[Introduction]

The Garret Miyake team at Colorado State University published their latest research in Angewandte Chemie, converting post-consumer polyethylene (PE) into reprocessable, chemically recyclable crosslinked polyethylene (XLPE) through a three-step catalytic strategy, providing an innovative solution for the circular economy of plastics.

 

Research Background 

Polyethylene (PE), as the world's most produced plastic (with an annual production exceeding 100 million tons), is difficult to degrade due to its chemical inertness. Traditional crosslinked polyethylene (XLPE) cannot be recycled because of its permanent crosslinked structure. Current upcycling technologies mostly focus on depolymerizing PE into small molecules or simple regeneration, making it hard to balance material performance and recycling characteristics.

 

Research Highlights  

1️⃣ Three-step catalytic conversion: Converting mixed PE waste into end-hydroxylated oligomers (Mn≈2.7-2.9 kDa) through dehydrogenation-metathesis-hydrogenation  

2️⃣ Hybrid crosslinking system: Dynamic crosslinker TETA (triazine derivative) provides reprocessability, while non-dynamic crosslinker Tri-HDI (isocyanate) maintains use stability  

3️⃣ Tunable properties: Co-polymerization with commercial Krasol® diol achieves a wide range of elastic modulus from 5-382 MPa and tensile strength from 1.5-17.3 MPa  

4️⃣ Closed-loop recycling: Selective depolymerization and recovery of raw materials under basic conditions, achieving high purity monomer recovery (recovery rate >85%) even when mixed with cable insulation  

[Introduction]

The Garret Miyake team from Colorado State University published their latest research in Angewandte Chemie, using a three-step catalytic strategy to convert post-consumer polyethylene (PE) into reprocessable, chemically recyclable cross-linked polyethylene (XLPE), providing an innovative solution for the circular economy of plastics.

Research Background 

Polyethylene (PE), as the most widely produced plastic globally (with an annual production exceeding 100 million tons), is difficult to degrade due to its chemical inertness. Traditional cross-linked polyethylene (XLPE) cannot be recycled because of its permanent cross-linked structure. Current upcycling technologies mostly focus on depolymerizing PE into small molecules or simple regeneration, making it hard to balance material performance and circularity.

Research Highlights  

1️⃣ Three-step catalytic conversion: Converting mixed PE waste into end-hydroxylated oligomers (Mn≈2.7-2.9 kDa) through dehydrogenation-metathesis-hydrogenation  

2️⃣ Hybrid crosslinking system: Dynamic crosslinker TETA (triazine derivative) imparts reprocessability, while non-dynamic crosslinker Tri-HDI (isocyanate) maintains use stability  

3️⃣ Tunable properties: Co-polymerization with commercial Krasol® diol achieves a wide range of elastic modulus from 5 to 382 MPa and tensile strength from 1.5 to 17.3 MPa  

4️⃣ Closed-loop Recycling: Selective depolymerization for material recovery under alkaline conditions, allowing for the pure monomer to be recovered at a rate greater than 85% even when mixed with cable insulation layers  

Key Technical Breakthroughs

1. Dynamic Network Design

Through the SNAr exchange reaction by retaining 10% of hydroxy-initiated triazine groups, XLPE-1 can be reprocessed three times at 150°C while maintaining over 90% of its mechanical properties. Dynamic crosslinking reduces the creep rate of the material at 110°C by 80% compared to the original PE.

2. Composite System Construction

The XLPE-3 obtained by copolymerizing PE oligomers with Krasol® HLBH-P 3000 diol (50:50) exhibits rubber-like elasticity, with a strain recovery rate of 72% after 10 cycles at 40% strain.

3. Actual Waste Validation

The XLPE-5 prepared from a mixture of milk jugs (HDPE) and plastic bags (LDPE) has a tensile strength of 15.1 MPa, an 84% increase over the raw materials. After selective depolymerization when mixed with cables, the insulation layer remains intact.