Many new international players have emerged in biopolymers, using new materials and formulations. Bioplastic Compounding Twin Screw Extruder provides excellent material compounding capabilities for all biopolymers. Regardless of the formulation, you should consider your equipment supplier as a development partner to achieve your goals regarding melt and extrusion quality, productivity, and other parameters. Make sure your equipment supplier has the facilities and expertise to help you test material formulations and improve your process.

Tips

We broadly divide biopolymeric compounds into three categories:

  • Starch-Based Polymer Compounds;
  • Bioresin compounds containing bioresins such as PHA, PLA or PHB;
  • Biopolymer compound blends, defined as compounds containing two or more bioresins, starch-based polymers and/or petroleum-based polymers).

Global bioplastics capacity is expected to grow to 4.8 billion pounds by 2024, as extrusion equipment makers and brand owners steadily turn their attention to these “green” materials. Here are some key processing considerations you need to know if you are looking to provide compounds to meet this need.

biodegradable twin screw extruder

I.

Purchase a biodegradable twin screw extruder with a higher degree of adjustment

Some extruders are designed with extreme flexibility. You can buy long extruders with 48:1 or 52:1 L/D and they have multiple options for venting and feeding positions.

Because biodegradable plastics are a rapidly developing industry, there are often new ideas, new or improved raw materials, and additives. It is much easier to open or close an available vent location or add or remove a side feeder from an available location, rather than buying a new barrel or expanding an extruder after the initial capital purchase.

II.

Keep in mind that biopolymers are generally hygroscopic

Here the biodegradable cookie tray is extruded and thermoformed by PHA

Plan for at least one atmospheric vent (sometimes two) and at least one vacuum vent (sometimes two). Biopolymers are often hygroscopic and require careful handling before processing. Placing a vent early in the extrusion process is effective in minimizing hydrolysis of the biopolymer and avoiding pre-drying of the material.

A vacuum exhaust port is required. Don’t think of the vacuum system as a non-essential add-on, it’s an integral part of the extrusion process and often the difference between making a quality product or not. A well-designed vacuum system also addresses the often corrosive nature of biopolymer volatiles, which can pay for itself by reducing maintenance and downtime and increasing production efficiency.

III.

Biopolymers are shear and pressure sensitive

biodegradable granules

Biopolymers break down quickly with too much heat or shear. Shear depends on screw speed and the gap between screw and barrel. To avoid damage, run the extruder at the lowest screw speed until the torque is too high (>90%) or the volume limit is hit, which is determined by the feeder or vent.

To avoid volume limits, use vents to release air and moisture. Place kneading blocks or counter-screws far from the feed or vent. Prevent high torque by designing the screw with a long, gentle mixing zone. Stabilize the feeder to reduce torque fluctuations, allowing the extruder to run at higher average torque.

A biodegradable twin screw extruder is a good mixer, but its pump efficiency is only 8% – 15%. That means the high pressure at the extruder outlet will greatly increase the melt temperature. Also, the high pressure can cause air flow at the vent near the outlet.
Making the die hole diameter bigger, increasing the filter screen mesh size, and raising the water and die temperatures during underwater pelletizing can all reduce the extruder outlet pressure. Threaded elements with a delivery pitch equal to one diameter are the most effective pumping elements.

A melt pump can be used between the extruder outlet and the die. The pumping efficiency of the melt pump is 25% to 35%. Using a melt pump minimizes melt temperature rise, saves extruder power, and produces a more stable extrudate stream. The cost of the melt pump can sometimes be easily justified by increasing the output of the extruder.

IV.

Biopolymers degrade rapidly, so decontamination is important

Biopolymers degrade faster than most petroleum-based polymers. If the bioplastic compounding twin Screw Extruder is to stand for more than 1 to 2 hours, it is strongly recommended to lower the barrel heating or turn off the heating.

If the extruder will remain heated for extended periods of time without running it, clean the extruder with a low-cost heat-stable polymer with a slightly higher melt viscosity than bio-resin. If the cleaning material is too viscous, it may appear as contamination within a few hours of restarting production.

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Source of content: From PTonline, author: Dean Elliott Xintec Translation

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