Quality assurance of natural rubber using the rubber process analyzer

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 proces s very differently. As a result, work was initiated in the American Society for Testing and Materials, Subcommittee D11.22, to study more effective wa ys of characterizing and testing shipments of natural rubber. Three differe nt case studies were completed by an ASTM D11.22 Task Group which show uniq ue advantages for rubber process analyzer (RPA) high strain testing in char acterization and quality assurance testing of natural rubber. Natural rubbe r lots with the same Mooney viscosity were identified that processed quite differently in the factory. The RPA was able to quantify this performance d ifference. A series of experiments was performed using the RPA to test sele cted sources of natural rubber. These raw NR samples were tested with the R PA as well as other traditional tests. Moreover, these selected natural rub ber samples were mixed in three selected ASTM formulations. These compounds were tested with the RPA and other traditional tests to determine the effe cts the different NR sources have on both uncured and cured compound proper ties. A wide range of RPA test conditions was used to determine the best te st correlations attainable for NR processing behavior as well as the compou nd cured properties imparted by the natural rubber grades. In addition, cor relations were made with changes in NR physical properties from air oven ag ing experiments (C) 1999 Elsevier Science Ltd. All rights reserved.