Radiation-induced changes in the structure of polypropylene

1959 ◽  
Vol 253 (1274) ◽  
pp. 322-330 ◽  
Keyword(s):  
Main Chain ◽  
High Energy ◽  
Theoretical Expression ◽  
Cross Linking ◽  
Gel Point ◽  
High Energy Radiation ◽  
Infra Red ◽  
Radiation Induced ◽  
Induced Changes ◽  
Good Agreement

Polypropylene undergoes both cross-linking and random main-chain fracture when exposed to high-energy radiation, the ratio of cross-linking to chain fracture varying with the dose received up to the gel point. An examination of the infra-red absorption spectrum of the irradiated polymer has shown that, in addition, vinylidine unsaturation ( R . R' /C=CH 2 ) is formed in the ratio of one vinylidene double bond to each chain fracture. The rate of main-chain fracture deduced from intrinsic viscosity measurements has been found to be initially (up to a dose of 35 Mrad) a function of the number of chain fractures produced, rather than proportional to the intensity of the radiation, as might have been expected from the behaviour of other polymers. After a dose of 50 to 60 Mrad an insoluble cross-linked gel can be separated from the polymer by solvent extraction, and the sol fraction decreases on further irradiation in accordance with the theoretical expression derived by Charlesby (1953), assuming that for every cross-link formed, one bond between two monomer units is broken. A mechanism for the radiation-induced changes is proposed, based upon the application of classical chemical kinetics, which is in good agreement with the observed phenomena.

High-Energy Radiation-Induced Changes in the Crystal Morphology of Cellulose

2004 ◽  
Vol 37 (7) ◽  
pp. 2668-2670 ◽  
Author(s):  
Frederick G. Morin ◽  
Byron D. Jordan ◽  
Robert H. Marchessault
Keyword(s):  
Crystal Morphology ◽  
High Energy ◽  
High Energy Radiation ◽  
Energy Radiation ◽  
Radiation Induced ◽  
Induced Changes

Radiation-Induced Crosslinking of Chlorobutyl and Polydiene Elastomers. Promotion by Polythiols

1975 ◽  
Vol 48 (5) ◽  
pp. 860-877 ◽  
Author(s):  
R. L. Zapp ◽  
A. A. Oswald
Keyword(s):  
Chain Scission ◽  
High Energy ◽  
Cross Linking ◽  
Crosslinking Reaction ◽  
High Energy Radiation ◽  
Dose Rates ◽  
Radiation Cure ◽  
60Co Source ◽  
Wide Range ◽  
Radiation Induced

Abstract The response of Chlorobutyl (CIIR), an elastomer with 1,1-disubstituted carbon atoms along the polymer chain, to ionizing radiation has been directed toward a predominantly crosslinking reaction by addition of 1–4 phr of thioetherpolythiols (TEPT) prepared by reaction of trivinylcyclohexane or cyclododecatriene with H2S or low-molecular-weight dithiols. From a fundamental viewpoint, the unique feature of the CIIR-TEPT system is the reversal of expected behavior for a polymer molecule containing 1,1-disubstituted carbon atoms when exposed to high energy radiation: instead of chain scission, cross-linking is the predominant physical change to an extent comparable to that obtained from thermal curing processes. The TEPT becomes part of the radiation-cured network, for, as the radiation dose is increased, there is progressive addition of thiol sulfur to the crosslinked network. Concomitantly, there is a progressive reduction in the chlorine content as radiation-induced vulcanization proceeds. These polythiols are also powerful accelerators of radiation-induced cross-linking of polydiene elastomers, especially those with appreciable amounts of pendent vinyl unsaturation, such as conventional SBR. Evidence exists that a blend of CIIR and SBR can be covulcanized by radiation-induced curing in the presence of TEPT. Experiments were conducted with gamma radiation from a 60Co source and with a 1.4 MeV electron beam at dose rates of 20–120 kJ/kg (2–12 megarads). Physical properties of fully compounded polythiol-promoted CIIR systems crosslinked by radiation are lower than comparable thermally cured compounds, but the strengths would be adequate for many applications. Compounding ingredients, especially common accelerators of sulfur vulcanization, provide a wide range of inhibitory action toward radiation precure. However, with selected types, especially organometallic derivatives which are less soluble in the compound, radiation cure can proceed with a minimum of inhibition.

A theory of network formation in irradiated polyesters

1957 ◽  
Vol 241 (1227) ◽  
pp. 495-507 ◽  
Keyword(s):  
Network Formation ◽  
High Energy ◽  
Cross Linking ◽  
Gel Point ◽  
Radiation Doses ◽  
Chain Reaction ◽  
High Energy Radiation ◽  
Inhibiting Factor ◽  
A Chain ◽  
Reacting Systems

Many polyester systems may be converted to insoluble materials when subjected to high-energy radiation. The radiation doses required are far lower than would be predicted on the theory of random cross-linking, indicating that the process involved is a chain reaction, acting through double bonds. Present theories of network formation are not applicable to such reactions. A mathematical analysis is given, applicable to a chain reaction the extent of which is limited by an inhibiting factor. The gel point and the solubility are deduced as functions of the cross-linking index and the inhibitor activity, for molecules of various sizes and distributions. These results are then related to the radiation dose. The model proposed may be applicable to chain reacting systems in which the reaction is not terminated by the interaction of two growing chains.

The cross-linking and degradation of paraffin chains by high-energy radiation

1954 ◽  
Vol 222 (1148) ◽  
pp. 60-74 ◽  
Keyword(s):  
Melting Point ◽  
Physical State ◽  
Main Chain ◽  
High Energy ◽  
Cross Linking ◽  
Cross Link ◽  
High Energy Radiation ◽  
The Cross ◽  
Solid Liquid ◽  
Α Particles

n -Paraffins from C 7 H 16 to C 36 H 74 and polyethylene polymers (Polythene and Winnothene) have been subjected to atomic pile radiation. For the paraffins there is a decrease in the melting-point, until, for a radiation dose R , they no longer melt at temperatures of 160° C or above. At about this same radiation the paraffin is turned into an insoluble gel. The product Rn ρ, where n is the number of carbons per atom, and ρ the density, is approximately constant from heptane (n = 7) to Polythene (n ~ 2000), although an anomaly may occur for Winnothene (n ~ 250). This indicates that the energy required to form a cross-link is approximately independent of chain length. An analysis of published experiments on methane and butane extends this conclusion down to n = 1. The results obtained by earlier workers when paraffinic gases are bombarded with deuterons and α-particles are explained in terms of the cross-linking phenomenon. Solubility measurements give similar values for Rn ρ in the case of Polythene and Winnothene, and show that for every cross-link formed, on the average about 0·35 C—C bonds in the main chain are fractured. Similar values are obtained for methane and butane. The energy absorbed per C—H bond fracture is about 12 eV, and the energy per cross-link is 24 eV. This corresponds to 0·5 % of carbons becoming cross-linked per unit radiation, independent of the physical state (solid, liquid or gaseous) of the irradiated paraffin. The importance of these results, as far as polymerization theory is concerned, is briefly discussed.

Radiation induced changes in the structure of poly iso butylene

1955 ◽  
Vol 232 (1188) ◽  
pp. 31-48 ◽  
Keyword(s):  
Absorption Spectrum ◽  
Main Chain ◽  
Average Energy ◽  
Ultra Violet ◽  
Chemical Mechanism ◽  
High Radiation ◽  
Infra Red ◽  
Radiation Induced ◽  
Induced Changes ◽  
The Relationship

Poly iso butylene suffers random main-chain fracture when exposed to high radiation. Identical results are produced by electron and γ -radiation and the average energy absorbed per break amounts to 20 eV at 20° C. The unsaturation produced is proportional to the number of breaks. A new absorption band appears in the infra-red at 11.25 μ , which indicates that a vinyl double bond of the type R 1 R 2 C═CH 2 has been introduced. The gases evolved on irradiation have been analyzed. A chemical mechanism for the degradation has been proposed. The energy per break varies with temperature, the relationship being somewhat similar to the inactivation behaviour of ionizing radiation on certain biological systems. The ultra-violet absorption spectrum is different for polymers which have been irradiated in vacuum or nitrogen from those irradiated in air but the number of main-chain breaks is not affected by the surrounding gas.

scholarly journals Modification of ethylene-norbornene copolymer by Gamma irradiation

2006 ◽  
Vol 60 (11-12) ◽  
pp. 311-315 ◽  
Author(s):  
Zorica Kacarevic-Popovic ◽  
Bojana Secerov ◽  
Milena Marinovic-Cincovic ◽  
Zoran Nedic ◽  
Slobodan Jovanovic
Keyword(s):  
Gamma Irradiation ◽  
Radiation Chemistry ◽  
High Energy ◽  
Spectrophotometric Analysis ◽  
New Combination ◽  
Polymeric Systems ◽  
New Class ◽  
Radiation Induced ◽  
Dsc Method ◽  
Induced Changes

The possibility of modifying polyethylene and many other polymers with high energy radiation has led to many useful applications. Due to their new combination of properties and the shortage of experimental data, the radiolysis of a new class of materials, cyclo-olefin copolymers (COC), polymerised from norbornene and ethylene using metallocene catalysts, is of great interest to the study of radiation chemistry and the physics of polymeric systems. Ethylenenorbornene copolymer, pristine and containing an antioxidant were subjected to gamma irradiation in the presence of air and in water. The irradiated copolymer was studied using IR and UV-vis spectrophotometric analysis. The radiation-induced changes in the molecular structure were correlated to changes in the glass transition temperature measured by the DSC method.

High energy radiation induced degradation of reactive yellow 145 dye: A mechanistic study

2020 ◽  
Vol 177 ◽  
pp. 109115
Author(s):  
Majid Muneer ◽  
Muhammad Imran Kanjal ◽  
Muhammad Saeed ◽  
Tariq Javed ◽  
Atta Ul Haq ◽  
...  
Keyword(s):  
High Energy ◽  
Mechanistic Study ◽  
High Energy Radiation ◽  
Energy Radiation ◽  
Radiation Induced
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