Performance of Recycled Polylactic Acid/Amorphous Polyhydroxyalkanoate Blends.

Area of Science:

• Materials Science
• Polymer Science
• Sustainable Materials

Background:

• Polylactic acid (PLA) is a biodegradable polymer with potential for packaging applications.
• PLA's brittleness limits its use; blending with amorphous polyhydroxyalkanoate (aPHA) enhances flexibility.
• Investigating the effects of recycling on PLA and PLA/aPHA blends is crucial for sustainable material utilization.

Purpose of the Study:

• To evaluate the impact of multiple heat histories (recycling) on the mechanical, rheological, and thermal properties of neat PLA and PLA/aPHA blends.
• To determine the suitability of recycled PLA and its blends for biodegradable packaging applications.
• To assess property changes after five reprocessing cycles in a single-screw extruder.

Main Methods:

• Preparation of neat PLA and PLA/aPHA blends (90 wt.% and 75 wt.% PLA).
• Subjecting materials to five heat histories using a single-screw extruder.
• Characterization of mechanical (tensile, impact strength), rheological (complex viscosity), and thermal (decomposition, glass transition, melting, crystallinity) properties.

Main Results:

• Decomposition behavior remained similar for recycled 100% PLA and 75% PLA blends, but decreased for 90% PLA blends with heat cycles.
• Glass transition and melting temperatures were unaffected by reprocessing; crystallinity increased with heat cycles.
• Complex viscosity decreased significantly after reprocessing, with smaller reductions for 100% PLA and 90% PLA blends after multiple cycles. No change was observed for 75% PLA blends after 2-5 cycles.
• Tensile properties were unaffected, but impact strength decreased for the 75% PLA blend with reprocessing.

Conclusions:

• Recycled PLA and PLA/aPHA blends retain properties suitable for thermoformed packaging.
• The 75% PLA blend shows a decrease in impact strength after recycling, while other properties remain largely stable.
• These findings support the incorporation of scrap material into neat resin for manufacturing biodegradable packaging, promoting a circular economy.