spectroscopy, gel permeation chromatography (GPC) and X-ray diffraction (XRD) techniques. FTIR and ¹H-NMR confirmed the formation of hydroxyl terminated polylactides. M _n was determined by ¹H-NMR, GPC and end group analysis. %χ _c was calculated from XRD spectra. Maximum mass conversion, M _n and %χ _c were observed at 5 mol% SnOct₂ and 5 mol% BDO concentration. At optimum temperature of 145 °C, these characteristics improved linearly with polymerization time up to 6 h and declined thereafter.     

Crystallinity of large single crystals of FAU-type zeolites with a wide range of Si/Al ratios

Large colorless single crystals of FAU-type zeolites were synthesized from gels with the composition xSiO₂ : 2.0NaAlO₂ : 7.5NaOH : 454H₂O : 5.0TEA, where x = 2.0–6.0. FAU-type zeolite with Si/Al = 1.26(4) was nearly pure and the maximum size of the single crystals was ca. 150 μm. In case of FAU-type zeolites with Si/Al = 1.54(5), the maximum size of single crystals was ca. 200 μm and the ratio of FAU/impurity was 0.07. The framework Si/Al ratio of the as-synthesized FAU-type zeolite tended to increase with the Si/Al ratio of gel composition. All of the large single crystals had good crystallinities for single-crystal X-ray diffraction, leading to enough numbers of significant reflections which have strong intensity. The structure of a single crystal of dehydrated zeolite Na-X (Si/Al = 1.41(4)) with composition |Na₈₀|[Si₁₁₂Al₈₀O₃₈₄]-FAU per unit cell was determined by X-ray diffraction methods in the cubic space group \( Fd \bar{3} m; \) a = 24.9434(6) Å at 294 K. The structure was refined by using all intensities to the final error indices (using only the 771 reflections for which F _o > 4σ(F _o)), R ₁ = 0.048 (based on F) and R ₂ = 0.188 (based on F ²). In the crystallographic studies, the Si/Al ratio of the synthetic FAU-type zeolite is 1.41(4) which is quite consistent with the SEM–EDS analysis.