Enthalpic Analysis of Vulcanization by Calorimetry. Thiuram Monosulfide/Sulfur Vulcanization of NR, BR and SBR

Abstract As demonstrated in the foregoing discussion, the chemical complexity of accelerated sulfur vulcanization reactions prevents detailed interpretation of the enthalpy-temperature and enthalpy-time relationship. Nevertheless, the following conclusions can be reached regarding the origin of the enthalpy terms observed under scanning and isothermal temperature regimes. (1) The total enthalpy observed under scanning conditions is the sum of all reactions occurring. This includes (among others) crosslink formation, formation of non-crosslinking sulfidic products and maturation or subsequent polysulfide reactions. (2) In the isothermal experiment, the major contribution to the observed enthalpy arises from reactions resulting in the formation of sulfidic products (although some maturation must be expected and its extent will depend upon the temperature and time of cure). (3) When a precured sample is scanned, the observation of an enthalpic term depends upon the original cure system used. It is small or unobserved, for example, when the sulfur/TMTM ratio is small or with sulfur donor cure systems. On this basis, the DSC scan of a vulcanizate is potentially useful for characterizing that vulcanizate, and in particular, for the rapid quality control assessment of the state of sulfidic products in the vulcanizate. (4) Evidence has been discussed which suggests that the origin of the enthalpy term obtained with vulcanizates which have been precured can be related to the polysulfidic products in the sample. In laboratory experiments, not reported here, the magnitude of this term is reduced as the vulcanizate is heat aged or over-cured, which again supports the conclusion that we are observing the maturation of polysulfidic products. (5) Finally, comparison of rheometer and calorimeter data indicates that, as expected, we are observing all, reactions accompanying cure in the calorimeter; whereas, the rheometer responds only to crosslinking and chain scission, factors having a large effect on viscosity. DSC does not detect chain scission reactions at normal cure temperatures because the rate of scission is too small.

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Dissipation and Leaching of Metriflufen under Field and Controlled Conditions

Weed Science ◽

10.1017/s0043174500063736 ◽

1981 ◽

Vol 29 (5) ◽

pp. 561-565 ◽

Cited By ~ 1

Author(s):

Noell K. Rogers ◽

Ronald E. Talbert

Keyword(s):

Growth Inhibition ◽

Laboratory Experiments ◽

Grain Sorghum ◽

Propanoic Acid ◽

Silt Loam ◽

Average Depth ◽

Soil Columns ◽

Treated Soil ◽

Temperature Regimes ◽

Moisture Conditions

Field and laboratory experiments were conducted in 1977 and 1978 to evaluate the movement and persistence in soil of metriflufen {methyl ester of 2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid} under different conditions. In the field, delaying incorporation of metriflufen did not affect its activity in Taloka silt loam for either year as shown by bioassay with grain sorghum [Sorghum bicolor(L.) Moench]. Metriflufen activity in the soil persisted for 63 and 40 days after application in 1977 and 1978, respectively. In the laboratory, metriflufen moved through saturated soil columns to an average depth of 7.5 and 18.5 cm following the addition of 2.5 or 10 cm of water to the columns. In a growth chamber bioassay, grain sorghum growth in treated soil gave a dose-response in a range of 0.02 ppmw (I10), 0.09 ppmw (I50), and 0.38 ppmw (I90). When soil treated with metriflufen at 1 ppmw was incubated for specified times under soil moisture levels of 5, 15, or 25% and temperature regimes of 15, 25, or 35 C, soil incubated at 15 C for as long as 75 days completely inhibited grain sorghum growth regardless of the other treatment variables. Grain sorghum growth inhibition was reduced with incubation time and warmer temperatures for treated soil maintained at 5 and 15% moisture, but sorghum growth inhibition persisted for treated soil incubated under wet (25% moisture) conditions.

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Solid-State C-13 NMR Studies of Vulcanized Elastomers X. N-t-Butyl-2-Benzothiazole Sulfenamide Accelerated Sulfur Vulcanization of cis-Polyisoprene at 75.5 MHz

Rubber Chemistry and Technology ◽

10.5254/1.3538622 ◽

1992 ◽

Vol 65 (2) ◽

pp. 427-443 ◽

Cited By ~ 10

Author(s):

M. R. Krejsa ◽

J. L. Koenig

Keyword(s):

Solid State ◽

Solid State Nmr ◽

Chain Scission ◽

Sulfur Concentration ◽

Nmr Studies ◽

Double Bond Migration ◽

Sulfur Vulcanization ◽

Equilibrium Swelling ◽

Cis And Trans ◽

Good Agreement

Abstract Accelerated sulfur vulcanized cis-polyisoprene was analyzed using C-13 solid-state NMR to determine the chemical microstructure of the network. Three formulations were analyzed consisting of varying accelerator/sulfur ratios. All formulations yielded similar network structures, but the amount of sulfurization varied with sulfur concentration. At low percent cure, only polysulfidic A-type cis-structures were found. For longer cure times, the A-type structures shortened to monosulfldic, and B-type polysulfidic structures, both cis and trans, were formed. The amount of trans-sulfurized product was constant with cure once this resonance appeared. No isomerization, chain scission, saturation, or double bond migration was detected. The NMR measurements appeared to show fairly good agreement with equilibrium swelling measurements.

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Effect of constant and fluctuating temperature regimes and seed source on the coleoptile length of tall and semidwarf wheats

Australian Journal of Experimental Agriculture ◽

10.1071/ea9870113 ◽

1987 ◽

Vol 27 (1) ◽

pp. 113 ◽

Cited By ~ 14

Author(s):

BJ Radford

Keyword(s):

Environmental Conditions ◽

Laboratory Experiments ◽

Seed Source ◽

Seed Maturation ◽

Wheat Cultivars ◽

Coleoptile Length ◽

Fluctuating Temperature ◽

Temperature Regimes ◽

The Mean ◽

Constant And Fluctuating Temperature

Laboratory experiments were carried out to determine the effects of constant and fluctuating temperature regimes on the final coleoptile length of 8 wheat cultivars (Banks, Cook, Gatcher, Hartog, Kite, Oxley, Shortim and Spica) and the effect of environmental conditions during seed maturation (seed source) on the coleoptile length of 5 cultivars (Banks, Bass, Cook, Kite and Oxley). Mean coleoptile length decreased from 10.8 cm at 15�C to only 3.1 cm at 35�C, a reduction within this temperature range of 1 cm for every 2.6�C rise in temperature. This indicates that, in warm soil, shallow sowing is necessary for satisfactory wheat establishment. Fluctuating temperatures (� 5�C about the mean) further reduced coleoptile length. The temperature x cultivar interaction was significant, differences among cultivars in coleoptile length occurring more at low than at high temperatures. The mean coleoptile lengths of the 8 cultivars varied from 8.7 to 14.5 cm at 15�C, but only from 2.7 to 3.6 cm at 35�C. Tall wheat cultivars (Gatcher and Spica) generally had longer coleoptiles than the 6 semidwarf cultivars. Tall wheats also had near-maximum coleoptile length at a wider range of temperatures than semidwarfs. Different environmental conditions during seed maturation (glasshouse v. field) changed the ranking of cultivars with respect to coleoptile length. The coleoptiles of Cook and Oxley were significantly longer when seed was field-ripened rather than glasshouse ripened, while those of Banks, Bass and Kite were similar in length under both ripening environments.

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Germination of Spotted Spurge (Chamaesyce maculata) Seeds in Response to Different Environmental Factors

Weed Science ◽

10.1614/ws-d-14-00162.1 ◽

2015 ◽

Vol 63 (2) ◽

pp. 502-510 ◽

Cited By ~ 19

Author(s):

Rayhaneh Asgarpour ◽

Reza Ghorbani ◽

Mohammad Khajeh-Hosseini ◽

Elmira Mohammadvand ◽

Bhagirath Singh Chauhan

Keyword(s):

Sodium Chloride ◽

Environmental Factors ◽

Laboratory Experiments ◽

Management Strategies ◽

Effective Management ◽

Night Temperature ◽

Continuous Darkness ◽

Tropical Regions ◽

Temperature Regimes ◽

Golestan Province

Spotted spurge, a C4species, is a summer annual weed, introduced to the Golestan province of Iran in 2006. A series of laboratory experiments were conducted at the Faculty of Agriculture, Ferdowsi University of Mashhad, Iran, to evaluate the influence of environmental factors on seed germination of spotted spurge. Seeds germinated over a constant temperature range of 25 to 45 C with a 14-h photoperiod and at 30 to 50 C in continuous darkness. Seeds germinated at alternating day/night temperature regimes of 25/15 to 45/35 C, with maximum germination (> 80%) at alternating day/night temperatures of 35/25, 40/30, and 45/35C. Germination increased from 23.5 to 98% as water potential increased from −0.6 to 0 MPa (control). Germination was > 85% at sodium chloride (NaCl) concentrations up to 80 mM, with no germination at 160 mM NaCl. Germination was not affected by pH, and it was > more than 95% at pH ranging from 4 to 9. The germination of seeds submerged in water for a period less than 3 wk was > 60%, whereas no germination was observed after 9 wk of submergence in water. The results of our study could help to develop effective management strategies for this species. The results also suggest that spotted spurge could invade most tropical regions of Iran.

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Solid-State C-13 NMR Studies of Vulcanized Elastomers XIII. TBBS Accelerated, Sulfur-Vulcanization of Carbon Black Filled Natural Rubber

Rubber Chemistry and Technology ◽

10.5254/1.3538756 ◽

1995 ◽

Vol 68 (4) ◽

pp. 551-562 ◽

Cited By ~ 30

Author(s):

Makio Mori ◽

Jack L. Koenig

Keyword(s):

Double Bond ◽

Solid State ◽

Carbon Black ◽

Natural Rubber ◽

Main Chain ◽

Chain Scission ◽

Nmr Studies ◽

Double Bond Migration ◽

Sulfur Vulcanization ◽

Basic Network

Abstract Solid state C-13 NMR has been used to compare the chemistry of accelerated vulcanization of natural rubber using N-t-butyl-2-benzothiazole sulfenamide in the presence and absence of carbon black. The carbon black filler has an influence on the vulcanization chemistry in addition to its accepted role in reinforcment and stabilization. The basic network structure formation is modified to the extent that crosslink desulfurization from poly to monosulflde structures occurs earlier in the cure in the presence of carbon black. No main chain scission or double bond migration was detected.

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Covering of cometary nucleus by refractory crust and its evolution into asteroid-like body

International Astronomical Union Colloquium ◽

10.1017/s0252921100031675 ◽

1999 ◽

Vol 173 ◽

pp. 365-370

Author(s):

Kh.I. Ibadinov

Keyword(s):

Laboratory Experiments ◽

Cometary Nucleus ◽

Sublimation Rate ◽

Cometary Nuclei ◽

Short Period Comet ◽

Short Period ◽

Brightness Decrease ◽

Crust Thickness ◽

Ice Sublimation ◽

Period Comet

AbstractFrom the established dependence of the brightness decrease of a short-period comet dependence on the perihelion distance of its orbit it follows that part of the surface of these cometary nuclei gradually covers by a refractory crust. The results of cometary nucleus simulation show that at constant insolation energy the crust thickness is proportional to the square root of the insolation time and the ice sublimation rate is inversely proportional to the crust thickness. From laboratory experiments resulted the thermal regime, the gas productivity of the nucleus, covering of the nucleus by the crust, and the tempo of evolution of a short-period comet into the asteroid-like body studied.

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When Does Voice Have to be More Than Only Listening? Procedural Justice Effects as a Function of Confident Leadership

Journal of Personnel Psychology ◽

10.1027/1866-5888/a000011 ◽

2010 ◽

Vol 9 (2) ◽

pp. 69-78 ◽

Cited By ~ 8

Author(s):

David De Cremer ◽

Maarten Wubben

Keyword(s):

Procedural Justice ◽

Interaction Effect ◽

Laboratory Experiments ◽

Negative Emotions

The present research examined how voice procedures and leader confidence affect participants’ negative emotions and willingness to withdraw. It was predicted that receiving voice would be valued out of instrumental concerns, but only when the enacting leader was high in confidence. Two laboratory experiments indeed showed an interaction between type of voice (pre-decisional vs. post-decisional) and leader’s confidence (low vs. high) on participants’ negative emotions and willingness to withdraw. In particular, post-decision voice only led to more negative responses than did pre-decision voice when the enacting leader was high in confidence. Negative emotions mediated this interaction effect of type of voice on willingness to withdraw. Implications for integrating the leadership and procedural justice literatures are discussed.

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