Chain Scission and Cross-Linking in the Radiation Degradation of Polymers: Limitations on the Utilization of Theoretical Expressions and Experimental Results in the Pregel Region

1979 ◽  
Vol 12 (1) ◽  
pp. 113-119 ◽  
Author(s):  
J. H. O'Donnell ◽  
N. P. Rahman ◽  
C. A. Smith ◽  
D. J. Winzor
Keyword(s):  
Chain Scission ◽  
Experimental Results ◽  
Cross Linking ◽  
Radiation Degradation

EXPERIMENTAL VALIDATION OF THE CHARLESBY AND HORIKX MODELS APPLIED TO DE-VULCANIZATION OF SULFUR AND PEROXIDE VULCANIZATES OF NR AND EPDM

2016 ◽  
Vol 89 (4) ◽  
pp. 671-688 ◽  
Author(s):  
M. A. L. Verbruggen ◽  
L. van der Does ◽  
W. K. Dierkes ◽  
J. W. M. Noordermeer
Keyword(s):  
Experimental Validation ◽  
Main Chain ◽  
Sol Gel ◽  
Chain Scission ◽  
Cross Linking ◽  
Cross Link ◽  
Practical Reality ◽  
Cross Links ◽  
The Cross ◽  
Theoretical Considerations

ABSTRACT The theoretical model developed by Charlesby to quantify the balance between cross-links creation of polymers and chain scission during radiation cross-linking and further modifications by Horikx to describe network breakdown from aging were merged to characterize the balance of both types of scission on the development of the sol content during de-vulcanization of rubber networks. There are, however, disturbing factors in these theoretical considerations vis-à-vis practical reality. Sulfur- and peroxide-cured NR and EPDM vulcanizates were de-vulcanized under conditions of selective cross-link and random main-chain scissions. Cross-link scission was obtained using thiol-amine reagents for selective cleavage of sulfur cross-links. Random main-chain scission was achieved by heating peroxide vulcanizates of NR with diphenyldisulfide, a method commonly employed for NR reclaiming. An important factor in the analyses of these experiments is the cross-linking index. Its value must be calculated using the sol fraction of the cross-linked network before de-vulcanization to obtain reliable results. The values for the cross-linking index calculated with sol-gel data before de-vulcanization appear to fit the experimentally determined modes of network scission during de-vulcanization very well. This study confirms that the treatment of de-vulcanization data with the merged Charlesby and Horikx models can be used satisfactorily to characterize the de-vulcanization of NR and EPDM vulcanizates.

Experimental results on the correlation between cross-linking, polarization and space charge in PMMA

1999 ◽  
Vol 48 (1) ◽  
pp. 5-7 ◽  
Author(s):  
P Notingher ◽  
S Malrieu ◽  
F Du Prez ◽  
F Schué ◽  
A Toureille
Keyword(s):  
Space Charge ◽  
Experimental Results ◽  
Cross Linking

scholarly journals Scission, Cross-Linking, and Physical Relaxation during Thermal Degradation of Elastomers

Polymers ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1280 ◽  
Author(s):  
Zaghdoudi ◽  
Kömmling ◽  
Jaunich ◽  
Wolff
Keyword(s):  
Operating Time ◽  
Thermal Exposure ◽  
Chain Scission ◽  
Cross Linking ◽  
Butadiene Rubber ◽  
Compression Set ◽  
Model Compression ◽  
Relaxation Measurements ◽  
Thermally Driven

Elastomers are susceptible to chemical ageing, i.e., scission and cross-linking, at high temperatures. This thermally driven ageing process affects their mechanical properties and leads to limited operating time. Continuous and intermittent stress relaxation measurements were conducted on ethylene propylene diene rubber (EPDM) and hydrogenated nitrile butadiene rubber (HNBR) samples for different ageing times and an ageing temperature of 125 °C. The contributions of chain scission and cross-linking were analysed for both materials at different ageing states, elucidating the respective ageing mechanisms. Furthermore, compression set experiments were performed under various test conditions. Adopting the two-network model, compression set values were calculated and compared to the measured data. The additional effect of physical processes to scission and cross-linking during a long-term thermal exposure is quantified through the compression set analysis. The characteristic times relative to the degradation processes are also determined.

Effect of Oxygen Concentration on Aging of Rubber Vulcanizates. II. Effect of Partial Pressure of Oxygen on Changes in Physical Properties Accompanying Oxidation

1953 ◽  
Vol 26 (3) ◽  
pp. 643-654 ◽  
Author(s):  
J. Reid Shelton ◽  
William L. Cox
Keyword(s):  
Physical Properties ◽  
Partial Pressure ◽  
Oxygen Concentration ◽  
Chain Scission ◽  
Cross Linking ◽  
Partial Pressure Of Oxygen ◽  
Aging Behavior ◽  
Storage Temperatures ◽  
Normal Storage ◽  
Oxygen Concentrations

Abstract The over-all rate of deterioration of physical properties increases with the oxygen concentration, as would be expected from the increased rate of oxygen absorption: The nature of the deterioration resulting from a given amount of oxygen absorbed is influenced also by changes in the partial pressure of oxygen in the aging atmosphere. It appears that chain scission is favored at higher oxygen concentrations, while cross-linking becomes of greater relative importance at lower oxygen concentrations. These data suggest that R⋅ radicals are more effective than RO2⋅ radicals in reacting with double bonds to form crosslinks. Heat aging in the absence of oxygen, as observed by heating a vulcanizate in lamp-grade nitrogen, results in considerable stiffening, particularly in the case of a GR-S black stock. This effect is observed primarily in the first few hours of heating, and may account for some of the erratic behavior observed in the early stages of aging when changes in physical properties are compared on the basis of amount of oxygen absorbed. Higher oxygen concentration brings about a more rapid oxidation, and also results in a higher proportion of chain scission compared to cross-linking for a given amount of oxygen absorbed. As tensile decay is the most evident sign of deterioration of Hevea stocks, it follows that the aging behavior of natural rubber in air at normal storage temperatures will be better than that predicted by high temperature testing in oxygen. In the case of GR-S stocks, on the other hand, oxidative hardening is the most serious result of aging, and consequently, the aging behavior of GR-S stocks in air at normal storage temperatures is poorer than would be expected on the basis of comparative tests in oxygen at higher temperatures.

Study on the Preparation of Chitosan-Based Resin

2010 ◽  
Vol 160-162 ◽  
pp. 1810-1815
Author(s):  
Jing Xian Li ◽  
Juan Qin Xue ◽  
Ming Wu ◽  
Yu Jie Wang ◽  
Wei Bo Mao
Keyword(s):  
Reaction Time ◽  
Reaction Temperature ◽  
Experimental Results ◽  
Raw Material ◽  
Cross Linking ◽  
Reactant Ratio ◽  
Experimental Conditions ◽  
Stirring Rate ◽  
Formaldehyde Crosslinking ◽  
New Type

With chitosan as the raw material, a new type of resin material is synthesized through formaldehyde crosslinking. The effects of the reactant ratio, the reaction temperature, the reaction time, the stirring rate and the system pH on the cross-linking rate are studied in detail. The resin material is then characterized by means of IR. The experimental results show that the reaction occurs mainly on the amino and the hydroxyl of chitosan. The chitosan-based resin material with good properties of sphericity and acidresistivity can be prepared under the optimal experimental conditions, which are found to be 1:5 for the ratio of chitosan and formaldehyde, 60°C for the temperature, 1 h for the reaction time, 440r/min for the stirring rate and 10 for the pH.

Kinetics of UV Irradiation Induced Chain Scission and Cross-Linking of Coumarin-Containing Polyester Ultrathin Films

2014 ◽  
Vol 47 (9) ◽  
pp. 2891-2898 ◽  
Author(s):  
Jeongwoo Lee ◽  
Murthy V. S. N. Maddipatla ◽  
Abraham Joy ◽  
Bryan D. Vogt
Keyword(s):  
Uv Irradiation ◽  
Ultrathin Films ◽  
Chain Scission ◽  
Cross Linking ◽  
Kinetics Of

Kinetic considerations on the mechanical behaviour of polypropylene + wood flour and polypropylene + sisal fibre blends

e-Polymers ◽  
2004 ◽  
Vol 4 (1) ◽  
Author(s):  
Carmen Albano ◽  
Rebeca Poleo ◽  
Jacobo Reyes ◽  
Miren Ichazo ◽  
Jeanette González ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Mechanical Behaviour ◽  
Wood Flour ◽  
Melt Flow Index ◽  
Degradation Process ◽  
Chain Scission ◽  
Flow Index ◽  
Cross Linking ◽  
Γ Irradiation ◽  
Sisal Fibre

Abstract This work is aimed at analyzing by means of simple mathematical models the effect of different integral doses of γ-irradiation on the mechanical properties and concentration of radicals of the blends of polypropylene (PP) + wood flour and PP + sisal fibre. The analysis of the results permits inferring that the kinetic behaviour of the mechanical properties and the concentration of radicals at low integral doses (≤ 10 KGy) are indicative of a complex degradation process, implying the possibility of cross-linking and chain scission reactions both in the polymer as well as in the filler. Consequently, it can be concluded that cross-linking reactions are predominant. The behaviour observed at higher irradiation doses means that both reactions (cross-linking and chain scission) occur, the breaking reactions being the prevailing ones. This study of the kinetic analysis of the tensile properties is based on the behaviour detected for the melt-flow index.

Degradation of Polymers

1962 ◽  
Vol 35 (5) ◽  
pp. 1157-1221 ◽  
Author(s):  
Leo A. Wall ◽  
Joseph H. Flynn
Keyword(s):  
Ionizing Radiation ◽  
Thermal Degradation ◽  
Natural Rubber ◽  
Ultraviolet Light ◽  
Recent Literature ◽  
Chain Scission ◽  
Experimental Results ◽  
Gel Formation ◽  
Vinyl Polymers ◽  
Kinetic Mechanisms

Abstract Recent literature pertaining to both the theoretical aspects and experimental results of the degradation of polymers by heat and radiation is reviewed and critically evaluated. Theories of random and chain thermal degradation of vinyl polymers and co-polymers are reviewed. The degradation of polymethacrylates, polyacrylates, poly-α-methylstyrene, polyolefins, polystyrene, other vinyl polymers, cellulose, polyesters, polyamides, dienes, natural rubber, and copolymers are discussed in the light of these theories. The thermodynamics and energetics of the degradation of these polymers is also reviewed. Chain scission, crosslinking, and gel formation and the kinetic mechanisms of these processes which take place during degradation of polymers by ionizing radiation and ultraviolet light are included. Degradative, rather than synthetic, effects are emphasized in the discussion.

CHANGES OF CHEMICAL STRUCTURE AND MECHANICAL PROPERTY LEVELS DURING THERMO-OXIDATIVE AGING OF NBR

2013 ◽  
Vol 86 (4) ◽  
pp. 591-603 ◽  
Author(s):  
Jiaohong Zhao ◽  
Rui Yang ◽  
Rossana Iervolino ◽  
Stellario Barbera
Keyword(s):  
Mechanical Property ◽  
Thermal Aging ◽  
Chemical Structure ◽  
Structural Changes ◽  
Elevated Temperatures ◽  
Chain Scission ◽  
Bending Test ◽  
Cross Linking ◽  
Butadiene Rubber ◽  
Oxidative Aging

ABSTRACT The accelerated thermo-oxidative aging of acrylonitrile–butadiene rubber (NBR) was studied at elevated temperatures. The chemical structure characterized by attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) and pyrolysis gas chromatography–mass spectroscopy (PGC-MS) showed the loss of low-molecular-weight additives, such as antioxidants and paraffin, and the formation of carbonyl groups and unsaturated double bonds. The cross-linking degree characterized by NMR and a swelling test showed that aging is a competitive process of cross-linking and chain scission. Cross-linking dominated the thermal aging of NBR most of the time, whereas chain scission began to increase after a long time at high temperatures. The changes of mechanical property magnitudes during thermal aging of NBR were studied by using the recovery from bending test (RFB) and tensile test. By comparing the physical property results and the structural changes, their relationship is discussed.

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