ANTEC® Recap: Moisture Levels Impede ‘Green’ Compounding

Posted: 05/11/2021

Biobased materials generate large volumes of steam that require costly new equipment to process

By Geoff Giordano

In addressing the commercialization realities of “green” materials, Adam Dreiblatt of CPM Extrusion Group highlighted the challenges compounders face in delivering performance on existing equipment at acceptable cost.

In a May 6 presentation at the virtual ANTEC® conference, Dreiblatt said many newly released resins have been around since the early inklings of a sustainability revolution 30 years ago and are being tweaked for current needs. He then offered perhaps the ultimate caveat for broader market adoption of the materials.

“If the converter needs to make modifications or buy new equipment in order to use this new material, it’s just not going to happen,” advised Dreiblatt, process technology director at CPM, Traverse City, Mich.

Blending more expensive green plastics with lower-cost materials like starch to produce drop-in solutions has been one approach to adoption, he explained. But resin companies and independent compounders hesitate to invest in new equipment that can handle such challenges as moisture and thermal sensitivity inherent in compounding these materials.

Most current equipment used to produce formulations such as nylon, glass fibers, polypropylene and talc was not designed for biobased materials. Dreiblatt noted that compounders using biofillers like hemp fiber must vaporize up to 12 percent of the material’s moisture once it goes into the machine. Furthermore, the loading level of some biofillers might create thermal conductivity that requires more cooling time for solidification or pelletizing. The issue going forward is “trying to make this work on existing equipment. Designing equipment dedicated for this service is no issue—but it’s not here today, at least not in a big way.” This can require changing screw design for twin-screw extruders and adding additional venting and mixing stages (see illustration).

The high moisture content of biobased fillers and fibers creates a large volume of steam that needs to be removed from extruders. A conventional back-vent, sufficient for low-moisture inorganic solids, does not have sufficient area for biobased materials and creates high vapor velocity, which also pulls polymer out of the barrel. One answer is to add more vents to the barrel. Courtesy of Adam Dreiblatt/CPM

Materials once known as “oxodegradables,” as well as new versions of conventional resins derived from renewable resources, are coming to market quickly with no impact on current compounding infrastructure, he said. True bioplastics like polylactic acid are typically used directly either as neat resins or in blends, where they introduce more moisture into the equation, and blended with starch to reduce cost. Biobased resins are more unstable and can burn under high temperature or shear. And lignin-based resins have no real commercial history yet.

But “these are temporary issues,” he concluded. “These will go away with time … with the advent of more demand.”

View on demand: Dreiblatt’s presentation, “Compounding for the Green Economy,” will be available on demand to ANTEC® attendees and those who register for access after the conference.

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