Peng Ye
Application Development Manager
Farrel Pomini
SPE Bioplastics and Renewable Technologies Division
Biodegradable resins play a crucial role in promoting sustainability. Unlike traditional petroleum-based resins, biodegradable plastics are often derived from biological sources and are either biodegradable or compostable. They help reduce environmental impact. At the end of life, depending on their composition, they can be mechanically recycled or decomposed into CO2, water, and biomass.
Biodegradable plastics are often polyester-based resins. Unlike polyolefins, their chemical bonds are more susceptible to shear, heat, and moisture. They can degrade quickly when exposed to excessive amounts of these elements. To ensure biodegradable polymers are processed effectively, there are three key equipment design innovations to be aware of.
Reduce residence time
A long residence time under high temperature is detrimental to biodegradable resins during processing. A traditional twin-screw extruder usually features high shear (including local peak shear typically occurring in the space between the tip of the screw elements and the barrel wall), high temperature, and long residence time. However, equipment that utilizes a non-intermeshing, two-rotor design with a much shorter rotor results in a shorter residence time. The shortened residence time reduces the risk of the biodegradable polymer degrading during processing.
Remove moisture
Biodegradable resins are prone to hydrolytic degradation if moisture is present in the molten resins. Drying the resin before the first stage of processing as well as adding a venting system to equipment can help to reduce moisture throughout the process. Any encapsulated air or moisture from resin can be vented from vent ports effectively. A vent capture system using centrifugal force can also be effective in trapping moisture.
Mix gently
Mixing gently is important to provide uniform shear to the resin. Equipment with a large free volume mixing chamber can be an effective solution for gentle mixing. It is also important to ensure that all resin, filler, and additives are repeatedly exposed to controlled levels of shear by repeated passage of the compound through the controlled shear region.
In addition to rotor speed and flow rate, the passage distribution function can further be controlled by the mixer orifice position and number of dams inserted into the mixing chamber. Understanding how to manipulate these elements helps the manufacturer control mixing intensity, resulting in a homogenous compound with excellent dispersion quality.
In addition to rotor speed and flow rate, the passage distribution function can further be controlled by the mixer orifice position and number of dams inserted into the mixing chamber. Understanding how to manipulate these elements helps the manufacturer control mixing intensity, resulting in a homogenous compound with excellent dispersion quality.
These overall processes use mechanical energy very efficiently, which has the added benefit of reducing energy consumption.
The plastics industry is innovating in the use and development of biodegradable resins due to their unique end of life characteristics and environmental attributes. Special considerations need to be given to processing these biodegradable resins due to their intrinsic properties. Machinery manufacturing is developing new systems and designs that are customized to the different qualities of these resins to respond to the ongoing move toward sustainability.
About FARREL POMINI: FARREL POMINI is the Continuous Mixer Business Unit of HF MIXING GROUP. Farrel was founded in 1848 and has operated continuously, beginning as a foundry and evolving into a global leader in the research, design, and manufacture of compounding equipment for the polymer processing industry. FCM™ technology was introduced in 1963. It has traditionally been utilized for highly filled masterbatch, carbon black masterbatch and PVC applications. It is now also used for biodegradable plastics compounding and mechanical & chemical recycling applications. The FCM™ has been shown to process biodegradable resins such as PLA, PHA, PBS and blends of them successfully. Visit https://www.farrel-pomini.com/applications/compounding/biodegradable-plastics/ to learn more about their offerings and see first-hand processing data of PLA, PHA runs on both lab-scale CPeX® and commercial-sized CP550 Compact Processor.
