There’s a common thread running through automotive components, reusable containers of different types, plastic parts, packaging and labeling, loudspeakers, polymer banknotes, stationery, textiles, carpets, ropes, and thermal underwear. It is Polypropylene, abbreviated as PP. PP is a recyclable thermoplastic polymer widely used in these applications. Rugged and unaffected by different chemical solvents, acids, and bases, the PP recycling code is as per the type of resin used, as in the case of all plastic products – PP’s resin identification code is 5. The global demand for PP materials is quite high. Transparency Market Research has indicated that presently the PP market worldwide is valued at more than $80 billion. By 2023 it should touch $133.3 billion according to the research agency.
PP recycling is vital for the environment
Of all plastic packaging products in the United Kingdom and the United States, PP is the single most used plastic packaging, thanks to its melting point and strong bearing. In the year 2010 alone five billion pounds of PP was produced in the United States. Sadly though, it has been revealed by the American Chemistry Council that PP is one of the least recycled post-consumer plastics, at a rate of below 1 percent for post-consumer PP foam. And this is a bad thing for the environment.
PP has a short life, so most of these thermoplastics land in landfills to be wasted. Twenty percent approximately of solid waste produced comprises some form of plastic which includes PP according to the US Environmental Protection Agency. This PP contained solid waste degrades very slowly in landfills, about 20 to 30 years to be fully decomposed. Naturally, this poses a severe threat to the environment. Additives used in plastic products may contain toxins such as lead and cadmium. Cadmium contained in plastic products has the potential to permeate and can affect some bio-systems. If you burn thermoplastics like PP it can discharge toxins and vinyl chloride. Against this backdrop Recycling Polypropylene assumes importance.
The Polypropylene Recycling Process
The Polypropylene Recycling Process comprises the collection, sorting, cleaning, reprocessing by melting and then producing new products from the recycled PP.. The reprocessing by melting and then producing the new product from the recycled PP are important steps in the Polypropylene Recycling Process. In the reprocessing phase, collected PP products are fed into an extruder where it is melted at 4640F (2400C) and cut into granules. The pellets are then ready to be used in the production of new products. Current technologies enable the melting of PP and its usage in the production of new items.
The power of Polypropylene
Polypropylene produces less solid waste by weight than PET, PS or PVC. Thus many recycling applications exist for Polypropylene: battery cases, paint cans, home storage, flower pots, pallets, crates, composite lumber, and more. In the US, out of the 51 largest US municipalities of the state, 44 collect polypropylene.
Polypropylene and high-density polyethylene (HDPE) produce significantly less CO2 equivalents by weight than PET, PS, and PVC. And Polypropylene parts can be 100% recycled for various useful purposes. A market for recycled PP (rPP) exists in an extensive range of products such as automotive applications, buckets, caps and closures, garden furniture, pallets, pipes, and more.
The Environmental Benefits of Recycling PP
When PP is recycled, there is a reduction in the consumption of raw, finite resources, such as oil and propane gas. Around 8% of the oil used worldwide (around 400 million tons) is implemented in the traditional methods of plastic production with 4% as ‘feedstock’ and another 4% in manufacturing. There is also an 88% reduction in energy usage if plastic is produced from plastic. So plastic to plastic recycling is environmentally friendly.
Given its inherent flexibility, PP can be recycled back into many different products, including clothing fibers, industrial fibres, food containers, dishware etc.
Cady Bag
Cady Bag understands and is focused on recycled packaging. The company is a vertically integrated manufacturer of flexible packaging and fabrics for niche markets. Our focus is on quality deliverables enabled by our empowered employees.
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:
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.
Click below for commercially available Labels, Inks and Adhesives that have achieved APR Design for Recyclability Recognition
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