Dynamic and isothermal thermogravimetric analysis of a polycyanurate thermosetting system

Isothermal and dynamic thermogravimetric analysis (TGA) were performed on a polycyanurate thermosetting material. The effects on thermal stability of the copper naphthenate catalyst were studied by comparing two systems with different amounts of catalyst. Tests were performed isothermally at temperatures ranging from 200°C to 240°C for times up to one week. Dynamic tests were also performed at rates from 0.1°C/min to 40°C/min at temperatures ranging from 180°C to 600°C. It is found that increasing the concentration of copper increased the weight loss in isothermal tests, but did not affect the overall activation energy. Conversely, in dynamic tests, copper concentration had no effect on weight loss. The results demonstrate the difficulties of extrapolating dynamic TGA data to use conditions in order to predict long-term thermal stability.     

Highly active peroxides in the radical polymerization of ethylene under high pressure — conversion and initiator usage

By using highly active peroxides, it is possible to reduce the polymerization temperature necessary for the synthesis of low density polyethylene. In order to examine a number of peroxides for their suitability as low temperature initiators, polymerization tests were carried out at 1900 bar, 70–140°C, with an average residence time of 30 s in a continuously operating laboratory facility equipped with a stirred autoclave. Apart from a number of perneodecanoates, two peroxy dicarbonates, a sulphonyl peroxide, and a difunctional peroxide were used. The initiator consumption was high at polymerization temperatures below 100°C. The results obtained with the different peroxides varied considerably. As the temperature increased, the initiator consumption decreased rapidly to reach almost the same level for all the individual peroxides at above 120°C. The difunctional compound that proved highly suitable for the low polymerization temperatures desired was 1,4-di-(2-neodecanoyl peroxy isopropyl)benzene, the consumption at 100°C of which amounted to 13 g initiator/kg PE. Using a quantity of 40 g initiator/kg PE, a reactor temperature of 82°C could be employed. The peroxy dicarbonates and tertiary butyl perneodecanoate gave less satisfactory results.     

Pilot-plant preparation of edible safflower oil

Summary Tests conducted on a pilot-plant scale with two lots of commercial, alkali-refined safflower oil demonstrate that no difficulty is experienced in producing a salad oil of good, initial quality with good flavor stability when stored at 60°C. in the dark. Although results indicate safflower oil is suitable for a salad oil, they should not be construed as indicating its stability as a cooking oil since tests of this type were not conducted. The addition of citric acid improved the oxidative stability of the oil, and citric acid plus propyl gallate gave even further improvement. No significant increase in flavor stability resulted from these additives. One of the divisions of the Agricultural Research Service, U. S. Department of Agriculture.     

Stability of carotene at elevated and room temperatures

Summary An attempt has been made to evaluate the elevated temperature test used for carotene stability studies in this laboratory. The stability of carotene in edible oils containing various added antioxidants was determined by storage at 25° C. and in some cases 40° C. and compared with stability as determined by the accelerated test at 75° C. In general, the results obtained at 75° C. were in agreement with those obtained at 40° and 25° C. With most of the better antioxidants the protection found at the lower temperature was better than that indicated by the rapid test. Solutions of carotene in edible oils, which ordinarily might lose a significant amount of carotene in a week or less at 25° C., can be protected by addition of antioxidants, and protection can be afforded for periods well over a year without such special precautions as refrigeration or storage under nitrogen or in evacuated containers. The effectiveness of nordihydroguaiaretic acid as an antioxidant for carotene has been confirmed by room-temperature storage tests. Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Interlaboratory study on lipid oxidation during accelerated storage trials with rapeseed and sunflower oil analyzed by conjugated dienes as primary oxidation products

Accelerated storage tests are frequently used to assess the oxidative stability of foods and related systems due to its reproducibility. Various methods and experimental conditions are used to measure lipid oxidation. Differences between laboratories make it necessary to determine the repeatability and reproducibility of oxidation tests performed under the same conditions. The objective of the present interlaboratory study was to evaluate the outcome of a storage test for two different bulk oils, sunflower oil (SFO) and rapeseed oil (RSO), during a period of 9 weeks at 20°C, 30°C, 40°C, and 60°C. Sixteen laboratories were provided with bottled oils and conducted the storage tests according to a detailed protocol. Lipid oxidation was monitored by the formation of conjugated dienes (CD) and the activation energy (E_a) was determined for comparative purposes and statistically evaluated. An increase in CD formation was observed for both oils when the storage temperature was increased in all laboratories. The E_a,1 ranged from 47.9 to 73.3 kJ mol⁻¹ in RSO and from 27.8 to 62.6 kJ mol⁻¹ in SFO, with average values of 58.2 and 46.8 kJ mol⁻¹, respectively. The reproducibility coefficients were 10.9% and 18.2% for RSO and SFO, respectively. Practical applications: In order to compare results on oxidative stability of foods derived from different studies, the reproducibility of storage tests and methods employed to evaluate the oxidation level should be considered. This study provides fundamental data on the reproducibility of lipid oxidation under accelerated storage conditions and defines important parameters to be considered for the conduction of experiments.     

Durable adhesives for large laminated timber

Large laminated timber (LT) made of hardwood is widely used as the main constitutional element of goods such as furniture, pianos and doors. A high durability of LT is essential to these products. This study focused on finding as to what adhesives were acceptable as highly durable adhesives for LT. Twelve different adhesives such as resorcinol-formaldehyde resin, aqueous emulsion-type isocyanate resin, poly(vinyl acetate) emulsion, epoxy resin, etc. were used. The durability of LT, i.e., the percentage of delamination length of LT under tests such as humidity and temperature cycling tests, and outdoor tests, was discussed in relation to the adhesive shear strength of a lap joint (LJ). The results showed that the percentage of delamination length under both low ?20°C for 16 h and high-temperature 50°C for 8 h cycling tests (temperature-resistance) on LT indicated a strong trend with the adhesive shear strength of the LJ exposed to dry air at 100°C for 24 h. In addition, the percentage of delamination length under outdoor exposure test for three months (outdoor-resistance) of the LT showed a trend with the adhesive shear strength of the LJ exposed to dry air at 100°C for 24 h, as well as with the adhesive shear strength of the LJ immersed in water at 60°C for 3 h. These trends pointed out that the thermal stability of the adhesive from ?20°C for 16 h up to 50°C for 8 h was an important parameter in order to improve adhesive durability for the LT.     

Curing octaepoxysilsesquioxane with different curing agents

Octaepoxysilsesquioxane (POSS-Ep) was first synthesized by the hydrolysis and condensation of γ-[(2,3)-epoxypropoxy]propyltrimethoxysilicane (KH-560) with the presence of ethanol and HCl at 55°C for 72 h. Then, it was cured with 4,4′-diaminodiphenylsulfone (DDS) and methylnadic anhydride (MNA), respectively. The curing reactions between POSS-Ep and DDS or MNA were investigated by FTIR. Thermal stability of the cured nanocomposites was studied by TGA. The micromophologies of the obtained hybrids were observed by SEM. FTIR results show that POSS-Ep can be cured completely with DDS or MNA to obtain the final organic–inorganic (O–I) hybrids after the same experimental curing cycle: 120°C/2 h + 140°C/2 h + 160°C/2 h + 180°C/2 h + 200°C/2 h. TGA results show that POSS-Ep/DDS hybrid displays better thermal stability than that of POSS-Ep/MNA hybrid. Initial thermal degradation temperature (Tdi) of POSS-Ep/DDS hybrid is 420°C, 195°C higher than that of POSS-Ep/MNA (225°C). SEM images of the fracture surfaces of the hybrids suggest the cured POSS-Ep possesses good mechanical properties. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis,characterization, and cure of allyl and propargyl functionalized indene as a thermoset composite matrix resin

Two highly functionalized resins were synthesized by the phase transfer reaction of indene with propargyl bromide or allyl chloride in the presence of strong base. The resins consisted of a mixture of tri- and tetrafunctional indenes with 60–80% of the product being tetrafunctional. The allylated (AL) and propargylated (PL) indene resins were thermally cured without added catalysts. Both resins exhibited a broad, highly exothermic cure with a peak energy at 320°C for AL resin and 282°C for PL resin. Thermal degradation of cured AL resin was found to begin at approximately 400°C with a carbon yield of 20% of its initial weight at 1000°C. Carbon yields for cured PL resin were excellent, with 68% retention of weight at 1000°C. Unidirectional, carbon fiber composites were fabricated from the substituted indene resins. AL–carbon fiber composites gave modulus values of 126 GPa and strength values of 967 MPa, while PL–carbon fiber composites gave modulus values of 116 GPa and strength values of 935 MPa in three-point bending tests. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 475–482, 1998     

Gold-Nano Particles Supported on Na-Y and H-Y Types Zeolites: Activity and Thermal Stability for CO Oxidation Reaction

Gold nano particles (GNP) were deposited on Na-Y and H-Y zeolite substrates using chloroauric acid (HAuCl₄) solution. The synthesized catalysts were then characterized and the catalytic activity toward CO oxidation reaction was investigated using a tubular fix bed micro reactor under atmospheric pressure. It was found that CO conversion of 100% and 5% can be achieved at 20 °C on Au/Na-Y and Au/H-Y fresh catalysts, respectively. Thermal stability of catalysts was also investigated by treating the catalysts at 400 °C for 4 h. After thermal stability test, activity tests of the catalysts at 20 °C were shown that CO conversion of Au/Na-Y catalyst was decreased to 65% whereas the activity of the Au/H-Y at 20 °C was increased up to 15%. Characterization tests were revealed that the structures of the zeolitic supports were remained unchanged after thermal pretreatment.     

Thermal Degradation of Condensed Tannins from Radiata Pine Bark

Abstract

In order to understand the influence of the inherent chemistry on the relative thermal stability of condensed tannins, the thermal degradation behaviors of various radiata pine bark extracts have been investigated using thermogravimetric analysis (TGA). Generally, results suggest pine bark extract fractions may be readily processed at temperatures below 200°C if co-extracted polysaccharides contents are minimized. Those extracts possessing greater carbohydrate content and lower tannin purity tend to have decreased thermal stability. The initial onset temperature for degradation of relatively crude extracts with high proportions of carbohydrate contents were relatively low (ca. 150°C), whereas extract purification to < 5% carbohydrate content gave increases in thermal stability of at least 50°C. The complicity of the carbohydrate content in the degradation of the tannin samples was also supported by calculated Ozawa activation energies and modulated TGA experiments. While no increase in the thermal stability was gained by acetylating the pendant hydroxyl groups of the pine bark tannin extract, chemical variations such as sulfonation have a large effect on thermal degradation, promoting lower degradation temperatures.     

Synthesis and characterization of a new class of thermosetting resins: Allyl and propargyl substituted cyclopentadiene derivatives

A series of all-hydrocarbon resins were synthesized by reacting cyclopentadiene allyl chloride, propargyl chloride, or a mixture of allyl chloride and propargyl ide, under phase transfer conditions. Phase transfer reactions with and without added solvents, and with either quaternary ammonium or crown ether catalysts, yielded similar products consisting of a mixture of 1,1-disubstituted cyclopentadiene (minor amount) and 2-3 isomers each of tri-, tetra-, penta-, and hexa-substituted derivatives. No further reaction of each these components possible. The overall substitution pattern varied little with changes in reaction conditions although limiting the allyl chloride content led to still reactive, partially substituted products. Incorporation of all-propargyl and high propargyl-to-allyl mixed functionalities on cyclopentadiene yielded products whose stability was very hindering their thorough characterization. Preliminary evaluation was there-carried out for mixed resins with lower propargyl functionality. The allyl substituted resin (allylated cyclopentadiene, ACP) underwent thermal cure lout initiator at around 200°C while allyl/propargyl substituted resin (7:1 ratio, APCP) showed a faster, lower temperature cure at around 120°C. Cationic cure of ACP was also initiated by a novel sulfonium salt at around 100°C. Neat resin when cured at 200°C gave material with a flexural storage modulus 2 of about 300 MPa. Further cure at 250°C raised the modulus to 1.2 GPa. resin gave composites with excellent properties when used with glass and on fibers. Flexural modulus values (by DMA) of ∼ 66 GPa were obtained for ACP/carbon fiber composites compared with 42 GPa for epoxy/carbon composites made in our laboratories using commercially available materials. The modulus values at 300°C dropped to 10% of the room temperature value for the epoxy composites, while the ACP/carbon composite maintained 60% of its room temperature value at 300°C. When brought back to ambient temperature, the modulus of latter sample had increased to 80 GPa and that of the epoxy composite dropped to 23 GPa. Glass fiber ACP composites performed similar to an epoxy composite up to 200°C but maintained properties up to 300°C while those of the epoxy were drastically reduced. TGA analysis of both cured ACP resin and its composites showed decomposition beginning at 375°C. Three-point-bending tests indicated very high modulus with brittle failure for ACP composites. Scanning electron micrographs showed moderate bonding of the new resin to both carbon glass fiber surfaces. This new class of thermosetting resins offers excellent potential for application in low-cost glass and carbon composites with good thermal and physical properties.     

The degradation behavior of high-voltage SnO2 based varistors sintered at different temperatures

In this research, for the first time, the stability of SnO₂ based varistor ceramics sintered in the range of 1250–1350 °C against DC-accelerated aging and impulse surge current tests, was systematically studied. Microstructural study of the sintered samples by XRD and FESEM indicated that the sintering temperature only affects densification and grain size, while phase composition remains intact. With the increase of sintering temperature from 1250 °C to 1350 °C, the mean grain size increased from 1.6 to 8 μm. The maximum nonlinear coefficient of 50 and the minimum leakage current density of 1.5 μA/cm² were obtained in the sample sintered at 1300 °C. The breakdown electric field decreased from 800 V/mm to 270 V/mm, when sintering temperature increased from 1250 °C to 1350 °C. The samples sintered at 1250 °C did not show stability against neither of DC-accelerated aging and impulse current tests. The varistors sintered at 1300 °C exhibited the excellent resistance to DC-accelerated aging degradation, while ceramics sintered at 1350 °C showed the best resistance to impulse current degradation.     

Synthesis and characterization of synthetic lubricants based on dibasic acid

Synthetic esters have long been used in a variety of applications due to their excellent thermal stability, excellent cleanliness, natural lubricity, and polarity. In the present work, we aimed to prepare some synthetic base oils through preparation of different dibasic esters by esterification of dicarboxylic acids (adipic acid and azelaic acid) with different linear alcohols (hexanol, octanol, and decanol) and branched alcohol (2-ethyl hexanol) at 120°C. The reaction yield ranges between 85% and 94%. Fourier-transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy were used to analyze the structures of the produced compounds. Using thermo gravimetric analysis (TGA), the heat stability of the produced esters was determined, and it was found that the prepared esters have high thermal stability. The degradation of the prepared esters takes place in the range between 300 and 600°C. The rheological behaviour of prepared esters shows Newtonian behaviours, which means that Newtonian fluids obey viscosity Newton's law. The viscosity is independent of the shear rate. The results showed that the lubricity properties, based on their pour point, flash point, and oxidation stability of the esters, were significantly affected by the linear and branched alcohols used. There is a slight increase in kinematic viscosity and viscosity index values with decreasing the internal chain length of the dibasic acid. The esters which were based on adipic acid such as C₁ exhibited maximum values of VI: 187 compared to those which were based on azelaic acid such as F₁ with VI: 182. Viscosity and viscosity index increases with increasing the number of carbon atoms of the used mono-ol alcohols. Using branched alcohols gave almost the same viscosity results compared to using linear alcohol with the same number of carbons. Almost all prepared esters give pour point results ≤ −30°C.     

Anaerobic digestion of waste activated sludge—comparison of thermal pretreatments with thermal inter‐stage treatments

BACKGROUND: Treatment methods for improved anaerobic digestion (AD) of waste activated sludge were evaluated. Pretreatments at moderate thermal (water bath at 80 °C), high thermal (loop autoclave at 130–170 °C) and thermo‐chemical (170 °C/pH 10) conditions prior to AD in batch vials (40 days/37 °C) were compared with inter‐stage treatments under the same conditions carried out between two separate steps of AD (19–21 days/37 °C). Combined treatment at 80 °C with CO₂/ NH₃‐stripping was also evaluated. RESULTS: Pretreatment at 80 °C had no effect on methane yield while inter‐stage treatment gave a 20% increase, compared with controls. Combining inter‐stage treatment with CO₂/ NH₃‐stripping gave an increase in pH (7.1 to 9.3), a drop in ammonia‐N concentration (910 mg‐N to 510 mg‐N) and a methane yield improvement of 31%. Pretreatment at 130 °C, 170 °C and 170 °C/pH 10 considerably increased the methane production within the first 4 days but the improvement following 40 days of digestion was only 13%, 9% and 2%, respectively. In comparison, inter‐stage treatment led to improvements of 9% (130 °C), 29% (170 °C) and 28% (170 °C/pH 10). All treatment processes increased sludge solubilization. CONCLUSION: Thermal treatment of waste activated sludge for improved anaerobic digestion seems more effective when applied as an inter‐stage treatment rather than a pretreatment. Copyright © 2010 Society of Chemical Industry     

High‐Temperature Compression Deformation Behavior of Fine‐Grained Carbon‐Bonded Alumina

Carbon‐bonded alumina with 33 wt% residual carbon was tested in compression at room temperature and at temperatures between 700°C and 1500°C in quasi‐static tests, creep tests, and stress relaxation tests. Therefore, a new high‐temperature test set up with inert gas chamber and inductive heating was used. The tests were accomplished by investigations of microstructure and Young's modulus. At room temperature, the results exhibit a pronounced hysteresis for the first loading cycle, which almost completely disappeared in subsequent cycles. The creep tests showed characteristic curves for compression whereas primary and secondary (stationary) creep occurred. Above 1000°C, a strong increase in creep rate was detected, whereas almost no creep was observed below this temperature. All creep curves were approximated with the models of logarithmic and Andrade creep. The activation energy for creep was found to be 263 kJ/mol above 1150°C. The resistance against stress relaxation showed an anomaly with a minimum between 1000°C to 1200°C and a maximum between 1300°C and 1400°C.     

Thermal exposure effects on the long‐term behavior of a mullite fiber at high temperature

The behavior of an oxide fiber at elevated temperatures was analyzed before and after thermal exposures. The material studied was a mullite fiber developed for high‐temperature applications, CeraFib 75. Heat treatments were performed at temperatures ranging from 1200°C to 1400°C for 25 hours. Quantitative high‐temperature X‐ray analysis and creep tests at 1200°C were carried out to analyze the effect of previous heat treatment on the thermal stability of the fibers. The as‐received fibers presented a metastable microstructure of mullite grains with traces of alumina. Starting at 1200°C, grain growth and phase transformations occurred, including the initial formation of mullite, followed by the dissociation of the previous alumina‐rich mullite phase. The observed transformations are continuous and occur until the mullite phase reaches a state near the stoichiometric 3/2 mullite. Only the fibers previously heat treated at 1400°C did not show further changes when exposed again to 1200°C. Overall, the heat treatments increased the fiber stability and creep resistance but reduced the tensile strength. Changes observed in the creep strain vs. time curves of the fibers were related to the observed microstructural transformations. Based on these results, the chemical composition of the stable mullite fiber is suggested.     

Spray Drying of Elderberry (Sambucus nigra L.) Juice to Maintain Its Phenolic Content

Spray drying was studied with Elderberry (Sambucus nigra L.) juice using a Buchi B-290 spray dryer. Different inlet temperatures ranging from 70°C to 120°C and two feed flow rates of 180 ml/hr and 300 ml/hr were considered for the experiment. The operating parameters were optimized in terms of total phenolic content retention, color, and powder recovery. The inlet temperature of 80°C with feed flow rate of 180 ml/hr gave high phenolic content retention with good color but lower recovery of the dried powder, i.e., less than 50%. To increase the recovery percentage during the drying process, the elderberry juice was spray dried with five different wall materials, i.e., soya milk powder, soya protein powder, isolated soya protein, gum acacia, and maltodextrin. Wall materials were evaluated in terms of total phenolic content retention, color of the powder, and mass recovery percentage. The gum acacia and maltodextrin gave better results and high recovery percentage, i.e., more than 70%. The best three combinations were stored under three different storage conditions in three different packagings to monitor the stability of the phenolic content and color of the powder.     

A study of the thermal behavior of graft copolymers of wool and methyl methacrylate

Thermal behavior of the natural and chemically modified wool fibers (treated with sodium hydroxide and formic acid and reduced with sodium bisulfite and thioglycollic acid) and of the graft copolymers of natural and modified wool with methyl nethacrylate (MMA) monomer was studied using dynamic thermogravimetry in air at a heating rate of 6°C/min to 600°C. The thermograms showed three distinct regions of weight loss for all the cases. A comparison of the temperatures of various percentage decompositions reveals that the thermal stability increased slightly with chemical modification of wool as compared to natural wool. Caustic soda and sodium bisulfite probably forms more stable lanthionine linkages, whereas formic acid improves the thermal stability perphas by modifying the noncrystalline region of the fiber. In the case of natural wool after graft copolymerization with MMA, thermal stability improves up to 325°C probably owing to the formation of new crosslinks, but after 325°C the thermal stability decreases owing to early decomposition of the polymer as compared to wool fiber. Similar effects are observed in all the chemically modified fibers except in wool reduced with sodium bisulfite, where thermal stability is found to increase after grafting even at higher temperature. The thermal stability was also computed from the primary thermograms by calculating the integral procedural decomposition temperature; the results show that thermal stability increases slightly with chemical modification of wool as compared to natural wool. In the case of natural wool with graft copolymerization with MMA, the overall thermal stability decreases, because the decrease of thermal stability after 325°C seems to be more prominent than the increase in thermal stability before 325°C. The same effects are observed in all the chemically modified fibers, except for fibers reduced with sodium bisulfite, where the overall thermal stability increases slightly with increase in graft-on.     

Temperature dependence of morphology and oxygen reduction reaction activity for carbon-supported Pd–Co electrocatalysts

In this study, we investigated the heat treatment temperature effect on the morphology and oxygen reduction reaction activity of carbon-supported Pd–Co alloy electrocatalysts. As prepared Pd–Co bimetallic nanoparticles showed a single-phase face-centered cubic disordered structure, and the mean particle size decreased with a Co content. In order to improve activity and stability, the catalysts were heat-treated in a temperature range of 300 to 700 °C. From the results of oxygen reduction reaction activity tests, the optimal heat treatment temperature was found to be 700 °C for the low Co content samples, while 300 °C was the best condition for the high Co content samples.     

Thermal Exposure Effects on the Strength and Microstructure of a Novel Mullite Fiber

The mechanical behavior of the novel fiber CeraFib75 after various thermal exposures is examined. This fully crystalline mullite fiber was developed to exceed the thermal stability of commercially available oxide fibers. Therefore, heat treatments at temperatures ranging from 1000°C to 1400°C for 25 h were performed and results compared to the well‐established Nextel^? 720 fibers. Mechanical characterization was realized with bundle tensile tests using acoustic emission sensors to determinate the fiber failure distributions. Investigations showed that the initial fiber microstructure of mullite grains with traces of alumina transforms starting at 1200°C. Changes include dissociation of the alumina‐rich mullite phase and grain growth. Thus, strength reduction is measured as a result of these microstructure transformations. Remarkably, at 1400°C, fibers become more fragile and Weibull statistics can no longer describe the failure distribution. A relation between the distribution shape and the load redistribution capability of fibers is suggested. This is more pronounced for Nextel^?720 fibers, which present much bigger grains and retain only 10% of their original strength. However, CeraFib75 fibers are more stable and exhibit a strength retention of 50% at the same conditions, which is attributed to the higher amount of mullite phase.