Rubber bond rupture

In past studies (3), Electron Spin Resonance, ESR, has been used to investigate bond rupture associated with stress-ozone degradation in unsaturated rubbers. It was believed that it might be enlightening to perform similar experiments on plastics ( 5, 8, 10, 11). In the study reported here the combined effects of environment (O3, N02 and S02) and sustained stress on the ultimate properties of Nylon 6 fibers are presented. These agents were found to have a profound effect on strength, toughness and the deformation-bond rupture kinetics. 

ESR has proven to be a very sensitive and Informative means of monitoring bond rupture In rubbers under combined stress and exposure to ozone (4). Ozone attacks the unsaturated bonds In deformed rubber. Such carbon-carbon double bonds are of course found In natural rubber and many other elastomers. All of the gum rubbers that were susceptible to cracking when stressed and tested In an ozone atmosphere exhibited a strong distinct ESR signal. 

Fujimoto, Migita and Kasuya (218) have shown that the ultimate elongation changes little with carbon content, but at fixed strain rate the temperature at which eb (max) is realized increases with black concentration (compare with Fig. 19). The authors suggest that bond rupture occurs mainly in the rubber matrix and scarcely at all at the surface of the carbon black. The greatest proportion of surface bond rupture is thought to occur at eb (max). 

Hanson and Martin applied the same approach to investigate the rupture of isoprene and butadiene oligomers in order to investigate covalent bond rupture in rubber.Using density functional theory, they identified the point of rupture where the unrestricted solution to the Kohn-Sham electronic wave functions falls below the restricted solution. This implies that the rupture process should be heterolytic and so this concept can only be applied for instances in which radical species are formed in the initial rupture event. 

Some of the papers referenced do this for rubber, nylon and tooth dentins. Peterlin, Zhurkov et al. and Becht have also made quantitative measures of bond rupture. In answer to your second question, our experimental evidence (J. Polym. Sci. A-1, 7, 2125 (1969) indicates only a small fraction of the total work of fracture can be attributed to primary bond rupture. The remainder may be attributed to secondary bond rupture, plastic and viscoelastic deformation somewhat analogous to work of plastic deformation at the tip of a crack in metals. 

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 chemical nature of the rubber determines which bonds are the weakest and are therefore more likely to be ruptured during mastication by the statistical concentration of mechanical energy about such bonds. An increase in the degree of asymmetry, an increase in the stiffness and the packing density of macromolecules facilitate mechanical scission resonance stability will influence the... 

Rubber Reclaim. For the traditional rubber "reclaim," crumb rubber is mixed with water, oil, and chemicals and heated under pressure, thus rupturing the carbon-sulfur bonds that cross-link the molecular matrix. The resulting partially devulcanized rubber may be formed into slabs or bales and shipped to manufacturers who process and vulcanize it for use as an alternative to virgin rubber to use in tires or to make mats and other rubber products. 

Low absorptive capacity primary foam dressings have been produced from a carboxylated styrene butadiene rubber latex foam. The foam is bonded to a non-woven fabric coated with a polyethylene film which has been vacuum ruptured. The basic foam is naturally... 

In the burst test a flat sheet of paper is clamped by a cireumferential ring and a small rubber diaphragm underneath is gradually inflated with fluid, foreing the sheet to bulge until it ruptures. The hydrostatic pressure at the moment of failure is measured. The virtues of the burst test are its simplicity and the speed with which it can be undertaken. The reeorded hydraulic pressure offers a quantitative measure of bonding between fibres. It is linearly related to tensile strength. 

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