PLA Recycling via Cyclizing Depolymerization
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Solution Overview
Problem
Current recycling methods for polylactide (PLA) are energy-intensive, require solvents, and result in thermo-mechanical degradation, contamination sensitivity, and racemization issues, making them inefficient and unsustainable for large-scale disposal.
Innovation Solution
A process involving the direct addition of a polyhydroxycarboxylic acid recyclate to the cyclizing depolymerization stage, where the recyclate is not further chemically pretreated, allowing for the production of intramolecular diesters like dilactide with minimal additional equipment and energy, maintaining high yields and optical purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If mechanical recycling is used for PLA, then recycling efficiency is improved, but thermo-mechanical degradation occurs leading to changes in polymer structure and negative influence on thermal, mechanical and rheological properties
Solution Approach 1:
The invention changes the chemical parameters of the recycling process by using selective depolymerization conditions (specific temperature range, catalyst presence, and reaction time) to convert PLA into dilactide monomer, avoiding the thermo-mechanical degradation that occurs in mechanical recycling while maintaining material quality
Solution Approach 2:
The invention replaces the mechanical recycling process (shredding, melting, reprocessing) with a chemical depolymerization process that converts PLA directly into its monomeric form (dilactide), thereby avoiding mechanical and thermal stress that causes polymer structure degradation
2Adaptability or versatility
If complete degradation of PLA into lactic acid is performed, then raw material recycling is achieved, but energy-intensive processes and complex purification are required
Solution Approach 1:
The invention optimizes the depolymerization parameters (temperature, catalyst, reaction conditions) to selectively produce dilactide monomer rather than complete degradation to lactic acid, reducing the need for energy-intensive purification steps while achieving effective raw material recycling
Solution Approach 2:
The invention extracts the valuable dilactide monomer directly from the PLA polymer through selective depolymerization, bypassing the need for complete degradation and subsequent complex purification processes required in conventional methods
3Ease of manufacture
If high molecular weight PLA is directly depolymerized, then processing simplicity is improved, but depolymerization rate is reduced due to lower end group concentration
Solution Approach 1:
The invention performs preliminary action by adding chain-splitting catalysts before the main depolymerization process to reduce the molecular weight of high molecular weight PLA, increasing the end group concentration and thereby accelerating the depolymerization rate while maintaining process simplicity
4Object-generated harmful factors
If PLA is composted, then biodegradation is achieved, but energetic potential is unused and no energy is generated
Solution Approach 1:
The invention changes the disposal approach from biological composting to chemical depolymerization under controlled parameters, converting PLA into valuable dilactide monomer that can be reused for new polymer production, thereby recovering and preserving the energetic potential of the material
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies the recycling process, reduces energy consumption, minimizes solvent use, and prevents thermo-mechanical degradation and racemization, enabling efficient and sustainable recycling of PLA into high-quality dilactide.
Implementation Method 1
a) polycondensation of a hydroxycarboxylic acid to an oligomeric hydroxycarboxylic acid
Implementation Method 2
b) cyclizing depolymerization of the oligomeric hydroxycarboxylic acid to obtain an intramolecular diester of the hydroxycarboxylic acid
Implementation Method 3
cyclizing depolymerization of the oligomeric hydroxycarboxylic acid to obtain an intramolecular diester
Data Source
Figure 1~3
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Figure 6~8
AI summary
The present invention relates to a process for producing an intramolecular diester of a hydroxycarboxylic acid, wherein in a first step a hydroxycarboxylic acid is polycondensed to form an oligomeric hydroxycarboxylic acid. This is followed by a cyclizing depolymerization of the oligomeric hydroxycarboxylic acid obtained in the first stage to form the intramolecular diester. The present invention is characterised in that in the cyclizing depolymerization stage a plastics recyclate is added. This plastics recyclate contains for example a polyhydroxycarboxylic acid derived from the hydroxycarboxylic acid employed in the first stage. The plastics recyclate may likewise contain a copolyhydroxycarboxylic acid or a blend containing the abovementioned (co)polyhydroxycarboxylic acid(s).