Vulcanized stress

Fig. 38. Stress—relaxation curve for a lightly vulcanized rubber (242). To convert Pa to dyn/cm, multiply by 10.

Microstructure. Whereas the predominate stmcture of polychloroprene is the head to tail /n7 j -l,4-chloroprene unit (1), other stmctural units (2,3,4) are also present. The effects of these various stmctural units on the chemical and physical properties of the polymer have been determined. The high concentration of stmcture (1) is responsible for crystallization of polychloroprene and for the abiUty of the material to crystallize under stress. Stmcture (3) is quite important in providing a cure site for vulcanization, but on the other hand reduces the thermal stabiUty of the polymer. Stmctures (3),(4), and especially (2) limit crystallization of the polymer. 

NR adhesives perform adequately under peeling stresses. The peel strength can vary from a few N/m in PSA formulations to substrate tear in vulcanized compounds used in hose, belting and tire products. 

Figure 9 Stress-strain curves for EPDM, vulcanized EPDM, Zn-SEPDM ionomer, and 50/50 blend of Zn-SEPDM and ZnSt2-...

Based on this analysis it is evident that materials which are biaxially oriented will have good puncture resistance. Highly polar polymers would be resistant to puncture failure because of their tendency to increase in strength when stretched. The addition of randomly dispersed fibrous filler will also add resistance to puncture loads. From some examples such as oriented polyethylene glycol terephthalate (Mylar), vulcanized fiber, and oriented nylon, it is evident that these materials meet one or more of the conditions reviewed. Products and plastics that meet with puncture loading conditions in applications can be reinforced against this type of stress by use of a surface layer of plastic with good puncture resistance. Resistance of the surface layer to puncture will protect the product from puncture loads. An example of this type of application is the addition of an oriented PS layer to foam cups to improve their performance. 

Very frequent are the cases of stress-induced crystallizations. A typical case is that of slightly vulcanized natural rubber (1,4-m-polyisoprene) which, under tension producing a sufficient chain orientation, is able to crystallize, while it reverts to its original amorphous phase by relaxation [75],... 

Figure 7.11 Stress relaxation curve for vulcanized natural rubber showing characteristic upswing at higher stresses...

Most of the sole materials in shoe manufacturing are made of non vulcanized thermoplastic (TR) and sulfur-vulcanized styrene-butadiene mbbers (SBRs), and adhesion is a cmcial industrial demand, as the stresses supported by shoes during use are by far more exigent than in many other... 

Produce stress-free moldings eliminating product distortion and warping after vulcanization... 

Fig. 83.—Stress-strain curve for gum-vulcanized natural rubber. The tensile force given on the ordinate axis is referred to the initial cross section.

Fig. 90.—The force of retraction at 25°C and its internal energy component for gum-vulcanized GR-S synthetic rubber. Upper curve, total force / middle curve, dE/dL)T,p from the intercepts of force-temperature plots at constant length lower curve, dE/dL)T.v from the intercepts of stress-temperature plots at constant elongation. (Roth and Wood. )...

EXPERIMENTAL STRESS-STRAIN BEHAVIOR OF VULCANIZED RUBBERS AT MODERATE ELONGATIONS... 

Fig. 96.—Theoretical and experimental stress-strain curves for simple elongation of gum-vulcanized rubber. (Treloar. )...

Anthony, Caston, and Guth obtained considerably better agreement between the experimental stress-strain curve for natural rubber similarly vulcanized and the theoretical equation over the range a = 1 to 4. KinelP found that the retractive force for vulcanized poly-chloroprene increased linearly with a — l/a up to a = 3.5. 

Similar results have been obtained for natural rubber vulcanized in like manner. Here also the observed equilibrium stress tends... 

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