Thermodynamic study of polymer–solvent systems by reversed-flow gas chromatography

Reversed-flow gas chromatography, a new method for studying heterogeneous catalysis, diffusion, adsorption, evaporation, and other related phenomena, is now applied to the determination of activity of the solvent in a polymer–solvent system in the whole range of polymer concentration, as well as for the calculation of excess partial molar thermodynamic functions of mixing. The systems used were polystyrene in cyclohexane, polyvinylacetate in cyclohexanone and polyvinylpyrrolidone in methanol. In the first system, which was studied in detail, weight fraction activity coefficients (a₁/w₁) at several temperatures (333.8–348.1 K) and various polymer concentrations (0.020–0.131 g/g) were determined. From the latter parameters weight fraction activity coefficients at infinite dilution (a₁/w₁)^∞ were computed. Flory–Huggins interaction parameters x and solubility parameters δ₂ were also determined. Finally, the thermodynamic parameters found by the present method are compared with those determined by other techniques or calculated theoretically.     

Effect of Enameling on the Strength and Dynamic Fatigue of Soda–Lime–Silica Float Glass

The effect of a glass enamel coating on the strength and fatigue behavior of float glass was investigated. Commercially available enamel that was comprised of Cu₂Cr₂O₄ pigment particles in a bismuth-zinc borosilicate glass matrix was applied to a soda–lime–silica float glass via screen printing, followed by fusion at elevated temperature. Strengths of the enameled specimens were evaluated in biaxial flexure using a ring-on-ring (ROR) test geometry, and the data were analyzed using a conventional two-parameter Weibull distribution. Enameling was found to significantly degrade the strength of the float glass. There was no statistical difference in the characteristic strengths of samples enameled on the air side (66 MPa) compared with samples enameled on the tin side (61 MPa) of the float glass. Fractographic analysis revealed that the failures in the enameled float glass samples initiated at pores and pigment aggregates in the enamel, whereas failures in float glass samples initiated solely from surface flaws. Dynamic fatigue tests were performed on enameled float glass and indented float glass samples to determine the effect of the enamel on the stress corrosion behavior of the enameled components. There was no statistically significant difference between the stress corrosion exponents for the float glass and enameled float glass specimens.     

Formation of hydrophilic starch coatings on polyethylene films

Thin starch coatings were deposited onto polyethylene (PE) film surfaces when PE films were immersed in 1% jet cooked starch solutions and the hot solutions were allowed to cool. Normal cornstarch, waxy cornstarch, high amylose cornstarch, and solvent‐extracted normal cornstarch (to remove native lipid) were used in these experiments. Amounts of adsorbed starch varied from about 0.03–0.05 mg per cm² of PE, and these starch coatings imparted hydrophilic properties to film surfaces, as evidenced by contact angle measurements. Although starch could be removed by gently rubbing water‐wet PE surfaces, air‐dried coatings were more firmly attached, and did not separate from the PE surface when films were bent or flexed. SEM images of starch‐coated film surfaces showed that starch was deposited as particles less than 1 μm in diameter, and also as aggregates of these submicron particles. Despite the fact that some starch samples contained only very small amounts of amylose and native lipid, surface‐deposited starch in all experiments contained 90–100% amylose; and exhibited the same V_h X‐ray diffraction pattern, indicative of helical inclusion complex formation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1781–1788, 2002; DOI 10.1002/app.10589     

Reaction kinetics modeling and thermal properties of epoxy–amines as measured by modulated‐temperature DSC. II. Network‐forming DGEBA + MDA

Reaction‐induced vitrification takes place in the network‐forming epoxy–amine system diglycidyl ether of bisphenol A (DGEBA) + methylenedianiline (MDA) when the glass‐transition temperature (T_g) rises above the cure temperature (T_cure). This chemorheological transition results in diffusion‐controlled reaction and can be followed simultaneously with the reaction rate in modulated‐temperature DSC (MTDSC). To predict the effect of T_cure and the NH/epoxy molar mixing ratio (r) on the reaction rate in chemically controlled conditions, a mechanistic approach was used based on the nonreversing heat flow and heat capacity MTDSC signals, in which the reaction steps of primary (E_1OH = 44 kJ mol^?1) and secondary amine (E_2OH = 48 kJ mol^?1) with the epoxy–hydroxyl complex predominating. The diffusion factor DF as defined by the Rabinowitch approach expresses whether the chemical reaction rate or the diffusion rate determines the overall reaction rate. A model based on the free volume theory together with an Arrhenius temperature dependency was used to calculate the diffusion rate constant in DF as a function of conversion (x) and T_cure. The relation between x, r, and T_g, needed in this model, can be predicted with the Couchman equation. An experimental approximation for DF is the mobility factor DF* obtained from the heat capacity signal at a modulation frequency of 1/60 Hz, normalized for the effect of the reaction heat capacity in the liquid state and the change in C_p in the glassy region with x and T_cure. In this way, an optimized set of diffusion parameters was obtained that, together with the optimized kinetic parameters set, can predict the reaction rate for different cure schedules and for stoichiometric and off‐stoichiometric mixtures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2814–2833, 2004     

Solubility parameters of hydrocarbons

Information available in the literature on vapor pressures, saturated vapor and liquid densities, and critical constants, for different hydrocarbons, has permitted the calculation of δ, the solubility parameter advanced by Hildebrand, at temperatures up to and including the critical point. For these hydrocarbons, the residual quantity, δ-δ_c was found to depend on 1-T_R according to the relationship, where k appears to be a constant within different classes of hydrocarbons. Values of δ calculated with this equation were compared with the corresponding values used to develop it, and produced an average deviation of 0.85% for 153 values considered which represented 17 hydrocarbons.     

Design of responsive double-hydrophilic A-b-(B-co-C) diblock terpolymers with tunable thermosensitivity

Double-hydrophilic poly[(oligo(ethylene glycol) methacrylate)-co-methyl methacrylate]-b-poly(2-(diethylamino)ethyl methacrylate), P(EGMA-co-MMA)-b-PDEA, diblock terpolymers were designed and explored in aqueous media. Thanks to the thermosensitivity of the P(EGMA-co-MMA) statistical block and the pH sensitivity of the PDEA block, these terpolymers form two distinct micellar self-assemblies at different conditions of pH and temperature. The thermosensitivity of these terpolymers can be tuned by controlling the LCST of the statistical block through its monomer unit composition.     

Volatile Emissions Triggered by Multiple Herbivore Damage: Beet Armyworm and Whitefly Feeding on Cotton Plants

Plants are commonly attacked by more than one species of herbivore, potentially causing the induction of multiple, and possibly competing, plant defense systems. In the present paper, we determined the interaction between feeding by the phloem feeder silverleaf whitefly (SWF), Bemisia tabaci Gennadius (B-biotype = B. argentifolii Bellows and Perring), and the leaf-chewing beet armyworm (BAW), Spodoptera exigua Hübner, with regard to the induction of volatile compounds from cotton plants. Compared to undamaged control plants, infestation with SWF did not induce volatile emissions or affect the number and density of pigment glands that store volatile and nonvolatile terpenoid compounds, whereas infestation by BAW strongly induced plant volatile emission. When challenged by the two insect herbivores simultaneously, volatile emission was significantly less than for plants infested with only BAW. Our results suggest that tritrophic level interactions between cotton, BAW, and natural enemies of BAW, that are known to be mediated by plant volatile emissions, may be perturbed by simultaneous infestation by SWF. Possible mechanisms by which the presence of whiteflies may attenuate volatile emissions from caterpillar-damaged cotton plants are discussed.     

Surface‐initiated atom transfer radical polymerization from Mg(OH)2 nanoparticles to prepare the well‐defined polymer‐Mg(OH)2 nanocomposites

Well‐defined polymer‐Mg(OH)₂ nanocomposites were prepared by atom transfer radical polymerization (ATRP). The ATRP initiators were covalently attached to the Mg(OH)₂ by esterification of 2‐chloropropionyl chloride with hydroxyl group. The amount of polymer grafted from Mg(OH)₂ can be controlled using a different catalyst system and adding a small amount of polar solvent. The well‐defined diblock copolymer, consisting of poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) were synthesized. The products were characterized by nuclear magnetic resonance, Fourier transform infrared, differential scanning calorimetry, and thermal gravimetric analysis. The morphologies of PS/PMMA and PS/PMMA/Mg(OH)₂‐g‐PS‐b‐PMMA blends are compared by using a scanning electron microscope. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3680–3687, 2007     

Effect of dopants on the performance of CuO–CeO2 catalysts in methanol steam reforming

Steam reforming of methanol was carried out over a series of doped CuO–CeO₂ catalysts prepared via the urea–nitrate combustion method. XRD analysis showed that at least part of the dopant cations enter the ceria lattice. The addition of various metal oxide dopants in the catalyst composition affected in a different way the catalytic performance towards H₂ production. Small amounts of oxides of Sm and Zn improved the performance of CuO–CeO₂, while further addition of these oxides caused a decrease in catalyst activity. XPS analysis of Zn- and Sm-doped catalysts showed that increase of dopant loading leads to surface segregation of the dopant and decrease of copper oxide dispersion. The addition of oxides of La, Zr, Mg, Gd, Y or Ca lowered or had no effect on catalytic activity, but led to less CO in the reaction products. Noble-metal modified catalysts had slightly higher activity, but the CO selectivity was also significantly higher.     

Rice bran‐filled biodegradable low‐density polyethylene films: Development and characterization for packaging applications

Rice bran was incorporated into low‐density polyethylene (LDPE) at different concentrations by compounding in a twin‐screw extruder and blown into films of uniform thickness. The rice bran incorporation influenced physical, mechanical, barrier, optical, thermal properties, and biodegradation of LDPE. The mechanical and optical properties decreased as the percentage of rice bran increased. The effect of rice bran on the morphology of LDPE blends was examined using scanning electron microscopy. Oxygen transmission rate and water vapor transmission rate increased with the increased content of rice bran. Addition of rice bran did not alter the melting temperature (T_m) of the blends; however the thermal stability decreased, while glass transition temperature (T_g) increased. Kinetics of thermal degradation was also investigated and the activation energy for thermal degradation indicated that for up to 10% filler addition, the dispersion and interfacial adhesion of rice bran particles in LDPE was good. Aerobic biodegradation tests using municipal sewage sludge and biodegradation studies using specific microorganism (Streptomyces species) revealed that the films are biodegradable. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4514–4522, 2006