Recrystallization studies on isotropic cold-crystallized PET: Influence of heating rate

The nanostructural changes associated to the multiple melting behaviour of isotropic cold-crystallized poly(ethylene terephthalate) (PET) have been investigated by means of simultaneous wide- and small-angle X-ray scattering, using a synchrotron radiation source. Variations in the degree of crystallinity, coherent lateral crystal size and long period values, as a function of temperature, for two different heating rates are reported for cold-crystallized samples in the 100-190 °C range. The Interface Distribution Function analysis is also employed to provide the crystalline and amorphous layer thickness values at various temperatures of interest. Results suggest that samples crystallized at both low (T_a = 100-120 °C) and high (T_a = 160-190 °C) temperatures are subjected to a nearly continuous nanostructural reorganization process upon heating, starting immediately above T_g (≈80 °C) and giving rise to complete melting at ≈260 °C. For all the T_a investigated, a melting-recrystallization mechanism seems to take place once T_a is exceeded, concurrently to the low-temperature endotherm observed in the DSC scans. For low-T_a and slow heating rates (2 °C/min), a conspicuous recrystallization process is predominant within T_a + 30 °C ≤ T ≤ 200 °C. In contrast, for high-T_a, an increasingly strong melting process is observed. For both, high- and low-T_a, an extensive structural reorganization takes place above 200 °C, involving the appearance of new lamellar stacks simultaneously to the final melting process. The two mechanisms should contribute to the high-temperature endotherm in the DSC scan. Finally, the use of a high heating rate is found to hinder the material's overall recrystallization process during the heating run and suggests that the high-temperature endotherm is ascribed to the melting of lamellae generated or thickened during the heating run.     

Factors and processes controlling methane emissions from rice fields

Understanding the major controlling factors of methane emissions from ricefields is critical for estimates of source strengths. This paper reports results on the relationship of different plant characteristics and methane fluxes in ricefields. Methane fluxes in ricefields show distinct diel and seasonal variations. Diel variations are mainly controlled by soil solution temperature and the partial pressure of methane. One or two distinct seasonal maxima are observed in irrigated ricefields. The first is governed by methane production from soil and added organic matter and a second at heading is plant derived. During ripening and maturity, root exudation, root porosity and root oxidation power may control methane emission rates. Rice plants play an important role in methane flux. The aerenchyma conduct methane from the bulk soil into the atmosphere. The amount of carbon utilized in methane formation varied among cultivars. A strong positive effect of rice root exudates on methane production imply that cultivar selections for lower methane emissions should not only be based on the gas transport capabilities but also on the quality and quantity of root exudates. Soils show a wide range of methane production potential but no simple correlation between any stable soil property and methane production is evident. Various cultural practices affect methane emissions. Defined aeration periods reduce methane emissions. Soil entrapped methane is released to the atmosphere as a result of soil disturbances. Mineral fertilizers influence methane production and sulfate containing fertilizer decrease methane production. The methane release per m² from different rice ecosystems follow the order: deepwater rice>irrigated rice>rainfed rice. Abatement strategies may only be accepted if the methane source strength of ricefields is reliably discriminated and if mitigation technologies are in accordance with increased rice production and productivity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Catalytic Oxidation of Industrial Wastewater Under Mild Conditions

Cerium?Czirconia-supported ruthenium and activated carbon catalysts were used in catalytic wet air (CWAO) and wet peroxide (CWPO) oxidation of industrial wastewater. Both catalysts were active in the removal of TOC and COD from the wastewater. The degree of biodegradation of organic matter increased during CWAO. Therefore, the CWAO process could be considered as a potential pre-treatment process integrated with subsequent biological treatment to achieve the required level of purification of wastewater.     

Nicrofer 5923 hMo,ein neuer hochkorrosionsbeständiger Werkstoff für die Chemische Industrie,die Umwelttechnik und verwandte Anwendungen

Alloy 59, a new highly corrosion resistant material for the chemical process industry, environmental pollutioncontrol and related applications

1 Vortrag anläßlich der ACHEMA '91, Frankfurt/Main, 09.–15. Juni 1991.

A new nickel-chromium-molybdenum alloy, Alloy 59 has been designed to withstand severest corrosive conditions as encountered in chemical process industry and today's environmental pollution control systems. This alloy, which is composed of about 59% nickel, 23% chromium and 16% molybdenum is compared to the common NiCrMo-alloys Alloy C-276, Allo C-4, Alloy 22 and Alloy 625. Conditions of corrosion testing have been varied between oxidizing and reducing mineral acids combined with differing halide contaminations. Furthermore, corrosion data in hot concentrated sulfuric acid and in technical relevant solutions of flue gas desulfurization plants are given. The general resistance to corrosion in sulfuric acid and in hydrochloric acid is highlighted in isocorrosion diagrams. Alloy 59 has an excellent resistance to uniform and localized corrosion in all these environments. The new Alloy 59 clearly outperforms the other NiCrMo-alloys C-276, C-4 and 22 as well under oxidizing conditions as in the strongly reducing hydrochloric acid environment. The time-temperature-sensitization-diagram demonstrates the alloy's excellent thermal stability and reveals an improvement compared to Alloy 22 or the well-known Alloy C-276. Alloy 59, therefore, can be used in the as-welded condition without any additional solution annealing treatment. The excellent corrosion resistance is not impaired if the alloy is processed or fabricated to equipment even in larger sections. Weldability with a matching filler metal is without problems as demonstrated i.a. in the varestraint test.     

Improvement of Formability by Oscillation of Internal Pressure in Pulsating Hydroforming of Tube

A new history of internal pressure in the hydroforming processes of tubes is developed to attain high formability. The effect of improvement of formability by the oscillation of internal pressure in a pulsating hydroforming process of tubes is examined using both finite element simulation and experiment. The deformation behaviour during the hydroforming is greatly affected by the oscillation of internal pressure. For a monotonic history of small internal pressure, the wrinkling was caused by insufficient bulging, whereas the necking and bursting occurred for a monotonic history of large internal pressure. The occurrence of these defects can be avoided by oscillating the internal pressure in the pulsating hydroforming. The improvement of formability in the pulsating hydroforming is due to both low pressure and oscillation of pressure. The effects of the amplitude and cycle number of pressure in the pulsating hydroforming on the deformation behaviour are investigated. It is found the oscillation of internal pressure is effective in preventing the occurrence of defects.     

Production of aromatics by catalytic fast pyrolysis of cellulose in a bubbling fluidized bed reactor

Catalytic fast pyrolysis of cellulose was studied at 500°C using a ZSM‐5 catalyst in a bubbling fluidized bed reactor constructed from a 4.92‐cm ID pipe. Inert gas was fed from below through the distributor plate and from above through a vertical feed tube along with cellulose. Flowing 34% of the total fluidization gas through the feed tube led to the optimal mixing of the pyrolysis vapors into the catalyst bed, which experimentally corresponded to 29.5% carbon aromatic yield. Aromatic yield reached a maximum of 31.6% carbon with increasing gas residence time by changing the catalyst bed height. Increasing the hole‐spacing in the distributor plate was shown to have negligible effect on average bubble diameter and hence did not change the product distribution. Aromatic yields of up to 39.5% carbon were obtained when all studied parameters were optimized. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1320–1335, 2014     

Adsorbent Production Using Oil Shale from the Kendyrlyk Deposit

The thermal activation of Kendyrlyk shale (at temperatures of 700–800°C) facilitates the production of a porous carbon material—activated shale. Currently available techniques such as electron microscopy and IR-spectroscopic analysis were used, and the elemental composition was determined. The morphology of the samples was studied, and the type of carbon modification was revealed; the adsorption characteristics of the samples were determined by the BET method. It was established that the specific surface area and the specific pore volume substantially increased as a result of the high-temperature activation of shale. The resulting activated shale was tested as an adsorbent.     

What Role Does Ozone Play in Preventing Dental Caries? An Evidence-Based Review

Ozone, which is also referred to as triatomic oxygen or trioxygen, is a naturally occurring inorganic molecule that consists of three oxygen atoms. Ozone has proven microbiological properties and, for this reason, it is extensively used in modern medical practices. Ozone is a powerful oxidant that demonstrates bactericide, virucide, and fungicide effects. The strong oxidation effect it produces results in the formation of highly reactive free radicals that have the capability to destroy microorganisms. Ozone has been proposed as a means of preventing caries, and existing research confirms that this form of therapy does have promising potential. However, very few clinical studies have examined the impact that ozone treatment can have on the management of caries lesions. This article presents a detailed literature review of existing peer-reviewed sources that have examined the role ozone plays in preventing and treating caries.     

Effect of amphiphilic compatibilizers on the filler dispersion and properties of polyethylene—thermally reduced graphene nanocomposites

Compatibilizers of different chemical structures and specifications were used to enhance the filler exfoliation in nanocomposites of polyethylene and thermally reduced graphene prepared by melt mixing route. The mechanical performance of the compatibilized nanocomposites was observed to be better than PE/G nanocomposites due to enhanced extent of filler exfoliation and distribution. Highest increase of 45% in tensile modulus and 13% in peak stress was observed in the composites. Overall, from the mechanical, rheological, thermal, and calorimetric properties, the compatibilizers with best performance were ethylene acrylic acid (EAA) copolymer and chlorinated polyethylene (CPE25). Furthermore, the extent of filler exfoliation was observed to increase with increasing EAA content thus confirming positive interactions between EAA and thermally reduced graphene, though no specific chemical interactions could be detected. The composite properties were observed to reach maximum around 7.5 wt % EAA content, followed by reduced performance due to extensive matrix plasticization. The observed behaviors were a result of interplay of opposing factors like filler exfoliation due to compatibilizer addition and matrix plasticization due to its lower molecular weight, thus the observed optimum comaptibilizer amount was specific to the compatibilizer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42484.