Solving plastics recycling challenges

Mike Mikolay and Iksoo Chun highlight the key challenges facing today’s plastics recycling stream, from material incompatibility to limited processing capabilities. They also showcases emerging solutions and technologies designed to improve recyclability and support a more circular plastics economy

The push towards a circular economy is one of the most significant industrial shifts of our generation. We are moving away from the linear “take, make, use, dispose” model and embracing a system where resources are reused, recycled, and repurposed.

Navigating the complexity of recycled materials

For the plastics, rubbers, and composites industries, this transition presents both immense opportunities and formidable technical hurdles. The primary challenge? The inherent variability of recycled feedstock.

Unlike virgin materials, which conform to precise, consistent specifications, post-consumer and post-industrial recycled materials are a mixed bag. They vary in composition, suffer from degradation after multiple processing cycles, and contain impurities. These inconsistencies can lead to unpredictable processing behavior and final products with compromised performance.

How additives can help

Advanced additives offer effective solutions to these challenges. By acting as compatibilisers, melt flow and viscosity modifiers, lubricants, coupling agents, and odor neutralizers, they transform imperfect feedstocks into viable materials. This not only improves processing efficiency but also enhances the quality of the final products.

Despite their significant benefits, advanced additives are not a one-size-fits-all solution. They often require careful customisation to address the unique challenges of each application. Variations in recycled feedstock compositions, differences in processing techniques, and diverse end-product requirements necessitate the use of tailored formulations or combinations of additives.

Struktol Company of America, LLC has been producing specialty additives for rubbers, plastics, and composites for decades, and we have witnessed a dramatic growth in the need for solutions to challenges with recycled feedstock. By fine-tuning additive solutions to meet these specific needs, manufacturers can ensure optimal performance, consistency, and quality in their final products, even when working with highly variable and imperfect recycled feedstock.

These additives are essential to making a circular economy for plastics both technologically feasible and economically sustainable.

Challenges of plastics recycling

To achieve a truly sustainable and circular economy for plastics, manufacturers must address various challenges across three critical levels. Each of these levels presents unique obstacles that require innovative approaches and targeted solutions:

1. Variability offeedstock

Demand for recycled content has surged as consumers, governments, and industries seek lower carbon footprints and less waste.

Producing new plastic from raw materials like petroleum uses significantly more energy than recycling. For plastic bottles, recycling uses up to 75% less energy, sharply cutting greenhouse gas emissions. Using recycled plastic can also reduce overall emissions by 30% to 80%. Additionally, regulations often promote recycling to reduce landfill and incinerator waste.

Yet, with this increased demand comes scarcity. High-quality recycled polymer streams are now heavily depleted, making it difficult for manufacturers to source the same materials consistently. Even when shipments from the same supplier are supposed to be the same polymer, their properties can differ significantly from batch to batch.

Unlike virgin feedstock, which is sourced from well-established international supply chains, recycled feedstock is often locally sourced, leading to fluctuations in quality, availability, and pricing. Another challenge: As large manufacturers continue to acquire recycling facilities and secure their own feedstock supply chains, smaller players need additive solutions to take advantage of alternative sources to maintain a resilient supply chain.

These inconsistencies demand significant flexibility in processing and tailoring of additive solutions to ensure the quality of the final product.

2. Processing issues

Recycled plastics introduce a range of rheological processing difficulties due to the mixed and inconsistent nature of the materials. Variability in properties such as melt flow index and viscosity impacts the efficiency and energy consumption of production processes.

For example, mixed feedstock may create flow issues that increase energy demands or cause uneven distribution in moulds, leading to longer production cycles and higher costs. Manufacturers must also contend with challenges in filling moulds completely and ensuring proper mould release, which are critical in achieving high production speeds and maintaining quality. Developing advanced additive formulations can help to improve material consistency, optimise flow properties, and reduce overall energy consumption during processing.

3. Quality and mechanical properties of end-products

The final level of challenge involves meeting stringent quality and aesthetic standards for recycled plastics. Recycled materials often exhibit issues such as odor, which can be particularly problematic in industries like automotive manufacturing, where end-users demand high performance and environmental comfort.

Additionally, mechanical properties such as impact resistance must be carefully optimised to ensure the durability of the product. Aesthetic aspects, including consistent colour and streak-free appearances, are also vital for consumer-orientated applications. By leveraging specialised additives, manufacturers can enhance the quality and appearance of recycled plastics to meet the expectations of both industrial and consumer markets.

Effectively navigating these multifaceted challenges demands a sophisticated blend of scientific understanding and practical application. This often necessitates close, iterative collaboration with an additive supplier possessing specialised expertise and a focused approach. Such a partnership involves continuous fine-tuning, an iterative process of trial and error, and a deep commitment to optimising additive formulations for precise material enhancement and process improvement.

Comprehensive additive solutions

Additive specialists collaborate with recycled plastics manufacturers to solve their unique challenges. They achieve this by leveraging a comprehensive menu of diverse additive technologies, expertly combining them to create tailored solutions that unlock enhanced performance in recycled plastics.

Odour control and VOC reduction

Odours in recycled plastics often result from residual contamination, decomposition of organic materials, or chemical reactions during processing. These unpleasant smells can discourage factory workers and consumers and limit the use of recycled plastics in high-end applications like consumer goods and food packaging.

This is particularly problematic in the automotive industry, which has strict standards due to enclosed spaces, health concerns, and consumer preferences for fresh-smelling interiors. Stagnant air trapped inside vehicles can become heated under sunny conditions, intensifying odors and creating an unpleasant and unhealthful environment for passengers.

Odour neutralisers and modifiers address this issue by eliminating or masking unwanted smells, resulting in cleaner, more neutral-smelling recycled materials. Odour reduction technology can help by minimizing or masking odours and may also reduce VOCs as an added benefit.

By enhancing sensory appeal, these additives can expand market opportunities for recycled plastics, particularly in applications where aesthetics and quality are essential.

Compatibilisers

The variability of recycled plastic feedstock makes compatibilisers and other additives essential for blending incompatible polymers, restoring degraded properties, and creating high-quality, consistent recycled products. Without them, manufacturers would be limited to using only the purest, most expensive recycled materials, undermining the environmental and economic goals of recycling.

Recycled plastic, particularly post-consumer waste, often contains mixed polymers like polycarbonate/ABS or polyethylene (PE)/polypropylene (PP). Reprocessing these mixtures can result in weak, brittle materials with poor mechanical properties.

Compatibilisers improve these mechanical properties and facilitate uniform filler dispersion. The molecular ‘bridges’ or ‘surfactants’ in these additives reduce the interfacial tension between incompatible polymers, allowing them to form a stable, homogeneous blend. This enhances the final material’s strength, enabling the use of mixed plastic streams that would otherwise be discarded.

New additives, such as reactive crosslinkers, help compatibilise and strengthen these mixed plastics, allowing them to be recycled into higher-value products.

Mixing aids also mitigate poor filler dispersion by enabling better integration of diverse plastic types and ensuring uniform distribution of additives within the polymer matrix.

Additives and chemical sorting often offer a more viable and economical solution than physical sorting. Unlike mechanical and optical methods, which struggle with contaminated, mixed, or dark plastics, additives handle a wider variety — including mixed, multi-layered, and black plastics. They improve compatibility between different polymers, which helps prevent mixed recycled materials from being thrown away.

MFI/viscosity modifiers and lubricants

MFI (Melt Flow Index)/viscosity modifiers and lubricants play a crucial role in enhancing the processability of recycled plastics by optimising their flow properties.

When recycled materials fall short of the required standards, additives can help — for example, transforming a material with a melt flow index of 5 into the equivalent of 30, making it suitable for a wider range of processes.

Injection molding and extrusion require different melt flow characteristics in the materials being processed. Specifically, injection moulding generally demands material with a higher melt flow, while extrusion benefits from materials with lower melt flow.

Lubricants minimise friction during processing, which not only reduces energy consumption but also decreases wear on machinery. The result is a more efficient manufacturing process with faster production cycles, improved mold filling, and easier part release — all contributing to cost savings and enhanced operational efficiency.

In some cases, blending PP with PE is intentional. PP is stiff and strong but can be brittle at low temperatures, while PE is more flexible and impact-resistant. By adjusting the blend ratio, recyclers can produce materials with predictable, tunable performance for specific uses, such as decking, car parts, or pipes.

The presence of PE can make it difficult to improve the melt flow of PP, posing a significant challenge for manufacturers. STRUKTOL VMO products offer a unique solution, specifically designed to overcome this issue. They enable an increase in the melt flow index (MFI) even when PE is present. The STRUKTOL VMO series enhances the melt flow properties of PP in blends containing up to 35% PE.

Physical and mechanical property enhancement

Specialized additives enhance both the physical properties and aesthetic appeal of recycled plastics, turning them into high-quality materials that can compete with virgin plastics. By promoting a more homogenous blend of components within the polymer matrix, additives improve strength and durability through superior dispersion that results in a stronger, more stable product. Impact modifiers help mitigate the inherent brittleness of recycled plastics, allowing the material to withstand greater stress, while specialised additives designed for outdoor use, such as those in wood-plastic composites (WPC), significantly reduce moisture absorption to prevent degradation and ensure long-term durability. In addition, antioxidant additives protect polymer chains from breaking down during the high-heat recycling process, extending the material’s lifespan and preserving overall performance through repeated use and reprocessing.

Beyond strength, achieving a superior surface appearance is key to marketability. Additives enhance the dispersion of pigments and fillers, ensuring a uniform, streak-free colour and a refined surface quality. By improving the overall finish, these agents help recycled products meet stringent aesthetic expectations.

Struktol has developed a new line of capstock compounds for WPCs, featuring a ‘soft feel’ surface. These compounds provide scratch and mar resistance, improved adhesion, and superior anti-slip properties. They are ideal for applications such as handrails, poolside decking, stairs, and ramps, or any other area needing a softer surface with enhanced grip.

The development of these additives is not simply reactive; it reflects a proactive approach to innovation. In practice, some additive manufacturers may pursue a dual track strategy: responding quickly to customer needs through short term projects, while also investing in long term research initiatives that anticipate future challenges. For instance, the rise of odour modifiers and capstock additives emerged not from a single customer request, but from internal brainstorming sessions that identified unmet needs in the industry. This dynamic is crucial to circular business practices. Recycling and upcycling challenges shift constantly as new waste streams emerge, virgin resin markets fluctuate, and regulations evolve. Innovation pipelines that combine responsiveness with foresight are better positioned to support sustainable manufacturing over the long term.

Partnering for success in recycled plastics

As the quality, composition, and availability of recycled feedstock become increasingly variable, and processing methods and product demands grow more complex, collaborating with expert additive specialists has never been more critical.

Companies like Struktol bring deep practical experience in creating innovative solutions and custom formulations to tackle challenges at every stage of recycled plastics manufacturing. By partnering with a skilled additives provider, manufacturers can ensure consistent material quality, enhance processing efficiency, and explore new opportunities for recycled plastics.

Mike Mikolay and Iksoo Chun are Research Fellows, Struktol Company of America, LLC.