Standard Test Method for Determination of Green Strength of Raw Rubber or Unvulcanized Compounds

The stress-strain properties of unvulcanized rubber (either in a compound or in the raw state) are important to certain processing operations in the rubber industry. These unvulcanized rubber properties are frequently referred to as “green strength,” denoting that the final vulcanization cycle has not yet been achieved.

Green strength is determined primarily by the physical and chemical characteristics of polymers, such as molecular weight, tendency to crystallize, degree of branching, and so forth. It is also related to the compound formulation, particularly filler and plasticizer content, and the presence of peptizers. Green strength can be a good indication of processing behavior. It is a particularly important characteristic for all processing operations in which elongation predominates.

Green strength is dependent on the test piece preparation, rate of extension, and test temperature. Therefore, a single-point method cannot be expected to give correlation between green strength and processing behavior over the whole range of processing conditions.