Natural rubber is composed of rubber component (around 94 %) and non-rubber components (around 6 %) such as proteins, phospholipids, carbohydrates, metals and others. The functional groups of the ends of rubber chains react with non-rubber components and make naturally occurring networks. At the same time, non-rubber components make micelles, agglomerates and crystals. The superior mechanical properties in natural rubber to synthetic analogue are owed to hierarchical multi-scaled structures, that is, naturally occurring network and multi-scaled structures of nonrubber components. Synchrotron X-ray, atomic force microscopy, optical microscopy and simultaneous stress strain measurement revealed the role of hierarcic multi-scaled structures and naturally occurring network in natural rubber.
Proteins in non-rubber components make multi-scaled (nano to micron) size of agglomerates and may not contribute to naturally occurring network since de-proteinized natural rubber show higher modulus and higher tensile strength and larger strain at break than original natural rubber in un-vulcanized state.