Pyrolysis-mass spectrometry correlations of crosslink density in natural rubber vulcanizates

Abstract Kinetics of crosslinking and network changes in unfilled and filled natural rubber vulcanizates with a dithiodimorpholine based accelerator system have been studied at 150° and 180°C. Results show that addition of HAF black enhances the polysulfidic crosslinks as well as the total crosslinks. This has been explained with the help of Coran's model wherein HAK black increases the rate constants. It is likely that the filler surface prevents desulfuration and undesirable side reactions involving the crosslink precursors. Increase of curing temperature by 30°C lowers the total crosslink density and increases the sulfur inefficiency.

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Effect of Crosslink Density on Cut Growth in Black-Filled Natural Rubber Vulcanizates

Rubber Chemistry and Technology ◽

10.5254/1.3547693 ◽

2002 ◽

Vol 75 (5) ◽

pp. 935-942 ◽

Cited By ~ 20

Author(s):

G. R. Hamed ◽

N. Rattanasom

Keyword(s):

Carbon Black ◽

Natural Rubber ◽

Crack Growth ◽

Crosslink Density ◽

Longitudinal Crack ◽

Test Pieces ◽

Filled Rubber ◽

Longitudinal Cracks ◽

Natural Rubber Vulcanizates ◽

High Crosslink Density

Abstract Tensile strengths, σb, of gum and N115-filled natural rubber test pieces, with and without edge pre-cuts, have been determined. At low crosslink density, the regular (uncut) σb of filled and gum vulcanizates is similar. However, at high crosslink density, the gum NR becomes brittle, while the corresponding filled rubber remains strong and resistant to cut growth. It is proposed that the tightly linked gum does not strain-crystallize appreciably during stretching, but that its filled counterpart does. Carbon black appears capable of inducing crystallization in a network that alone remains amorphous during extension. Filled vulcanizates of various crosslink densities have similar normal tensile strengths ( ≈ 30 MPa), but strengths differ, sometimes more than twofold, if a pre-cut is present. Lightly crosslinked specimens containing a small cut have strengths that depend very weakly on cut size, c. Furthermore, these develop long longitudinal cracks from which catastrophic rupture initiates. With larger cuts, strength decreases more rapidly with increasing c, there is less longitudinal crack growth, and rupture initiates near the original cut tip. In contrast, the strength of a highly crosslinked vulcanizate is sensitive to small cuts and test pieces exhibit minimal longitudinal cracking before failure.

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Reinforcing Effect of Silica and Silane Fillers on the Properties of Some Natural Rubber Vulcanizates

Rubber Chemistry and Technology ◽

10.5254/1.3547803 ◽

2003 ◽

Vol 76 (5) ◽

pp. 1290-1310 ◽

Cited By ~ 22

Author(s):

A. Ansarifar ◽

R. Nijhawan ◽

T. Nanapoolsin ◽

M. Song

Keyword(s):

Natural Rubber ◽

Crosslink Density ◽

Cyclic Fatigue ◽

Rubber Matrix ◽

Stored Energy ◽

Elongation At Break ◽

Reinforcing Effect ◽

Bound Rubber ◽

Technical Properties ◽

Natural Rubber Vulcanizates

Abstract The reinforcing effect of up to 6 parts per hundred rubber by weight (phr) bis- (3-triethoxysilylpropyl) tetrasulfide (TESPT), a bifunctional organosilane, on the crosslink density, bound rubber, and technical properties of some conventional accelerator/sulfur compounds of natural rubber, containing 30 phr precipitated amorphous white silica was studied. The crosslink density and bound rubber improved as a function of TESPT loading. The tensile strength, elongation at break, stored energy density at rupture, and cohesive tear strength deteriorated at low loading of TESPT, but they subsequently increased after the full amount of TESPT was introduced into the compound. The improved properties of the vulcanizate was due to the better dispersion of the filler in the rubber matrix. However, the cyclic fatigue life was adversely affected, and the hardness hardly changed as a result of adding TESPT to the rubber.

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Influence of Crosslink Density on Mechanical Properties of Natural Rubber Vulcanizates

Journal of Macromolecular Science Part B ◽

10.1080/00222348.2010.507453 ◽

2011 ◽

Vol 50 (7) ◽

pp. 1460-1469 ◽

Cited By ~ 49

Author(s):

Fei Zhao ◽

Weina Bi ◽

Shugao Zhao

Keyword(s):

Mechanical Properties ◽

Natural Rubber ◽

Crosslink Density ◽

Natural Rubber Vulcanizates

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EFFECT OF CURE EFFICIENCY ON PROPERTIES OF GUM AND BLACK FILLED NATURAL RUBBER VULCANIZATES

Rubber Chemistry and Technology ◽

10.5254/1.3577535 ◽

2011 ◽

Vol 84 (2) ◽

pp. 229-242 ◽

Cited By ~ 1

Author(s):

Gary R. Hamed ◽

Kanoktip Boonkerd

Keyword(s):

Electron Microscopy ◽

Tensile Strength ◽

Natural Rubber ◽

Crosslink Density ◽

Cure Time ◽

Cracking Pattern ◽

Natural Rubber Vulcanizates ◽

Scanning Electron ◽

Fracture Specimens ◽

Strength Effect

Abstract Effects of the sulfur cure efficiency on the reversion behavior and the normal and edge-cut tensile strength of gum and black filled natural rubber (NR) vulcanizates were studied. N, N-dicyclohexyl-2-benzothiazole sulfenamide (DCBS) was used as an accelerator. A series of five vulcanizates with high to low cure efficiencies was prepared by increasing the sulfur (S) to DCBS ratios within the range of 0.26–6.66. All vulcanizates were formulated to have the same crosslink density. The degree of reversion (%) calculated from cure curves of gum and black filled NR at 20 min above the cure time (tc100) passed through maximum with decreasing cure efficiencies. For both gum and black filled NR, the highest degree of reversion (%) was observed at the S/DCBS ratio of 1.17. The normal tensile strengths of gum and black filled NR were directly proportional to the cure efficiency. For gum NR vulcanizates, the edge-cut tensile strength was markedly influenced by cure efficiency. Similar to the normal tensile strength, the gum NR vulcanizates cured with the lowest cure efficiency showed the lowest edge-cut tensile strength. Effect of the cure efficiency on the edge-cut tensile strength was less in the case of black filled NR vulcanizates. However, the black filled NR vulcanizates cured with the lowest cure efficiency also showed the lowest edge-cut tensile strength. The cut tip characteristics of the fracture specimens were investigated using scanning electron microscopy. The gum specimens showed only the simple lateral cracking pattern, while all black filled specimens showed the longitudinal cracking pattern. Four different cracking patterns of the black filled specimens were identified. The distribution of cracking patterns depended strongly on the size of precut and the cure efficiency.

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