Before PP bottles are granulated, complete packages with labels and closures are likely to be sorted by a NIR optical sorter and run through a sensitive metal detector. These situations create the need for testing to evaluate the impact of a label on NIR optical sortation or metals detection:
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During the reclaiming process, mixed color PP packages are most likely washed in water near room temperature and with mild detergents. These wash conditions will have negligible impact on inks and adhesives and in most cases labels, inks and adhesives are expected to become included in the recycled PP product.
Automated sorting performance criteria:
Surface area is defined as the area of the label divided by the area of the side wall and shoulder of the container. The area of the neck ring, threaded finish, and base are not included in the area calculation. Metal decoration includes vapor deposited metal films, metal foils, or inks with metallic pigments.
Containers with no more than 55% surface area coverage by a label are expected to sort accurately in both NIR and color optical sorters. For labels with metal decoration see the section on Labels with metalized materials
Surface area is defined as the area of the label divided by the area of the side wall and shoulder of the container. The area of the neck ring, threaded finish, and base are not included in the area calculation. Metal decoration includes vapor deposited metal films, metal foils, or inks with metallic pigments.
Containers with no more than 75% surface area coverage by a label are expected to sort accurately in both NIR and color optical sorters. For labels with metal decoration see the section on Labels with metalized materials.
Metalized material content on labels below the preferred surface area per APR-RES-SORT-04 are considered preferred.
Metalized material includes vapor deposited metal films, metal foils, or inks with metallic pigments.
Polyolefin Film Labels
Polyolefin labels are commonly expected to be PP films or PE films. This includes film labels for each of conforming, adhered, and in-mold style of labels. Some additional considerations:
Film labels with density > 1.0 g/cm3designed to release from PP container in wash and sink in water per APR-O-S-01
When used with an adhesive that releases in the wash, film labels with density greater than 1.0 g/cm3detaches from the PP before the float-sink tank where it sinks and is removed. Even though the float-sink process is imperfect, the small amounts of this type of film label entering the extrusion process are not catastrophic.
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APR Design® for Recyclability Recognitions
Film labels with density > 1.0 g/cm3designed to stay adhered PP container in wash
When used with an adhesive that does not release in the wash, Film labels with density greater than 1.0 g/cm3 enters the extruder with the PP where they are incompatible.
Paper labels
The PP reclamation process involves water and agitation. The paper that detaches from the container when subjected to these conditions becomes pulp, which does not sink intact but remains suspended in the liquid, adding load to the filtering and water treatment systems. Paper remaining adhered to the PP travels with the PP to the extruder where the material carbonizes and causes color defects. Even after melt filtering, the burned smell and discoloration remain with the recycled PP thereby negatively affecting its potential reuse. Non-pulping paper labels used with non-releasing adhesives compound the problem since the entire label enters the extruder. Non-pulping labels, heavy enough to sink and durable enough to withstand the washing process that are used with releasing adhesives may alleviate this issue.
PVC film labels
PVC, when used with an adhesive that does not release in the wash, enters the extruder with the PP where they are incompatible. PVC degrades at PP extrusion temperatures and renders large amounts of the recycled PP unusable. When used with an adhesive that releases in the wash, these labels sink in the float-sink tank where they are removed. But because the float-sink tank is imperfect, and even a very small amount of PVC entering the extruder causes severe quality and yield problems, this material is detrimental.
None Specified
Labels that exceed the surface area coverage as described in Preferred Guidance section
Labels with high surface area coverage may interfere with detection of the PP container. The label substrate (film or paper), inks, and metal decoration can interfere with NIR detection when the label covers a high surface area of the container. Also, high label surface area coverage may cause an PP container to be sorted for a different resin if resin of label is not PP.
If one’s design is outside of the best practice guidance above, the labeled bottle must be evaluated using the APR test methods below.
DEFINITIVE TEST - NIR
Labels containing metalized materials that are above the maximum surface area coverage per Screening Test below.
Labels that have surface areas above the Preferred Surface Area specified in the Screening Test below would need to be tested using the Benchmark Test below to verify they are under the spherical equivalent thresholds.
Without further testing, metal foils with surface areas above the Preferred Surface Area in the table are categorized as detrimental due to a higher probability of being removed by the metal detector during sortation.
Solid foils will continue to render the package non-recyclable per APR’s definition.
SCREENING TEST
BENCHMARK TEST
Label inks
Some label inks bleed color in the reclamation process, discoloring the PP in contact with them and possibly diminishing its value for recycling. Since most recycled PP is colored, the impact of bleeding inks may not be significant; however, since the end use is not known beforehand, label inks should be chosen that do not bleed color when recycled. If inks redeposit on natural PP flake, this discoloring may diminish its value for recycling. Inks should remain adhered to the label and not bleed into wash water to avoid this potential discoloration.
The APR test protocol should be consulted to determine if an ink bleeds.
DEFINITIVE TEST
Direct printing on PP containers
Inks used in direct printing may bleed or otherwise discolor the PP during the recycling process or introduce incompatible contaminants that reduce the value of the recycled PP. The specific ink must be tested to determine its effect.
Companies that are considering direct printing technologies and are unsure of their compatibility with recycling should ask their suppliers to provide APR test results.
DEFINITIVE TEST
Label/Adhesive combinations where adhesive release and substrate float/sink behavior are not known.
Testing must show that adhesives will either wash off cleanly from the PP in the recycling process or be compatible with PP. Since typical PP recycling process conditions are not aggressive enough to remove all adhesive material, a certain amount of residual adhesive is to be expected in recycled PP. Such adhesive residue that is not removed from PP during the wash step is a source of contamination and discoloration when PP is recycled. For these reasons, minimal adhesive usage is encouraged.
The APR is developing a screening PP/HDPE Adhesive Test to classify adhesive as either wash friendly, non-wash friendly and compatible with PP, or non-wash friendly and incompatible with PP.
DEFINITIVE TEST
If you want to learn more, please visit our website Polypropylene Recycling Process.
Plastics have only been around for a little over a century, yet they’ve become part of almost every aspect of our lives. From children’s toys to food packaging, plastic materials are a ubiquitous part of 21st-century life. In fact, in roughly 70 years, there has been 8.3 billion metric tons of plastic produced, with around 6.3 billion metric tons of that becoming waste.
And only 9% of that waste has been recycled.
There’s a variety of reasons for this, and while our plastic waste continues to grow, advances in technology and changes to the way we consume are helping to make it more efficient and effective.
Plastic recycling is extremely important, both as a method to deal with our existing waste and as a component of both circular economy and zero-waste systems that aim to reduce waste generation and increase sustainability. There are social, environmental, and economic consequences surrounding our current waste generation and disposal habits, and whether that is the issue of microplastics or an estimated $2.5 trillion in damage and lost resources to fisheries, aquaculture, recreational activities, and global wellbeing, the impact is no longer in doubt.
However, meeting the challenges posed by plastics is not simple, and there exists a lack of awareness surrounding the plastic waste problem. Despite the fact that potential issues were first flagged in the 1960s, historically, there has been a lot of pushback against implementing real change—mainly from the plastics industry itself. Recently, the tide seems to be turning on this issue as more people look for sustainable options and educate themselves about why plastic recycling is important.
Today, as both consumers and businesses look to recycle more materials, there is a lack of knowledge on how to do it effectively. This creates issues in the form of contamination, either by mixing non-recyclable plastics with recyclable plastics or trying to recycle plastics soiled by things like adhesives, chemicals, and food remnants that further impedes the recycling process. Both of these problems can lead to plastics being sent to the landfill rather than recycled.
Another complication is found within the products themselves. While some goods, like water bottles and other drink bottles, are frequently made from a single, common plastic (such as PETE) allowing them to be easily recycled, many others are designed to use a mix of plastics, which can cause serious issues in our current plastic recycling process. What’s more, many products are a mix of plastics and non-plastics such as wood or metal. Sadly, these products won’t even go near a recycling center.
That said, the process for the recycling of plastic has seen a massive improvement in recent years and can be broken down into six basic steps.
The first step in the mechanical recycling process is the collection of post-consumer materials from homes, businesses, and institutions. This can be done by either local government or private companies, with the latter often a popular option for businesses.
Another option is taking plastics to communal collection points such as designated recycling bins or facilities. This may be as simple as a bottle bank on a street corner or as complex as a local waste site with large areas for various recyclable and non-recyclable municipal solid waste (MSW).
The next step in the plastic recycling process is sorting. There are several different types of plastic (see below), which need to be separated from each other by recyclers. Further to that, plastics might be sorted by other properties such as color, thickness, and use. This is done by machines at the recycling plant and is an important step to increase the efficiency of plants and avoid the contamination of end products.
Washing is a crucial step in the plastic recycling process since it removes some of the impurities that can impede the operation, or completely ruin a batch of recycled plastic. The impurities targeted in this step commonly include things such as product labels and adhesives as well as dirt and food residue. While plastic is often washed at this stage, it is important to remember that this doesn’t take away from the importance of ensuring plastics are as free from impurities as possible before disposal and collection.
The plastic is then fed into shredders, which break it down into much smaller pieces. These smaller pieces, unlike formed plastic products, can be processed in the next stages for reuse. Additionally, the resized plastic pieces can be used for other applications without further processing, such as an additive within asphalt or simply sold as a raw material.
Breaking down the plastic into smaller pieces also allows for any remaining impurities to be found. This is especially true of contaminants such as metal, which may not have been removed by washing but can be easily collected with a magnet at this stage.
Here, the plastic pieces are tested for their class and quality. First, they are segregated based on density, which is tested by floating the particles of plastic in a container of water. This is followed by a test for what is known as the “air classification”, which determines the thickness of the plastic pieces. It is done by placing the shredded plastic into a wind tunnel, with thinner pieces floating while larger/thicker pieces stay at the bottom.
This final plastic recycling process step is where the particles of shredded plastic are transformed into a usable product for manufactures. The shredded plastic is melted and crushed together to form pellets. It is worth noting that it is not always possible to compound all types, classification, and qualities of plastic at a single plant, so different grades of plastic are sometimes sent to other recycling facilities for this final step.
There are numerous types of plastic, and when trying to familiarize yourself with the plastic recycling process and avoid contamination, there are seven categories to remember. Chances are you have seen these symbols on products, and while they look like the “recycling symbol”, they actually indicate resin type, with some representing material that is not recyclable at all.
One of the most common types of plastic you are likely to come across – this is the resin used for the manufacture of products such as food containers and plastic bottles for water or soft drinks. PETE (sometimes referred to as PET) is widely recycled.
More rigid than PETE, this type of plastic is used in what will appear to be “sturdier” products such as detergent bottles, food and drink storage, bottle caps, some thicker shopping bags, and non-single-use plastic products like toys, helmets, and piping. Again, this type of plastic is widely recycled.
PVC is considered one of the most versatile and common plastic types and is used for applications such as water and waste pipes (due to it being very resistant to chemical and biological damage), flooring, signage, furniture, and more. While there are some methods developed to recycle PVC, it is not common and rarely found in general plastic collections. This is in large part due to the toxicity of PVC when processed.
While not as strong as HDPE, this low-density plastic is highly resilient and used across a wide range of products such as containers, playground fixtures, and plastic trash bags. This resin-type is recyclable, but many products can be excluded (such as plastic bags) since they pose the risk of clogging machinery and are deemed not worthwhile to recycle.
Commonly used in injection molding, this plastic can be found in products from bottle caps to surgical tools and clothing. While PP is recyclable, it is often rejected by processing centers due to the problems it poses, making the rate at which it is recycled far lower than other plastics.
This plastic is frequently used as disposable plastic containers for food, as insulated containers, and in packaging materials. Despite its abundance, PS is rarely recycled due to it not being cost-effective (in its most common form, expanded polystyrene or styrofoam, is 95% air) and requires more energy than it saves to recycle.
This category encompasses everything else, which can include combinations of any of the previous six as well as other lesser-used plastics. This classification also includes non-petrochemical plastics such as new plastics, polymers, and bioplastics. As such, anything marked with a number 7 is generally not included in the plastic recycling process but may have other waste solutions.
As it stands today, the plastics recycling process faces many challenges, and unlike glass and aluminum, plastics are not infinitely recyclable, meaning that with each subsequent processing, the recycled material degrades and is a lesser quality than virgin materials.
However, don’t miss the broader perspective. Today’s recycling process for plastic is leagues ahead of what it was just a few decades ago, with recycling rates growing, and continuing to grow, significantly. Innovations like chemical recycling are occurring to keep more plastics in the recycling loop for longer. What’s more, there are a growing number of alternatives to plastic items hitting the market.
As individuals and businesses increasingly engage with the plastic recycling process, we are likely to see it continue to improve. Along with the shift towards new products and plastic alternatives, this signifies a slow but steady movement in the right direction.
The plastic recycling process is likely to receive a huge boost as we become more conscientious in the way we use resources and manufacture products. In fact, while waste management concepts such as the circular economy and zero waste are broadly aligned with a move away from single-use plastics, recycling will remain a part of the waste management process for the foreseeable future, allowing us to gradually move away from unnecessary plastics and increase the recyclability of those that remain necessary.
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