Rupture of rubber

L. Mullins, Rupture of rubber. Part 9. Role of hysteresis in the tearing of rubber, Trans. Inst. Rubber Ind.,... 

Greensmith, H. W. (1956). Rupture of rubber. IV. Tear properties of vulcanizates containing carbon black. J. Pofym. Sci. 21, 175. 

Thomas, A. G. (1958). Rupture of rubber Part 5. Cut growth in natural rubber vulcanizates. J. Polym. Sci. 31,467. 

Figure 11.9 a) Flow lines in the milling zone and b) deformation and rupture of rubber... 

In the lightly cross-linked polymers (e.g. the vulcanised rubbers) the main purpose of cross-linking is to prevent the material deforming indefinitely under load. The chains can no longer slide past each other, and flow, in the usual sense of the word, is not possible without rupture of covalent bonds. Between the crosslinks, however, the molecular segments remain flexible. Thus under appropriate conditions of temperature the polymer mass may be rubbery or it may be rigid. It may also be capable of ciystallisation in both the unstressed and the stressed state. 

A.N. Gent and P.B. Bindley, Internal rupture of bonded rubber cylinders in tension, Proc. R. Soc. (London), A249, 195-205, 1958. 

Among elastomers, artificial rubbers have replaced natural rabber for many uses because of their high resistance to chemical attack by ozone, an atmospheric pollutant. When ozone reacts with polymer chains, it breaks CUCn bonds and introduces additional cross-linking. Breaking 7r bonds causes the rabber to sofien, and cross-linking makes it more brittle. Both changes eventually lead to rupture of the polymer structure. 

The large scale molecular motions which take place in the rubber plateau and terminal zones of an uncross-linked linear polymer give rise to stress relaxation and thereby energy dissipation. For narrow molecular weight distribution elastomers non-catastrophic rupture of the material is caused by the disentanglement processes which occur in the terminal zone, e.g., by the reptation process. In practical terms it means that the green strength of the elastomer is poor. 

In unfilled rubbers, which are not capable of strain-induced crystallization, the upturns on Mooney-Rivlin curves have shown to be absent 92 95). They disappear also in crystallizable rubbers at elevated temperatures and in the presence of solvents. On the other hand, the upturns do not appear for butadiene, nitrile and polyurethane rubbers if the limited chain extensibility function is introduced in the Mooney-Rivlin expression 97). Mark 92) has concluded that in the absence of selfreinforcement due to strain-induced crystallization or domains the rupture of the networks occurs long before the limited chain extensibility can be reached. 

Direct experimental observation of the rupture of agglomerates in uncured styrene-co-butadiene rubber (SBR) in simple shear flow was obtained by Collin and Peuvrel-Disdier (48), supporting the previously discussed mechanism. It is shown on Fig. 7.27. The shear rate was 6 s 1, yielding a shear stress of 130,000 Pa s. The agglomerate is broken into two large, about equal-sized pieces with some debris, and separated. 

Gaskets in both dry gas and liquid chlorine systems are made of rubberized compressed asbestos. For wet chlorine gas, rubber or synthetic elastomers are acceptable. PTFE is resistant to both wet and dry chlorine gas and to liquid chlorine up to 200 °C. Tantalum, Hastelloy C, PTFE, PVDF, Monel, and nickel are recommended for membranes, rupture disks, and bellows. 

As demonstrated in Figure 2, the specific volume of PC increases notably when crazes II are initiated, resulting in a loss in density of approximately 8% at the rupture of the specimen. This is comparable to that found for high impact polymers where the number of crazes is increased artificially by the incorporation of rubber particles. 

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