Elsewhere on this site Edward has wondered how much PAM solutions age with time so I’ve made a first attempt at measuring it. I prepared a 500 ml sample of PAM at .5 g/L with 0.01% propyl paraben (preservative) and stored it, covered, at room temperature. I then measured its apparent viscosity with a Ford #2 viscosity cup at intervals over a period of 70+ days. I did 4 repeats each time.
It takes several hours for the PAM to dissolve fully. The first measurement was 1 hour after the PAM was mixed into the water. There does appear to be some degradation after about a week.
You cannot dip the cup into PAM solution or pour PAM into the cup because it is self siphoning, so I filled the cup using a 60ml syringe. There is a possibility that there may have been some shear degradation of the PAM due to the repeated sucking into and squirting out of the syringe.
I probably ought to repeat the exercise with a large enough volume of PAM that it wouldn't be re-used, and perhaps also with samples of Guar and PEO for comparison.