Vitel® resins are versatile, high molecular weight, linear saturated copolyesters that are ideal for many applications, such as:
Comprised of different grades, Vitels offer varying processing capabilities and have certain considerations to keep in mind during use. Ideal for extrusion applications, the 1000 series in particular must have special care taken to maximize their performance. Gain insight into the importance of drying these resins and best practices for doing so.
Why Does the Vitel 1000 Series Need to be Dried?
Vitel resins are hydrophilic to a certain extent. This means they will absorb atmospheric moisture until equilibrium is reached. If the resins are not fully dried before extrusion and processing, the following issues can occur:
- Any remaining water will hydrolyze ester linkages on the copolyester and break down the resin’s molecular weight.
- Decreased molecular weight may result in a loss of the resin’s melt strength and possibly impact its flexibility, strength.
- There may be irregularities in the film coatings due to the loss of molecular weight.
Best Practices for Drying the Vitel 1000 Series:
Bostik recommends drying the resins to below 0.05% moisture content before proceeding with processing. To do this, consider the following:
- Use an in-line dehumidifier hopper dryer.
An in-line dehumidifier hopper dryer is more effective at removing excessive moisture than a standalone dehumidifier hopper dryer. This is because standalones can still allow for considerable moisture pickup from the atmosphere due to the time it takes to transfer the resin back to the line for process. As a result, this puts the resin at over the 0.05% moisture content limit in less than 10 minutes.
- Understand crystalline vs. amorphous when drying.
Crystalline resins do not rely on their glass transition temperature (Tg) as much for mobility in the crystalline state. Instead, the melt point (Tm) plays the major role. For these polymers, the Tm is much greater than the Tg. This means crystalline resins can be dried at higher temperatures, thus decreasing the retention time in the dryers.
However, the mobility of amorphous resins is greatly affected by the Tg. When above the Tg, the polymers’ hard, glass-like material will become soft. So, if amorphous resins are dried above the Tg, the granules fuse together. This is undesirable because large chunks of material cannot be fed through the extruder. To avoid this issue, dry amorphous resins below the Tg.
- Follow recommended drying times.
Bostik recommends you use the below drying times as starting points.
(insert chart from guide)
- Test moisture content prior to extrusion.
Even after drying the resins, it’s important to test their moisture content before extrusion. Keeping an accurate log of drying conditions for future extrusions is also a good idea.
For more information on drying Vitel resins for extrusions, please call 800-7-BOSTIK.