An anomalous reinforcement of ordinarily weak synthetic rubber

Synthetic rubbers were invented during the World War II due to the shortage of natural rubber in Europe and America. They are superior to natural rubber in various aspects except in strength. Despite a great amount of research work, they still cannot be stretched to strains predicted by theory. Nevertheless they can be strengthened by reinforcement, usually with carbon black or silica. However such reinforcement comes with the sacrifice of elongation, which may not be desirable in applications requiring high strains and relatively low stretching stresses. Such a phenomenon has attracted little attention from the academic community but is of considerable technical importance in the rubber industry. Here we show, for the first time, that ordinarily weak synthetic rubber networks can be made much stronger without altering their ability to reach high strains. Acrylonitrile butadiene styrene rubber (NBR), styrene butadiene rubber (SBR) and butadiene rubber (BR) were used to demonstrate the effect. Precipitated silica was used as the filler with polyethylene glycol to protect silica surface from becoming chemically bonded to the rubber matrix. We anticipate that this finding will have a great impact in terms of new applications and the development of related theories for these very important materials.