Stress Relaxation in Rubber II. Simultaneous Oxygen Absorption

1956 ◽  
Vol 29 (1) ◽  
pp. 250-262
Author(s):  
S. Baxteh ◽  
P. D. Potts ◽  
H. A. Vodden
Keyword(s):  
Stress Relaxation ◽  
Absorption Rate ◽  
Oxidative Degradation ◽  
Oxygen Absorption ◽  
Network System ◽  
Antioxidant Action ◽  
Basic Study ◽  
Aging Studies ◽  
Oxygen Absorption Rate ◽  
A New Technique

Abstract In any serious study of antioxidant action, it is essential that the oxygen absorption rate of a protected rubber be determined and the changes in the network system caused by the oxygen be assessed. This information is normally obtained from separate oxygen absorption and aging studies. A method is described in this article which enables simultaneous measurements of oxygen absorption and stress relaxation to be made on a given rubber sample. A number of antioxidants have been compounded with natural rubber and, from the results, an estimate is made of the molecules of oxygen absorbed per rubber chain cut. This is found to vary with the antioxidant, although some difficulties of interpretation are pointed out. Variations of deactivating effect among the antioxidants shows clearly that any attempt to understand oxidative degradation in terms of oxygen absorption or decay in physical properties alone is not possible. The method provides a new technique that is of value in any basic study of antioxidant action in elastomers.

Relationships between Chemical Structures of Crosslink Sites and Physical Properties of Vulcanized Rubbers. Part VI. Oxidative Degradation of EPDM Vulcanizates

1970 ◽  
Vol 43 (2) ◽  
pp. 431-444 ◽  
Author(s):  
M. Imoto ◽  
Y. Minoura ◽  
K. Goto ◽  
H. Harada ◽  
K. Nishihira ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Physical Properties ◽  
Oxidative Degradation ◽  
Oxygen Absorption ◽  
Chemical Structures ◽  
Early Stages ◽  
Absorption Measurements

Abstract Relationship between the chemical structures of crosslinks and the degree of oxidative degradation of EPDM vulcanizates was studied by stress relaxation and oxygen absorption measurements. It was found that the vulcanizates having C—Sx—C crosslink showed slower stress relaxation than the vulcanizate having other crosslink structures, i.e., C—S—C, C—C, and C—R—C. It was thought that C—Sx—C bond would reduce the scission of the network in oxidative degradation, since some polysulfide compounds had the same effect of protecting scission as antioxidant. The similar results were obtained in oxygen absorption measurements. In the case of heat aging, the vulcanizate having C—Sx—C linkage increased in crosslinks during aging and the rate of crosslinking was equal to the rate of scission of the network in the early stages, but the vulcanizates having other types of crosslinks did not show such behavior.

scholarly journals Assessment of the efficiency of oxygen absorption in rotor-pulsating apparatus

2018 ◽  
pp. 117-124 ◽  
Author(s):  
Oleksandr Obodovych ◽  
Vitalii Sydorenko
Keyword(s):  
Experimental Data ◽  
Energy Efficiency ◽  
Rotational Speed ◽  
Absorption Rate ◽  
Sodium Sulfide ◽  
Chemical Oxidation ◽  
Model Solution ◽  
Oxygen Absorption ◽  
Oxygen Absorption Rate ◽  
Aeration Conditions

This work presents the results of a study of the oxygen absorption rate in water solutions in the setup consisting of a jet unit and disperser-mixer, which is a rotor-pulsating apparatus. The purpose of the work was to evaluate the efficiency of the rotor-pulsating apparatus in the aeration of aqueous solutions. The experimental data were obtained by the method of chemical oxidation of sodium sulfide, part of the model solution, with air oxygen,. The influence of the rotor rotational speed on the oxygen absorption rate was determined by experiments. A comparison of aeration conditions, sulfite number, and energy efficiency in relation to the corresponding characteristics of some pneumatic and mechanical aerators found in the literature is provided.

scholarly journals Dynamic Crosslinking: An Efficient Approach to Fabricate Epoxy Vitrimer

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 919
Author(s):  
Yin Ran ◽  
Ling-Ji Zheng ◽  
Jian-Bing Zeng
Keyword(s):  
Stress Relaxation ◽  
Production Efficiency ◽  
Specific Property ◽  
Sebacic Acid ◽  
Compression Molding ◽  
Diglycidyl Ether ◽  
Self Healing ◽  
Gel Fraction ◽  
A New Technique ◽  
Transesterification Catalyst

Epoxy vitrimers with reprocessability, recyclability, and a self-healing performance have attracted increasingly attention, but are usually fabricated through static curing procedures with a low production efficiency. Herein, we report a new approach to fabricate an epoxy vitrimer by dynamic crosslinking in a torque rheometer, using diglycidyl ether of bisphenol A and sebacic acid as the epoxy resin and curing agent, respectively, in the presence of zinc acetylacetonate as the transesterification catalyst. The optimal condition for fabricating the epoxy vitrimer (EVD) was dynamic crosslinking at 180 °C for ~11 min. A control epoxy vitrimer (EVS) was prepared by static curing at 180 °C for ~11 min. The structure, properties, and stress relaxation of the EVD and EVS were comparatively investigated in detail. The EVS did not cure completely during static curing, as evidenced by the continuously increasing gel fraction when subjected to compression molding. The gel fraction of the EVD did not change with compression molding at the same condition. The physical, mechanical, and stress relaxation properties of the EVD prepared by dynamic crosslinking were comparable to those of the EVS fabricated by static curing, despite small differences in the specific property parameters. This study demonstrated that dynamic crosslinking provides a new technique to efficiently fabricate an epoxy vitrimer.

Accelerated Heat-Aging Studies on Fluorosilicone Rubber

1975 ◽  
Vol 48 (5) ◽  
pp. 944-952 ◽  
Author(s):  
S. H. Kalfayan ◽  
R. H. Silver ◽  
A. A. Mazzeo
Keyword(s):  
Weight Loss ◽  
Stress Relaxation ◽  
Repeat Unit ◽  
Accelerated Aging ◽  
Basic Mechanism ◽  
Inert Atmosphere ◽  
Polymer Backbone ◽  
Aging Studies ◽  
Relaxation Measurements ◽  
Fluorosilicone Rubber

Abstract The accelerated aging of a vulcanizate of fluorosilicone rubber was studied by four methods: infrared spectroscopy, GPC, weight loss, and stress relaxation, with the object of gathering information pertinent to understanding the basic mechanism of its aging. No changes were observed in infrared spectra of the rubber aged in air up to 315°C although severe degradation took place, as evidenced by high weight loss and drastic change in the physical condition of the test samples. It was concluded that although the polymer degrades, there is no change detectable within the precision of the analytical methods in the structure of the repeat unit of the elastomer. The gel-permeation chromatogram of unheated rubber showed peaks at MW 450 000 (95%) and 630 (5%). The low-molecular-weight component is very likely the cyclic tetramer of λ,λ′,λ″-trifluoropropylmethylsiloxane, the principal monomer of the FVMQ used. Heat aging increased the concentration of the 630 MW component, but rate studies were prevented by complications resulting from solvent-induced rubber degradation. Rapid decrease in the MW of FVMQ, as found by GPC, indicated random scission in the polymer backbone, as opposed to ordered unzipping of the repeat unit. The same conclusion was reached from the effects of crosslink density on stress relaxation. Activation energies obtained from weight-loss measurements (104 kJ/mol) were lower than those obtained from stress-relaxation measurements, (150–155 kJ/mol), suggesting that the processes being measured in each case may not be the same. Chemical stress relaxation takes place more rapidly in the presence of air than in an inert atmosphere, and intermittent stress-relaxation measurements indicate that crosslinks form during thermal aging in air, their rate first increasing and then decreasing.

Rubber Oxidation and Aging Studies Safe Limits of Sample Thickness

1951 ◽  
Vol 24 (4) ◽  
pp. 999-1016
Author(s):  
George W. Blum ◽  
J. Reid Shelton ◽  
Hugh Winn
Keyword(s):  
Natural Rubber ◽  
Accelerated Aging ◽  
Sample Thickness ◽  
Oxygen Absorption ◽  
Absorption Data ◽  
Synthetic Rubber ◽  
Constant Rate ◽  
Aging Studies ◽  
Safe Limits ◽  
Natural Rubber Vulcanizates

Abstract Safe limits of sample thickness for rubber oxidation and aging studies, such that the chemical reaction rather than the rate of diffusion will be rate-controlling have been investigated for natural-rubber vulcanizates and for four synthetic-rubber types. For studies involving the entire range of oxidation, including the autocatalytic stage of rapid oxygen absorption, the conventional 0.075-inch thickness is frequently not satisfactory for accelerated aging and oxidation studies if it is desired to avoid limitation by diffusion. Only in the GR-S black stock was this thickness found to be satisfactory up to a temperature of 100° C. The other stocks, including natural rubber, Butaprene-NXM, and Neoprene black and gum stocks all require thinner samples to ensure that the observed rate of oxygen absorption is free of limitation by diffusion. A method of calculating the probable limiting value of sample thickness, above which the rate of oxidation in the autocatalytic stage is limited by diffusion, has been developed on the basis of volumetric oxygen absorption data obtained with GR-S. The method has also been applied to natural-rubber vulcanizates and to other synthetic-rubber types to locate the approximate limiting values at various temperatures for oxidation and aging studies which extend into the autocatalytic stage of rapid reaction. The constant-rate period of oxidation is more important from a practical point of view than the autocatalytic stage, since properties are so seriously degraded as to make the rubber of little value before it reaches the final stage of rapid oxidation. Somewhat thicker samples may be used for studies that are confined to the earlier stages of oxidation. A 0.075-inch sample is free of limitation by diffusion in the constant-rate stage in the following cases: GR-S black and gum stocks at 110° C; Hevea black with added antioxidant at 100° C; and uninhibited Hevea black and gum stocks at 60° C. A 0.040-inch sample is satisfactory in this range for: uninhibited Hevea black at 100° and gum at 80° C; Butaprene-NXM black at 100° and gum at 90° C; and Neoprene black and gum stocks at 100° C.

Accelerated aging studies of UHMWPE. II. Virgin UHMWPE is not immune to oxidative degradation

2002 ◽  
Vol 61 (2) ◽  
pp. 323-329 ◽  
Author(s):  
A. A. Edidin ◽  
M. L. Villarraga ◽  
M. P. Herr ◽  
J. Muth ◽  
S. S. Yau ◽  
...  
Keyword(s):  
Oxidative Degradation ◽  
Accelerated Aging ◽  
Aging Studies

Basic Study on the Crushing of Frozen Soil by Shock Loading

2007 ◽  
Author(s):  
Toshiaki Watanabe ◽  
Hironori Maehara ◽  
Masahiko Otsuka ◽  
Shigeru Itoh
Keyword(s):  
Shock Wave ◽  
High Speed ◽  
Shock Loading ◽  
Underwater Explosion ◽  
Frozen Soil ◽  
High Speed Camera ◽  
Underwater Shock Wave ◽  
Basic Study ◽  
Underwater Shock ◽  
A New Technique

The aim of study is to confirm a new technique that can crush the frozen soil and/or ice block using underwater shock wave generated by the underwater explosion of explosive. This technique can lead to the earlier sowing, which can have the larger harvest because the duration of sunshine increases. Especially, in Hokkaido prefecture, Japan, if the sowing is carried out in April, we can expect to have 150% of harvest in the ordinary season. This technique is effective against the cold regions. For example, Korea, China, Mongolia, Russia, Norway, and Sweden, etc. At first, we carried out experiments usung a detonating fuse and ice block. The process of ice breaking was observed by means of a high-speed camera. In order to check about that influence we tried to give an actual frozen soil a shock wave.

scholarly journals Production of a-amylase in acid cheese whey culture media with automatic pH control

1998 ◽  
Vol 29 (4) ◽  
pp. 259-264 ◽  
Author(s):  
Rosana Ferreyra ◽  
Graciela Lorda ◽  
Antonio Balatti
Keyword(s):  
Enzyme Production ◽  
Cheese Whey ◽  
Culture Media ◽  
Oxygen Demand ◽  
Ph Control ◽  
Oxygen Absorption ◽  
Cell Aggregates ◽  
Lead Electrode ◽  
Oxygen Absorption Rate ◽  
Industrial Use

The influence of aeration and automatic pH control on the production of <FONT FACE="Symbol">a</FONT>-amylase by a strain of Bacillus subtilis NRRL 3411 from acid cheese whey was studied. Tests were carried out in a rotary shaker and in mechanically stirred fermenters. <FONT FACE="Symbol">a</FONT>-amylase was analysed according to DUN’s method. Oxygen absorption rate was determined by Cooper’s method. Cell oxygen demand was determined as oxygen consumption in a Warburg respirometer. The level of dissolved oxygen was measured by means of a galvanic silver-lead electrode. Results suggest the possibility of industrial use of acid cheese whey as a carbon source for <FONT FACE="Symbol">a</FONT>-amylase production, since the yield was similar to that produced with lactose. The highest <FONT FACE="Symbol">a</FONT>-amylase levels 10,000 DUN/ml units were not attained at higher aeration rates -431 mLO2/L.h-. The indicated value correspond to a 96 h process with automatic pH control at 7.5. These conditions resulted in double concentration of <FONT FACE="Symbol">a</FONT>-amylase. The enzyme production was directly related to growth in the form of cell aggregates.

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