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PS (Polystyrene, Resin Identification Code #6)

Polystyrene is typically used in applications requiring its stiffness, resistance to cracking, and ease of modification. This section of the design® guide applies to rigid PS. Expanded PS (EPS) is addressed in its own dedicated section.

A limited number of curbside PS collection systems exist in North America so this material does not currently meet the collection accessibility criteria established in “APR’s definition of recyclable” or by the FTC. Anticipating the development and growth of future PS recycling programs, the APR recommends the following guidelines:

 

  • BASE POLYMER
  • BARRIER LAYERS, COATINGS & ADDITIVES
  • COLOR
  • DIMENSIONS
  • CLOSURES & DISPENSERS
  • LABELS, INKS AND ADHESIVES
  • ATTACHMENTS
  • RESIN IDENTIFICATION CODE, RIC

The use of post consumer PS content is preferred.
The use of postconsumer PS in all packages is encouraged to the maximum amount technically and economically feasible.

Non-PS layers and coatings require testing to determine the appropriate APR recyclability category.
The use of non-PS layers and coatings can be detrimental to recycling of PS if not implemented according to APR test protocols.  Layers and coatings must either separate and be removed from the container wall in the recycling process or have no adverse effects on the polymer in future uses.   When used, their content should be minimized to the greatest extent possible to maximize yield, limit potential contamination, and reduce separation costs.

Test protocol:  TBD

Degradable additives (photo, oxo, or bio) require testing to determine the appropriate APR recyclability category.
Recycled PS is intended to be used in new products. The new products are engineered to meet particular quality and durability standards given properties of typical recycled PS.  Additives designed to degrade the polymer diminish the life of the material in the primary use.  If not removed in the recycling process, these additives shorten the useful life of the product made from the RPS as well, possibly compromising quality and durability.  

Degradable additives should not be used without testing to demonstrate that their inclusion will not materially impair the full service life and properties of any product made from the RPS that includes the additive. These additives must either separate and be removed from the PS in the recycling process or have no adverse effects on future uses.   When used, their content should be minimized to the greatest extent possible to maximize yield, limit potential contamination, and reduce separation costs.

Test protocol TBD

Additives require testing to determine the appropriate APR recyclability category.
The APR recognizes that other types of additives may be required for the performance of a particular package but are not addressed in this document.   Additives such as de-nesting, anti-static, anti-blocking, anti-fogging, anti-slip, UV barrier, stabilizer and heat receptor agents and lubricants should be tested to determine their compatibility with recycling.  Of particular concern are additives, which cause the polymer to discolor or haze after remelting since recycled material with poor haze or discoloration is greatly devalued and has limited markets. This is particularly troublesome since it is difficult to identify material with this effect until extremely late in the recycling process where a great deal of added cost has been imparted into the material. 

Test protocol: TBD

Optical brighteners are detrimental to recycling.
Like many other additives, optical brighteners are not removed in the recycling process and can create an unacceptable fluorescence for next uses of the recycled polymer containing the brighteners. It is difficult to identify material with this negative effect until extremely late in the recycling process where a great deal of added cost has been imparted into a material of low value due to the additive.

Clear unpigmented polymer is preferred.
Clear material has the highest value as a recycled stream since it has the widest variety of end-use applications.  It is the most cost effective to process through the recycling system.

Black color renders the package non-recyclable.
NIR sorting technology is not capable of identifying a black polymer and manual sorting cannot distinguish one black polymer from another.   Other separation techniques such as float-sink cannot be employed since many black polymers sink with PS/PLA.  Therefore, black packaging is considered a contaminant for nearly all reclaimers.

Size and shape are critical parameters in MRF sorting, and this must be considered in designing packages for recycling. The MRF process separates items by size and shape first, then by material.  Screens direct paper, and similar two-dimensional lightweight items, into one stream; containers and similar three-dimensional heavier items into another steam; while broken glass and smaller but heavy items are allowed to drop by gravity to yet another stream, which may or may not be further sorted.  Large, bulky items are typically manually sorted on the front of the MRF process.

Items more two-dimensional than three-dimensional render the package non-recyclable per APR definition.
Aside from not being captured in the plastic stream, they cause contamination in the paper stream. Items should have a minimum depth of two inches in order to create a three-dimensional shape for proper sorting. This issue is unrelated to the polymer type. The APR encourages and anticipates developments in MRF design and technology to improve capture and recovery of thin plastics; however, at the current time this technology either does not exist or is uninstalled in the majority of MRFs. 

Items smaller than 3 inches in all dimensions render the package non-recyclable per APR.
The industry standard screen size loses materials less than three inches to a non-plastics stream, causing contamination in that stream, or directly to waste.  These small packages are lost to the plastic recycling stream. It is possible that some small containers travel with larger ones when either the screens wrap with film or they are operated above their design capacity.  Film wrapping reduces the effective size of the screen and over-running provides a cushion of large items on which  the smaller items travel.  The design guidelines use clean screens operating at their design capacity for the determination of the recyclability category. The APR anticipates and encourages technology development to improve the process of small package recovery but currently these items are not recovered.

Items greater than two gallons in volume are detrimental to recycling.
Recycling machinery, particularly automatic sorting equipment, is not large enough to accept items larger than two gallons. Because larger containers jam the systems, most MRFs employ manual sortation before the automatic line to remove the large items. These items are recovered in a stream of bulky rigid containers that are sold and processed as polyethylene since the vast majority of bulky rigid items are comprised of this polymer. Other polymers either negatively effect or are lost by the polyethylene processing.

Polypropylene and polyethylene closures are preferred.
Since these polymers float, they are most easily separated from the bottle in conventional separation systems.  Additionally, the PS recycling process captures floatable polyethylene and polypropylene to create an ancillary stream of marketable material. Care must be taken when modifying the polyethylene or polypropylene to ensure the modifier does not increase the overall density to the point it sinks.  Note that these are not removed in the combined recycling process but, instead become a contaminate.  Minimizing closure size is advantageous to both processes.

Closure systems without liners are preferred.
Due to size and thickness, most liners are lost in the recycling process thereby slightly decreasing yield. Closures without liners do not experience this loss.

EVA and TPE liners in plastic closures are preferred.
Both EVA and TPE float in water and will be separated in the recycling process with the floatable polyethylene and polypropylene.  Since EVA and TPE are compatible with these polymers, and in fact enhance their properties, they are preferred.

Closures containing metal or metal foils require testing to determine the appropriate APR recyclability category.
Metal is difficult to separate from PS compared to the preferred closure systems (polypropylene and polyethylene) and adds both capital and operating costs to conventional reclamation processes.  Even a small amount of metal left in the recycled polymer stream will block extruder screens in remanufacturing.   Large metal items attached to PS packages may cause the package to be directed to the metal or waste stream in the recycling process, causing yield loss.  Small metal components such as spray dispenser springs unravel in the recycling process and blind screens, adding significant cost for removal at the end of the process.

Two PET test protocols are available that can be used for PS/PLA:

  • Screening Test:  New Eddy Current and Magnetic Test for Attachments
  • Definitive Test:  Closure Test

Closures made from thermoset plastics are detrimental to recycling.
These materials are heavier than water and sink in the float-sink tank with PS/PLA.   They are extremely difficult to separate from the recycled polymer flake, requiring a costly and inexact polymer flake sorter currently not installed in many reclaiming operations.

Closures containing silicone polymer are detrimental to recycling.
Silicone generally sinks in the float-sink tank with the PS/PLA and is difficult to remove with other methods, thereby causing contamination in the final product.

The use of PVC closures or closure liners render the package non-recyclable per APR.
PVC sinks and is extremely hard for the recycler to remove. The recycled PS stream is very intolerable to even minute amounts of PVC since it degrades quite easily.

Removing adhesives is a significant component to the cost of recycling.  The most recyclable packages use the lowest quantity of recycle-friendly adhesive.  Lower adhesive usage reduces processing cost and potential contamination risk.

Polypropylene or polyethylene labels with a specific gravity less than 0.95 are preferred.
These materials float in water so they are separated from the PS in the float-sink tank with the closures.  Since they are the same general polymer as most of the closures they do not contaminate or devalue this stream.  Care should be taken to ensure that any modifiers to the label material do not increase its density above 0.95.  Note that these are not removed in the combined recycling process but, instead become a contaminate.  Minimizing label size is advantageous to both processes.

Laminated labels require testing to determine the appropriate APR recyclability category.
Labels that break into small, very thin pieces of material are more difficult to manage in the recycling process because they behave erratically in a float-sink tank. Therefore labels that stay intact are preferred.  Carry-over of delaminated labels into the RPS can result in contamination.

One PET test protocol is available that can be used for PS:

  • Definitive Test: New Delamination Test

Full bottle sleeve labels require testing to determine the appropriate APR recyclability category.
Full bottle sleeve labels cover a large amount of the bottle surface with a polymer that is not the same as the bottle body.  Because of this, a sleeve label designed without considering recycling may cause a false reading on an automatic sorter and direct a PS bottle to another material stream where it is lost to the process.   Furthermore, some sleeve label materials cannot be removed in the recycling process and contaminate the RPS produced.  Sleeve labels that have been found compliant with the APR test protocols should be selected.

One PET test protocol is available that can be used for PS:

Pressure sensitive labels require testing to determine the appropriate APR recyclability category. Pressure sensitive labels generally require complete adhesive coverage which is greater than other typical label methods.  This raises the importance of the compatibility of the type of adhesive with the recycling process.  Adhesives resistant to washing in the recycling process allow labels to remain on the container and become contaminants in the final product. Adhesives that have been found compliant with the APR test protocols should be selected.

Two PET test protocols are available that can be used for PS:

Polystyrene labels are preferred for PS Containers.
PS is the same material as the bottle body so the label will behave like the bottle and be recycled along with it.

Label structures that sink in water because of the choice of substrate, ink, decoration, coatings, and top layer require testing to determine the appropriate APR recyclability category.
The reclaimers rely on float-sink systems to separate non-PS materials.  Label components that sink with the PS end up in the recycled polymer stream as contaminants.

High melting temperature plastic labels such as PET are preferred.
These labels sink in the float sink tank if one is employed and remain solid in the PS extruder so they can be removed through filtering.

Paper labels are detrimental to recycling (for pressure sensitive paper labels reference the pressure sensitive label category).
The PS reclamation process involves a hot caustic wash that removes glue and other label components to the levels required to render the RPS usable.  Paper, when subjected to these conditions, becomes pulp which is very difficult to filter from the liquid, thereby adding significant load to the filtering and water treatment systems.  Individual paper fibers making up pulp are very small and difficult to remove so some travel with the PS.  Paper fibers remaining in the RPS carbonize when the material is heated and remelted, causing quality degradation and a burnt smell to the polymer.  Non-pulping paper labels that resist the caustic wash process sink in the float-sink tank, thereby causing RPS contamination.  These , although removed when the polymer is melt filtered, carbonize causing the same effect.

Metal foil labels are detrimental to recycling.
Sorting equipment in the recycling process is designed to detect and eliminate metal from PS.  Even very thin metal foil labels may be identified as metal by the sorting equipment and cause the entire bottle to be rejected as waste, thereby creating yield loss.  If not detected, they pass through the process with the PS and cause contamination issues in the final product.

PVC labels render the package unrecyclable per APR.
This material is extremely difficult to remove in the recycling process due to its similarity in density to PS.

PLA labels affixed to PS containers render the package unrecyclable per APR.
This material is extremely difficult to remove in the recycling process due to its similarity in density to PS and cause quality problems for the end product.

Adhesives require testing to determine the appropriate APR recyclability category.
Adhesives that wash off cleanly from PS and remain adhered to the label are preferred.  Label adhesive that is not removed from PS, or which re-deposits on the PS during the wash step is a source of contamination and discoloration when PS is recycled.

The recycling process is designed to remove reasonably expected contamination from the surface of the container to a degree necessary to render the polymer economically reusable in further applications.  In practice, some adhesives are resistant to this process so are detrimental to recycling. In extreme cases, an adhesive and label cannot be separated from the PS/PLA and may render a package not recyclable.

Two PET test protocols are available that can be used for PS:

Label inks require testing to determine the appropriate APR recyclability category.
Some label inks bleed color in the reclamation process, discoloring the polymer in contact with them and significantly diminishing its value for recycling. Label inks must be chosen that do not bleed color when tested under this protocol. 

Two PET test protocols are available that can be used for PS:

*See the definitive test for the appropriate label type

Direct printing other than date coding requires testing to determine its compatibility with the recycling system.
Historically, inks used in direct printing tend to bleed or otherwise discolor the polymer during the recycling process, or introduce incompatible contaminants. In either case, the value of the recycled polymer is diminished.  Some inks used in direct printing do not cause these problems.  The specific ink must be tested to determine its effect. 

Two PET test protocols are available that can be used for PS:

Clear PS attachments affixed to PS containers are preferred.
Attachments made of the base polymer are recovered and recycled with the base polymer without causing contamination or yield loss, thereby generating the highest value.

Tamper evident sleeves and safety seals require testing to determine the appropriate APR recyclability category.
If tamper resistance is required in specific product applications, it should be an integral design feature of the bottle.  The use of tamper-resistant or tamper-evident sleeves or seals is discouraged as they can act as contaminants if they do not completely detach from the bottle, or are not easily removed in conventional separation systems.  If sleeves or safety seals are used, they should be designed to completely detach from the bottle, leaving no remains on the bottle. The material used should float and separate from the PS in the float-sink system.

One PET test protocol is available that can be used for PS:

Non-PS attachments such as handles require testing to determine the appropriate APR recyclability category.
These should not be adhesively bonded to the package and should readily separate from the package when ground.   They should be made from materials that float in water such as PP or HDPE.  If adhesives are used to affix attachments, their selection should consider the adhesive criteria within this document. 

One PET test protocol is available that can be used for PS:

Screening Test: Labels, Closures and Attachments Floatability Test

Metal and metal containing attachments are detrimental to recycling.
Examples include metal foils and metalized substrates that sink in water as well as metal sprayer balls and springs. In the recycling process these items are either identified and removed along with their PS component in the early stages, thereby causing yield loss, or they pass into the recycling process causing a contamination issue.  Since they are heavier than water they sink with the PS in the float-sink tank.  Many of these items are too small to be removed with machinery designed to remove metal such as eddy current and optical separators.  Springs in particular unravel and become entangled in filtering screens throughout the recycling process. 

*An APR test to delineate between metal items which render the package non recyclable per APR Definition and metal items that are detrimental to recycling is anticipated for 2017.

Paper attachments are detrimental to recycling.
The PS reclamation process uses a hot caustic wash to remove glue and other contaminants to the levels required to render the RPS usable.  Paper, when subjected to these conditions, becomes pulp which is very difficult to filter from the liquid, thereby adding significant load to the filtering and water treatment systems.  Individual paper fibers making up pulp are very small and difficult to remove so some travel with the final polymer.  Paper fibers remaining in the RPS carbonize when the material is reused causing quality degradation.

Welded attachments are detrimental to recycling.
A certain amount of a welded attachment cannot be separated from the main polymer in the recycling process.  These attachments, even when ground and made of floatable materials, cause contamination and yield loss issues in both cases: when the PS/PLA they are attached to causes the ground section containing both polymers to sink, or when the ground section floats.

RFID’s (radio frequency identification devices) on packages, labels or closures are detrimental to recycling).
Unless they are compatible with PS/PLA recycling and are demonstrated not to create any disposal issues based on their material content, the use of RFID’s is discouraged as it limits yield, introduces potential contamination, and increases separation costs.

PVC attachments of any kind render the package non-recyclable per APR.
The use of PVC attachments of any kind on PS packaging is undesirable and should be scrupulously avoided. This includes thermoforms of PVC that may be visually confused with PS thermoforms. Very small amounts of PVC can severely contaminate and render large amounts of PS useless for most recycling applications.  In addition, PVC is very difficult to separate from PS in conventional water-based density separation systems due to similar densities (densities greater than 1.0) that cause both to sink in these systems.

PLA attachments of any kind affixed to  a PS container render the package non-recyclable per APR.
The use of PLA attachments of any kind on PS packaging is undesirable and should be scrupulously avoided. Very small amounts of PLA can severely contaminate and render large amounts of PS useless for most recycling applications.  In addition, PLA is very difficult to separate from PS in conventional water-based density separation systems due to similar densities (densities greater than 1.0) that cause both to sink in these systems.

Use the correct Resin Identification Code symbol of the proper size as detailed in ASTMD7611 is encouraged.

 

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