A common and frustrating problem with polypropylene materials and especially filled polypropylene materials is surface moisture on the pellets. Polypropylene is not hygroscopic so it does not absorb moisture out of the atmosphere but if the pellets have moisture on the surface, it will cause the same problems as you would experience running wet hygroscopic material like nylon. You will experience splay and loss of physical properties.
A moisture analyzer is a great tool for any plastic processor to have. It will tell you for sure that you are drying the material adequately. It is also a great tool for material suppliers to have so that they can aid customers who are trying to troubleshoot problems.
How exactly a moisture analyzer works seems like a bit of witchcraft. You put a bit of material in, you choose some type of program and hit the start button. Ten to twenty minutes later, the readout shows a percentage. The process is a little bit more complex than just heating the material and burning off the moisture weighing the sample before and after. You don’t need a moisture analyzer to do that, you can do that with a lab dryer and lab balance. How does it work?
Nylon is one of the oldest and most commonly used thermoplastics but there still seems to be a lot of confusion about properly drying nylon and in general about how nylon is affected by moisture. Moisture in the raw material causes many processing issues and part failures and the affects that moisture has on molded parts seems to confound people as well. I hope in this article to clear some of this up.