The technology that enabled this development dates back to research performed at MIT in the 1970s that established a relationship between the moisture content of a resin and its dielectric properties. A company was formed in the early 1980’s to commercialize the technology as a lab instrument. It became part of the history of brilliant ideas that did not develop into commercial success. Part of the problem was that a calibration curve had to be created for each resin relating moisture content to dielectric properties. Once the curve was created, the moisture content could be measured using the bench top instrument. But the developers of the instrument did not provide a comprehensive library of curves with the instrument and there was a fee charged to the instrument user for each calibration curve. 

One manufacturer of resin dryers realized the potential of this technique to provide for an in-line moisture measurement system. But the method of mounting the expensive sensor made it too vulnerable to damage. Anyone who has seen a dryer disassembled in a plant for cleaning knows how rough the treatment can be. The technology was introduced and displayed at an NPE in the early 1990’s and died away quietly.

Now it is back courtesy of the folks at Novatec. The device is the beneficiary of the twenty years of advances in computing power that have made everything more achievable, and it reportedly comes with about two hundred materials already characterized. If your material is not among them, you can send in a sample to Novatec and they will run it for you. This technology represents an immense potential to prevent hygroscopic materials from being molded wet and producing parts made of degraded polymer. While not all materials that require drying will degrade if molded with excess moisture, many will. 

There are still a lot of processors who believe that if a material is wet they will be able to tell from the appearance of the purging or the molded parts. But this is incorrect and every year molders produce a lot of parts that have great aesthetics and diminished properties. A smaller segment of the industry has purchased loss-on-drying devices under the misguided notion that these instruments provide an accurate measurement of moisture content. And an extremely select group has invested in sensor-based instruments that actually measure moisture content accurately but involve a higher level of skill to operate and still require that someone withdraw a sample from the dryer and take it to the instrument for testing. (By the way, the moisture measurements that get plugged into the calibration curves are made using Karl Fischer titration, not loss-on-drying instruments.)

This development removes the need for all that. Moisture content can be read off the controller screen just like inlet air temperature or dew point. Of all the read outs that a dryer can provide, this is really the only one that matters. Everything else that is being monitored is simply a means to an end. The moisture content is that end. Now the challenge will be to get the processing community on board; investing in the technology and learning how to use it.

In addition, the resin suppliers are going to have to get serious about their recommendations for moisture content. There have been some interesting revisions over the years in some of these recommendations that really have no basis in science. For example, older literature for materials like PBT polyester and PPO quoted maximum moisture contents of 0.04% (400 ppm). Today many of the data sheets for these materials read 0.02% (200 ppm) even though neither polymer requires such low moisture content values for proper processing. And while 0.20% is an acceptable moisture content for processing unfilled nylon, it is not workable for a 40% glass-filled grade where only 60% of the compound is capable of absorbing water.

And some day, very far off in the future, perhaps we will stop talking about over drying when we start to observe a relationship between very low moisture content values and properties that are correspondingly better, not worse.

About the author: Michael Sepe, our analyst and author, is an independent materials and processing consultant based in Sedona, AZ. Mike has provided analytical services to material suppliers, molders, and end users for 20-plus years. You can reach him at [email protected]. This article reflects his opinion and not the official point of view of PlasticsToday.com.