Influence of internal strain on change of crosslink density of natural rubber vulcanizates by thermal ageing

Elastomers and Composites

Kim²

2013

Self Cite

ABSTRACT：Unfilled, carbon black-filled, and silica-filled natural rubber (NR) composites were aged with a circular deformation at 60 -90℃ and the recovery behaviors were investigated. The samples were aged under the altering aging medium systems of air and distilled water every day for 10 days. The order of the recoveries according to the filler systems was unfilled > silica > carbon black. The recoveries of the samples aged in the air to water altering system were greater than those of the samples aged in the water to air altering system. The initial aging medium dominantly influenced the deformation level. Ⅰ. IntroductionRubber components have been used for sealants and isolators because rubber material has a recovery property to return to its original shape from deformation. 1 Testing methods to examine the recovery behaviors of a rubber composite are compression set test 2 , compression stress relaxation (CSR) 3,4 , and circular deformation test [5][6][7][8][9][10][11] . Compression set test according to the ISO 815 (Rubber, vulcanized or thermoplastic-Determination of compression set at ambient, elevated or low temperatures) is a common method to measure the degree of deformation of a rubber composite under compression state. However, specimens for the compression set are relatively thick (28.7 mm diameter and 12.7 mm height) and many samples are required for aging experiments so that differences in the initial states of the samples such as dimensions and crosslink densities cannot be negligible. In sealing applications, stress relaxation of a polymeric seal after assembly directly reduces the sealing force. Stress relaxation tests are gaining greater relevance for the determination of rubber properties. However, CSR also needs a special equipment for the test and it is not convenient.The circular deformation test method is a simple and reliable method to investigate the recovery behaviors of a rubber article such as the degree of permanent deformation, instantaneous recovery, and recovery rate, because thin specimens with 2 mm thickness in uniform states are used. [5][6][7][8][9][10][11] And it is also a suitable testing method for an aging experiment under various aging media such as water and organic solvents, because the specimen is small and a special equipment is not needed for aging experiment. This method just requires changing a linear sample to a circular form by fixing both ends with a pin to investigate the recovery behaviors of a rubber article. When a linear sample of a vulcanized rubber is circularly deformed, the stress and strain vary uniformly across the thickness of the sample. 9 If states of a rubber composite such as crosslink density,

Section: Resultsmentioning

confidence: 99%

“…Previous studies provide a detailed description of the circular deformation test. [8][9][10][11][12][13][14] Experiments were performed three times and averaged.…”

Section: Aging Processmentioning

confidence: 99%

Section: ⅰ Introductionmentioning

confidence: 99%

Section: ⅰ Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Recovery Behaviors of Natural Rubber Composites Thermally Aged in Altering Medium Systems of Air and Water

Elastomers and Composites

Kim²

2013

Self Cite

“…Crosslink density of a rubber vulcanizate is changed by thermal aging. 4,[17][18][19][20] In general, when sulfur-cured rubber vulcanizates are thermally aged, the crosslink densities increase and the degree also increases as the aging temperature and time increase. [21][22][23] Crosslink density change by thermal aging is also one of reasons about permanent deformation of a rubber vulcanizate.…”

Section: ⅰ Introductionmentioning

confidence: 99%

Thermal Aging Behaviors of Weather Resistant Rubber Composites of EPDM, IIR, and BIIR

Elastomers and Composites

Kim²

2012

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ABSTRACT：EPDM, IIR, and BIIR composites were thermally aged and the crosslink density changes were investigated. Crosslink densities of the EPDM composite increased with increasing the aging time and temperature, whereas those of IIR and BIIR composites for long-term aging at high temperatures tended to decrease. Activation energies for the crosslink density changes of the EPDM composite were higher than those of the BIIR one. The experimental results were explained with the number of allylic hydrogens, activation of the zinc complex, the steric hindrance effect, and oxidation of rubber chain. Ⅰ. IntroductionR group rubbers such as natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), and acrylonitrilebutadiene rubber (NBR) have unsaturated hydrocarbon (C=C double bond) backbones. Due to the C=C double bond backbones, they have lots of allylic hydrogens which participate in sulfur crosslinking reaction. 1 Hence, degrees of crosslink density changes of the R group rubber composites by themal aging are relatively high, and their physical and chemical properties are also changed. 2-10 Of R group rubbers, isobutene-isoprene rubber (butyl rubber, IIR) has relatively good thermal resistance properties since it has only isoprene content with less than 3 wt%. 11,12 Crosslink type and degree of crosslink density of a rubber vulcanizate determine the physical properties such as modulus, hardness, resilience, elongation at break, heat build-up, and so forth. 13 Sulfide linkages, especially polysulfides, are dissociated by heating 14,15 and this brings about decrease of the crosslink density. Curatives, especially sulfur, in rubber vulcanizates make new crosslinks 16 and this results in increase of the crosslink density. Crosslink density of a rubber vulcanizate is changed by thermal aging. 4,[17][18][19][20] In general, when sulfur-cured rubber vulcanizates are thermally aged, the crosslink densities increase and the degree also increases as the aging temperature and time increase. [21][22][23] Crosslink density change by thermal aging is also one of reasons about permanent deformation of a rubber vulcanizate. [21][22][23] Brown and coworkers reported physical property changes of rubber composites after natural aging for 40 years and compared with the accelerated heat aging results. 24,25 Relative deviations for the physical property changes of naturally aged rubber vulcanizates were very big but the results were valuable. The big deviation of the physical property may be due to the difference in the initial states of the samples. A number of samples are needed to measure physical properties and to perform thermal aging for a long time. Sample size should be small to minimize the experimental errors, but relatively large sample size for measurement of the physical properties should

Recovery prediction of thermally aged chloroprene rubber composite using deformation test

J of Applied Polymer Sci

Han

2008

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The recovery prediction of chloroprene rubber (CR) composite from deformation was studied using the conventional compression set test and the circular deformation method to change a linear specimen into a circular shape. The CR composite was thermally aged at 60, 70, 80, 90, and 100C for 1, 6, 15, and 30 days. The recovery was measured as a function of the measuring time (or releasing time) from the compressed or circular deformation. For the compression set test, because the recovery decreased and then increased as the measuring time elapsed, it was not reasonable to calculate the instantaneous recovery from the curve fitting equation. For the circular deformation method, the recovery was continuously increased by increasing the measuring time. The linear correlation for curve fitting was very high and the instantaneous recovery was obtained from the linear curve fitting equation. The half instantaneous recovery time at room temperature could be predicted from the experimental results of the accelerated thermal aging test.