Can High-Density Polyethylene (HDPE) be recycled? 

High-Density Polyethylene (HDPE) is a widely used plastic made from the monomer ethylene. The unique physical attributes of HDPE make it extremely versatile for many uses, i.e. ropes, roofing tiles, plastic bottles, piping, etc. 

HDPE has certain unique physical and chemical properties that make it suitable for a wide variety of uses. It has high impact resistance and high melting temperature. HDPE has excellent tensile strength and strength to density ratio, these properties make it ideal for use in construction and food packaging. 

Due to its versatility and wide use, an efficient recycling system for HDPE is essential to ensure minimal waste and resource consumption. This article will focus on why HDPE is so widely used, how HDPE is globally recycled, and how it can be made sustainable for the future. 

Is HDPE recyclable? 

Yes, it is recyclable and it is widely recycled all over the world.HDPE is the second most recycled plastic after Polyethylene terephthalate (PET). 

HDPE is recycled by most municipalities, counties, and cities. The general recycling systems in most places accept HDPE. Whether your city has a single-stream or a multi-stream recycling system, decide where you throw your HDPE waste. 

You can throw out your plastic waste into the general curbside recycling bin in the US, but make sure you throw it in the bin labeled “Plastic” in Europe. 

What is HDPE? 

HDPE or PEHD is a plastic made from ethylene monomers. Ethylene is a petrochemical derived from fossil fuel. The resin identification number of HDPE is 2, which means containers with the number within the recycling sign are made of HDPE. 

It is the most recycled plastic besides Polyethylene terephthalate (PET).

Certain characteristics of HDPE make it an ideal material for making underground pipes, building materials, ropes, pavement and roof tiles, and food-grade containers. 

It’s got a high melting point, yet it’s moldable meaning it’s malleable once melting temperature is reached. 

It’s corrosion-resistant and has high tensile strength. 

HDPE is a durable yet lightweight material with a high density to weight ratio. This allows it to carry many folds of its weight. 

These useful properties are extremely hard to replace, which is why we must recycle HDPE to make it more sustainable for the future. 

How to recycle HDPE:

Make sure to wash your food packaging thoroughly before you throw it in the recycling bin. Also, properly empty the water and soda bottles before discarding them. Food contaminants on packaging disqualify them from being recycled, and these are tossed into the trash, and eventually end up in landfills. 

When dropping off your plastic waste, make sure the plastic bag you put all the plastic in is not tied up. Tied bags mostly get thrown into garbage since the sorting takes place manually. The workers in the facility simply do not have the time to go over each bag one by one. 

Now, HDPE-based shopping bags are still very common. Keep in mind that soft plastics like shopping bags are not usually recycled. Check your guidelines before throwing them in the recycling bin. 

In most cities, soft plastic is not accepted for recycling. Soft plastic is anything that scrunches up in your fist.  Now, the reason why these are usually not allowed is that they are too light and likely to get blown away by the wind. These could get stuck on equipment and cause damage. 

Now, most HDPE that is hard plastic is recyclable. You can identify HDPE packaging by the number 2 in the cyclical arrows. This is the resin identification number of HDPE. 

The process of recycling HDPE: 

 HDPE is a thermoplastic, which means it can be melted and molded into new shapes. Like most other plastics, HDPE is also thermomechanically recycled. 

The plastic is first moved to a materials recovery facility (MRF). Here these plastics are first put into bales. Then these are transported to recycling centers. 

HDPE has multiple grades, these are based on the thickness of the plastic. Thicker plastics are better grades. After sorting, the plastic is thoroughly cleaned with water and detergent.

Then it’s shredded. Once shredded, the plastic is passed into an extruder which melts the plastic and then creates pellets out of them. 

These pellets are the final product which is then shipped to a manufacturing plant where they can be melted and molded into a variety of products. 

What is HDPE used for? 

HDPE is an easily available alternative to more expensive packaging materials. Recycled HDPE makes very good roofing tiles, pavement tiles, piping, etc. Over the years, the use of HDPE has gradually increased. 

The upward trend in HDPE use is mainly because it’s affordable and versatile. HDPE is lightweight yet durable which makes it a perfect material for roofing and pavement tiles. 

Its non-reactive nature makes it ideal for non-corrosive piping. HDPE piping does not react with acids or bases, or chemicals in the soil. It is resistant to mold, mildew, and rotting, these properties make it ideal for underwater piping. 

It is also temperature resistant with a high melting temperature, this makes it a good reusable food container that is microwave safe. 

Even though plastic 2 has a high melting point, once it reaches this temperature it quickly melts. This molten plastic is extremely malleable and can be used to make milk jugs, water bottles, shampoo bottles, tiles, etc. 

HDPE has a high strength to density ratio, a 60g HDPE container can carry up to 3-4 Kgs. 

It is easy to see why HDPE is so widely used in multiple areas. It’s cheap, easily made, and very useful. However, its overuse has devastating consequences for the environment. 

How HDPE waste affects the environment: 

Our media is inundated with news about how plastic is slowly killing the environment. Sometimes literally, ill-disposed plastic is often ingested by avian or aquatic species. These plastics lodge into their stomachs, cause internal damage, or simply block the digestive tract of the animal. These animals then die slow and tragic deaths.

Proper management of plastic waste is of utmost importance. HDPE is relatively easy to recycle, yet no more than 30% of HDPE is recycled, the rest ends up in landfills or are incinerated. 

Poor disposal of these plastics allows these to end up in our oceans, resulting in marine life being affected as explained above. 

Incineration is also not the best way to dispose of HDPE as it releases carbon into the atmosphere. In countries where these plastics are burned in the open air, residents who live near these sites have developed severe breathing issues because of it. 

Burning plastic in the open air creates soot which is extremely toxic and can cause cancer and lung issues in people who inhale it for prolonged periods. 

To reduce HDPE waste, legislative changes need to take place. More efficient recycling systems and newer techniques that put HDPE into a closed-recycling loop are necessary. 

Can HDPE be sustainable? 

There has been a shift in focus from a linear economy to a circular economy in recent years. If HDPE can enter a circular economy then there is no need to ban it. It is after all a very useful material, any method by which it can be kept in use should be welcomed.

More efficient recycling systems where almost all HDPE is recycled is the first step. 

However, recycling, specifically mechanical recycling is not the answer. HDPE can be recycled around 10 times before its quality deteriorates. 

This means once it is recycled for the 10th time, it’ll end up in the landfills. There is a way to keep these plastics off of landfills, and it is called pyrolysis. This is a technique that is considered a type of chemical recycling where HDPE is broken into its monomer. This monomer can then be turned back into HDPE. 

The only way chemical recycling will be successful is if there are subsidies provided to companies that perform this technique. As things stand now, virgin HDPE is very cheap, this deters companies from investing in recycled HDPE. 

Legislation can change this and shift toward the use of recycled HDPE.

One thing is certain, for the time being, the best solution is to reduce the use of HDPE while we look for ways to recycle it with better efficiency. 

Conclusion: 

HDPE has certain unique physical and chemical properties that make it suitable for a wide variety of uses. It has high impact resistance and melting temperature. HDPE has excellent tensile strength and strength to density ratio, these properties make it ideal for use in construction. 

Due to its versatility and wide use, an efficient recycling system for HDPE is essential to ensure minimal waste and resource consumption. This article has focused on why HDPE is so widely used, how HDPE is globally recycled, and how it can be made sustainable for the future. 

Frequently Asked Questions (FAQs): Is #2 plastic recyclable? 

What does the number 2 in #2 plastic refer to? 

The numbers on a plastic container enclosed in circular arrows refer to the resin identification number of the plastic. Each number represents a different plastic type. 

What is #2 plastic? 

#2 plastic is known as high-density polyethylene (HDPE). It is made from a petrochemical named ethylene. 

Is HDPE widely used? 

Yes. It is a very common plastic used in a multitude of areas. 

Is HDPE  useful?

Yes, it is a very useful plastic. It is resistant to corrosive chemicals, heat, pressure, and has a high weight to density ratio. Additionally, it has a  very high tensile strength and is very lightweight and non-toxic. These properties qualify it to be used for making a host of products from pavement tiles, underground water pipes, ropes, food containers, water bottles, plastic shopping bags, etc. 

Is HDPE bad for the environment? 

Yes, as things stand, more and more virgin HDPE is being made each day instead of recycling the already available post-consumer HDPE. This increases carbon emission, energy and fossil fuel expenditures, plastic waste, and air pollution. 

Lastly, HDPE does not degrade and remains on the ground for centuries, overtime breaking down into smaller pieces of HDPE. 

Is HDPE environmentally friendly? 

No, not as things stand. It is not biodegradable, so it remains in landfills for centuries. With time it breaks down into smaller HDPE pieces. Animals near landfills or aquatic creatures ingest these small plastics, these lodge in their insides, and these creatures often die slow painful deaths. 

Can you recycle HDPE? 

Yes, it is recyclable. It is mostly recycled by a thermomechanical method, however, it is also recyclable by a chemical method where it is broken down to its base molecules. 

How do you recycle HDPE plastic? 

HDPE is recycled by a thermomechanical technique where the plastic is shredded, melted, and then turned into pellets. 

Is HDPE biodegradable? 

No, HDPE is not biodegradable. It can remain in landfills for centuries. 

Is HDPE food safe? 

Yes, it has a very high melting temperature and does not release toxic chemicals, making it ideal for reusable food containers. 

Reference: 

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  8. Loultcheva, M., Proietto, M., Jilov, N., & La Mantia, F. (1997). Recycling of high-density polyethylene containers. Polymer Degradation And Stability, 57(1), 77-81. DOI: 10.1016/s0141-3910(96)00230-3
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