Researchers in Japan have developed a synthetic rubber that has the same tensile strength as natural rubber. This is of great importance for the global rubber industry and reduces dependence on this important natural material.

Natural rubber is used in the manufacture of tires and other automotive parts, flooring, clothing, adhesives, anti-vibration pads and fasteners, rubbers, rubber boats, air ducts, hoses, sound-absorbing materials and much more – in total, it is used in more than 40,000 commercial products. The source of natural rubber is plants, mainly the Brazilian rubber tree Hevea brasilensis.

Rubber has such attractive properties as resilience, efficient heat dissipation, elasticity, impact resistance, excellent electrical insulation and abrasion resistance. Synthetic rubbers, although they have been extensively researched in recent decades, cannot yet easily mimic the characteristics of natural rubber.

However, despite its usefulness, the extraction and processing of natural rubber cause enormous damage to the environment. Rubber plantations are a major cause of deforestation. In addition, the lack of biodiversity resources leads to supply insecurity due to factors such as shrinking crop areas and potential crop failures. Reducing reliance on natural rubber is a key focus for researchers.

Since the beginning of the nineteenth century, the structure of natural rubber has been studied and analyzed by many researchers. Early work focused on the primary structure of natural rubber. More recent studies have shown that rubber is a nanocomposite. Its main component is cis-1,4-polyisopropene with minor non-rubber components such as proteins and lipids. Studies have shown that the vulcanization of natural rubber includes the role of non-rubber components through the interaction between proteins and zinc ions.

Reactions and phase separation during biosynthesis cause the formation of a nanophase-separated structure in natural rubber. The structure consists of natural rubber particles about 1 µm in diameter and a matrix of non-rubber components several tens of nanometers thick.

A team of scientists from ACS Applied Polymer Materials has developed a synthetic rubber that is identical to natural. The synthesis process was inspired by the biosynthesis of natural rubber and the process that forms what the researchers called the “island nanomatrix structure.” In their studies, the authors chemically attached nanoparticles to synthetic rubber particles ~1 µm in size dispersed in water. This process was followed by coagulation and drying steps. The authors preferred organic nanoparticles due to the organic nature of proteins. Graft polymerization at low temperatures of a suitable monomer, which is a precursor of a polymer having a relatively high glass transition temperature, on the rubber particles promoted the attachment of organic nanoparticles.

As a source, the researchers used synthetic cis-1,4-polyisoprene, which contained at least 98.5% cis-1,1-isoprene. The material was prepared by solution polymerization. The synthetic material was dissolved in volatiles followed by emulsification with water and solvent evaporation steps to create a synthetic latex. The researchers stabilized the latex by coating the cis-1,4-polyisoprene particles with rosin, followed by replacement with sodium dodecyl sulfate, just prior to styrene grafting.

The conversion of styrene during graft copolymerization at room temperature turned out to be insufficient – only 15% – only slightly increasing with an increase in the concentration of the initiator. The presence of rosin inhibited graft polymerization. Increasing the incubation temperature to 90 degrees Celsius solved this problem.

To visualize the nanostructure of the prepared synthetic rubber, TEM was used, which showed that this is the same island-nanomatrix structure of natural rubber. Stress-strain analysis has shown that when synthetic rubber contains this structure, the mechanical properties of the material are identical to those of natural rubber.

In addition, the results of the study showed that the optimal cure time for this synthetic rubber was the same as for its natural counterpart. In general, the results of these studies indicate the synthesis of synthetic rubber, which solves the traditional problems associated with its production.