Vulcanizate, gum

Figure 4. BR + IR is a 50/50 (wt) blend of synthetic cis-1,4-polyisoprene and cis-1,4-polybutadiene. Bl copolymers are random cis-1,4-butadiene-isoprene copolymers with the same composition. Results obtained with Rheovibron on gum vulcanizates at 110 Hz frequency.

Figure 10. X-ray diffraction pattern of BPR, gum vulcanizate. Extension ratio,...

Chloroprene rubber (CR) is well known for its high gum vulcanizate strength arising from strain-induced crystallization. The uncured rubber also shows storage hardening due to slow crystallization. It has excellent physical properties, weather... 

For both EPDM-LDH and XNBR-LDH nanocomposites, the various tensile properties are summarized in Table 13 and their typical stress-strain plots are shown in Fig. 58 [104]. In Fig. 58a, the gum vulcanizates of both rubber systems showed typical NR-like stress-strain behavior with a sharp upturn in the stress-strain plot after an apparent plateau region, indicating strain-induced crystallization. With the addition of LDH-C10 in the XNBR matrix, the stress value at all strains increased significantly, indicating that the matrix undergoes further curing (Fig. 58b). 

Fig. 58 Typical stress-strain plots of EPDM and XNBR gum vulcanizates (a), XNBR-LDH nanocomposites (b), and EPDM-LDH nanocomposites (c) [104]...

Figure 8-8. Stress strain curve for pure gum vulcanizate illustrating the difference in stress between the inside (A) and outside (B) circumference of ring test piece...

Figure I. Correlation between the relative tensile strength (TS)/(TS)0 or the time for the crack formation of NR gum vulcanizates, t and the oxidation potential of the amine used (see Table II)...

Figure 8. Relative tensile strength of IIR gum vulcanizate, (TS)/(TS)0 vs. the radical reactivity index of the amine compounded, Sr. Aging condition 100°C. for 48 hours...

Figure 11. Correlation between the time, tc, for the crack formation of NR gum vulcanizate and the nucleophilic reactivity index of the amine compounded, Sn (see Figure 1)...

The inherent strength and resilience properties simplify the matching of the rubber to the application. Where optimum elastic properties are required, the rubber can be used in essentially unfilled (gum) vulcanizate form. If fillers are required non-reinforcing types can often be used, instead of the reinforcing fillers that are essential for low-strength rubbers. 

Addition of fillers can dramatically change mechanical properties of elastomer materials. For example, a pure gum vulcanizate of general purpose styrene-butadiene rubber (SBR) has a tensile strength of no more then 2.2 MPa but, by mixing in 50 parts per hundred weight parts of rubber (p.p.h.r) of a active CB, this value rises more than 10 times to 25 MPa. How CB, being fine powder of practically no mechanical strength, can make reinforcement in rubbers, similar to... 

Table 18.11 Cure characteristics of gum vulcanizate (NR) and its ceramic composites (MODIFIED). (Reproduced from ref. 124 with...

Properties. The mechanical properties of E-SBR vulcanizates depend on the type and level of filler in the compound. Unfilled gum vulcanizates have very poor tensile strength and ultimate elongation, because the rubber lacks self reinforcing of the type found NR rubber vulcanizates, i.e., strain-induced crystallization. This inadequacy is offset by the addition of reinforcing fillers, i.e., carbon black or chemically coupled silica. At optimum loadings with reinforcing carbon black, mechanical properties similar to those of NR can be achieved. However, NR compounds exceed SBR compounds in tear strength because of NR s strain-induced crystallization. 

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