Temperature, concentration, and pumping effects on PAM viscosity

As polyacrylamide (PAM) use in irrigated agriculture increases, new methods are being sought to accurately and automatically apply PAM with irrigation water. PAM is also beginning to be used in sprinkler irrigation. However, little information is available about flow characteristics of PAM solutions. This study was conducted to investigate temperature, concentration and pumping effects on viscosity of two agricultural PAM formulations: a dry powder and an inverse oil emulsion. Flow tests, using solutions prepared from the dry powder PAM, showed that viscosity decreased as flow rate increased for concentrations greater than 400 ppm. Thus, accurately predicting PAM viscosity at concentrations greater than 400 ppm is difficult because viscosity varies not only with concentration and temperature, but with flow conditions. Flow rate changes due to temperature fluctuations, however, should be minimal for the oil emulsion PAM over typical temperature ranges occurring under field conditions if tubing diameter is greater than 10 mm and tubing length is less than 1 m, which should be adequate for all surface irrigation applications. The two PAM products tested had similar viscosity relationships with temperature and concentration. PAM viscosity for solutions with concentrations < 24 ppm only increased about 5% relative to water for each 10 ppm increase in PAM concentration. Pumping a 2400 ppm PAM solution just once through a centrifugal pump reduced viscosity 15 to 20%; pumping five times reduced viscosity approximately 50%. The viscosity reduction is thought to result from breaking or shearing the PAM molecules, reducing its effectiveness to stabilize the soil surface and reduce soil erosion.