How Many Times Can You Recycle Plastic?

Imagine a mountain of red Legos. They can be arranged in any form; a long chain, a giant tower, a house! The possibilities are infinite. This is the same principle that plastics use. One molecule, known as a monomer , is like a single Lego. The molecules can be arranged in any form, and used any number of times, to form a polymer . These polymers can be molded into various shapes while maintaining their durability. With just one set of ingredients, you can make a variety of shapes and forms.

With competitive price and timely delivery, Fangtai sincerely hope to be your supplier and partner.

 

While plastic's incredible durability is useful for us, it's not so good for the environment. Many plastics take hundreds of years to decompose, leading to pollution in oceans, soil, and air. Researchers are trying to develop biodegradable plastics. Another solution is recycling. By turning waste useful again, we can save plastic from landfills and oceans.

 

Unfortunately, recycling also has its limitations. Plastics cannot be recycled forever; but just how many times can they be recycled?

Abstract

Disposal of plastic waste has become a widely discussed issue, due to the potential environmental impact of improper waste disposal. Polyethylene terephthalate (PET) packaging accounted for 44.7% of single-serve beverage packaging in the US in , and 12% of global solid waste. A strategic solution is needed to manage plastic packaging solid waste. Major beverage manufacturers have pledged to reduce their environmental footprint by taking steps towards a sustainable future. The PET bottle has several properties that make it an environmentally friendly choice. The PET bottle has good barrier properties as its single-layer, mono-material composition allows it to be more easily recycled. Compared to glass, the PET bottle is lightweight and has a lower carbon footprint in production and transportation. With modern advancements to decontamination processes in the recycling of post-consumer recycled PET (rPET or PCR), it has become a safe material for reuse as beverage packaging. It has been 30 years since the FDA first began certifying PCR PET production processes as compliant for production of food contact PCR PET, for application within the United States. This article provides an overview of PET bottle-to-bottle recycling and guidance for beverage manufacturers looking to advance goals for sustainability.

Keywords:

PCR, rPET, recycling process, sustainability, legal compliance, chemical recycling, advanced recycling, beverage, food contact surface

1. Introduction

Plastic packaging accounts for 70% of the market of consumer products. Beverage packaging can primarily be classified into cold fill (such as aseptic), carbonated soft drinks, and hot fill. In choosing the appropriate beverage packaging material, the material must be able to withstand filling/handling temperatures, sustain the quality of the packaged beverage over its intended shelf life, and withstand internal pressurization requirements. Thermal stability requirements are dictated based on the operation for sterilization of the beverage and the container. Cold-fill beverages do not require sterilization. These will include water and high-acid beverages. Hot-fill beverages include high-acid and acidified products such as isotonic drinks, teas, and juice. Carbonated beverages (such as soft drinks) will require a package that does not deform with internal pressures up to 5 bar at room temperature. Choice of packaging material plays an important role in preventing degradation, in maintaining organoleptic qualities (scent, flavor, texture) and nutritional value (e.g., prevention of vitamin C oxidation in orange juice), and in ensuring consumer health and safety. Several packaging materials are appropriate in barrier and mechanical properties for use in beverage packaging. Beverage packaging includes glass bottles, aluminum cans, foil-laminated carton boxes, foil-laminated flexible pouches, and plastic bottles [1,2].

Polyethylene terephthalate (PET or PETE), which is a polyester plastic, is one of the most widely used packaging materials for beverages. Due to its excellent transparency, light weight, gas and water barrier properties, impact strength, UV resistance, and unbreakability (compared to a glass bottle), the production and use of PET bottles for beverage packaging has consistently increased worldwide. PET is a recyclable solution with performance benefits that are not available in alternative packaging options, such as glass bottles, aluminum cans, paperboard cartons, and other plastics. According to the data extracted from Euromonitor International (London, England), in the beverage industry, the PET bottle accounts for 67% of the market share between water, carbonated soft drinks, energy drinks, tea, and coffee. For single-serve bottles (<1 L), PET accounted for 44.7% of single-serve beverage packaging in the US in . In comparison, aluminum cans accounted for 39%, glass for 11%, and high-density polyethylene (HDPE) for 3.4%.

As with most plastics, PET is a petroleum-based polymer, and it does not readily decompose when released into earth's environments via plastic waste leakage. In , global plastic waste generated was approximately 141 million tons [3]. Packaging waste buried in landfills can still contribute to air, water, and soil pollution. Additionally, plastic leakage into landfills consumes available landfill space. It must be noted that the percentage of plastic in the landfill by volume is higher than that by weight [4]. Incineration of plastic packaging waste avoids consumption of landfill space and generates energy, but with the drawbacks of emissions creation and air pollution. The Great Pacific Garbage Patch is another example of unwanted plastic ending up in an undesirable place. Pollution from plastic waste, therefore, has been acknowledged as a major global environmental issue.

According to the United States Environmental Protection Agency (EPA) in , 35.7 million tons of plastic waste was generated in the United States, which was 12.2% of total municipal solid waste (MSW). In addition to PET bottle waste, this plastic waste included polyolefin and polyester bags, wraps, bottles, and jars. Approximately 27 million tons of plastic (18.5% of US plastic waste) was discarded into landfills. Only 4.5% of plastic packaging was recycled [5]. According to European Economic Area data for the EU in , 34.4 kg of plastic packaging waste was generated per EU inhabitant, on average. The EU recycled at a rate of 41% (14.1 kg) per inhabitant, on average [6]. Globally, PET accounted for 12% of total solid waste. The EU's Commission for the Environment has conceived pathways by which member countries may significantly reduce plastic waste leakage. These pathways include concepts for incentivizing change in consumer behavior, improvement of waste management involving waste collection, waste separation and recycling, as well as the restriction of wastes accepted into landfills [7].

Source reduction, also known as waste prevention, is defined by the EPA as 'a change in the design, manufacturing, purchasing or use of materials or products (including packaging) to reduce their amount or toxicity before they become municipal solid waste' [8]. To control and reduce plastic waste, source reduction can be implemented utilizing principles of waste management practice (reuse, reduce, redesign, and recycle packaging) in combination with packaging innovation. Many geographical regions, including North America, Europe, and South Asia, have encouraged a recycling program and/or adopted a policy for packaging waste management. These have included deposit systems, taxes, and plastic bag bans.

Bottle reuse through returnable bottle systems has been widely practiced in South America and in several European countries [9,10,11], thus achieving waste reduction. However, in most regions, PET bottles are intended for single-use packaging and are disposed after first use. To reduce the environmental impact from packaging waste and to drive sustainability in plastic packaging, municipal recycling programs have been implemented to capture recyclable material streams. The inclusion of recycled plastics in food contact packaging has been slow to establish, due to preconceived concerns for food safety. However, with increased public pressures and increased adoption among manufacturers, this perception is beginning to change [12].

Post-consumer recycled (PCR) material can be used as the primary packaging material for food contact applications. As such, there has been a steady increase in the collection and recycling of PET bottles into PCR. PET recycling technology has been widely implemented and advanced for more than five decades [13,14,15]. These advancements continue with improved methods of recovery and conversion into PCR pellets. Moreover, bottle-to-bottle recycling development diverts this PCR pellet from downcycling applications. Considering the ensemble of bottle-to-bottle and bottle-to-strapping/textile/injection applications, PET has become one of the most successfully recycled plastic materials.

Processes for the recycling of PET packaging waste have become increasingly developed, but knowledge of the unit operations involved in these recycling processes has remained specific to recyclers. Beverage manufacturers harbor concerns regarding the food contact safety of PCR produced from PET containers that may have previously packaged chemicals or household products. Hazardous compounds potentially absorbed into the PET polymer may migrate into food stuff if they are not properly removed during recycling [16]. Available methods, such as the management of waste collection, super clean process, and advanced recycling, offer pathways to produce PCR PET with the removal of chemical contamination. These processes have the potential to produce PCR PET with contaminant levels similar to virgin PET [17].

The objective of this review article is to provide a framework for beverage manufacturers when making the decision on whether to consider PCR PET options for beverage products. The pertinent details about recycling, applications, food safety, regulations, and future trends are discussed in detail to assist these manufacturers.

3. Recycling Operation for PCR PET

3.1. Sortation and Purification

Virgin PET is designed to purpose. Grades target specific ranges for intrinsic viscosity and crystallization rate, depending on the application (e.g., water, hot fill, carbonated soft drink, thermoforming). Tailoring of the virgin material is done with control over the input comonomer, comonomer content, and catalyst system. Additive packages are added at the resin manufacturer or converter to convey performance advantages. Additive packages may include, but are not limited to, reheat additives, toners, colorants, and oxygen barriers.

The PET recycle stream is initially composed of PET containers, container closures, labels, and residues from consumer products. As such, the recycle stream has the potential to contain high-density polyethylene (HDPE) and polypropylene (PP) from the closure. Adhesive, polyethylene terephthalate glycol (PETG), paper, and polyvinyl chloride (PVC) may enter the final recyclate from container labeling. In addition to product residues retained by the packaging, dirt and non-intentionally added substances may enter the recyclate from the reclamation process.

rPETs produced from mechanical recycling processes contain a portion of the contaminants entering the recycle stream. Contamination is reduced via various sorting unit operations, as shown in A,B. These unit operations may include near-infrared (NIR) material identification and separation, color recognition and separation, eddy-current separation, float/sink density separations, and elutriation removal of labels. More recently, artificial intelligence (AI) has been implemented in the sortation process. Through deep learning and vision systems, AI can identify and pick non-PET containers to remove them from the recycle stream.

Open in a separate window

Advanced or chemical recycling of PET, described earlier, reduces the recycle stream to much smaller molecules, or even monomer blocks. Non-PET contamination is removed, and the repolymerized PET crystallization rate and IV can be tailored to the intended application, as shown in . Management of process residuals from chemical recycling is non-trivial since these residues, particularly DEG, can affect both the copolymer composition (as co-monomer) and the flexibility of the re-polymerized PET (as internal slip agent).

Open in a separate window

IV in mechanically recycled PET is targeted via polycondensation reactions. The two main approaches to targeting IV are: (1) enhancing IV on the incoming PET flake, and (2) enhancing IV in the outgoing PET pellet. Both techniques make use of holding the PET in inert environments at a temperature of 190'210 °C. When IV is increased in the flake entering the extruder (e.g., Erema® systems; chain extenders, solid-phase reactor polycondensation) flake is simultaneously dried (reducing hydrolysis and IV losses in the extruder). When increasing IV in the flake, volatiles are removed from the flake; however, volatiles generated during degradation in extrusion will remain with the finished product. Solid-state polymerization (SSP) is performed on the pellet outside of the extruder. SSP has the added benefit of volatiles removal for volatiles present before and generated during the extrusion process. For instance, it can lower the acetaldehyde and ethylene glycol, and hence minimize concentration of 2-methyl-1,3-dioxolane [110].

Mechanical recycling of PET with an appropriate level of repolymerization can produce a product with IV suited to purpose. The contamination extent of non-additives in the final mechanically recycled product is dependent on the efficacy of the sortation operations. Even in the case of highly efficient non-additive removal, the final mechanically recycled rPET will contain a blend of the various comonomers, catalysts, toners, colorants, and functional additives present in the incoming stream.

3.2. Super Cleaning Process

Non-food contamination poses a risk to consumer safety [25]. Non-food PET bottles, which may have previously contained solvents or harmful chemicals, are inevitably collected in the PET recycle stream and fed into the recycle process. Non-food containers, thus, can contaminate the rPET product. It is desirable to keep these non-food PET bottles in the collection stream. Super-clean recycling, also called deep-clean recycling, has been used to increase the efficient decontamination of recycled PET bottles for re-use in direct food contact packaging. There are three stages to the super-clean process: (1) high-temperature wash, (2) gas wash, and (3) chemical wash [16,111]. More specifically, the super-clean process makes use of high temperature washing, vacuum, surface treatment, melt filtration, and melt degassing to remove contamination [112]. In the flake wash, chemicals such as caustic soda (with the assistance of ethylene glycol) hasten the contaminant removal. SSP is likewise employed to remove contaminants. Heating the PET to 200 °C brings the contaminants to the surface of the PET pellets or flakes. Next, vacuum or inert gas treatment is applied to mobilize and remove the contaminants from the surface and out of the recyclate stream.

Cleaning efficiency depends on the quantity of non-food bottles in the recycling feed stream. Super-clean bottle-to-bottle recycling was first developed at plant scale in Beaune, France [16]. Several countries, including the US, Netherlands, Germany, Switzerland, and Australia, have followed with the construction of super-clean plants [113,114].

4. Processing and Performance Differences between Virgin PET and Post-Consumer Recycled PET

PCR PET behaves differently than virgin PET in several different ways. The process required to make a container with a given grade of PCR is not just a material change. Processing could be challenging for individuals not skilled in the art. When manufacturing containers with virgin PET, the process tends to be repeatable every time new production is started. When using PCR, different lots from the same supplier can behave very differently. This is because the ingredients or raw materials that go into producing the PCR can vary from batch to batch. For beverage containers, the virgin material primarily falls in three categories:

• (1)

  Water grade (low IV, acetaldehyde suppression, could have additives to enable ultrathin bottle walls);

• (2)

  Heat-set grade (higher IV, DEG suppression, co-monomers to suppress hot-fill shrinkage, could have additives to aid reheating and crystallization);

• (3)

  Carbonated soft drink (CSD) grade (highest IV, co-monomers to resist expansion).

When bottles made from these resins are recycled, each bale of bottles may contain different levels of the described virgin grades. The final PCR PET pellet may have many different co-monomers, additives, and levels of additives. Additionally, depending on impurities and colors included in the feed stock, the resultant color of PCR may vary. PCR manufacturers try to minimize these influences, but the converter needs to plan and adapt to variation. Variability is pronounced due to seasonality (as consumption patterns change with the season) and bottle bale source (when including various geographies feeding into the recycled stream). Variability in PCR material properties impact converter processing and the functionality of the product. Converter risk includes impact to preform injection stability and to the stability of the blow molding processes. Variation in PCR may impact the consumer's sensory experience of the product, both visually and during consumption. The bottle manufacturing process can impact the final PCR PET bottle quality.

4.1. Injection

4.1.1. Drying of Material and Injection Pressure

PET requires drying before processing to avoid loss of molecular weight or intrinsic viscosity (IV). During storage, PCR tends to pick up moisture faster compared to virgin material. This difference in moisture adsorption/absorption may be due to differences in crystallinity between the virgin and PCR plastic pellets. Lower crystallinity results in easier propagation of moisture into the plastic pellet from the atmosphere. PCR can be lower in crystallinity compared to virgin material, and the shell of the pellet can be less crystalline than its core. During injection of preforms, the crystalline shell melts, but not the higher crystallinity core. The screw recovery and barrel temperature profile will need to be adjusted to avoid gumming issues. During the recycling process, vinyl ester end groups can generate, and they can cause yellowing or browning of PET during drying [115]. As a result, some PCRs require drying at relatively low temperatures for longer durations. Longer dryer times pose a productivity issue. Differences in dryer time requirements between PCR and virgin PET present a significant operational challenge when drying a pellet blend. A balance needs to be struck to ensure both materials are dry without degradation. With lot-to-lot variation in PCR, chosen conditions need to be applicable to a range of material properties.

4.1.2. AA Generation

Acetaldehyde (AA) is a known byproduct of processing PET. It is a naturally occurring flavoring compound, which is perceived as a sweetener. AA is typically a problem with unflavored water, where the consumer expects odorless and flavorless product. With PCR composition varying lot-to-lot, the risk of AA generation can change from lot to lot. While this may not be a critical concern if the PCR is being used for hot-fill or carbonated sweetened products, this is critical to the injection of preforms for water bottles.

4.1.3. Haze Due to Additional Nucleation Sites

Preforms made with PCR may contain haze. Two likely reasons are the additional nucleation sites and the availability of smaller chains (that crystallize more readily), generating haze as a result. Often, preform haze can be rectified by increasing the cooling time in the injection cycle. Increases to cycle time have the negative impacts of reduced productivity, increased degradation, increased AA, and increased cost. The cycle time penalty can be anywhere between 10% and 30%.

4.1.4. Degradation of IV

Intrinsic Viscosity (IV) is a gauge of molecular chain length and thus a predictor of strength of the material. When a resin goes through the injection molding process, it generally reduces in chain length. With virgin resins, for normal injection conditions and good drying practices, this loss is well understood and is usually no more than 0.03 dL/g. With PCR, this loss is relatively unpredictable. Mechanically and chemically recycled materials can have different residual compounds in the PCR that can negatively affect stability when processed through a high-heat and high-shear environment (e.g., the conditions inside of the extruder). Residual reactants and catalyst used to depolymerize PET during chemical recycling, if not removed effectively before PET is repolymerized, will act to depolymerize the PET during injection. The resulting drop in IV during injection could be significant. Sensitivity to degradation conditions may vary from batch to batch.

4.2. Preform and Container Appearance

The PCRs can vary significantly in color, between lots and between manufacturers. The variation between different grades is presented in .

Open in a separate window

The crystallinity in the pellet gives it a white appearance. This white envelope is not representative of the eventual color of a transparent article. An image of preforms made with 100% PCR from various manufacturers is shown in . As can be observed in the image, appearance can vary significantly from manufacturer to manufacturer.

Open in a separate window

As shown in , a stark difference in color is seen at the preform level, where plastic wall thickness is about 10 times that of the final bottle. When preforms are converted into bottles, transparency increases, and color density decreases with the reduction of wall thickness. Color differences are most visible in the bottle finish, where thickness is maintained.

Contact us to discuss your requirements of pet recycling machine factory. Our experienced sales team can help you identify the options that best suit your needs.

Additional reading:
**How effective is a PE PP washing recycling line?** A PE PP washing recycling line is highly effective for converting plastic waste into reusable materials. It reduces environmental impact, promotes

Open in a separate window

demonstrates the range of bottle mid-section color and haze, as measured on Colorquest' equipment. With the thin wall, the lightness dimension of color scale (L* value) of the container is barely different than the virgin container. The other two dimensions a* (green-red dimension) and b* (blue-yellow dimension) are relatively closer. The difference in % haze and in yellowness index is more significant.

Table 1

PET TypeL*a*b*% HazeYellowness IndexVirgin94.61'0.040.600.741.13PCR Grade A94.83'0.100.772.341.39PCR Grade B94.88'0.141.321.922.42PCR Grade C93.19'0.172.646.204.99PCR Grade D94.65'0.140.822.591.47Open in a separate window

4.3. Blow Molding

4.3.1. Preform Heating (Energy Requirements)

Mobilizing the PET polymer chains for blow molding requires heating the PET in the preform body above its glass-transition temperature, most often accomplished with near-infrared radiation from heating lamps. Preform color affects the efficiency of absorbing near-IR radiation. Processing of the preform into a bottle can vary greatly when using PCR, as opposed to virgin PET. As discussed earlier, PCR composition varies. The amount of reheat additive can therefore vary from batch to batch. Material will vary in reheat concentration based on source. For example, if PCR is sourced from Asia, where reheat additives are not commonly used, the PCR will likely not have reheat additive. Similarly, for the American market, PET resins for water and CSD applications are likely to have lower levels of reheat additives than PET resins meant for heatset applications like isotonic drinks and juices. When US material is recycled, the resultant PCR will vary in reheat additive content from batch to batch based on changing concentrations of water, CSD, and heatset bottles. Generally, PCRs that appear cleaner are likely to require more heating energy (unless they have been supplemented with reheat additive) when blow molding, as compared to their darker PCR counterparts.

Darker PCRs tend to have more gate swing or off-centered gates, leading to bottle wall thickness variation on the horizontal plane (also known as side-to-side wall thickness variation in the blow molding industry). Lot-to-lot preform color variation will impact IR absorption and the bottle material distribution. The process parameters (recipe) for blow molding may need to be adjusted every time bottles are produced. That said, those experienced in blow molding are able to adjust the processes whenever there is such a need.

4.3.2. Material Distribution Variation

Plastic bottle material distribution refers to the variation in weight in the vertical direction. In engineered applications, such as bottles meant for hot-fill or CSD, control over material distribution ensures the desired functional performance. As explained earlier, the process recipe may require finetuning with PCR composition and color changes. Polymeric chain lengths or molecular weights could have a wider distribution with PCR. As such, material stretch is more variable than for virgin PET, leading to more variation in the material distribution. These factors combined usually result in a more variable distribution of material within the body of the bottle, as compared to bottles made with virgin material.

4.3.3. Scrap Rate

Inclusions in the PCR PET can lead to container ruptures during blow molding. Variation in material distribution can lead to final container rejection. The scrap rate when producing containers from PCR PET tends to be higher than the scrap rate for virgin material. The scrap rate greatly depends on the specific grade and lot of PCR, the % PCR in the container, and the container performance requirements. A clean mechanically recycled or chemically recycled PET with few inclusions and high clarity would not be expected to have a significant scrap rate. Similarly, when blending 10% or 15% PCR with virgin PET, the scrap rate would not be expected to raise any red flags. Forgiving applications (such as non-pressurized water) and container shapes without complex geometry (or fine lettering) have wider specifications and wider operating windows, allowing operation at acceptable scrap rates with some container variation. Challenging and performance-demanding applications, such as hot fill and CSD, require precise material distribution. The scrap rate will tend to be higher for demanding applications.

4.4. Container Performance

4.4.1. Bottle Shrinkage When Exposed to Heat

Dimensional stability is a concern for hot-fill containers, where bottles are exposed to temperatures equal to or exceeding 85 °C (185 °F) for many minutes. Issues with dimensional instability post-filling include shrinkage in height and/or diameter, uneven standing surfaces, and ovalization (impacting ability to properly secure a label). Virgin PET grades intended for hot-fill applications are designed to have lower levels of diethylene glycol (DEG). This particular byproduct of PET manufacturing leads to shrinkage in container height, diameter, and overall capacity, as well as deformation of features. For PCR, which is a mixture of different PET grades, the DEG content may vary drastically lot to lot. As a result, the shrinkage of the container post-hot-fill may vary. Shrinkage of bottles containing PCR would vary but would generally be expected to be higher than that observed in virgin-material containers. Careful bottle crystallinity management can mitigate this shrinkage.

4.4.2. UV Light Performance

In some circumstances, PCR can reduce some UV light transmittance. As discussed in Section 4.2, containers made with PCR content may display a yellow/brown tint, especially with increasing content levels. is taken from one experiment where light transmission was measured on virgin, 25% PCR, and 100% PCR samples. In this specific case, the transmission of UV light (330 nm'400 nm) was reduced between 10% to 50% compared to the virgin control. This performance would again be affected by the grade and lot of PCRs. Food and beverage products with UV sensitivities may benefit from this attribute.

Open in a separate window

4.4.3. Topload

Resistance to topload, also known as compressive strength, is the ability of the bottle to resist buckling under load. PET bottles can withstand a significant compressive load. As a result, secondary packaging for many beverage PET containers can be minimized for palletization. Introduction of PCR may impact the bottle's compressive strength. If the PCR used is of lower average molecular weight than the virgin material it is replacing, increased PCR content may lead to decreased topload strength. Likewise, wide molecular weight distribution in bottles containing high PCR content may lead to variable topload performance.

4.4.4. Burst Strength and Thermal Expansion

Burst strength and thermal expansion, which are critical performance attributes for pressurized containers (e.g., CSD products), may be affected by the lower average molecular weight and wider molecular weight distribution characteristic of some PCRs. Generally, burst pressures reduce, and expansions increase, with increasing PCR content. Inclusions in the plastic wall may lead to unpredictable and lower burst pressures.

5. Application and Limitations

5.1. Cold-Fill Applications

In many beverage applications, 100% PCR container options are available. These are mainly cold-fill beverage containers not exposed to pressure from carbonation or hot product. Such products include still water, chilled juices, tea, coffee, milk, and other cold-chained or aseptically filled (bottle sterilized with peracetic acid) products. The main functional requirements of these bottles are product containment, topload strength, and recloseability. These bottles are not required to withstand pressure, heat, or vacuum.

Color is a performance attribute impacting consumer visual appeal. One way to influence color is through the use of toners. Consumers tend to have a negative perception of slightly yellow containers for clear beverages like still water. Toners are typically designed to counterbalance yellow tones for such applications. A typical color range of containers containing PCR contrasted with one with toner is demonstrated in .

Open in a separate window

Acetaldehyde may impact the flavor profile. When making bottles for flavorless products, like water, acetaldehyde in the PCR PET container needs to be monitored closely. AA scavengers may be used to mitigate risks associated with impacting the flavor profile.

5.2. Heat-Set Bottles for Hot-Filled and Aseptic Products

Both hot-filled and some aseptic product containers require thermal stability. Aseptically filled containers that are sterilized with the hot application of hydrogen peroxide in the liquid or the vapor phase require thermal stability. Hot-filled containers are sterilized on contact with the heated product. As mentioned in Section 4.4.1, deformation on thermal treatment is minimized with adequate crystallinity. DEG content of the PCR will negatively impact the ability of the container to withstand heat without deformation. Containers that are filled hot also need to resist deformation resulting from vacuum generated when the product cools to room temperature or below. Material distribution within the container is critical to deformation resistance.

Increased preform heating during blow molding will increase the final container crystallinity and the resistance of the container to thermal deformation. As preform temperature increases, material may drift off-center. Inability to achieve sufficient crystallinity may be a concern with Asian PCRs, without reheat additive. Both process and reheat additive use must be balanced to generate sufficient crystallinity. So far, there have not been any heat-set bottles with 100% PCR commercialized in the North American market. That should change soon.

5.3. Pressurized Containers

Containers used for pressurized products, such as carbonated soft drinks (CSD), present a significant challenge when increasing PCR content. While 10% or 15% PCR incorporation is not difficult, increasing to 100% PCR content is problematic. A very clean PCR grade is required. PET resins for CSD require longer molecular chain lengths (also known as higher intrinsic viscosity). Inclusions result in ruptures while blow molding, leading to holes in the container. Inclusions are most problematic when they occur in the highest stretch areas (e.g., the base feet).

Bottles made with PCR may exhibit high expansion after filling with pressurized product. If not managed, expansion may lead to issues like label flagging and reduced shelf life. The single most important factor in forming 100% PCR bottles is the selection of the PCR. The PCR for CSD applications needs to be clean and of high molecular weight. Such PCRs are in limited supply. Some large beverage corporations have launched 100% PCR CSD bottles, but the roll-out has been limited due to supply limitations of the required PCR grades.

6. Regulatory Requirements

Plastic bottles are an attractive option for beverage packaging as they are recyclable and have a lower carbon footprint than alternative packaging. PCR PET must not pose a threat to consumer health and safety, especially for beverage packaging applications. During the collection process, non-food packaging containers and/or bottes containing additives that are not approved for food contact may enter the recycle stream. These materials are known as non-intentionally added substances (NIAS), substances that are not added to the food contact PET, but may be present in the bale and in the flake feed streams to the food grade PCR recycling process. These additives and materials will be present in the PCR PET and may contaminate food packaged within the final PCR PET article. It is important to quantify and control the risk, from a food safety perspective. Regulations regarding the reuse and recycling of PET vary between countries. In this section, we will cover some of the pertinent regulations related to PCR production and its use. This section will provide a framework for PCR's acceptability in various countries.

In the United States, the Food and Drug Administration (FDA) regulates the usage of PCR containers. There are three major concerns: (1) hazardous contaminant migration from the PCR to the food; (2) non-food-contact plastic and non-FDA-regulated material interaction with the packaged food, resulting from inclusions within the PCR; and (3) additives added to PCR that are not FDA compliant for food contact. To overcome these issues, the FDA considers the production of PCR on a case-by-case basis. The FDA issues informal notices on the suitability of PCR production processes for the production of food-contact-compliant material. Manufacturers considering the sale of PCR PET at a food contact grade must submit process documentation to the regulatory agency (FDA in the United States) for review. Three elements of the documentation are:

• (1)

  Description of the controls that are in place to prevent non-PET plastics from entering the PCR production stream.

• (2)

  Documentation and evidence of efficient contaminant removal. If requested, a surrogate contaminant will be used to validate the recycling process and demonstrate the effective removal of the contaminant. Additional migration modeling and testing can be used to demonstrate contaminant reduction to below 0.5 ppb (the dietary concentration that assumes negligible exposure for use with food products).

• (3)

  Description of how the plastic will be used. With food contact materials, these descriptors include temperature range for use, type of food, duration of contact, and if the plastic will be used in a single-use or repeated application.

The FDA has determined that methanolysis and glycolysis tertiary recycling processes are suitable for the production of food-contact-grade PET; surrogate testing is not needed. Tertiary recycling processes are expected to produce high-purity materials. Mechanically recycled (secondary recycling) PCR PET does not allow for fine filtration and contaminant extraction. Hence, migration testing is necessary with mechanical recycling. Mechanically recycled PET must demonstrate residual reduction. Residual migration from the final PCR article must not exceed 1.5 μg/person/day estimated daily intake (EDI). There are several surrogates that are recommended for testing the efficacy of the recycling process. Challenge tests are designed for five categories of potential migrants: (1) volatile polar (chloroform, chlorobenzene, 1,1,1-Trichloroethane, diethyl ketone); (2) volatile non-polar (toluene); (3) heavy metal (copper, (II) 2-ethylhexanoate); (4) non-volatile polar (benzophenone, methyl salicylate); and (5) non-volatile non-polar (tetracosane, lindane, methyl stearate, phenylcyclohexane, 1-Phenyldecane, 2,4,6-Trichloroanisole). The surrogate test for heavy metals in PET is not required, based on evidence that PET does not readily absorb metal salts [116].

Regarding European Food Safety Authority (EFSA) regulation 282/, every recycling process needs to be approved before production [117]. While 5% of the feed stream to PET bottle recycling processes is assumed to be non-food containers on average, it could be up to 20% in specific instances [118]. The final contaminant concentration must be below 3 mg/kg (ppm) per substance.

7. Conclusions and Future Trends

PCR PET production, conversion, and regulations are presented in this comprehensive review for the beverage industry. The push towards sustainability in beverage packaging would not be possible without the great efforts of material reclaimers, PET recyclers, converters, beverage manufacturers, and societal contributions from responsible consumers. Bottle-to-bottle recycling provides a significant reduction to environmental burdens.

In the last decade, the use of PCR PET has seen tremendous growth due to advancements in collection and recycling technology. Looking to the future of PET recycling, one of the most important areas of development is in the commercialization of chemical recycling technology, where PCR PET can be restored to virgin-like performance. Lab-scale technologies are rapidly scaling-up to pilot and production facilities. As an example of an advanced recycling, an enzyme-based technology has been developed to catalyze the hydrolysis of PET into TPA and EG [119]. In , they announced the successful launch of their industrial demonstration plant, with a commercial manufacturing facility following by .

There are several 'speed bumps' to future increases in the conversion of PCR PET. Currently, there are only a handful of suppliers of PCR PET, and availability will be an issue as more beverage manufacturers adopt PCR PET. Limited supply will drive cost higher. As demand increases, PCR resin suppliers incur less pressure from competitors to provide a superior-quality product. Increased prices for PCR and variable quality are both barriers to adoption. Increasing public scrutiny of plastic packaging materials, from both environmental groups and legislative bodies, will spur adoption. Younger consumers are demanding the elevated use of recycled materials. Future investment in new recycling technologies and commercial adoption must be supported by recycling legislation and increased consumer recycling. The demand will continue to increase as PCR mandates come online. Mandates that have already been passed are depicted in . California (CA), Washington (WA), and New Jersey (NJ) plan to implement up to 50% PCR beyond '. Currently, there are no methods to detect the amount of PCR in a bottle, which presents a research opportunity that could be beneficial to recyclers and beverage manufacturers. This presents an interesting problem for the manufacturers and regulatory agencies, as enforcement of PCR mandates is difficult without such methods. In addition, there are also gaps in the detection of additives in PCR. Future research in detection methodologies will allow rapid prototyping and adoption of PCR in mainstream production and distribution of beverages.

Open in a separate window

The scientific data on combination of different grades of PET and how the mixture behaves in bottle manufacturing and performs for various applications is severely limited. The interaction of oxygen scavengers with PCR and its performance are also not available in the literature. Future research in this area can help with the adoption of PCR and the sustainability drive of beverage manufacturers.

Design enhancements of bottles for recycling (design for recycling) will be key to future collection and sortation to increase the yield and supply of PCR. The Association of Plastic Recyclers (APR) in the USA and the European PET Bottle Platform (EPBP) in the EU, both trade associations, have created a set of design guidelines for PET articles for recycling [120]. For example, the cap of the PET bottle can be made of either PP or PE. PP and PE are separable from the PET in the recycler's float/sink tank. Polyesters classified with resin identification code (RIC) #1 must have a crystalline melting point between 225 °C and 255 °C.

Another initiative is digital watermarking for smart package recycling, also called HolyGrail 2.0. The idea of the initiative is to develop a technology for enhanced sortation of PET at a large scale [121,122,123]. The digital watermark could be the size of a postage stamp, integrated into the label and able to carry an array of information related to product, stock-keeping unit (SKU), manufacturer, type of plastic and layers, food vs. non-food use, and so on. Such design and traceability initiatives and technological breakthroughs may enhance the future of recycling.

Incorporation of PCR content into existing PET bottles is a first step towards a circular economy with zero leakage. Small steps will provide confidence in recycling processes, supplier's capabilities, comparable cost, overall package, product performance, and eventually, wide adoption of the 100% PCR PET bottle.

Funding Statement

This work was supported by USDA National Institute of Food and Agriculture, Hatch project .

Author Contributions

Conceptualization, P.B. and D.K.M.; methodology, P.B., G.C., P.K., D.K.M. and J.B.; formal analysis, P.B., G.C., P.K., D.K.M. and J.B.; investigation, P.B.; resources, D.K.M.; data curation, P.B., G.C. and P.K.; writing'original draft preparation, P.B., G.C., P.K. and D.K.M.; writing'review and editing, P.B., G.C., P.K., D.K.M. and J.B.; visualization, P.B., G.C. and P.K.; supervision, D.K.M.; project administration, D.K.M.; funding acquisition, D.K.M. All authors have read and agreed to the published version of the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Publisher's Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Want more information on plastic washing recycling machine? Feel free to contact us.