Significance and Use 4.1 Extensional viscosity is a measure of the resistance of a liquid to stretching forces, such as those occurring during the disruption of liquid films and the formation of sprays used in agriculture and other purposes including painting operations or metal working. This method for measurement of a Screen Factor, gives a relative value for extensional viscosity, which may be used: 4.1.1 To compare the potential for drift control of different polymers. 4.1.2 To compare the relative extensional viscosity component of different spray tank mixtures. 4.1.3 To determine the extent of breakdown of polymer solutions used as drift control additives during the recirculation of the solutions through pumps and screens. 4.1.4 To use as a parameter in the Spray Drift Task Force Models for droplet size prediction. 4.2 It should also be noted that many drift control polymers are irreversibly destroyed during the recirculation of spray mixes by pumping with high shear pumps such as gear or centrifugal pumps. It is advisable to subject the test mixture to similar pumping regimes to simulate practical conditions before carrying out the extensional viscosity test. Measurements of extensional viscosity are the only presently known method of determining the extent of this breakdown properties of dilute polymer solutions. 4.3 This method is intended to produce a relative value for extensional viscosity. The purpose of the method is to compare the extensional viscosity produced by different polymer types or concentrations of polymer in spray tank mixes.Scope 1.1 This test method covers the determination of the relative extensional viscosity or Screen Factor (SF) of dilute agricultural spray mixes. 1.2 The test can be used for tank mixes containing dissolved, emulsified or dispersed materials, or mixtures. 1.3 Results may be affected by the quality of the water used. Make-up water quality should therefore be specified in the presentation of results. 1.4 Proper safety and hygiene precautions must be taken when working with pesticide formulations to prevent skin or eye contact, vapor inhalation, and environmental contamination. Read and follow all handling instructions for the specific formulation and conduct the test in accordance with good laboratory practice. Note 1: References to the development of extensional viscosity from dissolved polymers, extensional viscosity effects on the droplet size distribution of sprays, and measurements of screen factor on recirculated spray mixes containing polymers are available.2,3 1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
