Kinetics of Urethan Cleavage in Crosslinked Polyurethans

1967 ◽  
Vol 40 (4) ◽  
pp. 1230-1237
Author(s):  
Ajaib Singh ◽  
Leonard Weissbein
Keyword(s):  
Stress Relaxation ◽  
Relaxation Data ◽  
Network Chain ◽  
Transient Stress ◽  
Precise Control ◽  
Positive Identification ◽  
Thermodynamic Constants ◽  
Different Temperatures ◽  
Order Of Magnitude ◽  
Kinetics Of

Abstract A series of clean, well defined polyurethan networks was synthesized from polyester glycols, 2, 4-tolylene diisocyanate, and 1, 1′, 1″-trimethylolpropane by means that afforded precise control over the content of urethan groups per network chain. The thermal cleavage of these networks was studied using the technique of stress relaxation. Analysis of the stress relaxation data on each network structure revealed two exponential decay processes differing in rate by about an order of magnitude. The rate of the slower process, which dominates the overall stress decay, was shown to be directly dependent on the content of urethan groups per network chain. Positive identification of this process with urethan cleavage was thereby established. The kinetic and thermodynamic constants associated with urethan cleavage were then calculated from data on this process at different temperatures. The more transient stress decay process was not uniquely definable, but probably originated from the cleavage of one or more types of weak linkages found in small but variable proportions in the different polyurethan networks. The nature and origin of these weak linkages was discussed.

Relaxation Processes in the Deformation of Unloaded Rubbers and the Influence of the Degree of Vulcanization

1951 ◽  
Vol 24 (4) ◽  
pp. 810-819
Author(s):  
B. A. Dogadkin ◽  
M. M. Reznikovskii˘
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Elastic Deformation ◽  
Relaxation Processes ◽  
Spatial Network ◽  
Relaxation Properties ◽  
Constant Rate ◽  
Different Temperatures ◽  
Kinetics Of

Abstract 1. It is shown that the process of stress relaxation at different initial elongations as well as the process of deformation at constant rate for unloaded rubbers at different temperatures (20–70° C) can be represented quantitatively by equations suggested in earlier works. Likewise the possibility of expanding the theories proposed for the kinetics of high-elastic deformation of spatial polymers is substantiated. 2. It is shown that the relaxation properties of soft unloaded vulcanizates of natural rubber and many synthetic rubbers do not undergo essential changes during vulcanization. 3. The conjecture is expressed that the invariability of the relaxation properties during vulcanization continues until the bonds of the spatial network are distributed sufficiently widely not to influence the activity or heat movement of the chain segments between them.

Modeling the kinetics of corn tortilla staling using stress relaxation data

2002 ◽  
Vol 53 (3) ◽  
pp. 237-247 ◽  
Author(s):  
Boostrapa Limanond ◽  
M.Elena Castell-Perez ◽  
Rosana G Moreira
Keyword(s):  
Stress Relaxation ◽  
Relaxation Data ◽  
Corn Tortilla ◽  
Kinetics Of

Phenomenological model for the reaction order n in the kinetics of curing an elastomer EPDM

MRS Advances ◽  
2019 ◽  
Vol 4 (59-60) ◽  
pp. 3299-3310
Author(s):  
S. Gómez-Jimenez. ◽  
A.M. Becerra-Ferreiro. ◽  
E. Jareño-Betancourt. ◽  
J. Vázquez-Penagos.
Keyword(s):  
Reaction Order ◽  
Cure Kinetics ◽  
Analytical Description ◽  
Crosslinking Reaction ◽  
Precise Control ◽  
Short Period ◽  
Rate Of Reaction ◽  
Different Temperatures ◽  
Kinetics Of ◽  
Modelling And Optimization

AbstractThe precise control of curing reaction parameters allows a better crosslinking polymer. Modelling and optimization of this process require a correct kinetic of curing model. The kinetics of the crosslinking reaction is studied for the ethylene propylene diene monomer (EPDM) synthetic elastomer by mobile die rheometer (MDR). The kinetic parameters of reaction were calculated from Kamal-Ryan, Sestak-Berggren, and the Isayev-Deng methods at different temperatures. An Arrhenius-type function for the order of reaction n is introduced to improve the adjusting. Finally, a graphical and analytical description of the cure kinetics was developed. The order of reaction is predicted to better establishment of processing time. It was noted that for EPDM at higher temperatures, the increase of the rate of reaction occurs in short period of time, which could cause premature curing if the supply system is inadequate.

Phenomenological effect of temperature on the order n of the reaction of the curing kinetics in an EPDM polymer

2021 ◽  
pp. 1-12
Author(s):  
Salvador Gomez-Jimenez ◽  
Ana Maria Becerra-Ferreiro ◽  
Eduardo D Jareño-Betancourt ◽  
Jose M Vazquez-Penagos
Keyword(s):  
Cure Kinetics ◽  
Analytical Description ◽  
Curing Kinetics ◽  
Effect Of Temperature ◽  
Crosslinking Reaction ◽  
Precise Control ◽  
The Best Approximation ◽  
Short Period ◽  
Different Temperatures ◽  
Kinetics Of

Abstract The precise control of curing reaction parameters allows a better crosslinking polymer. Modeling and optimization of this process require a correct kinetic of curing model. The kinetics of the crosslinking reaction is studied for the ethylene propylene diene monomer (EPDM) synthetic elastomer by movile die rheometer (MDR). The kinetic parameters of reaction were calculated from Kamal-Ryan, Sestak-Berggren, and the Isayev-Deng methods at different temperatures. An Arrhenius-type function for the order of reaction n is introduced to improve the adjusting. A comparative study of Sestak-Berggren and Isayev-Deng models was made to validate and determine which model best describes the behavior of vulcanization. The best approximation was obtained with the model Isayev-Deng. Finally, taking the model with the best fit, a graphical and analytical description of the cure kinetics was developed. The order of reaction is predicted to better establishment of processing time. It was noted that for EPDM at higher temperatures, the increase of the rate of reaction occurs in short period of time, which could cause premature curing if the supply system is inadequate.

Effect of the ionizing radiation on the kinetics of the reduction by hydrogen of NiO-Fe2O3 mixed oxides of various genesis

1986 ◽  
Vol 51 (8) ◽  
pp. 1561-1570 ◽  
Author(s):  
Milan Pospíšil ◽  
Jan Topinka
Keyword(s):  
Radiation Effects ◽  
Mixed Oxides ◽  
Chemical Properties ◽  
Fast Neutrons ◽  
Chemisorbed Oxygen ◽  
First Case ◽  
Different Temperatures ◽  
Negative Effect ◽  
Order Of Magnitude ◽  
Kinetics Of

The kinetics of the reduction by hydrogen of two series of NiO-Fe2O3 mixed oxides of different composition was studied in the temperature range 320 - 410 °C using thermogravimetry. Both series were prepared from different precursors that were thermally decomposed at different temperatures. The oxidizing ability of the surface ( the content of chemisorbed oxygen) is the only parameter from all physico-chemical properties studied that changed significantly during the pre-irridation of the system by 60Co gamma radiation (dose 505 kGy), by fast neutrons from the 252Cf source (dose Dn = 110 Gy) and by accelerated electrons (3 MeV, dose 500 kGy). A positive radiation effect was observed in the first case while the irritation by neutrons and electrons resulted in a negative effect. The magnitude of the effect depends on the composition and genesis of the system and it decreases in the sequence γ, e-, n. The radiation induced changes in the reduction kinetics of mixed oxides change their magnitude and sign in dependence on the composition and genesis. Not only the increase by an order of magnitude of the rate of the initial phase of the reduction which was ascribed to the partial reduction of hematite to magnetite but also the acceleration of the second step (reduction of Fe3O4 to Fe) was observed after the exposure to photons or fast neutrons. The radiation changes induced by electrons are limited only to the surface of the irradiated solid and they affect only the first step of the reduction. The maximum positive effect was observed in the region of high excess of hematite and its magnitude decreases with the increasing content of nickel oxide. The radiation effects decrease with the increasing temperature of the reduction and at about 400 °C the effect of irradiation is completely annealed.

Radiolytic Stress Relaxation of an Ethylene Propylene Copolymer

1966 ◽  
Vol 39 (4) ◽  
pp. 982-991
Author(s):  
Hyuk Yu ◽  
Leo A. Wall
Keyword(s):  
Stress Relaxation ◽  
Elastic Properties ◽  
Chain Scission ◽  
Network Chain ◽  
Ethylene Propylene ◽  
Initial Network ◽  
Γ Rays ◽  
Kinetics Of

Abstract The kinetics of network chain scission induced by γ-rays has been studied by stress relaxation at constant elongation under vacuum and in air. The rate of chain scission of a 1:1 ethylene propylene copolymer was found to be independent of initial network chain density, and the initial rates were roughly the same in air and under vacuum. Parameters for crosslinking induced by γ-rays were obtained by sol extraction and by measurement of elastic properties of the resulting networks. Values of G for scission and crosslinking and gel dose, obtained by stress relaxation, by elastic properties, and by sol extraction, were found to agree with each other.

Comparative Labelling and Biokinetic Studies of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn)

1977 ◽  
Vol 16 (01) ◽  
pp. 30-35 ◽  
Author(s):  
N. Agha ◽  
R. B. R. Persson
Keyword(s):  
Complex Formation ◽  
Significant Influence ◽  
Room Temperature ◽  
Ph Value ◽  
Maximum Activity ◽  
Reduction Step ◽  
Labelling Yield ◽  
Different Temperatures ◽  
Kinetics Of

SummaryGelchromatography column scanning has been used to study the fractions of 99mTc-pertechnetate, 99mTcchelate and reduced hydrolyzed 99mTc in preparations of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn). The labelling yield of 99mTc-EDTA(Sn) chelate was as high as 90—95% when 100 μmol EDTA · H4 and 0.5 (Amol SnCl2 was incubated with 10 ml 99mTceluate for 30—60 min at room temperature. The study of the influence of the pH-value on the fraction of 99mTc-EDTA shows that pH 2.8—2.9 gave the best labelling yield. In a comparative study of the labelling kinetics of 99mTc-EDTA(Sn) and 99mTc- DTPA(Sn) at different temperatures (7, 22 and 37°C), no significant influence on the reduction step was found. The rate constant for complex formation, however, increased more rapidly with increased temperature for 99mTc-DTPA(Sn). At room temperature only a few minutes was required to achieve a high labelling yield with 99mTc-DTPA(Sn) whereas about 60 min was required for 99mTc-EDTA(Sn). Comparative biokinetic studies in rabbits showed that the maximum activity in kidneys is achieved after 12 min with 99mTc-EDTA(Sn) but already after 6 min with 99mTc-DTPA(Sn). The long-term disappearance of 99mTc-DTPA(Sn) from the kidneys is about five times faster than that for 99mTc-EDTA(Sn).

scholarly journals Reduction Mechanism of Fine Hematite Ore Particles in Suspension

2021 ◽  
Author(s):  
Zhiyuan Chen ◽  
Christiaan Zeilstra ◽  
Jan van der Stel ◽  
Jilt Sietsma ◽  
Yongxiang Yang
Keyword(s):  
Particle Size ◽  
Temperature Drop ◽  
Reduction Rate ◽  
Reduction Process ◽  
Reciprocal Relationship ◽  
Drop Tube ◽  
Surface Nucleation ◽  
Order Of Magnitude ◽  
Relationship Of ◽  
Kinetics Of

AbstractIn order to understand the pre-reduction behaviour of fine hematite particles in the HIsarna process, change of morphology, phase and crystallography during the reduction were investigated in the high temperature drop tube furnace. Polycrystalline magnetite shell formed within 200 ms during the reduction. The grain size of the magnetite is in the order of magnitude of 10 µm. Lath magnetite was observed in the partly reduced samples. The grain boundary of magnetite was reduced to molten FeO firstly, and then the particle turned to be a droplet. The Johnson-Mehl-Avrami-Kolmogorov model is proposed to describe the kinetics of the reduction process. Both bulk and surface nucleation occurred during the reduction, which leads to the effect of size on the reduction rate in the nucleation and growth process. As a result, the reduction rate constant of hematite particles increases with the increasing particle size until 85 µm. It then decreases with a reciprocal relationship of the particle size above 85 µm.

scholarly journals Thermodynamic and detailed kinetic study of the formation of orthophthalaldehyde-agmatine complex by fluorescence intensities

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Khémesse Kital ◽  
Moumouny Traoré ◽  
Diégane Sarr ◽  
Moussa Mbaye ◽  
Mame Diabou Gaye Seye ◽  
...  
Keyword(s):  
Complex Formation ◽  
Thermodynamic Parameters ◽  
Initial Rate ◽  
Reaction Medium ◽  
Standard Entropy ◽  
Step Size ◽  
Formation Reaction ◽  
Different Temperatures ◽  
Kinetics Of ◽  
Complex Formation Process

Abstract The aim of this work is to determine the thermodynamic parameters and the kinetics of complex formation between orthophthalaldehyde (OPA) and agmatine (AGM) in an alkaline medium (pH 13). Firstly, the association constant (Ka) between orthophthalaldehyde and agmatine was determined at different temperatures (between 298 K and 338 K) with a step size of 10 K. Secondly, the thermodynamic parameters such as standard enthalpy (ΔH°), standard entropy (ΔS°),and Gibbs energy (∆G) were calculated, where a positive value of ΔH° (+45.50 kJ/mol) was found, which shows that the reaction is endothermic. In addition, the low value of ΔS°(+0.24 kJ/mol) indicates a slight increase in the disorder in the reaction medium. Furthermore, the negative values of ΔG between −35.62 kJ/mol and −26.02 kJ/mol show that the complex formation process is spontaneous. Finally, the parameters of the kinetics of the reaction between OPA and AGM were determined as follows: when the initial concentration of AGM (5 × 10−6 M) is equal to that of the OPA, the results show that the reaction follows an overall 1.5 order kinetics with an initial rate of 5.1 × 10−7Mmin−1 and a half-life of 8.12 min. The partial order found in relation to the AGM is 0.8. This work shows that the excess of OPA accelerates the formation reaction of the complex.

scholarly journals Ice Coverage Induced by Depositing a Water Drop onto the Supercooled Substrate at Extreme Low Vapor Pressure

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 691
Author(s):  
Yugang Zhao ◽  
Zichao Zuo ◽  
Haibo Tang ◽  
Xin Zhang
Keyword(s):  
Vapor Pressure ◽  
Substrate Temperature ◽  
Water Drop ◽  
Industrial Processes ◽  
Aircraft Icing ◽  
Ice Coverage ◽  
Fundamental Understanding ◽  
Order Of Magnitude ◽  
The Impact ◽  
Kinetics Of

Icing/snowing/frosting is ubiquitous in nature and industrial processes, and the accretion of ice mostly leads to catastrophic consequences. The existing understanding of icing is still limited, particularly for aircraft icing, where direct observation of the freezing dynamics is inaccessible. In this work, we investigate experimentally the impact and freezing of a water drop onto the supercooled substrate at extremely low vapor pressure, to mimic an aircraft passing through clouds at a relatively high altitude, engendering icing upon collisions with pendant drops. Special attention is focused on the ice coverage induced by an impinging drop, from the perimeter pointing outward along the radial direction. We observed two freezing regimes: (I) spread-recoil-freeze at the substrate temperature of Ts = −15.4 ± 0.2 °C and (II) spread (incomplete)-freeze at the substrate temperature of Ts = −22.1 ± 0.2 °C. The ice coverage is approximately one order of magnitude larger than the frozen drop itself, and counterintuitively, larger supercooling yields smaller ice coverage in the range of interest. We attribute the variation of ice coverage to the kinetics of vapor diffusion in the two regimes. This fundamental understanding benefits the design of new anti-icing technologies for aircraft.

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