A Professor Plastics Feature ArticleSee Other Articles
Yes, I love polypropylene and polyester and silicones and all sorts of other plastics. But high-density polyethylene (or HDPE) plastic has been courting my favor recently. Not only is it one of the most versatile of plastics—used in everything from hard hats to house wraps—it’s also widely recycled, in both its rigid form (e.g., containers) and flexible form (e.g., bags).
Produced in fits and starts in the 1930s in the United Kingdom, HDPE production really took off in the 1950s in the U.S. and has skyrocketed in popularity, making it today’s most widely used type of plastic. It’s made by stringing together ethylene molecules (thus “poly” “ethylene”), which are derived predominately from natural gas resources in the U.S.
So HDPE is not only versatile, it’s popular. It’s kinda like the Meryl Streep of plastics.
Why so popular? Here’s why:
- It’s lightweight yet super-strong. That’s why an HDPE milk jug that weighs 2 ounces can carry a gallon of milk. And why many carmakers use HDPE fuel tanks—lighter weight car parts can help increase fuel efficiency.
- It’s impact resistant. Drop the toy truck down the stairs and it bounces.
- It’s long lasting and weather resistant, so that plastic lumber deck in the backyard can entertain generations of families.
- It resists mold, mildew, rotting, and insects, so it’s great for underground pipes used to deliver water.
- And it’s easily molded into nearly any shape, providing one of the primary benefits of most plastics: malleability.
Like many other plastics, HDPE often replaces heavier materials, in part because our society and many companies are pursuing sustainability goals, such as reducing the amount of material used in packaging and products. “Lightweight and strong” can translate into “less impact on the environment.” For example, a recent study of six types of packaging found that plastics can deliver more food with significantly less waste, energy use, and global warming potential than alternatives.
So where do you typically use it? Well, I’ve mentioned some uses above, but you likely handle HDPE bottles and containers on a daily basis, for food, beverages, personal care products such as shampoo, and household products. Plus bread bags and those handy bags in the grocery store produce aisle. Even cereal box liners. The list of uses is huge (remember: versatile and popular).
Didn’t I mention recycling?
If you flip over your bottle of laundry detergent, it probably has the number 2 imprinted, surrounded by a chasing arrow. That’s HDPE’s resin identification code. The code was designed decades ago to help get plastics recycling off the ground (although today community recycling programs are less likely to ask for plastics by the resin code number than in the past).
Thanks to collective efforts tracking back to the 1990s, when plastics recycling really started to grow, HDPE has become quite skilled at evading landfills. Nearly all curbside recycling programs today in the U.S. accept HDPE bottles, which has helped HDPE bottles break the billion pound mark for recycling in 2012.
Recycled HDPE has proven almost as versatile and popular as its “virgin” counterpart—it’s used in many of the same applications noted above. Some of the more typical uses include:
- Recycled plastic storage containers (What is Bakelite?);
- Recycled plastic lumber;
- Recycled plastic outdoor patio furniture;
- Recycled plastic playground equipment;
- Recycled plastic automobile parts; and
- Recycled plastic trash cans, compost bins, and recycling bins (which seems apropos, no?)
Learn More: The density of plastic
Remember those cereal liners I mentioned? Kellogg has even packaged one of my favorite breakfasts in a stand-alone cereal bag — no need for an outer box — that contains recycled HPDE.
So like the high school prom queen who lettered in three sports and graduated top of her class, HDPE is a multi-talented and well-liked material with a stellar future in front of it.
Just don’t say that around polypropylene….