NR or Natural Rubber
Common chemical composition:
La gomma naturale (NR) è una sostanza naturale che si estrae dall’Hevea Brasiliensis sottoforma di lattice, che altro non è che un liquido composto da una soluzione acquosa di composti inorganici e composti organici ad alto peso molecolare, appunto la gomma naturale.
Natural rubber is a macromolecular substance composed of just carbon and hydrogen atoms. Its molecular formula is (C5H8)n,with one double bond for every 5 carbon atoms (with the CIS configuration). It has the cis-1,4-polyisoprene structure, with a repetitive monomer unit. Natural rubber, while possessing many useful properties, also has certain negative characteristics.
At one time, rubber products were sticky and smelly, deforming when warm and becoming brittle when cold. Thus, mechanical treatments and compounds of suitable additives were tried to stabilize the properties of rubber. Success was initially achieved using the masticator with concentric cylinders devised by T. Hancock, which weakened the material and made it more flexible and suitable for absorbing additives (1820). Then, chemical and physical processing methods for the compounds were researched and, using suitable solvents (ether, turpentine, oil), relatively stable rubber solutions were obtained, suitable for waterproofing fabrics (C. MacIntosh, 1823) and producing flexible wires (T. Hancock, 1837).
Complete stability of the properties of rubber was achieved in 1839 by Charles Goodyear who invented vulcanization, a process which creates cross-links between the polymer chains by heating rubber in the presence of sulfur. Cross-linking
increases the strength of rubber and serves as “memory” in a certain sense, helping the polymer revert to its original shape after being stressed.
Natural rubber has various fundamental properties:
- Excellent adhesion properties in the raw form that cannot be surpassed by any elastomer;
- High tensile strength, surpassed only by urethane elastomers;
- Low hysteresis heating;
- High gas permeability;
- High electrical resistance;
- Very low weather resistance;
- Good abrasion and tear resistance;
- Almost no resistance to oils and hydrocarbons;
Over-vulcanization produces Ebonite, a rigid and fragile substance that is highly resistant to chemicals.
Fields of Application:
Natural rubber has various fields of application. It is used in the automotive industry.
Natural rubber is also excellent for finished parts that come into contact with salt water such as subsea pipe gaskets. Another important use of this rubber type is in the naval sector where it is used in engine mounts, flexible joints and applications featuring contact with seawater.