A measure of effective crosslinks in formaldehyde-modified cotton celluloses

Sol-gel fractions have been measured for cotton celluloses crosslinked with formaldehyde under widely different conditions of reaction and have been employed for estimation of the efficiency of crosslinking in the various processes. Most efficient utilization of formaldehyde for insolubilization of molecular chains is indicated for an aqueous process (form W′) and least efficient utilization is indicated for a nonaqueous process (form D′), the difference in efficiency being approximately a factor of 40. Interpretation of sol-gel data has been made relative to a model assuming random reaction of crosslinking agent throughout the cotton cellulose and by relationships developed by Charlesby and Pinner and by Shultz. This leads to estimates of relative numbers (moles) of effective chain elements per gram, v_e (i.e., twice the number of effective crosslinks), which decrease in the following sequence for cottons at the 0.20% level of formaldehyde (i.e., 6.7 × 10^?5 mole/g.): aqueous process, higher formaldehyde concentration (W′, v_e = 4.8 × 10^?5), vapor process (V, v_e = 1.75 × 10^?5), bake-cure process (C, v_e = 1.37 × 10^?5), aqueous process, lower formaldehyde concentration (W, v_e = 0.95 × 10^?5), nonaqueous process (D, v_e = 0.03 × 10^?5).     

Thermal Isomerization of Azulene. Single-Pulse Shock Tube Investigation

The thermal isomerization of azulene was studied behind reflected shocks in a pressurized driver single-pulse shock tube. The temperature range covered was 1050–1400 K at overall densities of ∼2.5 × 10⁻⁵ mol/cm³. The main reaction of azulene under these conditions is a unimolecular isomerization to naphthalene, but it also isomerizes, although at a much lower rate, to another isomer. The suggested “tetracyclic triene” intermediate structure for the azulene-naphthalene isomerization can lead also to transition states that can describe isomerizations to 1-methylene-1H-indene and 1, 2,3-metheno-1H-indene,2,3-dihydro. Small quantities of C₂H₂, C₄H₂, C₆H₆, and C₆H₅-C≡CH were also found in the post-shock samples, particularly at high temperatures. The Arrhenius parameters of the two high pressure limit rate constants for the isomerization processes are: azulene → naphthalene, k₁ = 10^12.93 exp(–62.8 × 10³/RT) s⁻¹ azulene → second isomer, k₂ = 10^12.42 exp(–69.5 × 10³/RT) s⁻¹ A discussion of the mechanism for these isomerization processes is presented.     

Ultrafast preparation of branched poly(methyl Acrylate) through single electron transfer living radical polymerization at room temperature

Ultrafast preparation of branched poly(methyl acrylate) (BPMA) with high‐molecular weight through single electron transfer living radical polymerization (SET‐LRP) of inimer at 25°C has been attempted, atom transfer radical polymerization (ATRP) at 60°C was also carried out for comparison. Gas chromatography, proton nuclear magnetic resonance, and triple detection size exclusion chromatography were used to analyze these polymerizations. As expected, SET‐LRP system showed much faster polymerization rate than ATRP system, the calculated apparent propagation rate constants (k_p^app) are 3.69 × 10^?2 min^?1 and 6.23 × 10^?3 min^?1 for SET‐LRP and ATRP system, respectively. BPMA with high‐molecular weight (M_w._MALLS = 86,400 g mol^?1) compared with that in ATRP (M_w.MALLS = 61,400 g mol^?1) has been prepared. POLYM. ENG. SCI., 54:1579–1584, 2014. © 2013 Society of Plastics Engineers     

The use of DTA to study spontanceous ignition of cellulose

The use of differential thermal analysis has enabled spontaneous ignition behaviour of cotton cellulose to be investigate. The temperature. T_i, at which the onset of spontaneous ignition occurs is recorded as a function of the oxygen concentration of the flowing oxygen-nitrogen atmosphere to which the cellulose sample is exposed in the DTA furnace, when heated at a defined heating rate. The dependence of T_i, on heating rate has enabled the activation energy, E_p, of the rate-determining flammable pyrolysis product reaction to the determined using both a previously derived simple kinetic model and the technique of Ozawa. E_p, increases from a lower limiting value of 112 kJ mol^?1 at zero oxygen concentration to an asymptote value of 169 kJ mol^?1 at oxygen volume concentrations above 30%. This effect is described in terms of oxygen catalysis of competing pyrolysis routes. At a given heating rate, increased oxygen concentration reduces T_i. A plot of 1/T_i versus In [O₂] gives two liner regions which intersect at an oxygen concentration of about 20%, suggesting that two combustion mechanisms exist, one above and the other below this value. Below this concentration, which is similar to the conventional limiting oxygen for cellulose, significant char remains, suggesting that ignition of gaseous products only occurs. If the difference in slopes is sttributed to the variations in E_p with oxygen concentration, then a value for the activation energy of gaseous product oxidation, E_ox = 215 kJ mol^?1 is derived.     

PERTECHNETATE REMOVAL BY MACROPOROUS POLYMER IMPREGNATED WITH 2-NITROPHENYL OCTYL ETHER (NPOE)

ABSTRACT

The loading kinetics of TcO₄ ^? from water and 1?M NaOH solution to macroporous polymer (MPP) impregnated with 2-nitrophenyl octyl ether (NPOE) are reported. The loading process can be simply expressed as: -ln (1 - [TcO₄ ^?]_MPP / [TcO₄ ^?]_MPP,e) =k t +A, where [TcO₄ ^?]_MPP and [TcO₄ ^?]_MPP,e respectively refer to the pertechnetate concentration in the MPP phase at time t and the equilibrated value, and A is a constant. With TcO₄ ^? in water and in 1?M NaOH as loading solutions, the overall mass transfer coefficients k are estimated to be 0.058?min^?1 and 0.067?min^?1 and the saturated loading capacities of TcO₄ ^? are 8.0 × 10^?8?mol/g wet MPP and 5.6 × 10^?8?mol/g wet MPP, respectively. TcO₄ ^? can be easily stripped from loaded MPP by >1?M HNO₃ solution. Loading-stripping cycling and breakthrough experiments demonstrate a good performance of NPOE-impregnated MPP, in particular with TcO₄ ^?-containing water as the loading feed.     

The anodic dissolution of nickel—1: Perchlorate and fluoride electrolytes

A potentiostatic sweep technique has been used to study the anodic dissolution of nickel in acidic perchlorate, acetate and fluoride solutions. At slow potential sweep rates a prepassive film exists throughout the anodic region in perchlorate and acetate electrolytes. By the use of fast sweeps, or by the addition of F^?, film formation and growth is sufficiently reduced to reveal a linear anodic. Tafel region. The rate of active dissolution, which is independent of [H⁺] and [F^?], obeys the following rate law; i = 2Fka_w exp [βFE/RT], with β = 0·53.The following mechanism is proposed for active dissolution, with the first step rate-determining: (1) Ni + H₂O → NiOH_ads + H⁺ + e^?, (2) NiOH_ads → NiOH⁺ + e^?, (3) NiOH⁺ + H⁺ ? Ni²⁺ + H₂O. Prepassivation is thought to occur from the intermediate NiOH_ads through a solid state mechanism.     

The decomposition of nitric oxide on a heated platinum wire

The catalytic rate of decomposition of pure nitric oxide on platinum (2NO → N₂ + O₂) was measured employing the batch, hot-wire technique at wire temperatures in the range 900–1200°C and at total pressures from 400–2260 torr. Chemisorbed oxygen is known to inhibit the rate of this reaction but very little surface oxygen is present at these elevated temperatures and thus an effectively clean platinum surface was realized. Also the experiments were limited to low conversions and thus low oxygen partial pressures (P_O2 → O₂), again minimizing the likelihood of oxygen inhibition. A Rideal—Eley type rate expression: ?r (moles NO reached/cm² . sec) = k₂P²_NO/(1 + K₁P_O2 + K₂P_NO) describes quite well the dependence of the measured rate of the NO partial pressure on P_NO. In contrast the data are not fit well by a Langmuir—Hinshelwood type rate-expression, similar to that above except for a unimolecular term P_NO in the numerator. Owing to the large values of P_NO and low conversions used in the present study with P_O2 → O, the study focused on the kinetics with respect to NO itself. For the above Rideal—Eley mechanism: k₂ ? 4·63 × 10^?4 exp (?8,600/RT) mol/cm² . atm² . sec and K₂ ? 3 · 5 × 10^?2 exp (11,300/RT) atm^?1.     

Kinetics of dimerisation of gaseous keten

The dimerisation of gaseous keten in the temperature and pressure ranges 225 to 323 °C and 6 to 155 mmHg, respectively, is essentially homogeneous and of the second order in carbon-coated reactors, k = 10^5.25 exp(?74 000/RT) l mol^?1 s^?1. The entropy of activation, at – 166.4 J K^?1 mol^?1, agrees closely with values obtained in solution for the dimerisation or cycloaddition reactions of other ketens.     

ULTRASOUND-ASSISTED N-ALKYLATION OF PHTHALIMIDE UNDER PHASE-TRANSFER CATALYSIS CONDITIONS AND ITS KINETICS

In this work, N-butylation of potassium phthalimide was carried out under ultrasonic-assisted phase-transfer catalysis condition using n-bromobutane as an alkylating agent. The mechanism of the solid-liquid reaction of alkyl halide and potassium salt of phthalimide in an organic solvent was verified in this work. The kinetics of the reaction depends on the amount of catalyst, agitation speed, type of quaternary ammonium salts, volume of water, type of organic solvent, volume of organic solvents, temperature, and the frequency of the ultrasound. Five different onium salts were examined for the reaction and tetrahexylammonium bromide showed maximum catalytical activity. An improvement of the reaction outcome (yield and reaction time) was achieved through the immersion of the reactor into an ultrasound bath. The rate of the reaction is two times faster under ultrasonic condition (k_app = 10.7 × 10^?3 min^?1) than silent condition (k_app = 5.5 × 10^?3 min^?1) and is five times faster when the reaction is carried out in acetonitrile medium than in cyclohexane medium. The reaction is very fast under anhydrous condition. Based on the experimental data, a rational mechanism for the reaction is proposed.     

Isomerization of α-pinene to camphene

The catalytic isomerization reaction of α-pinene to camphene over a clinoptilolite catalyst was investigated in a batch reactor open to the atmosphere between 130 and 155°C. The catalyst was selective to the isomerization of α-pinene to camphene. The effects of several variables, such as reaction temperature, amount of catalyst, stirring speed and catalyst particle size, on the conversion of α-pinene and selectivity to camphene were determined. The reaction fits a first-order parallel reaction with rate constants of k ₁ = 3.020·10^?2 e ^?33381.6/RT for the production of camphene and of k ₂ = 1.576·10^?2 e ^?31096.53/RT for the production of limonene.     

Comments on the reactivity of methoxy pentadecyl phenyl isocyanate isomers

The reactions of 2-methoxy-4-pentadecyl phenyl isocyanate and 4-methoxy-2-pentadecyl phenyl isocyanate with excess 2-ethyl hexanol originally reported by Ghatge and co-workers to follow zero order kinetics have been re-examined on the basis of their data and shown to follow more realistically the product catalyzed pseudo first order kinetics. The new rate constant, k_s (sec^?1) for the spontaneous reaction and k_p (li. mole^?1 sec^?1) for the product catalyzed reaction are found to be: k_s = 0.57 × 10^?6 and k_p = 34 × 10^?6 for 2-methoxy-4-pentadecyl phenyl isocyanate and k_s = 1.2 × 10^?6 and k_p = 82 × 10^?6 for 4-methoxy-2-pentadecyl phenyl isocyanate.     

CO2 gasification of wood charcoals derived from vacuum and atmospheric pyrolysis

The gasification of biomass derived char obtained via vacuum and atmospheric pyrolysis of Populus tremuloides has been studied in the ranges of 725–960°C and 0.1 to 6 MPa. CO₂ was used as the oxidizing gas. The results show that char reactivity is influenced by the preheating rates and that pressure effects are significant between 850°C and 950°C. A correlation based on the expression: df/dt = k₀{exp(-E/RT)}(1 - f)^af^βP^yCO₂ was used to fit the experimental data. In general, vacuum pyrolysis derived char showed a higher reactivity than atmospheric pyrolysis chars. An explanation based on a higher oxygen content of the vacuum pyrolysis char is suggested.     

Gasification of carbon by CO2: A transient kinetics experiment

A transient kinetic technique was used to measure the intrinsic rate constant k₂ of the reaction C(O) → CO + C_f, where C_f is an available site and C(O) is an occupied site. It was found that k₂ = 10^{11.6 ± 2.3} exp[ −(225 000 ± 39000)/RT]min⁻¹. Two systems were studied, one using an uncatalysed carbon, the other a Ca-catalysed carbon. The gasification rates for these two systems differed by a factor of 100, yet they yielded the same k₂. This strongly supports the contention that Ca catalyses the system by increasing the number of active sites.     

Radiation-induced graft copolymerization of styrene to cellulose

The radiation-induced graft copolymerization of styrene to cellulose has been studied in vacuo at 30°C and at dose rates from (0.37 to 8.73) × 10^?2 W/kg. Dioxan was used as solvent for monomer and polystyrene homopolymer, and water (2% total volume) was incorporated as swelling agent for cellulose. The concentration of styrene in the bulk medium was varied from 0.432 to 3.46 moles/l., and the rates of both grafting and homopolymerization were shown to be proportional to [monomer] · [intensity]^1/2. The value of 3.3 × 10^?4 l. mole^?1 sec^?1 derived for k_p²/k_t in homopolymerization is similar to that for normal free-radical polymerization of styrene. However, reduced termination during grafting yielded a much higher value (58 l. moles^?1 sec^?1). Degradation of cellulose in the absence of monomer was followed viscometrically, and values of 13.5 and 24.6 were derived for G (scission) in vacuo and in air, respectively.     

The Free-Radical Cleavage of the Disulfide Bond (Studied by Pulse Radiolysis)

Reaction of H atoms with glutathione leads rapidly to H + RSSR → RS · + RSH. The first observed product is RS, the spectrum of which is obtained. The spectrum of the RS?SR radical was obtained by direct attack of e^?_aq on glutathione. The rate constants of these processes were also measured. k_e?aq + RSSR = (2.7 ± 0.3) × 10⁹ M^?1 sec^?1 k_{H + RSSR} = (1.0 ± 0.2) × 10¹⁰ M^?1 sec^?1 When the OD of RS?SR is plotted vs pH a titration curve is obtained. This is due to the protonation of RS?SR with a rate constant of 2.6 × 10¹⁰ M^?1 sec^?1 which is probably followed by a cleavage to RS and RSH. In both cases the RSSHR radical cannot be detected. The spectrum attributed to the RSSHR radical is more likely to be that of RS.     

Effect of diantimony trioxide on direct esterification between terephthalic acid and ethylene glycol

Experiments at various Sb₂O₃ concentrations were made in a pilot plant and the effect of Sb₂O₃ on continuous esterification between terephthalic acid (TPA) and ethylene glycol (EG) was obtained. Reaction rate constants of the previously reported reaction scheme were determined to fit with the experimental data obtained. It was found that the effect of Sb₂O₃ on reaction rate constant (k_i) can be expressed as follows.

• k₁ = (3.75 × 10^?4Sb + 1.0) × 1.5657 × 10⁹exp(?19,640/RT)
• k₂ = (4.75 × 10^?4Sb + 1.0) × 1.5515 × 10⁸exp(?18,140/RT)
• k₃ = (6.25 × 10^?4Sb + 1.0) × 3.5165 × 10⁹exp(?22,310/RT)
• k₄ = (4.50 × 10^?4Sb + 1.0) × 6.7640 × 10⁷exp(?18,380/RT)
• k₅ = (3.50 × 10^?4Sb + 1.0) × 7.7069 × exp(?2810/RT)
• k₆ = (1.75 × 10^?4Sb + 1.0) × 6.2595 × 10⁶exp(?14.960/RT)
• k₇ = (3.75 × 10^?4Sb + 1.0) × 2.0583 × 10¹⁵exp(?42,520/RT)

Simulation of esterification with these reaction rate constants at various Sb₂O₃ concentrations was made and the following results were obtained.

• 1 Sb₂O₃ accelerates the esterification reaction between TPA and EG.
• 2 Sb₂O₃ accelerates the main reaction and its effects on side reactions are minor. The higher the addition rate of Sb₂O₃, the lower the carboxyl end-group concentration (AV) and diethylene glycol content (DEG).
• 3 The comparison between simulation with potassium titanium oxyoxalate (PTO) in the previous report and with Sb₂O₃ in the present report shows that the acceleration of polycondensation reaction by Sb₂O₃ is higher. DEG formation rate is lower with PTO than Sb₂O₃.

     

Synthesis,photodegradation, and energy transfer in a series of poly(ethylene terephthalate–co–4,4′-biphenyldicarboxylate) copolymers

Poly(ethylene terephthalate) (PET) filament yarns were photostabilized by addition of 0.5–4.0 mole % dimethyl 4,4′-biphenyldicarboxylate (4,4′-BPDC) to the polymerization feed. The mechanism of photostabilization is proposed to be a triplet–triplet energy transfer from excited terephthalate units to ground-state biphenyldicarboxylate units. The mechanism of transfer is reported to be via an electron exchange mechanism, with the “quenching sphere” calculated to be 14.9 Å. Kinetic studies show the “pseudo” zero-order rate constant of initial photodegradation to decrease from 3.4 × 10^?19 for the PET homopolymer to 2.0 × 10^?19% breaking strength loss/quantum exposure/cm² for the copolyester containing 4.0 mole % of the 4,4′-biphenyldicarboxyl moieties. The photophysical processes available to the dimethyl 4,4′-biphenyldicarboxylate monomer were characterized by absorption and luminescence studies. In solution, dimethyl 4,4′-biphenyldicarboxylate was shown to emit an intense fluorescence from a ²(π,π*) state and a weaker (～10^?2×) phosphorescence from a ¹(π,π*) state derived from the ¹A→supn1L_b absorption. The copolymer yarns were shown to exhibit both fluorescence and phosphorescence from the biphenyldicarboxylate units: the fluorescence from direct excitation, the phosphorescence by sensitized transfer.     

Photoelectrocatalytic humic acid degradation kinetics and effect of pH,applied potential and inorganic ions

This study addresses the removal of humic acid (HA) dissolved in an aqueous medium by a photoelectrocatalytic process. UV₂₅₄ removal and the degradation of color (Vis₄₀₀) followed pseudo‐first order kinetics. Rate constants were 1.1 × 10^?1 min^?1, 8.3 × 10^?2 min^?1 and 2.49 × 10^?2 min^?1 (R² > 0.97) for UV₂₅₄ degradation and 1.7 × 10^?1 min^?1, 6.5 × 10^?2 min^?1 and 2.0 × 10^?2 min^?1 for color removal from 5 mg dm^?3, 10 mg dm^?3 and 25 mg dm^?3 HA respectively. Following a 2 h irradiation time, 96% of the color, 98% of the humic acid and 85% of the total organic carbon (TOC) was removed from an initial 25 mg dm^?3 HA solution in the photoanode cell. Photocatalytic removal on the same photoanode was also studied in order to compare the two methods of degradation. Results showed that the photoelectrocatalytic method was much more effective than the photocatalytic method especially at high pH values and with respect to UV₂₅₄ removal. The effect of other important reaction variables, eg pH, external potential and electrolyte concentration, on the photoelectrocatalytic HA degradation was also studied. Copyright © 2003 Society of Chemical Industry     

A comparative study to predict the interphase modulus in polymer nanocomposites

In this study, the interphase modulus (E_i) in polymer nanocomposites is calculated by two methods and the calculated results are compared at different conditions. In the first method, the experimental moduli of samples are applied to Ji model and suitable “E_i” is calculated. In the second method, a multilayered interphase is considered, in which the Young's moduli of layers (E_k) depend to the distance between the nanoparticle surface and the polymer matrix by power function of “Y” parameter. The “E_i” is calculated for multilayered interphase assuming the same and different layer thicknesses (t_k) by Parallel and Series models. Finally, the “E_i” values calculated by the explained methods are compared for two reported samples. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44076.     

On the electrochemical behavior of H2O2 AT Ag in alkaline solution

Electrochemical oxidation and reduction of H₂O₂ on Ag were studied in alkaline solution of 10^?3?0.3 M H₂O₂ and 2 × 10^?3 ?1.0 M KOH under N₂ bubbling. Steady i-φ curves obtained by a cyclic potential sweep method in a potential range where no electrode oxidation takes place, lead to the following results: (1) i^c_d (A cm^?2) (cathodic limiting current density) = 1.0 × [H₂O₂]^1.0_T (M), (2) i¹_d (A cm^?2 (anodic limiting one) = i^c_d ([KOH] ? [H₂O₂]_T) or 1.0 × [KOH] < [H₂O₂]_T), (3) φ_m (V) (mixed potential) = 0.126-0.060 log [KOH]^1.0 and (4) (?φ/?i)_φ=φm (Ωcm²) (reaction resistance at φ = φ_m) = 0.057 × [H₂O₂]^?1.0_T (M^?1), where [H₂O₂]_T designates a total H₂O₂ concentration and the others have their usual meanings.The above results are explained by the following mechanism; HO^?₂ formed by the reversible chemical reaction, H₂O₂ + OH ? HO^?₂ + H₂O, is oxidised in anodic reaction by two steps: HO^?₂

HO₂ (a) + e^? and HO₂(a) + OH^? → O₂ + H₂O + e^?, whereas in cathodic reaction, H₂O₂ is reduced by H₂O₂ + e^?

OH(a) + OH^?, OH(a) + e^? → OH^?. Here,

designates a rate determining step,Catalytic decomposition of H₂O₂ on the electrode is also discussed.