Quality assurance of natural rubber using the rubber process analyzer

Abstract For many years the Mooney viscometer and the Wallace plastimeter have been used to classify and to measure the quality and processability of different grades of natural rubber (NR). However, it is well known that two lots of natural rubber can have very similar Mooney viscosities, but mix and process very differently. As a result, work was initiated in the American Society for Testing and Materials, Subcommittee D11.22, to study more effective ways of characterizing and testing shipments of natural rubber. Three different case studies were completed by an ASTM D11.22 Task Group which show unique advantages for rubber process analyzer (RPA) high strain testing in characterization and quality assurance testing of natural rubber. Natural rubber lots with the same Mooney viscosity were identified that processed quite differently in the factory. The RPA was able to quantify this performance difference. A series of experiments was performed using the RPA to test selected sources of natural rubber. These raw NR samples were tested with the RPA as well as other traditional tests. Moreover, these selected natural rubber samples were mixed in three selected ASTM formulations. These compounds were tested with the RPA and other traditional tests to determine the effects the different NR sources have on both uncured and cured compound properties. A wide range of RPA test conditions was used to determine the best test correlations attainable for NR processing behavior as well as the compound cured properties imparted by the natural rubber grades. In addition, correlations were made with changes in NR physical properties from air oven aging experiments