Polyethylene Recycling

It’s no big secret that plastic, in all its varied forms, plays a huge role in the functioning of contemporary society. From supermarket bags to high-tech industrial applications, plastic is seemingly ubiquitous. This synthetic material has given us—and continues to give us—a wide range of conveniences and innovations, from the frivolous to the undeniably important.But it’s equally undeniable that plastic has its downsides. Its durability and resistance to biodegrading processes (except for a few counterexamples, such as aliphatic polyesters) pose an ongoing threat to the environment. There is a staggering amount of plastic waste in the world today, and figuring out how to manage all this material has commanded the attention of many leading environmental scientists.

To a very large extent, these efforts revolve around the management of polyethylene, the most common type of plastic. How common? No less than 60 million tons of this material is produced each and every year1. Luckily, there are ways to recycle polyethylene and reduce its burden on the environment. We’ll explore the subject of recycling in more detail below, but first let’s back up a little. What is polyethylene? What is it used for? Let’s take closer look at this extremely common synthetic material.

There are various types of polyethylene, but the two most common are low-density polyethylene (LDPE) and high-density polyethylene (HDPE). 

What Is Low-Density Polyethylene?

Originally created in the 1930s, low-density polyethylene is a thermoplastic made from petroleum. Its molecular structure is marked by a central chain of carbon atoms and a number of secondary chains that branch outward. This gives the substance a relatively low-density structure—hence the name. The practical effect of this branching is to lend the material a flexible character while still enabling it to retain a high degree of tensile strength; as a result, the material has strong scratch and impact resistance. It also tends to be fairly translucent. In addition, LDPE provides a good degree of resistance to water vapor and many chemicals.

Commercial LDPE products bear the recycling (resin ID) code “4.”

What Is High-Density Polyethylene?

High-density polyethylene, or HDPE, came on the scene a few decades after the invention of its low-density cousin. Also made from petroleum, HDPE is marked by a molecular structure devoid of polymer branching. As a consequence, its polymer chains are packed more closely together; this is what makes it “high density.” HDPE is characterized by very high tensile strength, strong impact resistance, low moisture absorption, and chemical-resistance. It is both non-toxic and non-staining.

Commercial HDPE products bear the recycling (resin ID) code “2.”

Differences between LDPE and HDPE

In some ways, low-density and high-density polyethylene are quite similar. Both substances are marked by a high degree of scratch resistance; both are suitable as food containers or wrappings; both are sterilizable. Fortunately for the environment, both materials are also 100% recyclable. Despite the contrast implied by their respective names, the two substances are actually very similar in density, with HDPE only slightly higher in this category.

However, the non-branching molecular structure of HDPE does give it a substantially higher tensile strength and rigidity than LDPE. High-density polyethylene also provides superior resistance to heat and chemicals. In addition, it tends to be more opaque than LDPE.

LDPE has the edge in a few other categories, though. For one thing, it retains its pliability better in cold environs.
It also provides better impact resistance. The flexibility of LDPE, combined with its chemical resistance, makes it useful in a wide variety of applications, as we will see below.

Uses of LDPE

A large number of commercial products use low-density polyethylene. The following is only a partial list of the kinds of products commonly made from LDPE.

Dry cleaning bags	Cling wrap	Newspaper bags
Squeeze bottles	Trash-can liners	Six-pack rings for soda pop
Juice bottle laminate	Grocery bags	Tubing
Prosthetics	Bread bags	Trays
Sandwich bags	Wash bottles	Ice cream lids

Uses of HDPE

Tougher and stronger than LDPE, high-density polyethylene is used for a broad range of products. Its relative opacity makes it ideal as a container for many types of commercial goods. The list of HDPE products includes but is not limited to the following items:

Auto parts	Vinegar bottles	Telecom ducts
Motor oil bottles	Toys	Liquid dish detergent bottles
Antifreeze containers	Vehicle fuel tanks	Pipes
Fabric softener containers	Cutting boards	Lotion bottles
Bleach bottles	Liquid laundry containers	Valve boxes
Folding chairs	Folding tables	Distilled water bottles
Meter boxes	Milk jugs	Cereal box liners

Recycling Issues

The amount of plastic out there is truly staggering to contemplate. Americans use 2.5 million plastic bottles every hour2, and all that material doesn’t simply disappear into thin air after it has been thrown away. The vast amount of plastic piling up in landfills across the globe constitutes a major threat to the well-being of the Earth’s environment. LDPE and HDPE make up a substantial portion of the world’s plastic waste products. As highly durable non-biodegradable materials, they will be around for many years unless steps are taken to recycle them.

But why bother recycling plastic? Isn’t it more trouble than it’s worth, as some commentators claim? Far from it. There are a number of benefits associated with recycling old LDPE and HDPE containers and products.

• Recycling LDPE and HDPE products takes about half as much energy as incineration disposal3.
• Recycling LDPE and HDPE helps reduce the expense associated with manufacturing products made from these materials.
• Recycling LDPE and HDPE helps reduce the expense associated with waste disposal (e.g., landfill costs).
• It is cheaper to make LDPE and HDPE from recycled matter than to use new materials.

Not only does recycling help the environment, it also provides extra income for businesses. Plastic scrap can be a useful revenue source. Companies like Polychem USA pay significant sums for LDPE and HDPE waste.

Products Made from Recycled LDPE & HDPE

The great thing about recycling is that it puts this old material to good use. You may be surprised at the wide variety of products made from recycled LDPE and HDPE. Below is a partial list of everyday products commonly manufactured with recycled plastic:

• Furniture
• Floor tiles
• Trash cans and crates
• Shipping envelopes
• Paneling
• Gardening tools
• Rope
• Toys
• Plastic lumber

Contact Polychem USA today for more information about our plastic scrap purchasing program.

Sources

1 . http://www.independent.co.uk/news/science/polythenes-story-the-accidental-birth-of-plastic-bags-800602.html
2 . http://recyclingfacts.org/content/plastic-recycling-facts
3 . http://recyclingfacts.org/content/plastic-recycling-facts