Challenges in PET Bottle Cap Design: Considerations for Global Recycling Systems

Ruben Nance, Program Director for the Preferred Design Recognition Program at the Association of Plastic Recyclers (APR), emphasized that although PET closures have environmental potential, they introduce complications at the sorting and reprocessing stages:

Color contamination: PET plastic caps are often colored for brand identity. These pigments can contaminate otherwise clear PET bottle flake streams, lowering the purity and value of post-consumer recycled material.

• Viscosity and processing differences: PET used in caps is often thermoformed or injection-molded, with lower intrinsic viscosity (typically below 0.74 dL/g). The APR Design Guide considers materials with IV below 0.72 dL/g as detrimental to recycling.
• Additives and compatibility: PET caps may contain additives not found in blow-molded bottle-grade PET, which can cause discoloration or reduce the mechanical properties of recycled pellets.
• Separation challenges: Unlike high-density polyethylene (HDPE) or polypropylene (PP) caps, which float and are easily separated from PET flakes, PET caps sink in float-sink tanks—making separation more difficult and increasing contamination risks unless caps are uniformly clear.

Paul Bahou, President of Global Plastics Recycling in California, stated that HDPE caps remain ideal for recycling operations: “PET caps will sink, meaning that unless all of these caps are uniformly clear, it’s going to be a disaster. HDPE caps work great. I don’t know why they want to reinvent the wheel on this one.”

PET bottle caps are still a relatively new concept in the packaging landscape, and leading companies such as Origin Materials, which has begun producing PET closures, are taking a cautious approach. The firm advocates for colorless caps and is exploring dye technologies that degrade during recycling to avoid contamination.

Additionally, the webinar addressed tethered caps—closures designed to remain attached to the bottle to reduce litter and increase capture rates. While mandated in the European Union as of 2024, similar legislation is under discussion in U.S. states such as California and Illinois. APR supports the tethering concept but notes that caps may still detach during recycling, and consumer behavior remains a variable.

Industry Insight

The case highlights important considerations for companies in Southeast Asia, the Middle East, and Latin America that are scaling up PET bottle recycling programs. While mono-material solutions may align with long-term sustainability goals, HDPE and PP caps remain the most practical and recycling-compatible options in current systems.

Introducing PET caps without parallel investments in infrastructure and consumer education could inadvertently disrupt flake purity, lower resin value, and complicate bottle-to-bottle recycling efforts. Regional manufacturers are advised to evaluate design shifts holistically—balancing branding, recyclability, and system readiness.

Source: resource-recycling.com