Learn about the various HDPE (high-density polyethylene) types, recycling considerations, and how label adhesives impact both colored and natural HDPE. Find out how label adhesives play in a role in enabling HDPE to increase recycling for durable packaging applications.
When looking for ways to increase recycling in your label manufacturing, it’s important to assess the performance, processing and recycling capabilities of different plastic polymers. In particular, HDPE (high-density polyethylene) is suitable for durable, chemical-resistant packaging, as it provides a barrier against moisture or gas. However, HDPE substrates need to undergo varying processing and recycling steps depending on the type being used. Each one can impact your label adhesive’s ability to meet the necessary performance levels and appropriate recycling capabilities. Therefore, it’s important to ensure the right adhesive for the right type is chosen.
Learn about HDPE, how it differs from other common plastics and what to consider with the different types when choosing a label adhesive.
Learn about HDPE, how it differs from other common plastics and what to consider with the different types when choosing a label adhesive.
What is HDPE?
As a thermoplastic polymer made from petroleum, HDPE is one of the most commonly used (and therefore, recycled) plastics in food or consumer goods. It is known for its high strength-to-density ratio, meaning it is strong and lightweight. Additionally, HDPE can be melted and reprocessed depending on the type used, enabling circularity for second or third generational use. Some of HDPE’s key features include:
- High environmental exposure resistance: HDPE is resistant to chemicals, UV radiation and moisture, making it suitable for packaging that requires barrier properties or is being used in outdoor applications.
- Versatility: From rigid to flexible grades that are approved for food contact, HDPE can be used for a combination of food and consumer goods packaging such as bottles, containers, medical trays, personal care and cleaning products.
- Temperature resistance: HDPE is compatible for both low and high-temperature applications, which allows it to be used outside of packaging such as automotive or industrial applications.
How HDPE Compares to PET and PP
The other most common plastics for food and consumer goods rigid packaging include PET (polyethylene terephthalate) and PP (polypropylene); however, it’s important to know they do not always offer the same capabilities as HDPE in the following areas:
- Density: HDPE’s high density gives more rigid strength compared to PP, which is why HDPE is used for rigid bottles, containers and pipes over PP. PET has even higher density than HDPE, plus it offers transparency properties that makes PET a popular option for clear plastic packaging. If that transparency is not necessary, HDPE can be more suitable for rigid packaging.
- Recycling capabilities: Both PET and some HDPE can be used to either remake the same products or create new products from their resins or fibers by breaking down their plastics into flakes for extrusion. This decreases the demand for virgin plastic production by keeping current plastic in the circular system and reducing overall energy usage. While PP can be reused for new applications, too, its recycling rates can vary based on market demand and local recycling facility abilities, because it is commonly recycled into products such as battery cases and plastic lumber.
- Ease of Processing: HDPE is relatively easy to process for applications that need structural stability due to its high melt flow characteristics that help simplify extrusion and injection molding. On the other hand, PP has a lower melting point and processing temperature requirement for enhanced energy efficiencies. However, PP will not be able to produce the same level of structural stability as HDPE. Further, PET needs higher temperatures than HDPE, which will require more energy usage during production.
How Different Types of HDPE Impact Label Manufacturing
A label’s construction can be designed specifically for an HDPE packaging application and its specific recycling recommendations. When a label’s construction is designed for an HDPE package, it’s important for you as the label converter to decide what types of HDPE will allow your label to address the application performance needs and recycling requirements. This is because the HDPE type can impact how the label’s adhesive formulation will be able to provide the necessary durability, versatility and temperature resistance.
Types of HDPE to Consider
Even though recycling occurs further into the value chain, you as the converter can impact how your end-use label assists an HDPE package in entering the recycling stream. Further, the application itself can determine what label adhesive will be most effective, which involves understanding the two types of HDPE and how they are recycled.
Colored HDPE is used in packaging applications such as shampoo bottles or laundry detergent capsule containers. It can be produced in a variety of colors and is commonly used when the plastic color appearance plays a role in aesthetics and branding. To get the desired color, pigments or dyes are added to the HDPE pellets before melting and molding occurs. This coloring process typically does not impact the HDPE’s strength or chemical resistance, but it can influence UV stability if that’s a concern. For recycling, colored HDPE is granulated and dyed black. While colored HDPE is recyclable, it does not contribute to circular recycling because the shredded plastic is sold into different markets to develop recycled applications like drainage piping or park benches.
Natural HDPE is common for dairy packaging such as milk jugs. It comes in a notably translucent to opaque white form, produced directly from the polymerization process without any pigments or dyes to alter its color. Natural HDPE can be easily processed through various manufacturing techniques such as injection molding, blow molding and extrusion; it also can be processed differently than colored HDPE since it does not go through the coloring process. Natural HDPE can, however, be susceptible to UV degradation over time if exposed to sunlight. Similarly to PET (though sorted separately), natural HDPE is ground up into flakes, moved through a sink float process, extruded and recycled back into HDPE milk jugs. This means HDPE does contribute to circular recycling, allowing less virgin plastic to be developed since recycled, natural HDPE can be used for second or third generational use. After natural HDPE has been recycled enough times to where it becomes permanently discolored, it will then enter the colored HDPE recycling stream and be dyed black.
How Label Adhesives Play a Role in Colored HDPE and Natural HDPE
Knowing whether the package is made of colored HDPE or natural HDPE will help you determine whether your label adhesive needs to provide wash-off capabilities for enhanced circular recycling.If your end-use label is adhering to a colored HDPE package, it will not need wash-off performance, because it will be ground up during the recycling process with the package and made into another product for a different market. However, your adhesive should provide strong adhesion and recyclable compatibilities; since it will be granulated and reused, it still needs the bonding strength to adhere long-term. The facestock within your label should also be compatible with the HDPE substrate.
A label for natural HDPE does require wash-off capabilities, since the package must be free of any residue before entering the recycling stream. This means your label adhesive must adhere well to the HDPE substrate so it lasts for the lifespan of the application; however, it also has to remove easily with a hot caustic wash from the HDPE package. Since a wash-off label adhesive will be used while it’s recycled as natural HDPE, the label will never enter the colored HDPE recycling stream even when the discolored natural HDPE is moved into that stream.
The right label adhesive solution will offer formulations specifically designed to ensure your label adheres to the HDPE type and can be recycled accordingly:
Colored HDPE: Formulations based on hot melt adhesive technology or tackified, waterborne acrylic adhesive technology provide the necessary adhesion levels to ensure the label will stick to the HDPE substrate during their lifespan and throughout the granulated recycling process. These two options can also allow you to base your decision on your current equipment.
- Hot melt adhesive technology is comprised of 100% solids. After melting upon heat activation, hot melt adhesives form a bond while cooling. This process can occur numerous times, allowing hot melt adhesives to be reusable, which makes them useful for colored HPDE recycling as an individual, recyclable component.
- Waterborne acrylic adhesives offer strong bonding and adhesion with a low environmental impact. This makes them especially useful in applications with environmental concerns, including colored HDPE recycling. Waterborne acrylic adhesives, however, do not require extremely high temperatures like traditional hot melt adhesives, enabling fast processing speeds.
How Bostik Plays a Role in Helping Label Manufacturing for HDPE
As the adhesives division of the Arkema Group, Bostik is committed to developing compatible label adhesive solutions that will enhance your abilities to increase HDPE recycling with your end-use labels. With our abilities to custom formulate to fit your label needs, we are here to provide insight on the latest adhesive technologies that can help you ensure your label adheres to HDPE substrates and enables the proper recycling processes. Further, our hot melt, bio-based adhesives can allow you to heighten the adhesive’s sustainability features by implementing raw materials derived from renewable biomass.
Are you ready to expand your label’s recycling capabilities for HDPE packaging? Contact a Bostik expert to learn how our label adhesives can make it easy to provide sustainable integrity across the value chain with your end-use labels.
Are you ready to expand your label’s recycling capabilities for HDPE packaging? Contact a Bostik expert to learn how our label adhesives can make it easy to provide sustainable integrity across the value chain with your end-use labels.
©2023 Bostik, Inc. All Rights Reserved
All information contained herein is believed to be accurate as of the date of publication, is provided “as-is” and is subject to change without notice. To review our full U.S. Legal Disclaimer, visit: https://bostik.com/us/en_US/privacy-policy/legal-disclaimer
All information contained herein is believed to be accurate as of the date of publication, is provided “as-is” and is subject to change without notice. To review our full U.S. Legal Disclaimer, visit: https://bostik.com/us/en_US/privacy-policy/legal-disclaimer