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Making Products Greener: Choose the Best Plastic

This article was written by Jeremy Faludi in November 2006. We're republishing it here as part of our month-long editorial retrospective.

One of my gigs these days is to be the green design consultant for a small startup making a consumer electronics device. Along the way, I've researched a bunch of stuff, and figured it would be nice to share some of the knowledge with others. (And if you know more about it than I do, I'd be happy to hear about it in the comments!) So this post is the first in a small series on making a product greener--not pie in the sky research-lab stuff, but things any company can do today. It's about choosing good plastics.

plastic_basket.jpg Almost everything you buy these days is injection-molded out of plastic. That's because plastic is amazingly useful. It's not going to go away. (The Environmental Literacy Council has a nice little history of plastic on their site.) And for most products it's environmentally better than using aluminum or other metals, and unfeasible to replace it with wood or other fibers. The ideal would be to find a material with the useful properties of plastic with none of the downsides. We're not there yet, but we're farther than you think.

What plastic is best to use?

Greenpeace has a helpful list of what plastics are the best and worst, and why. Biopolymers are the best, followed by polyolefins (PE/PP/HDPE) second, PET third, ABS / polycarbonate / polyurethane / polystyrene fourth, and PVC worst. Here are the details, from their site and others who have written about this:

Biopolymers (called "bio-" because they are made from plant cellulose or starch, not petroleum) usually use the least toxic ingredients, do not release toxic gases or other substances into the environment during the product's life, and certainly use the least fossil fuel for their manufacture. (Ideally they'd use none.) Some biopolymers are compostable.

Polyolefins (PE, HDPE, and LDPE are all polyethylene, PP is polypropylene) are the best petroleum-based plastics because they use fewer toxic chemicals than other plastics. They're also very widely recycled (recycling codes #2, #4, and #5.)

PET / PETE (polyethylene-terephthalate; in clothes it's called polyester) is not as good as simple polyethylene because more additives are put into it (usually UV stabilizers and flame retardants), but it's still widely recycled (recycling code #1).

ABS (acrylonitrile-butadiene-styrene) and Polycarbonate (PC) are what almost all consumer electronic device cases are made out of--computers, cell phones, MP3 players, you name it. Some are just ABS or PC, most are a blend of the two. The ingredients for both ABS and polycarbonate are suspected to be carcinogenic, some are also mutagenic; polycarbonate uses nasty solvents in its manufacture. They are both perfectly recyclable but are rarely recycled in municipal systems because they fall into recycling code #7, "other". Polystyrene (PS) has carcinogenic ingredients like ABS (both contain styrene), but is also damages human reproductive system. It's also recyclable but not often recycled (recycling code #6).

PVC (polyvinyl chloride), uses more toxic ingredients for its manufacture, because in addition to carcinogens like vinyl chloride, it also requires plasticizers to be flexible, and these plasticizers are more toxic than the base plastic itself. Besides the manufacturing hazards, dioxin and other toxins like DEHP (a plasticizer connected to reproductive illness) outgas, leach, and flake off PVC during its use in your home; when thrown away, these chemicals also leach into groundwater in landfills. This is why they are the worst on the list. They can be recycled (recycling code #3), but rates are generally low. The good news is they were never in consideration for our product anyway.

What plastics did the company consider?

Bioplastics were the first choice. We've written about the researchers at the University of Warwick who made cell phone cases out of a biodegradable polymer which comes with an embedded sunflower seed--just drop the case in the ground and it composts and releases its seed. We've also mentioned how NEC made a cell phone whose case was made out of the bio-plastic PLA reinforced with kenaf fiber. Both of these projects were groundbreaking and took extensive R&D to accomplish. They have yet to be duplicated by other manufacturers. PLA is being used by itself in many applications--mostly food packaging--and although it is still new to the market, it is quickly becoming the most successful bio-plastic. We've written about PLA before, but the best article about it on the web is by Smithsonian Magazine. The more prosaic Nylon 11, which has been around for decades, is also a bio-plastic: it is made from castor bean oil. However, since it was not invented with ecological impact in mind, it is not compostable and does not save significant energy in its manufacture like PLA does.

Unfortunately the company I was working for, like most normal companies, does not have years to research cutting-edge materials like the University of Warwick or NEC. They also have tight engineering requirements for the product which made it unfeasible to use off-the-shelf PLA or Nylon of any kind. In fact, as great as PLA is, it has the problem of melting at 114°C, which means it'll melt if you leave the product on your dashboard on a hot sunny day.

In the end, the product's engineering requirements dictated that we use polycarbonate or ABS. At first I was dead-set against that because they are recycling coded "other", so almost no cities in the US recycle them. However, the biggest impact of our little electronic device will be the circuit board, not the case, and we will have a takeback program with a strong incentive for users to send their old devices back to us. The companies who take electronics for recycling all recycle polycarbonate and ABS, so we can consider them recyclable materials after all. Still, using recyclable plastic is not enough. You're not really recycling unless you're making your device from recycled material. I investigated using 100% recycled plastic as our material, so that we do not cause any new plastic to be manufactured, and so that we can prevent existing plastic waste from going to landfills.

Using recycled plastic: easier than you think

Recycled plastic is very easy to come by, and in fact is cheaper than virgin plastic. Most people don't know this. When I called GE plastics, their sales rep said post-consumer resins are "nearly impossible" to find; GE sells a 50%-recycled-content resin for $2.60 per pound (as compared to $20/lb. for similar virgin resin) which uses post-industrial waste instead of post-consumer. However, a quick look through the Thomas Register turned up a long list of companies that do recycled plastic in the US; many of them sell ground-up ("regrind") polycarbonate and ABS for less than a dollar a pound, some as little as 60 cents per pound. The main trouble with this (and the reason that GE doesn't do post-consumer plastic) is quality-control. Recycling companies get every imaginable color and grade of materials, some of it painted or coated, and not everything is ground up into exactly the same-sized chunks; their sorting processes have to be extremely good for their end product to be reliable and consistent. If you try to injection mold with inconsistent material, you end up with streaks through your plastic that are at the very least an aesthetic problem, reduce optical clarity in transparent parts, and can also be a structural problem (making the plastic easier to crack). However, quality control exists if you are willing to pay for it, and since brand-name virgin resins can cost $10 or $20 per pound, it is easy for a recycler to be competitive. New Life Plastics has some good photos of their process / facilities on their website. At least one company I talked to, Maine Plastics in Michigan, promised their regrind is as good for injection molding as virgin, and that if the melt is bad, they'll take it back and give credit for what you paid. As for aesthetics, any regrind can be dyed black, and that was our color of choice anyway, so that doesn't present a problem. Also, if you're going for boring-computer-beige ABS, there're mountains of that lying around.

Recycled plastic is trickier to use than virgin plastic, but not insurmountably tricky. In theory, any thermoplastic can be ground up, melted down, and reused infinitely without degrading. (It's not like paper recycling where the paper fibers get cut up during the recycling process and become less sturdy with each cycle--the molecular chains that make up thermoplastics are far too small to be cut up by recycling machinery.) However, in practice injection molding a plastic does stress the material, so recycled plastic has different properties than virgin plastic. The main difference is that when using it for injection-molding, it has a higher viscosity, so you have to tweak your process. Some studies have shown that you can use up to15-20% recycled content without affecting your process at all, but if you want to use 100% recycled material as we do, some adjustments will have to be made and some trial-and-error will be required to get it working properly. Even then, your reject rate will be higher (perhaps 5% rather than 2%); but this is a small disadvantage in the face of the large environmental (and also financial) gains made by using recycled material. Of the several people I talked to (both plastic recyclers and manufacturers), there was no consensus about whether polycarbonate or ABS or a PC/ABS blend would give the best results when using 100% recycled material. Since the device requires a clear window (which would have to be polycarbonate, since ABS is never transparent) it seemed best to use polycarbonate for everything. The fewer different kinds of material you use, the more recyclable your device is.

It's surprising that more consumer electronics companies don't make their products out of at least partially recycled plastic, given how easy it is to come by and how cheap it is. I look forward to the process of working with a contract manufacturer to use recycled plastic when we get to the manufacturing stage. Obviously it would have been even better to use a recycled PET or polyolefin, but that would have required a significant redesign of the product; maybe in version 2.0 we can get there. Maybe by that point there will be even better biopolymers around.

Design Notes From The Field: Choosing Good Plastics is part of our month long retrospective leading up to our anniversary on October 1. For the next four weeks, we'll celebrate five years of solutions-based, forward-thinking and innovative journalism by publishing the best of the Worldchanging archives.

Image credit: The Environmental Literacy Council

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Just wondering - has anything changed/improved since this was first posted?

Posted by: Brenda Schroeder on 10 Sep 08

My comment about the article concerns the following misleading sentence: "Polystyrene (PS) has carcinogenic ingredients like ABS (both contain styrene), but is also damages human reproductive system." While it is true that both polystyrene and ABS are made from styrene, the allusion to styrene being a "carcinogenic" ingredient is wrong. No regulatory agency anywhere in the world has classified styrene as a known human carcinogen. The U.S. EPA currently is evaluating styrene's potential carcinogenicity and is expected to render a decision within the next two years. In addition, styrene is not known to affect the human reproductive system.

Posted by: Joseph Walker on 11 Sep 08



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