Effect of Blowing Agent Type in Rigid Polyurethane Foam

Rigid polyurethane foams have been fabricated from polymeric MDI and polypropylene glycols (PPG) synthesized with two different initiator compositions using two different types of blowing agents, viz., the conventional HCFC 141b and environmently friendly HFC 365 mfc. It was found that the two blowing agents gave identically the same cream time, gel time, and tack‐free time. The HFC 365 mfc gave foams with smaller cell size, greater core density and compression strength, whereas HCFC 141b gave better dimensional stability and thermal insulation. For the same type of blowing agent, the initiator containing more toluene diamine gave greater core density, compression strength and thermal insulation     

Thermophysical characterization of aqueous ternary system containing n-tris-[hydroxymethyl]methyl-3-amino propanesulfonic acid and glycol (PG or DPG or TPG)

In this present work, a thermophysical property characterization of aqueous ternary system containing n-tris-[hydroxymethyl]methyl-3-aminopropanesulfonic acid (TAPS) and glycol was done. Thermophysical properties, including refractive index, density, and electrolytic conductivity, measurements were considered. The glycols considered are propylene glycol (PG), dipropylene glycol (DPG), and tripropylene glycol (TPG). The measurements were done over a temperature range of 298.15 K to 343.15 K and at normal atmospheric pressure. Different concentrations (4% to 16% by weight TAPS or 56% to 44% water, in a fixed amount of glycol – 40%) were used. The effects of temperature and compositions on the measured properties were discussed and then correlated based on the equation proposed for aqueous salt–glycol systems. Calculation results show that the applied model was satisfactory in representing the measured properties in the aqueous ternary systems containing TAPS and considered glycols.     

Hemichrome Determination by Thermal Lensing with Polyethylene Glycols for Signal Enhancement in Aqueous Solutions

The thermal lens technique is proposed for the determination of total hemoglobin in the form of reversible hemichrome. The conditions were optimized (concentration of sodium dodecyl sulfate, 2?mM) to attain the maximum sensitivity with the use of polyethylene glycols as signal enhancers. For polyethylene glycols with molecular weights 1500–35000 Da in a concentration range of 5–15% w/w (5–25?mM), the influence on thermal lens signal enhancement was estimated. It is shown that the use of 5% w/w polyethylene glycol 2000 provides the maximum increase in the thermal lens enhancement factor (by 40%) in comparison with unmodified aqueous solutions. The detection limit of iron(II) tris(1,10-phenanthrolinate) as a model system is 60?nM. Under these conditions, the thermal lens detection limit of hemichrome is 10?nM, which shows a 15-fold enhancement compared to spectrophotometry. Modification of the medium with polyethylene glycols decreases the limit of detection of hemichrome determination by 15% in comparison with unmodified aqueous solutions due to better reproducibility for the range of concentrations from 0.02 to 0.9?µM.     

Effect of glycols used as glycolysis agents on chemical structure and thermal stability of the produced glycolysates

In this study, the influence of glycols on chemical structure and thermal stability of glycolysates as polyurethane intermediates were investigated. The intermediates were obtained by the glycolysis process of waste polyurethane foams in the reaction with different glycols ranging from ethylene glycol to hexane-1,6-diol. The used glycols were not separated from the product after the glycolysis process has been terminated. The effects of different weight ratio of glycols to polyurethane (PU) foam on chemical structure and thermal stability were investigated by FTIR, GPC, and TG/DTG. FTIR analysis of the glycolysates revealed their similar chemical architecture as manifested by the similarity of absorption peaks within the entire wavenumber range of spectra. This may indicate that the glycol has no influence on the chemical composition of glycolysates. GPC analysis showed that the glycolysates were characterized by polydispersity smaller than 2 which is lower as compared to some commercial polyols used for PU synthesis. GPC chromatograms showed that the applied glycols and the conditions of PU glycolysis allowed recreation of the original polyol as documented on the chromatograms by a single, well-formed peak at the beginning of retention time. Based on TG thermograms, it was established that glycol used in transesterification of PUs affected the temperature at which the loss of glycolysate mass by 5 and 10?% occurs. It was also observed that glycol affected the temperature at which the decomposition rate of glycolysates was the highest.     

Latent heat nano composite building materials

Heat storage for heating and cooling of buildings reduces the conventional energy consumption with a direct impact on CO₂ emissions. The goal of this study was to find the physico-chemical fundamentals for tailoring phase change material (PCM)-epoxy composites as building materials depending on phase change temperature and latent heat using the optimal geometry for each application. Thus, some nano-composite materials were prepared by mixing a PCM with large latent heats with epoxy resin and Al powder. Some polyethylene glycols of different molecular weights (1000, 1500, and 2000) were used as PCMs. Subsequently these PCM-epoxy composites were thermo-physically characterized by DSC measurements and found to be suitable for building applications due to their large latent heat, appropriate phase change temperature and good performance stability. Moreover these cross-linked three dimensional structures are able to reduce the space and costs for encapsulation.     

Reactivity of polyesters in glycolysis reactions: Unexpected effect of the chemical structure of the polyester glycolic unit

Kinetic studies of PET glycolysis by diethylene glycol (DEG), dipropylene glycol (DPG), glycerol (Gly) and mixtures of these glycols have shown, in a previous study, that the order of reactivity of the glycols differs according to the conditions of temperature and catalysis. Indeed, their global reactivity depends both on their chemical reactivity and physico-chemical properties.Glycolysis of model polyesters which are liquid at the reaction temperature, which allows us to overcome the problem of the polyesters' solubility, were studied to compare the chemical reactivity of these glycols. Three oligoesters were synthesized from dimethyl terephthalate and three different glycols namely triethylene glycol, ethylene glycol and hexanediol to form, respectively, PE₃T, OET and PTHD.Results showed that the order of reactivity of the glycols is the same for PET, OET and PTHD but different for PE₃T. Indeed, DPG without catalyst has a particular and unexpected behaviour: its reactivity seems to be strongly influenced by the presence of oxygen atoms in the chain.     

Thermodynamic characteristics and intermolecular interactions in aqueous solutions of oxyethylated glycols

The thermodynamic characteristics of aqueous solutions of mono-, di-, tri-, and tetraethylene glycols were calculated in the entire range of compositions of the mixtures for various temperatures. The specific and nonspecific terms of the total energy of intermolecular interaction were determined within the framework of a model approach using the internal pressure as a measure of nonspecific interactions in a liquid. The concentration ranges with different types of intercomponent association and of structural organization of solutions depend on the temperature and number of ether groups in the glycol molecules.     

Model for predicting the composition of copolyesters: Polymerization of terephthalic acid, 2,2′-oxydiethanol,and 2,2-dimethyl-1,3-propanediol

Copolyesters of two glycols and a dicarboxylic acid moiety are frequently made to obtain specific physical properties. In the synthesis of these polymers an excess of glycol is used in the ester-exchange reaction and then removed during the polycondensation reaction to form a high-molecular-weight product. A model has been developed to predict the final polymer composition. The derivation is based on equilibria of reaction species (free glycol, polymer chain ends, and ester links) and the relative vapor pressures of the two reacting glycols. Calculated results are compared with experimental results of poly(2,2′-oxydiethylene: 2,2-dimethyl-1,3-propylene terephthalate)s. There is good agreement between calculated and experimental compositions. The model can be used to calculate the glycol concentrations that must be used to make a specific polymer composition. This model should also be useful in the calculation of other mole ratios of glycol to dicarboxylic acid that will make the same composition.     

Thermomechanical and fractographic behavior of poly (HDDA‐co‐MMA): a study for its application in microcantilever sensors

Polymer‐based materials have drawn significant attention lately for their application in design and fabrication of thermomechanically stable highly sensitive three‐dimensional (3D) micromechanical sensor structures. Among these materials, 1,6 Hexane diol diacrylate (HDDA) has been extensively explored in laser‐based 3D microfabrication by microstereolithography. The thermomechanical properties of poly HDDA are important for their end use application in microcantilever‐based sensors. The present work explores the optimization of these properties by copolymerization of HDDA and methyl methacrylate (MMA) for these specific applications. The dynamic mechanical analysis, thermal expansion and mechanical studies were carried out for different compositions of poly (HDDA‐co‐MMA). An increase in MMA content in the copolymer matrix resulted in the enhancement of the thermomechanical stability. The variations of thermal expansion coefficient (CTE) for different compositions were also studied. Microhardness, uniaxial tensile, and flexural tests along with Poisson's ratio were determined to understand the mechanical properties of these compositions. The scanning electron micrographs of fractured surfaces of all the compositions were analyzed to understand the fracture mechanism of various compositions of this copolymer. Copyright © 2012 John Wiley & Sons, Ltd.     

Temperature-responsive hydrogels from cellulose

The aim of this work is to prepare the temperature-responsive cellulosic hydrogels undergoing a large volume change in an aqueous solution on heating or cooling. To this end, we prepared 0-methyl cellulose (MC) and O-(Z-hydroxy-3-butoxypropyl) cellulose (HBPC) which precipitate out of solution on heating without forming gel. MC and HBPC derivatives prepared by homogeneous reactions were proved to be promising raw materials for the cellulosic hydrogels mentioned above. The results on the phase separation of the derivatives were discussed in terms of the distribution of substituents along the cellulose chain and in the anhydroglucose units.     

Periodic Mesoporous Organosilicas as Efficient Nanoreactors in Cascade Reactions Preparing Cyclopropanic Derivatives

In this work, three organosilica precursors functionalized with carbamate moieties were synthesized by condensing of 3‐isocyanatopropyltriethoxysilane and coupling regents of either hydroquinone (HQ), bisphenol A (BPA), or 1,1′‐bi‐2‐naphthol (BN). These organosilica precursors were covalently bonded in the framework of periodic mesoporous organosilicas by co‐condensation and hydrolysis with tetraethyl orthosilicate (TEOS) under hydrothermal treatment. The compositions and physical properties were characterized with FTIR, XRD, thermogravimetric/differential thermal analysis (TG/DTA), ²⁹Si NMR, ¹³C NMR spectroscopies, SEM, TEM, and BET technologies. These characterizations suggest that three different structures were formed as the result of different sizes and compositions of the organosilica precursors. The three mesoporous organosilicas were applied as heterogeneous catalysts in the one‐pot cascade Knoevenagel and Michael cyclopropanic reactions for the synthesis of cyclopropanic derivatives and showed excellent activity and selectivity. The highest conversion was obtained with mesoporous catalyst (MC)‐HQ owing to its ordered mesostructure, highest surface area, and weakest stereo effect of the organic linking groups compared with MC‐BAP and MC‐BN. This methodology employed cheaper and more easily obtainable raw materials as reagents over the traditional alkene additive system and these heterogeneous catalysts exhibit superior performance and recyclability than typical homogeneous organic catalysts.     

Thermal conductivity of dry anatase and rutile nano-powders and ethylene and propylene glycol-based TiO2 nanofluids

Thermal conductivity behaviour was studied for two TiO₂ nano-powders with different nanocrystalline structures, viz. anatase and rutile, as well as nanofluids formulated as dispersions of these two oxides up to volume concentrations of 8.5% in two different glycols, viz. ethylene and propylene glycol. Because it is known that titanium dioxide can exhibit three different crystalline structures, the dry nano-powders were analysed using X-ray Diffraction to determine the nanocrystalline structure of the powders. Two different techniques were employed in the thermal conductivity study of the materials. Dry nano-powders, with and without compaction, were analysed at room temperature by using a device based on the guarded heat flow meter method. Nanofluids and base fluids were studied with a transient hot wire technique over the temperature range from (283.15 to 343.15) K. The base fluid propylene glycol was measured by using both techniques in order to verify the good agreement between both sets of results. The experimental measurements presented in this work were compared with other literature data for TiO₂ nanofluids in order to understand the thermal conductivity enhancement as a function of nanoparticle concentration. Different theoretical or semi-theoretical approaches such as Maxwell, Peñas et al., Yu-Choi were evaluated comparing with our experimental values. A parallel model was used to predict thermal conductivities employing experimental values for dry nanopowder.     

Kinetics of sorption of poly(ethylene glycols) of various molecular masses by globular carbon

The kinetics of adsorption of poly(ethylene glycols) with molecular masses in the range 300–15000 from aqueous solutions by globular carbon with different radii of curvature of particles is studied. The kinetic adsorption coefficients of poly(ethylene glycols) are calculated. The dependences of the kinetic absorption coefficient on adsorbent dispersion and molecular mass of poly(ethylene glycol) are discussed.     

Determination of glycols by HPLC with refractive index detection

A simple and fast HPLC method for the determination of glycols is described. It is characterized by a reversed-phase separation using water as eluent and a refractive index detection. The method was applied to investigate the biodegradation of glycols in a laboratory activated sludge plant and to determine the content of glycols or alcohols in detergents. The detection limit is 4 mg/l ethylene glycol or propylene glycol in an aqueous sample.     

Mn–Co spinel protective–conductive coating on AL453 ferritic stainless steel for IT-SOFC interconnect applications

This paper presents research on the synthesis and properties of the Mn_1.5Co_1.5O₄ (MC) spinel powder, as well as its application for the preparation of a MC thick film on the AL453 steel to be used for metallic interconnect material in IT-SOFCs. In order to prepare the MC micropowder with excellent homogeneity of the chemical and phase compositions, EDTA gel processes were utilized. In order to improve the contact electrical resistance between an AL453 steel interconnect and the La_0.8Sr_0.2FeO₃ (LSF) cathode and protect the cathode from Cr poisoning, the surface of the AL453 steel was coated with a protective manganese cobaltite spinel matrix using screen printing in combination with an appropriate heat treatment. The oxidation of the AL453/MC composite layer carried out in the air–H₂O gas mixture at 1,073 K for 55 h showed that the spinel coating may serve as an effective barrier against outward Cr diffusion from the AL453 steel and, therefore, significantly inhibit the formation of volatile Cr vapors from the chromia scale. The contact ASR study of the interconnect–cathode interface in the AL453/MC/LSCM/LSF/LSCM/MC/AL453 system carried out in the range of 723?1,073 K in air showed a very large drop in ASR compared to the resistance of the AL453/LSCM/LSF/LSCM/AL453 system without the spinel coating.     

Intelligent Fibrous Substrates with Thermal and Dimensional Memories

Binding of polyethylene glycols to any fibrous substrate (such as a natural cellulosic or wool, or synthetic fibers polyester, polyamide or polyolefin) is achieved by in situ network polymerization with polyfunctional resins and acid catalysts. The modified substrates contain crosslinked polyethylene glycols that impart several improved functional properties. Two of these properties (thermal adaptability and reversible shrinkage in the wet and dry states) make it appropriate to categorize the modified fibrous substrates as “intelligent materials”. The thermal and dimensional/shape memories of the substrates are influenced and, hence, controlled by the molecular weight of the polyol, crosslink density, curing conditions to affix the polyol and construction of the fibrous substrate. Verification of these effects has been noted by thermal analysis and infrared thermography (for thermal memories) and by measurement of power generated and work performed during wet shrinkage of appropriate substrates (for shape memories). Numerous potential commercial applications are described and some are being actively pursued. © 1997 John Wiley & Sons, Ltd.     

Selective detector of 1,2-propylene glycol dinitrate, 1, propylene glycol mononitrate,and 2-propylene glycol mononitrate using gas chromatography/ thermal energy analyzer or liquid chromatography/ electrochemical detection

Mono- and di-nitrated propylene glycols can be separated and detected using either a gas chromatogph equipped with a nitro-specific thermal energy analyzer (g.c./t.e.a.) or a high-performance liquid chromatograph equipped with an electrochemical detector in the reductive mode (l.c./e.c.). The g.c./t.e.a. exhibits a linear range of three orders of magnitude and provides detection limits in the μg ml^?1 range or lower for these three compounds. The l.c./e.c. provides a linear response over two orders of magnitude and is best suited for the determination of propylene glycol dinitrate. Trapping of these glycols on Amberlite XAD-2 resin is discussed.     

DNA hydrogels: New functional soft materials

Deoxyribonucleic acid (DNA) hydrogel is a network of crosslinked DNA strands swollen in aqueous solutions. The crosslinks may be physical or chemical, such as the hydrogen bonds or ethylene glycol units, respectively, connecting the strands belonging to different double‐helical DNA molecules. As DNA network strands in the hydrogels exhibit properties similar to those of the individual DNA molecules, such soft materials are a good candidate to make use of the characteristics of DNA such as coil‐globule transition, biocompatibility, selective binding, and molecular recognition. Physical DNA hydrogels with an elastic modulus in the order of megapascals can be prepared by subjecting semidilute aqueous solutions of DNA to successive heating–cooling cycles between below and above the melting temperature of DNA. Chemical DNA hydrogels can be prepared by connecting the amino groups on the nucleotide bases through covalent bonds to form a three‐dimensional DNA network in aqueous solutions. In this article, we summarize the preparation strategies of DNA hydrogels with a wide range of tunable properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Specific features of nonstoichiometric interpolymer complexes of poly(acrylic acid) and poly(ethylene glycol) as protectors of copper nanoparticles in aqueous sols

Advantages of interpolymer complexes for use as amphiphilic protectors of nanoparticles during the formation and stabilization of sols are considered. The effects of the ratio of poly(acrylic acid) and poly(ethylene glycol) and the molecular mass of poly(ethylene glycol) on the mean size and size distribution of copper nanoparticles in sols formed via the reduction of divalent copper ions in mixed aqueous solutions of these polymers are investigated. It is shown that sols of metal nanoparticles with small sizes and narrow size distributions are formed even when poly(ethylene glycols) with chain lengths below the “critical” chain length and a small PEG-to-PAA base-molar ratio are used. This is evidence for efficient protection of the formed copper nanoparticles by the interpolymer complex PEG-PAA under conditions of its instability and for self-organization of oligomeric PEG chains in complex macromolecular shields of nanoparticles.     

Thermal stability of plasma deposited polysilanes

A new method for studying thermal stability and concomitant chemical composition changes on thermal treatment of thin polymeric films is presented. It is applied to the study of thermal properties and modification of properties of polysilane-like materials with variable dimensionality prepared by radio frequency plasma enhanced chemical vapour deposition (CVD). Structure and microphysical properties of these materials, modified by progressive annealing, are examined by fluorimetry, FTIR absorption spectroscopy and XPS. In addition, the role, bonding conditions and structural environments of organic moieties as well as their influence on thermal degradation processes are examined. It is found that plasma polysilanes undergo three consecutive thermal degradation processes: Si-Si bond cleavage, elimination of side groups and final carbide formation. Presence of disorder and crosslinking stabilises the plasmatic material in comparison to classically prepared polysilanes. Nanostructural units in low dimensional polysilanes enable the peak of the luminescence to be adjusted in the spectral range from near UV (360 nm) to red (600 nm).