Chain Scission in the Oxidation of Hevea. III. Effect of Temperature

1956 ◽  
Vol 29 (4) ◽  
pp. 1274-1275
Author(s):  
E. M. Bevilacqua
Keyword(s):  
High Efficiency ◽  
Hydrocarbon Chain ◽  
Chain Scission ◽  
Solution Viscosity ◽  
Effect Of Temperature ◽  
Volatile Acid ◽  
Vulcanized Rubber ◽  
Complete Destruction ◽  
End Groups ◽  
Oxygen Requirements

Abstract When molecular oxygen reacts with raw Hevea rubber in latex at 90° C, two molecules of carbon dioxide and two molecules of “volatile acid” (one molecule of acetic acid and one molecule of formic acid) are produced for each apparent scission of the hydrocarbon chain, estimated from changes of solution viscosity. This corresponds to the complete destruction of one isoprene unit, and if the several hydrocarbon end groups are oxidized, requires a minimum of six molecules of oxygen per scission. Estimates of oxygen requirements for scission during the accelerated oxidation of vulcanized Hevea rubber much lower than this have been made. It has been suggested that the apparent high efficiency of scission in vulcanized rubber is the result of the predominance of scission at crosslinks over random cutting of the hydrocarbon chain. To investigate the less likely possibility that the mechanism of the reactions which leads to scission changes sharply with the rate of oxidation, the earlier estimates of yields of scissions and of volatile acids during the oxidation of Hevea latex at 90° C have been supplemented by measurements at 70° C and at 110° C.

Synthesis of powder metallurgy Ti-3Fe-2Al alloy using high-frequency induction heating

2019 ◽  
Vol 34 (01n03) ◽  
pp. 2040031
Author(s):  
Stella Raynova ◽  
Khaled Alsharedah ◽  
Fei Yang ◽  
Leandro Bolzoni
Keyword(s):  
Mechanical Properties ◽  
Powder Metallurgy ◽  
Induction Heating ◽  
High Frequency ◽  
High Efficiency ◽  
High Vacuum ◽  
Residual Porosity ◽  
Effect Of Temperature ◽  
Vacuum Furnace ◽  
High Frequency Induction

A powder metallurgy approach was applied for the synthesis of an [Formula: see text] Ti-2Al-3Fe alloy. Blends of the elemental Ti, Al and Fe powders were compacted and subsequently sintered. High-frequency induction heating (HFIH) instead of conventional high-vacuum furnace heating was used for the sintering, due to its high efficiency. The effect of temperature on the level of densification, residual porosity and mechanical properties was studied. Electron dispersive spectrum analysis was used to study the dissolution and homogenization of the alloying elements. The results showed that a short induction sintering (IS) cycle in the range of 10–15 min is sufficient to achieve significant powder consolidation, evident by the increase of the density and mechanical properties. The residual porosity diminishes with the increase of the sintering temperature. Full dissolution of the alloying powders is completed after sintering at temperatures above those of [Formula: see text]- to [Formula: see text]-phase transformation.

Effect of Temperature on the Yield of Lignin Extracted Using Microwave-Assisted Acetosolv from Empty Fruit Bunch Fibers

2020 ◽  
Vol 981 ◽  
pp. 240-244
Author(s):  
Muhammad Nor Arifin Yaakob ◽  
Rasidi Roslan ◽  
Nurjannah Salim ◽  
Siti Noor Hidayah Mustapha ◽  
Sarani Zakaria ◽  
...  
Keyword(s):  
Active Sites ◽  
High Efficiency ◽  
Paper Industry ◽  
Acid Catalyst ◽  
Biomass Composition ◽  
Effect Of Temperature ◽  
Composition Analysis ◽  
Empty Fruit Bunch ◽  
Microwave Assisted ◽  
Microscopy Images

Acetosolv technique is considered as one of the best alternative way to extract technical lignin from biomass as it has high efficiency and environmentally friendly. In this study, microwave-assisted acetosolv technique were used to extract lignin from oil palm empty fruit bunch (OPEFB) in the presence of 3% sulfuric acid catalyst reacted at various temperature. The yield of the extracted acetosolv lignin were calculated using modified Technical Association of the Pulp and Paper Industry biomass composition analysis (TAPPI) method. The result showed that, as the temperature increased from 90 to 110 °C, the yield of lignin extracted also increase from 43.07 to 76.98%. The presence of guaiacyl and p-coumarate indicates the presence of active sites at C-3 and C-5 of aromatic ring for polymerization reactions. Scanning Electron Microscopy images showed that removal of lignin are intensified as the microwave-assisted acetosolv temperature increased.

scholarly journals Numerical Modeling of High Conversion Efficiency Mo/CZTS/CdS/ZnO/ FTO Thin Film – Based Solar Cells

2021 ◽  
Author(s):  
Samer H. Zyoud ◽  
Ahed H. Zyoud ◽  
Naser M. Ahmed ◽  
Anupama R. Prasad ◽  
Sohaib Naseem Khan ◽  
...  
Keyword(s):  
Thin Film ◽  
Numerical Modeling ◽  
Solar Cells ◽  
Solar Cell ◽  
Conversion Efficiency ◽  
High Efficiency ◽  
Short Circuit ◽  
Photovoltaic Cells ◽  
Effect Of Temperature ◽  
Cell Parameters

This article describes in detail the numerical modeling of a CZTS (copper zinc tin sulfide) based kesterite solar cell. The Solar Cell Capacitance Simulator -one-dimension (SCAPS-1D) software was used to simulate MO/CZTS/CdS/ZnO/FTO structured solar cells. The parameters of different photovoltaic thin-film solar cells are estimated and analyzed using numerical modeling. The effects of various parameters on the performance of the photovoltaic cell and the conversion efficiency are discussed. Since the response of the solar cell is also contingent on its internal physical mechanism, J-V characteristic measures are insufficient to characterize the behavior of a device. Different features, as well as different potential conditions, must be considered for simulation, disregarding the belief in the modeling of a solar cell. With a conversion efficiency of 25.72%, a fill factor of 83.75%, a short-circuit current of 32.96436 mA/cm2 and an open-circuit voltage of 0.64V, promising optimized results have been achieved. The findings will be useful in determining the feasibility of fabricating high-efficiency CZTS-based photovoltaic cells. The efficiency of a CZTS-based experimental solar cell is also discussed. First, the effects of experimentally developed CZTS solar cells are simulated in the SCAPS-1D environment. The experimental results are then compared to the SCAPS-1D simulated results. The conversion efficiency of an optimized system increases after cell parameters are optimized. Using one-dimensional SCAPS-1D software, the effect of system parameters such as the thickness, acceptor and donor carrier concentration densities of absorber and electron transport layers, and the effect of temperature on the efficiency of CZTS-based photovoltaic cells is investigated. The proposed results will greatly assist engineers and researchers in determining the best method for optimizing solar cell efficiency, as well as in the development of efficient CZTS-based solar cells.

scholarly journals Thallus sectioning as an efficient monospore release method in Pyropia yezoensis (Bangiales, Rhodophyta)

2019 ◽  
Vol 32 (4) ◽  
pp. 2195-2200 ◽  
Author(s):  
Nianci Chen ◽  
Lei Tang ◽  
Xiaowei Guan ◽  
Rui Chen ◽  
Min Cao ◽  
...  
Keyword(s):  
High Efficiency ◽  
Low Cost ◽  
Economic Value ◽  
Northern China ◽  
Pyropia Yezoensis ◽  
Effect Of Temperature ◽  
Seeding Strategy ◽  
Increasing Demand ◽  
Short Time ◽  
Release Method

AbstractThe red seaweed Pyropia yezoensis is a marine crop of important economic value and is widely cultivated in the coastal areas of northern China. The current seedling-raising system relies on the germination of conchospores, a process not fast enough to meet the increasing demand from farmers. In this study, we developed a monospore-dependent seedling method based on the asexual reproduction of the Pyropia thallus. The Pyropia thallus was physically sectioned into small pieces (microthalli) that were cultivated at 15 °C. The algal cells in the microthalli became morphologically condensed, underwent cell division, and then developed into monospores on the 5th day. The monospores were able to attach to the seeding rope in 24 h and germinated into healthy thalli. To optimize the efficiency of monospore release, we tested the effect of temperature and the size and original positions of the microthalli as well as the age of the mother thallus. Microthalli with a size of 30–50 cells from the middle and apex of 21-day-old thalli cultivated at 15 °C yielded the optimum production of monospores. Theoretically, in this thallus-to-thallus seeding strategy, 0.1 g of thallus could produce at least 107 monospores, with the same number of offspring thallus seedlings. Taking all of these advantages together, including the high efficiency, short time, low cost and easy operation, this physical sectioning method could serve as a promising seed source especially for new cultivars with superior traits in Pyropia farming and rapid replenishment of seedlings when thalli undergo disastrous diseases.

Efficient modulation of end groups for the asymmetric small molecule acceptors enabling organic solar cells with over 15% efficiency

2020 ◽  
Vol 8 (12) ◽  
pp. 5927-5935 ◽  
Author(s):  
Gang Li ◽  
Dandan Li ◽  
Ruijie Ma ◽  
Tao Liu ◽  
Zhenghui Luo ◽  
...  
Keyword(s):  
Solar Cells ◽  
Small Molecule ◽  
Organic Solar Cells ◽  
High Efficiency ◽  
End Groups

Three asymmetric SMAs based on dithieno[3,2-b:2′,3′-d]pyrrole that exhibit a high efficiency of 15.31%, which is the highest value in asymmetric acceptor-based binary organic solar cells.

A Study of the Mechanism of the Deactivation Effect

1954 ◽  
Vol 27 (1) ◽  
pp. 157-164 ◽  
Author(s):  
Jacques Le Foll
Keyword(s):  
Chemical Structure ◽  
A Priori ◽  
Natural Aging ◽  
Chain Scission ◽  
Nitro Compounds ◽  
Active Part ◽  
Relaxation Phenomena ◽  
Chain Molecules ◽  
Vulcanized Rubber ◽  
The Subject

Abstract The only method by which significant differences between the effects of antioxygenic agents and deactivating agents can be detected has been found to be a study of relaxation phenomena. An investigation by this method has also furnished further support to the theories of Tobolsky and his coworkers. The changes which take place during aging in the physical properties of vulcanized rubber are the result of two independent phenomena which occur simultaneously: (1) chain scission, and (2) formation of intermolecular bonds. As far as the aging of vulcanizates of natural rubber under normal conditions, e.g., socalled natural aging, is concerned, the chief phenomenon involved is scission of the chain molecules. In principle, therefore, there are two methods for combatting the deterioration of rubber on aging: (1) to impede chain scission by obstructing the fixation of oxygen, and (2) to promote the progressive formation of intermolecular bonds which compensate for the effects of the scission process. The first of these processes is that in which antioxygenic agents play the active part; in the second process, deactivating agents play the active part. From this viewpoint, deactivating agents play a part analogous to that of accelerators, and they may be regarded as representing a special type of acceleration. This theory makes possible a better understanding of a number of facts which, a priori, seem surprising: (1) the relationships of both chemical structure and mode of action of accelerators and deactivating agents, and (2) the protective effect of litharge, peroxides, and nitro compounds, all of which are vulcanizing agents. With respect to the intimate mechanism of the deactivating effect, one question remains unanswered, viz., how are intermolecular bonds formed under the influence of deactivating agents? This question recalls the question of the function of vulcanization accelerators, which has been the subject of many investigations, but which still remains a mystery.

Degradation of Polyisoprene Networks by Oxygen

1960 ◽  
Vol 33 (1) ◽  
pp. 51-59 ◽  
Author(s):  
E. M. Bevilacqua
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Present Report ◽  
Hydrocarbon Chain ◽  
Gas Absorption ◽  
Oxygen Absorption ◽  
Low Molecular Weight ◽  
Oxidation Reactions ◽  
Vulcanized Rubber ◽  
Mechanism Of Oxidation

Abstract The insolubility of vulcanized rubber and the relatively low concentration at which oxidation reactions completely degrade the vulcanizate have made it necessary that indirect methods be used to study the reaction of molecular oxygen with rubber. The literature contains many reports of measurements of the absorption of oxygen by vulcanized rubber, which is easy and convenient experimentally. In some of these the rate of oxygen absorption has been the only property measured. This alone gives little information about the mechanism of oxidation, although the fact that the general form of curves of oxygen absorption as a function of time can be predicted by equations based on the known mechanism of oxidation of low molecular weight olefins is indirect support for similar mechanisms of oxidation of polymers. The technologically important reaction accompanying oxidation of natural rubber is scission, not detected by gas absorption measurements. It has been studied principally by determining the decay in stress of a sample at constant strain. The results suggest that scission occurs by a first order process at selected sites in the network. This has been interpreted to mean that crosslinks are the primary locus of oxidation in vulcanized rubber. Estimates of the amount of oxygen required for breaking a bond are available only for samples vulcanized with sulfur. From these it may be calculated that initially 4– 5 moles of oxygen is required per scission, when allowance is made for the effect of entanglements on stress. A marked difference between the relaxation of peroxide-cured and sulfur-cured samples has been reported. Horikx has made an extensive investigation of the solubility and swelling of oxidized vulcanized rubber. His results show that the hydrocarbon chain must be broken during oxidation. The mechanism of scission of unvulcanized rubber has been determined; in this work it was found that low molecular weight products are an important index of scission reactions. The present report describes preliminary work on the scission mechanism in vulcanized natural rubber which has two objectives; to repeat Horikx's experiments with vulcanizates incapable of further cure, and to determine whether low molecular weight products accompany the scission reaction.

Soft Vulcanized Rubber. Effect of Temperature and Oxygen Pressure on Aging Rate

1937 ◽  
Vol 10 (2) ◽  
pp. 336-345
Author(s):  
J. H. Ingmanson ◽  
A. R. Kemp
Keyword(s):  
Oxygen Pressure ◽  
Mechanical Strain ◽  
Accelerated Aging ◽  
Effect Of Temperature ◽  
Aging Rate ◽  
Vulcanized Rubber ◽  
Rubber Compounds ◽  
Cause Of Failure ◽  
Service Conditions ◽  
Oxidation Effect

Abstract IMPORTANT to the manufacturer and consumer of rubber goods are suitable accelerated aging tests for predicting readily the life of rubber articles under the variable storage and service conditions encountered. Since service conditions may involve the exposure of rubber to wide variations of temperature, light, and atmosphere under various types of mechanical strain, there is obviously need for a variety of tests, each designed to emphasize factors which are most important in any given set of service conditions. Since the primary cause of failure of soft vulcanized rubber in service is oxidation, emphasis has been placed on tests which accelerate the oxidation effect. The most widely adopted and generally satisfactory procedure of this type is the Bierer and Davis oxygen bomb method which involves heating the rubber under oxygen pressure. In Bierer and Davis' original publication (2), results were shown on the effect of increasing oxygen pressure in increments of 28.1 kg. up to 112.5 kg. per cm. on the aging of two different rubber compounds at the three temperatures, 50°, 60°, and 70° C. Their results showed that in some cases there was a uniform increase in aging rate with increased pressure and in other cases the rate increased rapidly up to a pressure of 28.7 kg. per sq. cm. but more slowly with further increases in pressure. In a later investigation (3) the same authors employed a pressure of 21.1 kg. per sq. cm. and 60° C. throughout. For the past ten years most laboratories have used an oxygen pressure of 21.1 kg. per sq. cm. and a temperature of 70° C., which may therefore be considered as standard.

Effect of Temperature on Tensile Properties of Vulcanized Rubber

1934 ◽  
Vol 7 (2) ◽  
pp. 371-386
Author(s):  
A. A. Somerville ◽  
W. F. Russell
Keyword(s):  
High Temperature ◽  
Tensile Properties ◽  
Room Temperature ◽  
Point Of View ◽  
Effect Of Temperature ◽  
Curing Conditions ◽  
Vulcanized Rubber ◽  
Before And After ◽  
Temperature Test ◽  
Better Than

Abstract The tensile properties and tear resistance of a large number of commercial inner tubes, before and after aging by different methods, are studied at 0°, 25°, and 100° C. A number of uncured bus-truck tube stocks are also studied from the point of view of their capacity to withstand high temperatures. The effect of testing rubber at 100° C. as compared with room temperature is discussed; how some compounds collapse at 100° C., while others have tensile properties equal to, or better than those at 25°, is shown. The effect of testing artificially aged specimens at 100° C., as well as at 25° C., is discussed; the high-temperature test may reveal conditions of deterioration and overcure that are not noticeable in the 25° tests. The compounding and curing conditions that lead to high tensile properties at 100° C., as well as those which cause inferior quality, are discussed.

Sign in / Sign up

Export Citation Format

Share Document