Natural rubber NR:
Composing:
Production of the natural product begins at the plantation where a slit is made into the bark of the rubber tree to allow the flow of a milky sap. This latex consists of water, polyisoprene, and small quantities of other ingredients such as proteins and carbohydrates. It is collected and coagulated with formic acid in large tanks. The coagulum is then squeezed between rollers, to remove excess water and dried. Much of it is then baled and shipped off to the rubber processor.

Although the chemical building block of the polymer is always the same, polyisoprene, NR is available in many grades related to its 'dirt' content (remember it comes from a tree) and precise method of production. Popular grades are ribbed smoked sheet (RSS) and technically specified rubber such as SMR (Standard Malaysian Rubber) and SIR (Standard Indonesian Rubber).

To achieve more consistent viscosity control of NR a specialized grade known as SMR CV (constant viscosity) is available. This grade has 0.15% of a hydroxylamine salt added to prevent a 'cross-linking' phenomenon known as storage hardening, which causes an increasing viscosity during storage.

Properties and Applications:
NR has high mechanical strength and can be compounded to have excellent elasticity(ability to snap back to their original shape). NR has very good abrasion resistance which, with its low relative cost, makes it a significant choice for slurry pump liners, impellers and tank linings.

It has very good dynamic mechanical properties and is therefore used in tires, rubber spring and vibration mounts. It also has very good low temperature resistance and its high temperature heat aging resistance limit for 'continuous' use is in the region of 75℃. Inherent weather resistance provided by the raw gum elastomer is poor. Significant components of weather, from the rubber technologists point of view, are UV light and ozone. Addition of carbon black to a compound gives resistance to UV, antiozonants and waxes, and helps with ozone resistance. Ozone attack is of most concern for thin products and those that are subjected to stretching in service. Electrical insulation is very good and, like all elastomers, is dependant on compounding. Dilute mineral acid and dilute base resistance is good. Solvents follow the polarity rule, thus resistance to petroleum oils is poor while resistance to alcohols(such as ethanol and methanol) and ketones is much better.