General Properties
Short Name:
Name:
NR
Natural rubber
NR is a natural product and is produced from the white milky juice (latex) of the rubber tree. The artificially manufactured kind is designated isoprene rubber (IR) and is made up of isoprene (2-methyl-1,3-butadiene) as a monomer. NR is an entirely 1,4 cis isomer. The 1,4 polyisoprene is also a natural product called gutta-percha. For more on cis-trans isomerism. Carbon black is often added in order to increase the tensile strength and abrasion resistance of the material, as well as for coloring.
Structural Formula
Properties
| Glass Transition Temperature | -72 to -55°C |
|---|---|
| Melting Temperature | 25 to 40°C |
| Melting Enthalpy | 67 J/g |
| Decomposition Temperature | 375 to 400°C |
| Young's Modulus | 1 to 5 MPa |
| Coefficient of Linear Thermal Expansion | 180 to 260 *10-6/K |
| Specific Heat Capacity | 1.91 to 2.08 J/(g*K) |
| Thermal Conductivity | 0.13 to 0.15 W/(m*K) |
| Density | 0.91 to 0.93 g/cm³ |
| Morphology | Amorphous rubber, partly with hard segments |
| General properties | High stability and high elasticity. High elongation at break. Good abrasion resistance |
| Processing | Cross-linking by means of sulfur incl. accelerator (e.g., mercaptobenzothiazole or sulfenamide) and activator (zinc oxide and stearic acid) |
| Applications | Tire industry. Technical rubber goods (e.g., rubber springs, band conveyors). Medical engineering. Toys. Shoe soles |
NETZSCH Measurement
| Instrument | DSC 204 F1 Phoenix® |
| Sample Mass | 13.00 mg |
| Isothermal Phase | 7 min |
| Heating/Colling Rates | 10 K/min |
| Crucible | Al, pierced lid |
| Atmosphere | N2 (40 ml/min) |
Evaluation
Natural rubber (NR) is mainly amorphous with a small amount of crystalline (hard) segments. This can be seen from the glass transition step at -63°C (2nd heating, red, midpoint) which is overlapped by an enthalpy RelaxationWhen a constant strain is applied to a rubber compound, the force necessary to maintain that strain is not constant but decreases with time; this behavior is known as stress relaxation. The process responsible for stress relaxation can be physical or chemical, and under normal conditions, both will occur at the same time. relaxation, and from the shallow, broad melting transition between -10°C and 50°C (peak temperature: approx. 28°C, 2nd heating) with a heat of fusion of only 1.5 J/g. An even smaller melting enthalpy of 0.5 J/g was observed in the 1st heating (blue).