Highlights of Low-Density Polyethylene

Professor Plastics

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The history of high density polyethylene

Quick, what’s the difference between low-density polyethylene (LDPE) and high-density polyethylene (HDPE)?

Yes, this will be on the quiz…

To help you answer that question, I covered HDPE plastic in a previous article, so you can bone up on that polymer if you need to. And I’ll cover LDPE plastic here.

Clearly these two polymers are similar because both are named polyethylene. In fact, LDPE was the first polyethylene to be produced, so it’s sorta like HDPE’s senior cousin, (which always causes problems at the Polymer family get-togethers).

But as the names suggests, LDPE has a lower “density” than HDPE. That just means it has a bit less mass compared to its volume. For example, lead is dense. Whipped cream is not.

LDPE also has more molecules that branch out, as opposed to staying in perfect rows. (That part will not be on the quiz…).

LDPE’s lower density and branched molecules give it somewhat different properties than HDPE, although they do share some similar uses, such as packaging. LDPE/HDPE differences typically cause them to be collected separately for recycling … but not always (more on that later).

LDPE is resistant to impact (doesn’t break easily), moisture (water proof), and chemicals (can stand up to many hazardous materials).

Know it or not, you likely use LDPE every day, for many very good reasons. For example, let’s say you need to carry something home from your trip to the store (shopping bags). You may want to supply your child’s lunch with a non-refrigerated drink (juice boxes or “aseptic” packaging). Or your child may like playing make believe (toys). And, of course, nobody wants to grab naked copper electrical wire (insulation on electrical wires and cables).

Plus there are many industrial and agriculture uses, particularly as plastic film and packaging to protect all sorts of products.

It’s worth stopping for a second and noting the sustainability benefits of lightweight plastics used in packaging, in particular really lightweight plastic film, one of the major uses of LDPE. Thankfully, plastic packaging is becoming increasingly recognized for its contributions to sustainability. The very nature of plastics – lightweight yet strong – makes them ideal for all sorts of packaging and helps minimize the environmental impact of the packaging.

For example, a 2014 study that looked at six common packaging categories (including film/wraps) found that replacing existing plastic packaging in the U.S. with non-plastic alternatives could:

  • require 4.5 times more packaging material by weight,
  • increase energy use by 80 percent, and
  • result in 130 percent more global warming potential.

Wow. Those are big numbers. Plastic packaging clearly can deliver more goods with significantly less waste, energy use, and global warming potential. There’s something I can feel good about.

Back to recycling… Many items made with LDPE are collected for recycling in communities across the nation. Rigid LDPE products (bottles, containers, lids, caps, etc.) typically are collected in curbside recycling programs.

But flexible LDPE bags and wraps are different. Clean and dry bags and wraps made with LDPE (and HDPE) are collected at more than 18,000 retailers nationwide. This includes bags for groceries, newspaper delivery, dry-cleaning, bread, produce, and so on, plus product overwraps, bubble wrap, and cereal box liners. (A limited number of communities collect plastic bags and wraps at curbside. Check with your community.)

And recycling rates for bags and wraps are growing. So… what happens to all that LDPE collected for recycling? When recycled, LDPE is given a second chance to live on as other useful products, such as:

  • Shipping envelopes
  • Garbage can liners
  • Floor tile
  • Paneling
  • Furniture
  • Compost bins
  • Trash cans
  • Landscape timber
  • Outdoor lumber

Recycling LDPE and other plastics can help lighten our load on the environment. How? EPA says that recycling in America significantly reduces energy use and greenhouse gas emissions and can create more and better jobs than landfilling.

So LDPE will continue doing its part to deliver more goods with less waste, energy use, and global warming potential than alternatives. And you can do your part by recycling rigid LDPE items in your curbside bin and flexible LDPE bags and wraps at participating retail stores.

Now… ready for the quiz?