Natural rubber

Natural rubber is cis-polyisoprene

We can see that the structure of NR is far more complex than the simple structure of poly-cis isoprene, which is why isoprene rubber does not have the same performance as NR rubber; natural rubber molecular weight in addition to containing the main intermediate cis isoprene, but also contains two end groups – α, w’, the results of the study showed that α-end group for the formation of phosphate ester groups and phospholipids in conjunction with each other, and the w’-end group for the formation of a number of trans isoprene combined with some kind of special protein. The w’ end group is formed by the binding of several trans-isoprenoids to a specific protein, combined with the structure above.

The two most important properties of NR are explained below:
(1) Huge molecular weight, can reach millions of levels, difficult to process, high gel content, need to be plasticised.

The reason for the large molecular weight is that the alpha end groups of natural rubber form a gel network through hydrogen bonding or intermolecular forces.
②Tensile crystalline properties

Non-rubber components in NR rubber, such as fatty esters, proteins, etc. can be used as heterophase nucleation points to promote rapid crystallisation of NR rubber under stretching.

③Why does the Menni viscosity rise after the natural rubber compound is prepared? –Storage hardening

In fact, this problem is still related to the structure of NR, in the process of storage NR end group will re-form hydrogen bonds, resulting in gel, so that the hardness of the rubber mixing rose, the Mooney viscosity rose.

4、NR properties

Above the main characteristics of NR has spoken very clearly, I will briefly summarise:

① raw rubber Green high strength, extrusion, calendering performance is good, smooth surface of the extruded material, low shrinkage rate

② elasticity: natural rubber has a medium elasticity, BR>NR>IIR, this is mainly from the bit resistance considerations

③Strength: NR has the most excellent tensile properties in general rubber, excellent strength.

④Processing performance: high molecular weight, high Mooney viscosity of raw rubber, need to be plasticised for further processing.

⑤Low temperature resistance: medium to high: glass transition temperature is around -70℃.

⑥ solvent resistance: if a material neither reacts nor dissolves with a solvent, the material is resistant to the solvent. NR is a non-polar rubber, not resistant to non-polar gasoline, diesel fuel, transformer oil, and is resistant to polar solvents: water and ethanol.

(7) chemical reaction properties: NR rubber has a high chemical reaction activity, so that NR aging resistance is poor, must be anti-aging treatment; at the same time, NR’s high chemical reaction activity can also be prepared epoxidation NR, hydrogenation NR, for the two kinds of special NR, later to find a time to write an article specifically on the chemical modification of rubber, which is still a lot of doorway.