This application note presents an analysis of concentration dependent viscosity data for solutions of nylon 66 in formic acid previously measured with the fully automatic VROC® Initium. The intrinsic viscosity is first extracted from the viscosity data in the semi-dilute concentration regime with the Martin equation. Coefficients found in the literature are then used to estimate the molecular weight of the polymer from the intrinsic viscosity with the Mark-Houwink-Sakurada equation.
When you download the application note, you will be able to see that we use nylon 66 in formic acid and our preparation time is by rotating for a minimum of 2 hours. According to ASTM D789, it is recommended to shake for a minimum of 1 hour. There are many users who even rotate for 2 weeks.
Overall, nylon 66 and formic acid are not immediately miscible. It takes quite a long time for the two solutions to interact and often results in a cloudy solution which is the key indicator that the the two are just not miscible. However, after 2 hours or even 2 weeks of rotation, the solution becomes a lot more homogenous enabling a more smooth solution to work with.
Slow rotation also helps with preventing bubble formation which is another reason to use the rotator for a given period of time.