Study on the surface properties of grafted polyethylene particles by inverse gas chromatography

Inverse gas chromatography (IGC) studies on the surface of polyethylene (PE) particles grafted with acrylic acid and acryl amide have been reported. Surface properties of the virgin and grafting‐modified PE were compared by IGC. The dispersive contributions of the surface free energy γ and the K_A and K_B parameters expressing the ability of the stationary phase to act as Lewis acid or Lewis base were calculated. The results showed that the γ value increased significantly after grafting. The PE samples grafted with acrylic acid and acrylamide showed a predominantly basic character while the virgin PE was acidic. All of these suggested that the surface of PE has been modified through the grafting reaction, and thus is expected to improve its adhesions with other polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Surface activity and micellar behavior of dimethylamino‐ and trimethylammonium‐ tipped oxyethylene–oxybutylene diblock copolymers in aqueous media

Surface activity and micellar behavior in aqueous media in the temperature range 20–50°C of the two block copolymers, Me₂N(CH₂)₂OE₃₉B₁₈, (DE₄₀B₁₈) and I^?Me₃N⁺(CH₂)₂OE₃₉B₁₈, (TE₄₀B₁₈) in the premicellar and postmicellar regions have been studied by surface tensiometry, viscometry, and densitometry. Where E represents an oxyethylene unit while B an oxybutylene unit. Various fundamental parameters such as, surface excess concentrations (Γ_m), area per molecule (a) at air/water interface and standard Gibbs free energy for adsorption, ΔG have been investigated for the premicellar region at several temperatures. The thermodynamic parameters of micellization such as, critical micelle concentrations, CMC, enthalpy of micellization, ΔH, standard free energy of micellization ΔG, and entropy of micellization ΔS have also been calculated from surface tension measurements. Dilute solution viscosities have been used to estimate the intrinsic viscosities, solute‐solvent interaction parameter and hydration of micelle. Partial specific volume and density of the micelle were obtained from the density measurements at various temperatures. The effect of modifying the end group of the hydrophilic block was investigated by comparing the behavior of trimethylammonium‐ and dimethylamino‐tipped copolymers, designated TE₄₀B₁₈, and DE₄₀B₁₈, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The solubility of gases and volatile liquids in polyethylene and polyisobutylene at elevated temperatures

The solubility of gases and volatile liquids in low-density polyethylene (LDPE) and polyisobutylene (PIB) at elevated temperatures has been correlated, using the experimental data available in the literature. In the present study, a Henry's constant K_p at a total pressure of approximately 1 atm defined as P₁ = K_PV, where P₁ is the partial pressure of the solute in the vapor phase and V is the solubility (cm³ solute/g polymer at 273.2 K and 1 atm), is correlated for nonpolar solutes with the following expressions: (1) For LDPE, ln(1/K_P) = ?1.561 + (2.057 + 1.438ω) (T_c/T)²; (2) For PIB, ln(1/K_p) = ?1.347 + (1.790 + 1.568ω) (T_c/T)², in which ω is the acentric factor and T_c the critical temperature of the solute. In obtaining the above correlations we have used 27 solutes covering 115 data points for LDPE, and 18 solutes covering 148 data points for PIB. We have calculated values of 1/K_p from the literature data reported in terms of the retention volume (V), weight-fraction Henry's constant (H₁), activity coefficient at infinite dilution (Ω), Flory–Huggins interaction parameter (χ), or V/P obtained from high pressure sorption experiments. The correlations obtained in this study permit one to estimate with reasonable accuracy the solubility of gases and volatile liquids in either LDPE or PIB, with information on the acentric factor (ω) and critical temperature (T_c) only. The relationship for LDPE is also applicable for solubilities in high-density polyethylene. Relationships for the heat of vaporization of solutes from infinitely dilute LDPE or PIB solutions are also derived from the temperature variation of 1/K_p.     

Sensitivity analysis of catalytic conversion of n-C6

The present paper is a case study of an application of sensitivity analysis in chemical kinetics. Emphasis is laid upon chemical interpretation of sensitivity information and on identification of the most important model important model parameters. The kinetic model for reforming of C₆ hydrocarbons proposed by Mobil [14] is extended to the analysis of the behavior of n-hexane conversion in an adiabatic reactor. The importance of six initial conditions (feed composition and initial temperature) is analyzed by the computation of normalized first order sensitivity gradients (y/y) (δy_i/δy). The relative importance of 21 model parameters α_j is estimated by the computation of normalized sensitivity gradients of the type (α_j/y_i) (δy_i/δα_j). The influence of the decisive model parameters ΔH and ΔH (activation enthalpies of benzene hydrogenation and methyl cyclopentane isomerization, respectively) as well as operating parameters is presented. The problem of uncertainly in the value of ΔH and its influence on the model solution is also sown. Finally, some advantages of the application of normalized gradients of the explanation of process behavior are discussed.     

Dispersion,crystallization kinetics,and parameters of Hoffman–Lauritzen theory of polypropylene and nanoscale calcium carbonate composite

Isothermal and nonisothermal crystallization of polypropylene (PP)/calcium carbonate (CaCO₃) with two particle sizes (250–300 nm and 20–25 nm) were studied by differential scanning calorimeter. Equilibrium melting temperature (T) determined from both linear and nonlinear Hoffman–Weeks relations showed that the composites had a lower T as a result of the CaCO₃ particles destroying the crystal of PP. Kinetics of the isothermal and nonisothermal crystallization was described by Avrami equation. For the first time, without the assumption of a constant U* value, Lauritzen–Hoffman parameters (U* and K_g) were evaluated directly by data‐fitting method for isothermal crystallization, and by Vyazovkin's method for nonisothermal crystallization. K_g values obtained were similar with and without the assumption of a constant U*and comparable to those in the literature. Both U* and K_g indicate the dual role the CaCO₃ particles as nucleating agents to enhance the crystallization and as obstacles to the chain movement to reduce the crystallization. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

The higher alcohol synthesis over promoted Cu/ZnO catalysts

Alkali oxides added to methanol catalysts increase the formation of ethanol, n-propanol and isobutyl alcohol. This result has been known for many years, yet few quantitative studies have been reported in the literature. Data obtained on a commercial copper-zinc oxide catalyst promoted with K₂ CO₃ are presented and compared with published work. The optimum promoter concentration was about 0.5% by weight. The H₂ to CO feed ratio was important in determining the higher alcohol selectivity. The rate of production of isobutyl alcohol varied as p p while for methanol, ethanol and n-propanol both exponents were positive and less than 1.6. Decreasing the hydrogen to carbon monoxide ratio from 2 to 0.5 more than doubled the isobutyl alcohol selectivity. Chain growth schemes predicting the higher alcohol selectivity are presented and estimates of the parameters are given.     

Numerical and experimental investigation of three-dimensional flow in extrusion dies

The univariant element, Q₁ P₀, and the multivariant elements, QP₀ and R P₀, are compared for the numerical simulation of the flow in extrusion dies. The pressure distribution obtained by using the Q₁ P₀ element was found to be afflicted with the checkerboard pressure mode. On the other hand, the multivariant elements, Q P₀ and R P₀, gave accurate and physically reasonable velocity and pressure distributions. The computed values of the pressure drop across extrusion dies matched well with the pressure drop determined experimentally.     

Viscoelasticity of some engineering plastics analyzed with the modified stress-optical rule

The complex Young's modulus, E*(ω), and the complex strain-optical coefficient, O*(ω), of poly(ether sulfone) (PES), polysulfone (PSF), and polyethermide (PEI), were measured over the frequency range 1 to 130 Hz. The data were analyzed with a modified stress-optical rule: The Young's modulus was decomposed into two complex functions, E(ω) and E(ω); the modified stress-optical coefficient, C_R and C_G, associated with the rubber (R) and glass (G) components, respectively, were determined. The results for six polymers, including polystyrene, poly(α-methyl styrene), and bisphenol A polycarbonate were compared with each other. One of the coefficients, C_R, equivalent to the stress-optical coefficient in melts, mainly depended on the way in which phenyl groups were connected to the chain. The other, C_G, was in the range of 20 to 40 Brewsters, and did not strongly depend on the details of polymer structure. The component function, E(ω), which was located in the glassy region and originated from the high glassy modulus, was almost the same in shape when plotted against ω with double logarithmic scales. The R component, E(ω), located at the long time end of the glass-to-rubber transition zone, was slightly sensitive to the molecular structure of polymers.     

Adsorption of a gold‐iodide complex (AuI2−) onto cellulose acetate‐polyaniline membranes: Equilibrium experiments

The adsorption of AuI complex onto acetate cellulose‐polyaniline membranes was investigated. Kinetic experiments showed a rapid adsorption of this complex, which was attributed to an ion‐exchange mechanism. Equilibrium adsorption results were represented by the Langmuir model, showing a correlation coefficient of 0.9852. Langmuir parameters K and Q_m were found to be 0.2937 L mg^?1 and 1.2394 mg g^?1, respectively. Approximately 94% of AuI was adsorbed when a solid/liquid ratio of 40 g L^?1 (grams of membrane/ liter of solution) was used. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Denitrifying kinetics involving the distributed ratio of reductases

A suspended-growth batch reactor was used to denitrify synthetic wastewater containing various proportions of nitrate and nitrite. A competitive phenomenon between nitrate- and nitrite-reductase was studied utilizing various proportions of nitrate and nitrite in an anaerobic environment with a temperature of 30°C and methanol as carbon source. By using a non-linear regression technique, biokinetic constants of the maximum specific reduction rates of nitrate and nitrite (k₁, k₂) and the Monod half-saturation coefficients of nitrate and nitrite (K_s1, K_s2) for the proposed two-step denitrifying kinetics were 1·29 day^?1, 0·89 day^?1 and 14·3 mg NO-N dm^?3, 10.9 mg NO-N dm^?3, respectively. The result obtained from a series of chemostat studies indicated the Monod-type kinetic model was more accurate when the distributed ratio of nitrate- and nitrite-reductase in the proposed two-step denitrifying kinetics was taken into account.     

Several features of vinyl chloride–diallyl phthalate suspension copolymerization

Vinyl chloride–diallyl phthalate (VC–DAP) suspension copolymerization was carried out in a 5‐L autoclave and 200‐mL stainless steel vessel at 45°C. The apparent reactivity ratios of VC–DAP suspension copolymerization system were calculated as r_VC = 0.77 and r_DAP = 0.37. It shows that VC–DAP copolymer contains no gel when the feed concentration of DAP (f) is lower than a critical concentration (f_cr, inside the range of 0.466–0.493 mmol/mol VC at 80–85% conversion), the polymerization degree (DP) of copolymer increases with the increase of f and conversion. VC–DAP copolymer is composed of gel and sol fractions when f is larger than f_cr. The DP of sol fraction decreases as f increases, but the gel content and the crosslinking density of gel increase. The gel content also increases as conversion increases. The results also show that the index of polydispersity of molecular weight of sol changes with f, a maximum value appears when f is close to f_cr. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 156–162, 2000     

Morphological studies of the modified materials: Low-density polyethylene/poly(acrylic acid)/europium(III) and low-density polyethylene/poly(acrylic acid)/uranyl ion

The morphology of low-density polyethylene (LDPE) modified by in situ sorption and thermal polymerization of acrylic acid (AA) in the matrix was examined. The microstructure of the LDPE/poly(acrylic acid) (PAA) materials after Eu³⁺ and UO ion exchange was investigated. The phase behavior of these materials was analyzed using X-ray diffraction, scanning electron microscopy (SEM), and thermal measurements (DSC). The X-ray dif-fraction studies showed that PAA is located at amorphous region of the matrix. The LDPE/PAA surface, as investigate by SEM, was apparently homogeneous before and after Eu³⁺ and UO ion exchange, respectively. Two T_g values were found for the LDPE/PAA material before and after Eu³⁺ ion exchange. Also, three and four T_g values were found for LDPE/PAA after UO ion exchange depending on the amount of UO in the modified matrix. This indicates microphase domains in the LPDE/PAA-, LPDE/PAA/Eu³⁺-, and LPDE/PAA/UO -modified materials, although a lack of visible phase separation in the micrographs was observed. © 1996 John Wiley & Sons, Inc.     

Simultaneous sorption and diffusion of a 4-aminoazobenzene derivative and its conjugate acid in cellulose membrane carrying sulfonic acid groups

An azo dye, 2-methyl-N,N-bis(2-hydroxyethyl)-4-aminoazobenzene (nonionic dye) and its conjugate acid (cationic dye) are simultaneously adsorbed by the cellulose membranes carrying sulfonic acid groups from a slightly acidic aqueous solution. Sorption equilibria of the nonionic and the cationic dye are described in terms of the Henry's partition and the ionic exchange mechanism, respectively, in the latter case, the ion exchange constants obtained for the membrane with sulfonic acid group content (SAG) = 261 meq/kg at 30°C are K = 1.43 × 10^?5 and K = 0.542, respectively, where Na, H, and DH refer to sodium, hydrogen, and cationic dye ions. The diffusion coefficients of the nonionic dye (D_N) and the cationic dye (D_C) in the membranes were estimated from the permeation data of the dyes through the membrane. Both D_N and D_C decrease with increasing SAG. The ratio D_N/D_C ranged in 2.2–10, the ratio increases with the SAG.     

Surface free energy analysis of polymers and its relation to surface composition

The dispersion force component of surface free energy, γ, and the nondispersive interaction free energy between solid and water, I, were determined by the two-liquid contact-angle method, i.e., by the measurement of contact angles of water drops on plain solids in hydrocarbon, for commercialy available organic polymers such as nylons, halogenated vinyl polymers, polyesters, etc. A method to estimate the I values from the knowledge of the polymer composition is also proposed, on the basis of the assumption of the spherical monomer unit and the sum of interactions between functional groups and water molecules at the surface.     

Study on the thermal stability of heterogeneous nucleation effect of polypropylene nucleated by different nucleating agents

The thermal stability of the heterogeneous nucleation effect of polypropylene (PP) nucleated with an organic phosphate (A) and two kinds of sorbitol derivatives (B and D) was investigated by DSC multiscanning. For pure PP, the peak temperature of crystallization (T) was little changed with an increasing number of DSC scans, indicating that nucleation of PP is thermally stable. For the PP nucleated with an organic phosphate (PPA), the temperatures at the onset of crystallization (T) and at the completion of crystallization (T); the peak temperature of crystallization (T) and melting (T); and the heat of crystallization (ΔH_c) and fusion (ΔH_m) of PP are higher than those of pure PP and were little influenced with an increasing number of DSC scans. For PP nucleated with the sorbitol derivatives (PPB and PPD), the T, T, T, and T decreased with an increasing the number of scans. These results indicated that the thermal stability of heterogeneous nucleation effect of the nucleating agent A is higher than that of nucleating agents B and D. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1643–1650, 2002     

Bulk and surface compression viscosities of high and low density polyethylenes

Bulk compression flow of high density polyethylene (HDPE) and low density polyethylene (LDPE) have been measured at temperatures of 423 to 463K, pressure up to 150 MPa, and bulk compression rates of about 1.0 to 200.00 × 10^?5 s^?1. Bulk and surface compression modulus of elasticity (L and K_s), longitudinal bulk compression viscosity (η_L), and surface compression viscosity (η) are described as a function of compression rates (k_v and k_s), compression deformations (k_v percent and K_s percent), and temperature (T). Bulk and surface compression flow activation energies are of the order of 40 to 100 KJ/mol and 3.84 KJ/mol, respectively.     

Elastic characteristics of branched-network polymers

The computed dependencies of elastic characteristics of branched-network polymers were obtained on the basis of the Takayanagi series model. The moduli ratio (λ) for branched-network and branched polymers increases as a result of an increase of the moduli ratio of network and branched phases (E/E) and the network phase fraction (V_net). The λ-increase as a function of V_net is larger than in the case of the E/E dependence. On the basis of computed dependencies, the experimental results for the radiation crosslinked SBS block copolymer were considered. The experimental results agree with the computed de-pendencies for the hetergeneous branched-network polymers with E/E ≈︁ 20. The influence of entanglements on the elastic characteristics of branched-network polymers is discussed. © 1996 John Wiley & Sons, Inc.     

Liquid–solid mass transfer for cocurrent gas–liquid upflow through solid foam packings

This article presents the liquid–solid mass transfer characteristics for cocurrent upflow operated gas–liquid solid foam packings. Aluminum foam was used with 10, 20, and 40 pores per linear inch (PPI), coated with 5 wt % Pd on γ‐alumina. The effects of gas velocity (u_g = 0.1?0.8 m m s^?1) and liquid velocity (u_l = 0.02 and 0.04 m m s^?1) are studied using the Pd/Bi catalyzed oxidation of glucose. The volumetric liquid–solid mass transfer coefficient, k_lsa_ls, is approximately the same for 10 PPI and 20 PPI solid foams, ranging from 2 × 10^?2 to 9 × 10^?2 m m s^?1. For 40 PPI solid foam, somewhat lower values for k_lsa_ls were found, ranging from 6 × 10^?3 to 4 × 10^?2 m m s^?1. The intrinsic liquid–solid mass transfer coefficient, k_ls, increases with increasing liquid velocity and was found to be proportional to u. Initially, k_ls decreases with increasing gas velocity and after reaching a minimum value increases with increasing gas velocity. The values for k_ls range from 5.5 × 10^?6 to 8 × 10^?4 m m s^?1, which is in the same range as found for random packings and corrugated sheet packings. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Adiabatic compressibility of polyelectrolytes: Poly(N-dimethylaminoethyl methacrylate) and its copolymer with acrylic acid

The adiabatic compressibility of poly(N-dimethylaminoethyl methacrylate) and of three copolymers of N-dimethylaminoethyl methacrylate and acrylic acid, ranging in composition from 33 to 58 mole-% amino groups, has been studied. The ?V of the polymer shows a slight decrease (2.4 cc/mole), while the ?K is found to have increased considerably (51 × 10^?4 cc bar^?1 mole^?1) compared to that of the monomer. The latter is apparently due to the more compressible nature of the polymer than that of its monomer. The experimentally observed ?K₂⁰ and ?V₂⁰ values for the three copolymers containing 58%, 43%, and 33% amino groups are ?2.5 × 10^?4 cc bar^?1 mole^?1 and 164.5 cc/mole, ?32 × 10^?4 cc bar^?1 mole^?1 and 177.5 cc/mole, and ?55 × 10^?4 cc bar^?1 mole^?1 and 211.3 cc/mole, respectively, whereas the calculated values are less by 19.4 × 10^?4 cc bar^?1 mole^?1 and 3.2 cc/mole, 49.5 × 10^?4 cc bar^?1 mole^?1 and 19.9 cc/mole, and 73 × 10^?4 cc bar^?1 mole^?1 and 16.4 cc/mole, respectively. This decrease is attributed to the interaction of acid and base groups in the molecules. The ?K₂⁰ and ?V₂⁰ values have been resolved into their ionic components ?K and ?V. Since the magnitude of electrostriction is higher in fully neutralized salt than in unneutralized salt, the ?K_2i⁰ and ?V_2i⁰ values are lower as expected. The difference in these values for the polybase and its salt is 23.7 × 10^?4 cc bar^?1 mole^?1 and 7.5 cc/mole, respectively, which may be due to the electrostrictive effect. In excess NaCl (1.0M), the magnitude of electrostriction is somewhat reduced and ?V_2i⁰ and ?V_2i⁰ approach values more or less equal to those of the unneutralized polymer. The 100% neutralized hydrochloride salt of poly(N-dimethylaminoethyl methacrylate) shows greatly increased reduced viscosity over that of the feebly basic parent polymer due to the characteristic polyelectrolytic expansion in dilute aqueous solution. The copolymer containing excess amount of amino groups (58%) shows similar behavior, while the other two copolymers containing fewer amino groups (43% and 33%) show a contraction of chains, which may be ascribed in interaction of the carboxyl ions that are freshly formed on dilution with the amino groups in the copolymer chain.     

The fractal and scaling analysis of chemical reactions

It is shown that the geometrical factor controlling a thermooxidative degradation course is effective spectral dimension d or factor β. In turn, parameters d and β are a function of a polymer melt structure characterized by its fractal dimension Δ_f. The applicability of this or that scaling relationship allows the evaluation of general features of chemical reactions in the thermooxidative degradation process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2343–2347, 2004