RECYCLING: The Importance of Quality-Assurance Testing for Recycled Materials

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Consider investing in these tools to ensure your material makes the grade.

Recycled plastics can vary from prime resins in a number of ways. However, for high-end consumers of recycled materials, the expectation for their performance and quality is not much different than for prime resins. Cleaning up a recycled feed stream so it meets the level of quality needed by the end user can be a very technology-intensive process. And as a result, a rigorous testing protocol needs to be followed to ensure quality and consistency to meet customer specifications.

Certainly, the higher the performance demands on the application that the recycled content will be used in, the more important it becomes that material is of consistent, high quality. In the earlier days of plastics recycling, much of the recycled material went into lower-end applications that perhaps didn’t require such rigorous quality-assurance testing and consistency. But today, brand owners and processors continue to push the boundaries, driving recycled materials into higher-end applications such as food contact and durable goods like electronics and automobiles. With such demanding end uses, recyclers are expected to deliver near-prime quality.

Those recyclers serving higher-end markets, and customers with narrow material specifications, already understand the quality-assurance process required to deliver consistent product. However, the recyclers that have this quality-testing capability are still in the minority. In today’s economic climate, most recyclers are not thinking about expanding operations, but expanding testing protocols. The latter only requires investment in lab testing equipment as a strategic, lower-cost approach to focusing on quality as a differentiator in challenging economic times. Here, we’ll explore some of the testing protocols and requirements that higher-end customers are looking for in a recycling partner.

For many applications, brand owners are not willing to compromise aesthetic quality or performance of their products. Environmental benefits are no longer linked inextricably with trade-offs in performance, since recycled content really can reach near-prime qualities with today’s reclamation technologies. To ensure quality, customers using recycled content in high-performance applications will ask recyclers to measure things like intrinsic viscosity (IV), presence of additives and chemicals, and ash content; and control for contaminants and appearance, similar to the expectations they set for prime materials used in manufacturing.

“As more and more companies publish their sustainability goals, the use of recycled resins is transitioning from just a low-cost alternative to a specified part of many new products. This transition is forcing recyclers to recognize that their products must now meet the same high quality and performance characteristics as virgin resin,” says Ron Whaley, CEO of Geo-Tech Polymers, a recycler in Waverly, Ohio. “Today, recyclers must be ready and capable to provide testing and certifications that their virgin competitors have been providing for years.”

Companies looking for high-quality recyclate need assurance that a recycler can meet both volume and quality requirements. So what type of testing equipment should recyclers have in their lab in order to perform the type of quality-assurance testing that customers increasingly need? Because processors and brand owners often have expectations that recycled content will perform as near to prime resin as possible, the quality testing equipment is likely quite similar to what you’d find being used at a prime-resin supplier or specialty compounder. The equipment listed below covers the very basics in testing that most recyclers will need. Additional equipment many be needed to meet specific customer requirements. If they have not already, recyclers should consider investing in the following:

 •  Melt indexers. Melt flow is perhaps the most fundamental of material specifications. A measure of melt flow is essentially a measure of the molecular weight of the material,  which will indicate performance in various applications. If a recycler would like to offer a more thorough diagnostic of the viscosity of material, they may want to invest in a capillary rheometer.

 •  Moisture analyzer. Just as if you would want to measure moisture content in a prime pellet, it is important to measure moisture content in recycled flakes. Residual moisture can create issues in the extrusion process. Because water is commonly used in recycling processes to separate plastics by density (sink/float) and to remove contaminants, there’s lots of opportunity to reintroduce moisture to the flake during recycling. Just as with prime resins, too much moisture in recycled plastics can result in issues such as poor coloration and splay, reduced impact and tensile strength, and other processing and performance issues. 

 •  Near-infrared spectroscopy. Because recycled materials often come from a mixed stream, testing with an NIR unit can provide an idea of how pure the material ultimately is. This can be particularly necessary for resins that have similar densities, such as PP and PE, which may not be fully separated by density or other non-NIR separation technologies. Comparing the spectra of the recycled material with spectra of known resins, you can tell which resins your recycle sample might contain and suggest levels of purity.

 •  X-ray fluorescence. For some applications and markets, there are materials that are prohibited from use in manufacturing, even if those materials are legacy materials that are reintroduced through the recycling value chain. Those prohibitions can include brominated flame retardants and chlorine-containing materials, both of which can only be detected at the elemental level through x-ray analysis.  To ensure additives are not present in recycled plastics that could render an entire batch of material non-conforming, XRF analysis should be part of the testing protocol for certain streams and customers.

 •  Oven. Ash content can be another issue that customers will want recyclers to control for. Many applications can tolerate a filler, but there is usually a threshold for how much filler is acceptable. Ash content can be determined by placing samples in an oven, where the polymer can be burned off and the remaining ash content can be measured. In particular, users of post-consumer nylon will often need to know the ash content or set a limit on what the ash content can be in each batch.

 •  Automatic tensile tester. One of the most fundamental tests of prime resin materials, tensile testing, is also crucial for recycled materials. Customers will want to know that those materials will live up to expectations of durability and performance.  

 •  Blenders. Lastly, for batches that have been tested and might be slightly off-spec, blending the off-spec batch into on-spec batches in small doses will keep the off-spec material from being a total loss. As the old adage goes, the “solution to pollution is dilution.” This can absolutely work in recycling, so long as the “pollution” is not an outright prohibited material or additive. Having blending capability gives recyclers a good deal of freedom to create value out of material that might not otherwise meet customer requirements.

While most of this testing equipment will not be new to those that supply the industry with prime resins, it is not necessarily commonplace in the U.S. for recyclers to have these in-house testing capabilities. But as customer demands for recycled content continue to grow more sophisticated, so will recyclers’ need to match the quality-assurance and testing capabilities commonly employed by suppliers of prime resin. 


Kim Holmes is the sr. director of Recycling & Diversion at the Society of the Plastics Industry, where she heads up the efforts of the Recycling Committee and sustainability projects for the industry.  Before joining SPI in 2013, she was the owner and principal consultant at 4R Sustainability, where she worked on projects specifically related to recycling plastics and electronics. Contact: (202) 270-0058;