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Many new players have emerged in the Biopolymer space with new materials and many new formulations. Co-Rotating Twin Screw Extruders provide excellent material mixing capabilities for all Polymers, including Biopolymers. You should consider your machinery supplier as a development partner to achieve your goals in the areas of melt and mix quality, production rates, and other parameters, regardless of formulation. Make sure your machinery supplier has the facilities and the know how to help you test material formulations and improve your processes.
As with any compounding project, a certain amount of trial and error is inevitable in process development for new Biopolymer formulations. Some are successful from the start; others needs more work to become commercially viable.
Biopolymer compounds characterize into three categories:
Here are some key processing considerations for Bio Resin compounds and Biopolymer compounded blends on a Co-Rotating Twin Screw Extruder:
Modular Twin Screw design: Design the equipment for maximum flexibility; purchase long extruders having 48:1 L/D, with multiple vent and feed location options. It’s much easier to open or close up an available vent location, or to add or remove a Side Feeder from an available location, than to purchase new barrels or extend the Extruder after the initial capital purchase.
Biopolymers are typically hygroscopic and require cautious handling prior to processing. It is effective to place an atmospheric vent early in the extrusion process to minimize hydrolysis of the Biopolymer and to avoid pre-drying of the materials. A vacuum vent is a requirement. Don’t think of a vacuum system as a non-essential add-on; it is an integral part of the extrusion process that is often the difference between making a quality product or not.
Biopolymers rapidly degrade when exposed to excessive heat and / or shear. The shear exposure of the material is directly proportional to the Extruder screw speed and inversely proportional to the gap between the extruder Screws and the Barrels.
Biopolymers degrade rapidly, making purging important: Degradation of Biopolymers is more rapid than most petroleum based Polymers. It is highly recommended to lower the Barrel heat or turn the heats ‘OFF’ if the Extruder is going to be standing for more than 1 to 2 hr. If the heats are left on for long periods while the Extruder is not running, purge the Extruder with a low cost heat-stable polymer that has a slightly higher melt viscosity than the bio resin. If the viscosity of the purge material is too high, it can show up as contamination for many hours after starting up production again.
Screw Diameter (mm)
Effective L/D ratio
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