Sometimes users may only ask for how long the vulcanized compound can be pulled without breaking. This is another essential material property in stress-strain testing of standard dumbbell specimens as specified by ASTM and ISO. The following protocols may help formulators meet user needs.
1. SBR
SBR polymerized by emulsion at -10 °C instead of 50 °C can give the compound better tensile elongation.
2. NR
Among the various grades of NR, plasticized natural rubber CV60 rubber has the highest tensile elongation.
3. Neoprene and fillers
In neoprene formulations, inorganic fillers with large particle size rather than small particle size should be used to improve the elongation of the tensile break. In addition, replacing reinforced or semi-reinforced carbon black with hot cracking carbon black can improve the elongation of the tensile break.
4. TPE and TPV
Thermoplastic elastomers and thermoplastic vulcanizates tend to be anisotropic, especially for injection molded elastomers at high shear rates, where tensile elongation and tensile strength depend on the direction of their processing flow.
5. Carbon black
The use of carbon black with low specific surface area and low structure and reduced filling amount of carbon black can improve the tensile elongation of the compound.
6. Talcum powder
Replacing the same amount of carbon black with small particle size talc can improve the tensile elongation of the compound, but has little effect on the tensile strength and may increase the modulus at low strain.
7. Sulfur vulcanization
An outstanding advantage of sulfur compared with peroxide vulcanization is that it can make the rubber material have a higher tensile elongation. Generally, high-sulfur vulcanization systems can impart better tensile elongation to the compound than low-sulfur vulcanization systems.
8. Gel
Synthetic adhesives like SBR generally contain stabilizers. However, mixing SBR compounds at temperatures above 163°C can produce loose gels (which can be rolled open) and compact gels (which cannot be rolled open and are not soluble in certain solvents). Both gels reduce the tensile elongation of the compound, so the mixing temperature of the SBR must be treated with caution.
9. Mixing
Compounding improves the dispersion of carbon black, which helps to improve the tensile elongation of the compound.
10. Effects of molecular weight
For NBR raw rubber, the use of low mooney viscosity and low molecular weight can improve the elongation of the tensile break. Emulsion SBR, dissolved SBR, BR and IR are also suitable for this.
11. Degree of vulcanization
In general, the low degree of vulcanization can lead to a high tensile elongation of the compound.
