The Importance of Stabilization Technology

November 26, 2024|Uncategorized

Stabilization additives support circularity by improving PCR content quality and consistency.

By James Lloyd, Business Development Director for the Special Additives Business at Baerlocher USA

A Material Reclamation Facility (MRF) conveyer system transfers material to the separation stage. © R_Yosha – stock.adobe.com

Major consumer packaged goods (CPG) brand owners – making up approximately 30 percent of the market, as noted in the Ellen MacArthur Foundation 2023 Annual Progress Report¹ – have committed to reducing virgin resin consumption by incorporating specific amounts of recycled plastic content in their product packaging by 2025, although some have pushed deadlines out by several years. One of the practical challenges is sourcing appropriate volumes of recycled plastic resin and incorporating it at increasing percentages, while meeting high standards for quality, aesthetics and consistency. As brands respond to new legislative initiatives such as Extended Producer Responsibility (EPR)² and recycled content directives, demand for post-consumer recycled (PCR) resin will continue to increase. Obtaining enough consistent, high-quality PCR content while supply is stretched thin will require the means to maintain the physical properties of plastic as it goes through the mechanical recycling process.

One important solution is the use of stabilization technology. When added to PCR plastic, stabilizers help protect the molecular structure of the polymer and inhibit physical property degradation caused by the heat and shear stresses of the mechanical recycling process, resulting in improved melt and color stability and enhanced processing efficiency.

Importance of PCR Content Stabilization

Post-consumer recycled resin stabilization is becoming more important as the recycling industry moves beyond its initial focus on polyethylene terephthalate (PET), the resin that is most widely available and easiest to recycle. Now, efforts are concentrating on polyolefin plastics: polyethylene (PE) and polypropylene (PP). Polyolefins are susceptible to changes in viscosity due to degradation by crosslinking and chain scission during thermal processing. Also, as virgin materials, they have a much broader range of melt flow, density, molecular weight and other properties than do PETs, increasing the need for stabilization.

While virgin resin typically contains antioxidant (AO) stabilizers to protect the integrity of the resin as it is manufactured, much of it is consumed in its production The result is insufficient residual amounts of AO in the finished product to fully protect the resin through conversion. Therefore, stabilizers are especially critical for the mechanical recycling of PCR content. When added during the extrusion melt filtration process, designed to remove impurities, stabilizers can improve the physical properties and processability of recycled PE (rPE) and recycled PP (rPP) and help recycled materials meet the quality expectations of brand owners.

Stabilization packages are typically blends comprising antioxidants and antacids (acid scavengers) but can also contain other functional additives to address customer-specific needs. Antioxidants protect the PCR content against oxidation caused by heat and shear forces, as noted previously. The primary AO supplies long-term stability of the finished product, while the secondary AO scavenges the molecular impurities produced through processing and protects the primary AO, saving it to protect the finished product.

Acid scavengers neutralize acidic impurities, safeguarding the polymer from unwanted chemical reactions. They can add lubricity to the polymer, helping maintain good material flow and reducing shear. Acid scavengers also help protect recycling equipment and mold tools from corrosion, helping recyclers and converters reduce maintenance and downtime.

Benefits of Stabilization Technology

By maintaining or enhancing physical and mechanical properties in polyolefin PCR content during mechanical recycling, stabilization additives also help support sustainability goals.

Stabilization helps achieve the following:

Higher percentages of PCR content: When manufacturers and brands are confident in the quality, performance and consistency of recycled plastic streams, they will be more inclined to incorporate higher percentages of PCR content in their product packaging. This helps brands and processors reduce virgin plastic usage and decrease total carbon footprint.
New applications containing PCR content: Higher-quality recycled PCR content can be used in new applications that demand premium materials, helping to increase the use of PCR content.
Longer useful life of applications: Stabilizers can help avoid oxidation in the final packaging as measured by oxygen induction time (OIT), extending their shelf life and avoiding costly recalls.
Increased value of PCR Content: Encouraging recycling depends in part on incentivizing reclaimer/recyclers. The ability to increase the value of their finished product through stabilization helps reclaimer/recyclers increase profits, attract new customers and expand their business.
Contributing to the solution to potential shortages: When supply of premium-quality PCR content becomes tight, reclaimers and converters may have to turn to lower-quality sources. In this situation, stabilizers can help improve the overall quality of mechanically recycled PCR resin and reduce scrap at conversion. The right stabilizers can also improve certain mechanical properties, such as top load strength in blow-molded containers and tear resistance in blown film, making these PCR content streams suitable to increase the utilization of recycled plastic in the finished packaging.

What to Look for in a Stabilizer that Enables the Use of PCR Content

When choosing a chemical stabilizer for recycled content, consider these factors:

Functionality: Look for a product with multiple capabilities that enhance PCR content and processability.
Safety: To enable use of PCR content in food and beverage packaging, look for a stabilizer made with raw materials that conform to pertinent regulations. Further, dust-free formulations help reduce the risks of explosion, protect worker health and avoid impacting air quality during the recycling process.
Cost-effectiveness: Controlling costs in the volatile recycling market can be a major issue. Stabilizer packages can be used in neat or masterbatch form. The low letdown of 0.4 – 0.3 percent for leading neat additives can help reduce system costs and increase profits compared to the masterbatch form.
Usability: Choose a stabilization product form that is suitable for existing dosing equipment.

Mini Case Study

One example of the measurable benefits of stabilization involved a PE film converter with quality issues caused by PCR content – specifically, an excessive number of large gels that affected the surface finish and strength of the film. The company had already addressed feedstock variability by securing a reliable and consistent source of mechanically recycled PE resin. The next step was adding a suitable stabilizer package to the PCR content prior to the melt phase of the recycling extrusion process.

The company wanted to improve the quality and consistency of its secondary packaging film and increase the percentage of recycled content in the finished product.

To quantify improvements, the size and number of gels were measured in samples containing 30 to 70 percent PCR content, with and without stabilization. Tests showed 50 to 80 percent reductions in the occurrence of gels and a substantial reduction in gel size in the stabilized material.

Conclusion

Recyclers must contend with variables, from price and supply fluctuations to a patchwork of state and municipal recycling regulations – many of which are out of their control. However, they do have some control over the quality and consistency of PCR content, thanks to stabilization technology. By adding a stabilization product to their process, recyclers can improve the quality and consistency of their materials, help to meet growing demand from consumers and brands for increased recycled content in packaging, and make a greater contribution to lowering carbon footprint and enhancing global circularity efforts.

About the Author

James Lloyd is the New Business Development Director for the Special Additives business of Baerlocher USA. He is responsible for consumer packaged goods brand owner engagement and promotion of the company’s Baeropol T-Blend and RST stabilizer additives for the plastics recycling industry and Baerolub Aid – PFAS free PPA additives for blown film, pipe and wire & cable.