Processing Technologies International (PTi) has successfully demonstrated that its “dryerless” twin-screw sheet extrusion production system can convert mixed regrind (PETG and APET) into processable, high-quality thermoformed sheet for consumer packaging.
No dryer and crystallizer needed
“Our dryerless twin-screw system is a new option that is well suited to process post-consumer and post-industrial PET GAG regrind, unlike conventional extrusion systems that require a dryer and a crystallizer,” said Sushant Jain, senior scientist for PTi.
In production-scale trials
Production-scale trials were run on PTi’s 85-mm high-vacuum twin-screw extruder with 100% GAG scrap. Clear mixed material sheet was produced thus demonstrating a successful method to recycle GAG sheet scrap. The final blend was composed of approximately 20% PETG/80% APET.
Many thermoformers use a PET-GAG sheet which is a PETG/APET/PETG multilayer sheet structure for consumer packaging. The benefit of this structure is that the PETG layers offer superior heat sealing and printing properties over APET. However, the scrap from this sheet structure ends up in a landfill because extruders can’t effectively process this material with conventional equipment.
Dryerless extrusion system suited to process mixed PETG and APET sheet scrap
Recycling the trim and thermoforming skeleton scrap is a challenge due to the widely different drying temperatures for PETG and APET, according to PTi’s Jain. PETG’s drying temperature is 150°F (66°C) while APET’s is approximately 300°F (149°C). At higher temperatures, pellets/flake can agglomerate and plug up the crystallizer and dryer. The HVTSE dryerless extrusion system is suited to process mixed PETG and APET sheet scrap. PTi’s patented High-Vacuum Twin-Screw Extruder (HVTSE) technology, which allows PET to be processed without the need for crystallizing and drying, can easily convert this material into usable sheet.
Single atmospheric and dual high-vacuum, vent system
HVTSE* systems ranging from 85 to 170mm are capable of processing PET at rates ranging from 2,300 lb per hour (1,045 kg/hr) to 5,500 lb/hr (2,500 kg/hr), and convert a variety of resins including post-consumer and industrial PET/PLA, PP, HDPE, HIPS and more. The energy-efficient design allows virgin or recycled PET to be processed without the need for raw material drying and crystallizing. It employs a single atmospheric and dual high-vacuum, vent system with a co-rotating twin-screw extruder. This novel approach allows moisture and other volatiles to be removed as part of the extrusion process.
Significant energy savings
The dryerless sheet extrusion system also delivers significant energy savings: The HVTSE process provides a reduction of about 80-85 kWh/1000 lbs in energy consumption versus conventional PET processing. This savings equates to more than 31.6 gigawatt hours of annual power consumption when factored across PTi’s 470 million pounds of theoretical installed HVTSE PET capacity base. The resultant energy savings could mean a reduction in CO2 gas emissions of more than 23 million pounds per year from fossil-fuel burning power plants, the company estimates.