The Kinetics of Melting Crystallization of Poly-L-Lactide

The influence of non-isothermal melt crystallization on thermal behavior and isothermal melt crystallization kinetics of poly-L-lactide (PLLA) were investigated by differential scanning calorimetry (DSC), polarizing micrograph (POM) and x-ray diffraction (XRD). Crystallization performed at lower cooling rates (2°C·min^?1) is accompanied by a variation of the kinetics around 118°C. The glass transition temperature of PLLA decreases with increase of cooling rate, and the crystallinity at the end of crystallization increases with decreasing cooling rate. The size of PLLA spherulites increases with a decrease in the cooling rate, and PLLA becomes almost amorphous cooled at rapid rate (>10°C·min^?1). PLLA exhibits an Avrami crystallization exponent n = 3.01±0.13 in isothermal crystallization in the range from 90°C to 140°C. According to Hoffman-Lauritzen theory, two crystallization regime are identified with a transition temperature occurring at 118°C, and the value of K_g(II)/K_g(III) is 2.17 [K_g(II) = 6.025 × 10⁵K², K_g(III) = 1.307 × 10⁶ K²].     

An experimental study on the performance of a condensing tumbler dryer with an air-to-air heat exchanger

The performance of energy consumption in the closed-loop tumbler dryer with a condenser for clothes drying is evaluated as a function of the heater capacity, the drying air flow rate inside the dryer, and the cooling air flow rate. The clothes dryer in laundries used in this study consists of a tumbling drum, condenser for condensing the humid and hot air flowing out the rotating drums, and electric heater for heating the circulating drying air. Tests were performed at the heating capacity of 1.9 kW to 2.7 kW, the drying air flow rate of 60 m³/h to 140 m³/h, and the cooling air flow rate of 100 m³/h to 240 m³/h. The total energy consumption, the drying time, and the condensate water rate were also investigated. Parametric results showed that a larger heater power resulted in shorter drying time. With increasing heater power, the air temperature and the condensate rate increased due to the higher humidity ratio in the air. The drying air flow rate and the cooling air flow rate did not have a significant effect on drying performance.     

Production of the fungal exopolysaccharide scleroglucan by cultivation of Sclerotium glucanicum in an airlift reactor with an external loop

Sclerotium glucanicum NRRL 3006 was cultivated in a 120 dm³ working volume airlift reactor with external recirculation loop for the production of the exopolysaccharide (EPS), scleroglucan. When culture pH was not controlled EPS production, at a range of air flow rates, was poor (<2 kg m^?3). Biomass formation generally increased with increasing aeration rate. When culture pH was controlled at 4·5 ± 0·2 EPS production was maximal at an air flow rate of 100 dm³ min^?1 and fell as air flow rate decreased. Operation of the reactor at a high (100 dm³ min^?1) air flow rate for the early part of the process (up to 96 h), followed by a low air flow rate (20 dm³ min^?1), led to reduced biomass and oxalate formation, and a slight increase in EPS concentration relative to operation at a constant air flow rate of 100 dm³ min^?1. EPS production in this pneumatically-agitated reactor was equal to the highest levels reported in small-scale stirred tank reactors.     

Numerical Analysis and Experimental Validation of Distillation Process for Purification of Tellurium

Numerical analysis was performed on a vacuum distillation process for Te purification. The effects of temperature gradient and Ar gas flow rate and vacuum level on the evaporation behavior of Te were investigated through a series of simulations with a diffusion-coupled convection model. An overall yield of up to 95% of 4 N pure Te was achieved at an average distillation rate of ～5.6 × 10^?4 g · cm^?2 · s^?1 from 2 N pure indigenous Te. The diffusion and condensation factors of impurities were investigated under different distillation conditions such as vacuum degree, temperature and argon flow rate. It was found that the numerical model could be used to predict impurity level during vacuum distillation process of Te and designing and optimization of a larger-scale distillation process also could be possible with a sufficient reliability.     

Struktur und elektrische Leitfähigkeit von polymeren organischen Halbleitern

In this review article we want to give information about low molecular and polymer organic semiconductors, which were recently synthesized in our institute. Specific electric conductivities up to σ_298°K = 9.0 · 10^?5Ω^?1 · cm^?1 and thermic activation energies of E = 0.30 eV of polyenearylenes, respectively -heteroarylenes were measured. Polyazomethines have a maximum σ_298°K = 3.3 · 10^?9Ω^?1 · cm^?1 and E = 0.35 eV. Polymers with indophenine units have conductivities up to σ_298°K = 1.1 · 10^?4Ω^?1 · cm^?1 and E = 0.39 eV. A maximum of σ_298°K = 5.0 · 10^?2Ω^?1 · cm^?1 and E = 0.05 eV was found for bis-(1.2-dicyanoethylenedithiolo)-metal salts. Polymers with a phthalocyanine- or hemiporphyrazine-like structure achieve a conductivity of σ_298°K = 2.3 · 10^?2Ω^?1 · cm^?1 and E = 0.15eV. Coordination polymers of dimercaptomaleic acid, respectively their monoamide show a maximum of σ_298°K = 3.2 · l0^?lΩ^?l · cm^?1 and E = 0.20 ev. Polymers with σ_298°K ≤1.5 · 10^?5 Ω^?l · cm^?l and E ≥ 0.5 eV were obtained by the polymerization of succinonitrile. All the investigated substances show an electronic conductivity. The existence of an ionic conductivity could, in all cases, be excluded by using direct current measurements over a long period of time.     

Effect of venting range hood flow rate on size-resolved ultrafine particle concentrations from gas stove cooking

Cooking is the main source of ultrafine particles (UFP) in homes. This study investigated the effect of venting range hood flow rate on size-resolved UFP concentrations from gas stove cooking. The same cooking protocol was conducted 60 times using three venting range hoods operated at six flow rates in twin research houses. Size-resolved particle (10–420?nm) concentrations were monitored using a NanoScan scanning mobility particle sizer (SMPS) from 15?min before cooking to 3?h after the cooking had stopped. Cooking increased the background total UFP number concentrations to 1.3?×?10³ particles/cm³ on average, with a mean exposure-relevant source strength of 1.8?×?10¹² particles/min. Total particle peak reductions ranged from 25% at the lowest fan flow rate of 36?L/s to 98% at the highest rate of 146?L/s. During the operation of a venting range hood, particle removal by deposition was less significant compared to the increasing air exchange rate driven by exhaust ventilation. Exposure to total particles due to cooking varied from 0.9 to 5.8?×?10⁴ particles/cm³·h, 3?h after cooking ended. Compared to the 36?L/s range hood, higher flow rates of 120 and 146?L/s reduced the first-hour post-cooking exposure by 76% and 85%, respectively.

© 2018 Crown Copyright. Published with license by Taylor & Francis Group, LLC     

Effect of preparation pH on properties of silica gel

Silica gels were obtained by drying the silica hydrogels formed at pH values between 1 and 4 at 100°C. The bulk density of the 2–3 mm diameter fraction decreased from 0·62 g cm^?3 to 0·20 g cm^?3 as the preparation pH increased from pH 3 to pH 3·65. The apparent density of silica gels was between 1·43 and 1·95 g cm^?3. Isotherms for the adsorption of water vapour on samples prepared at different pH values showed hysteresis in all cases. Thermogravimetry analysis showed that the amount of bound water was in the range of 4·4 to 5·5% on a dry weight basis. Specific heats were determined by a differential scanning calorimetry method using a sapphire standard and were between 0·82 and 0·97 J g^?1 K¹.     

Microwave drying of wastewater sludge: Experimental and modeling study

This study investigates experimentally and using mathematical modeling the microwave drying of wastewater sludge with determination of moisture diffusivity at different drying conditions. The drying behavior was observed at different power levels (480, 840, and 1,080 W) and different initial masses (90, 120, and 150 g). The observed drying kinetics were divided into three parts: a short adaptation period, a long constant drying rate period, and a falling drying rate period. The maximum drying rate was observed during the constant rate period. Mainly, the results show that the drying rate decreases with the initial mass increase (from 0.45 kg·kg^?1·min^?1 for 90 g to 0.25 kg·kg^?1·min^?1 for 150 g) and increases with an increase in power level (from 0.15 kg·kg^?1·min^?1 at 480 W to 0.45 kg·kg^?1·min^?1 at 1,080 W). The measurement of the sample dimensions shows that shrinkage can occur and, depending on the drying conditions, it ranged between 0.42 and 0.37 of the sample initial volume. Presenting a more accurate solution of the diffusion model by incorporating shrinkage and finite dimensions of the sample is the novelty of this study. The drying conditions influenced the diffusion coefficient, which ranged from 1.53 × 10^?7 to 7.67 × 10^?7 m²s^?1. Similar to the drying rate, the diffusion coefficient was directly proportional to the power level and inversely proportional to the initial mass. Activation energy was determined using an Arrhenius relationship of the diffusion coefficient as a function of the ratio initial mass to the power level.     

Investigating the use of cooling surfaces in solid‐state fermentation tray bioreactors: modelling and experimentation

The effect of wall cooling in tray‐type solid‐state fermenters was investigated by cultivation of Aspergillus niger ATCC 10 864 on wheat bran. Temperature, moisture, pH and glucoamylase activity in the bed were monitored. Application of the heat exchanger plate reduced the overall water loss but increased the heterogeneity of moisture distribution in the bed. Moisture content increased markedly close to the heat transfer plate while the upper regions of the bed dried out. The thermal conductivity of the bed was measured to be 0.19 W m^?1 K^?1. At these conditions and depending on the air flow rate, 58–82% of the metabolic heat was removed via conduction towards the plate. A mathematical model was developed to describe the behaviour of the system. Model predictions were in good agreement with the experimental results. Diffusion coefficients of water vapour and oxygen in the bed were estimated to be around 1.3 × 10^?5 m² s^?1 and 1 × 10^?5 m² s^?1 respectively. Based on these values the mathematical model describes the way oxygen and water vapour diffusion influences biomass growth and moisture distribution in the bed. Copyright © 2004 Society of Chemical Industry     

Kinetics of polyurethane formation between glycidyl azide polymer and a triisocyanate

Kinetics of the polyurethane formation between glycidyl azide polymer (GAP) and a polyisocyanate, Desmodur N‐100, were studied in the bulk state by using quantitative FTIR spectroscopy. The reaction was followed by monitoring the change in intensity of the absorption band at 2270 cm^?1 for NCO stretching in the IR spectrum, and was shown to obey second‐order kinetics up to 50% conversion. The activation parameters were obtained from the evaluation of kinetic data at different temperatures in the range of 50–80°C. The enthalpy and entropy of activation were found to be ΔH^? = 44.1 ± 0.5 kJ · mol^?1 and ΔS^? = ?196 ± 2 J · mol^?1l · K^?1, respectively. Dibutyltin dilaurate (DBTDL) was used as the curing catalyst. The kinetic study of the polyurethane formation between GAP and Desmodur N‐100 showed that the reaction is enormously speeded up in the presence of the catalyst, and the reaction obeys second‐order kinetics, provided that the catalyst concentration is kept constant. An investigation on the rate of the catalysed reaction depending on the catalyst concentration provided the order of the reaction, with respect to the DBTDL catalyst concentration, and the rate constant for the catalytic pathway of the reaction. The rate constant for the catalytic pathway was established to be 4.37 at 60°C, while the uncatalyzed reaction has a rate constant of 3.88 × 10^?6 L · mol^?1 · s^?1 at the same temperature. A rate enhancement factor of 23 was achieved by using 50 ppm catalyst. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 918–923, 2001     

Effect of pore characteristics on permeability of sintered diatomite filter for microfiltration

Diatomite, because it is inherently porous and irregular, presents an interesting opportunity to investigate how the processing conditions of green bodies and the incorporation of spherical pores affect the final properties of a sintered ceramic filter. The water flux of a diatomite filter sintered at 1200°C was 6·3×10⁴ L m^?2 h^?1 bar^?1, which is higher than the water fluxes of typical ceramic filters such as spherical fly ash (1·6×10⁴ L m^?2 h^?1 bar^?1), γ-alumina (～1·0×10³ L m^?2 h^?1 bar^?1) and zirconia (1·6×10³ L m^?2 h^?1 bar^?1) filters. The results obtained in this study show that the pressure applied during the processing of green bodies and the incorporation of spherical pores directly affect pore characteristics and accordingly determine the permeability of the sintered diatomite filters.     

Acetic acid/water separation by pervaporation with silica filled PDMS membrane

Silica‐filled polydimethylsiloxane (PDMS) composite membranes are prepared on a polytetrafluoroethylene support structure. The structure and the performance of the membranes are characterized by scanning electron microscope, Fourier transform infrared spectroscopy, X‐ray diffraction, and thermogravimetry. The pervaporation process for acetic/water separation is performed within the PDMS membranes. The vulcanization temperature was found to have a great influence on the separation performance of the membrane. The addition of silica can significantly improve the pervaporation flux and enhance the thermal stability of the membrane. With an increase in the feed temperature, selectivity decreases and permeation flux increases. Performed with a pure PDMS membrane vulcanized at 30°C, the separation factor at first will increase, then decrease when the feed flow rate was increased from 14 to 38 L · h^?1. The maximum separation factor is achieved when the feed flow rate is 26 L · h^?1. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Determination of specific heat of phenol formaldehyde resol resins by differential scanning calorimetry

The specific heat, Cp, was determined by DSC on a series of resol-type phenol formaldehyde resins with varying phenol formaldehyde molar ratio. The extrapolated Cp values at 25°C vary between 1.181-1.206 kJ · kg^?1 K^?1 and the dCp/dT ratio was found to be 0.0042kJ · kg^?1K^?2 in the temperature range of 70–125°C.     

Homogeneous precipitation synthesis and thermoelectric properties of Ca2Co2O5 ceramics

Abstract

Homogeneous precipitation method was applied to synthesise Ca₂Co₂O₅ powders using calcium nitrate, cobalt nitrate and urea as raw materials. Uniform plate-like Ca₂Co₂O₅ powders with an average grain size of 1 μm can be obtained by calcining the precursor for 8 h at 1073 K in the air. The Ca₂Co₂O₅ ceramics were gained after sintering for 4 h at 1083 K using uniaxial pressure moulding and then sintering technique. The thermoelectric properties of ceramic samples were measured from 303 to 973 K, and the result shows that the electrical conductivity, Seebeck coefficient, thermal conductivity and figure of merit of the sample are 2236·85 S m^?1, 175·95 μV K^?1, 1·01 W m^?1 K^?1 and 0·69 at 973 K respectively.     

Adsorption of cadmium and zinc from aqueous solution on natural and activated bentonite

The adsorption of cadmium and zinc ions on natural bentonite heat-treated at 110°C or at 200°C and on bentonite acid-treated with H₂SO₄ (concentrations: 0·5 mol dm^?3 and 2·5 mol dm^?3), from aqueous solution at 30°C has been studied. The adsorption isotherms corresponding to cadmium and zinc may be classified respectively as H and L types of the Giles classification which suggests the samples have respectively a high and a medium affinity for cadmium and zinc ions. The experimental data points have been fitted to the Langmuir equation in order to calcualte the adsorption capacities (X_m) and the apparent equilibrium constants (K_a) of the samples; X_m and K_a values range respectively for 4·11 mg g^?1 and 1·90 dm³ g^?1 for the sample acid-treated with 2·5 mol dm^?3 H₂SO₄ [(B)-A(2·5)] up to 16·50 mg g^?1 and 30·67 dm³ g^?1 for the natural sample heat-treated at 200°C [B-N-200], for the adsorption process of cadmium, and from 2·39 mg g^?1 and 0·07 dm³ g^?1, also for B-A(2·5), up to 4·54 mg g^?1 and 0·45 dm³ g^?1 [B-N-200], for the adsorption process of zinc. X_m and K_a values for the heat-treated natural samples were higher than those corresponding to the acid-treated ones. The removal efficiency (R) has also been calculated for every sample; R values ranging respectively from 65·9% and 8·2% [B-A(2·5)] up to 100% and 19·9% [B-N-200], for adsorption of cadmium and zinc.     

Hyperbranched Acrylate Copolymer via Initiator‐Fragment Incorporation Radical Copolymerization of Divinylbenzene and Ethyl Acrylate: Synthesis,Characterization, Hydrolysis,Dye‐Solubilization,Ag Particle‐Stabilization,and Porous Film Formation

Summary: Soluble hyperbranched acrylate copolymers were prepared by the copolymerization of divinylbenzene (0.10 mol · L^?1) and ethyl acrylate (0.50 mol · L^?1) using dimethyl 2,2′‐azoisobutyrate of high concentrations (0.30–0.50 mol · L^?1) as initiator at 70 and 80 °C in benzene. The copolymer formed at 80 °C for 1 h showed the weight‐average molecular weight of 2.5 × 10⁵, the small radius of gyration of 10 nm, the low second virial coefficient of 5.7 × l0^?7 mL · g^?2 as shown by the MALLS measurements at 25 °C in tetrahydrofuran, and also the very low intrinsic viscosity of 0.10 dL · g^?1 at 30 °C in benzene. The hyperbranched copolymer exhibited an upper critical solution temperature (35 °C on cooling) in an acetone‐water (60:11 v/v). The copolymer showed an ability to encapsulate and transfer Rhodamine 6G as a dye probe and could stabilize Ag nanoparticles. The porous film was prepared by simply casting an acetone solution of the hyperbranched copolymer on a cover glass. The copolymer molecules radially arranged on the surface layer of the spherical pores as observed by the polarized optical microscope. The hyperbranched acrylate copolymer was hydrolyzed by KOH to yield poly(carboxylic acid).

Optical microscope image (crossed polarizers) of a porous film from copolymer solution in acetone.     

Vapour permeation applied for the separation of water from organic compounds and gases using asymmetric polyetherimide/polyvinylpyrrolidone capillary tubes

Asymmetric integrally skinned capillary tubes were produced from the polymers PEI (polyetherimide) and PVP (polyvinylpyrrolidone) for vapour permeation modules which were applied for the separation of water from organic compounds and gases. Water treatment and recovery of desirable organic compounds was achieved. The capillary tubes had intrinsic permeability coefficients of 7.5 × 10^?7 mol/m²·s·Pa for water and 1.6 × 10^?9 mol/m²·s·Pa for 1-propanol for a 1:1 mass ratio vapour feed mixture under pyrolysis conditions. The vapour was fed at the interior of the capillary tubes with total pressure of 30 kPa; the permeate total pressure was 14 kPa, and the temperature was 86°C. Modules, with surface areas up to 1.0 m², were constructed and tested with feed flow rates as high as 4 kg/h with a process development unit. Tests were performed with the vapours from wood chips and contaminated soils subjected to vacuum pyrolysis.     

Elaboration and characterisation of low cost ceramic support membrane

Abstract

A porous tubular ceramic membrane was prepared from low cost Tunisian clay. The characterisation of the raw material and the effect of the sintering temperature on the morphology, pores size distribution and the mechanical properties of the ceramic membrane were studied. A ceramic membrane fired at 1000°C for 1?h presented a mean pore diameter of ～1·04?μm. The porosity was equal to 38?vol.-%. The filtration of a 0·5?g?L^?1 bovine serum albumin solution indicated that the limiting flux of permeate was 245?L?h^?1?m^?2?bar^?1, which corresponded to a retention rate of about 13%.     

Adsorption of chlorophyll-a from acetone solution on natural and activated bentonite

The adsorption of chlorophyll-a on bentonite desiccated at 110°C, untreated and acid-treated with H₂SO₄ solutions over a concentration range between 0·25 and 2·50 mol dm^?3, from acetone solution at 25°C has been studied. The adsorption isotherms may be classified as using Giles' classification, as type S (untreated sample and 0·25 mol dm^?3 H₂SO₄-treated sample), type H (0·50 mol dm^?3 H₂SO₄-treated sample) and type L (1·00 and 2·50 mol dm^?3 H₂SO₄-treated samples). This fact suggests that the bentonite surfaces (low, high and medium affinity, respectively) behave in differently relation to the adsorption of the chlorophyll-a molecules. The experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (K_f) of the samples; K_f values range from 0·43 mg kg^?1 for the untreated bentonite up to 108·89 mg kg^?1 for the 0·50 M H₂SO₄-treated bentonite. The removal efficiencies (R) have also been calculated and range from 5·71% for the untreated bentonite up to 85·18% for the 0·50 M H₂SO₄-treated bentonite.     

Optimal sintering parameters for Al2O3 optoceramics with high transparency by spark plasma sintering

Transparent Polycrystalline Alumina (PCA) optical ceramics were fabricated at a high heating rate and low temperature by spark plasma sintering (SPS). Maximum pressure (100?MPa) at dwell time keeps the grain size small irrespective of the dwell time. A heating and cooling rate of 100°C?min^?1 at the sintering temperature of 1150°C for a dwell time of 1?h at 100?MPa yielded highly densified samples with the good transparency of 63 and 83% in visible and infra-red region, respectively. Optoceramics yielded a mechanical hardness of (3000 Hv)/ 29.42?GPa and a thermal conductivity of 21?Wm^?1?K^?1.