Catalytic subcritical water hydrolysis for selective PLA recovery from PHA/PLA polymer blends

Overview

This research program develops a catalytic subcritical water hydrolysis (SWH) process to selectively recover lactic acid from PHA/PLA polymer blends commonly used in food packaging. By precisely tuning reaction conditions, the process targets PLA depolymerization while leaving PHA intact for downstream reprocessing. The approach addresses a critical challenge in bioplastic recycling, where mixed polymer streams are difficult to separate using conventional mechanical methods. This selective chemical recycling pathway supports circular economy objectives by converting waste PLA into a valuable monomer feedstock.

Technical specifications

The process exploits the unique properties of subcritical water, where the dielectric constant changes rapidly at elevated temperatures and pressures, enhancing water's affinity for PLA and accelerating hydrolysis reactions.

Key technical features:

• Selective PLA depolymerization at temperatures between 50 and 200 degrees Celsius, well below the 200 to 300 degree range required for PHA hydrolysis
• Catalyst screening across acidic (e.g., sulfuric acid), basic (e.g., sodium hydroxide), and ionic liquid catalysts to maximize PLA conversion
• Reaction time optimization from 0.25 to 24 hours to balance yield and selectivity
• PHA remains in solid phase for easy separation via filtration
• Lactic acid yield target of up to 94 percent under optimized catalytic conditions
• Thermal characterization using TGA and DSC to inform reaction design
• Product analysis using GPC for molar mass and HPLC for lactic acid quantification

Technology readiness level

This project is at an early-to-mid stage of development with a six-month validation timeline. The research team brings over five years of experience in subcritical and supercritical water depolymerization of plastic and film packaging waste. Prior published work has demonstrated PLA conversion rates of approximately 90 percent at 180 to 200 degrees Celsius via SWH, and 94 percent conversion at 130 degrees Celsius using ionic liquid catalysts. The current effort focuses on optimizing catalytic SWH specifically for PLA/PHA blend systems provided by an industry partner, with the goal of identifying optimal conditions for high-purity lactic acid extraction. All characterizations and reactions will be replicated three times to ensure reproducibility.