It’s common knowledge that plastic waste is a problem; no point in belaboring that. If you are involved in New Product Development then you have an opportunity to address that problem, and to generate a competitive advantage at the same time. What follows will explain why and how to use Recycled Plastics in New Product Development.
Demand Drives Corporate Behavior
New Product Development usually involves the design and fabrication of custom plastic parts. Engineers use plastics because they are both cost-effective and durable. Those virtues lead to some unfortunate outcomes. Cost-effective materials are easy to throw away. Durable materials persist for a long time after they are discarded. Those properties have resulted in some disturbing trends:
- 50% of the plastic produced every year is for single-use products.
- 8 million metric tons of plastic enter the ocean every year.
- Only an estimated 9% of plastic is ever recycled.
Consumers are increasingly aware of those facts and have shown a willingness to pay more for products that incorporate better alternatives. This market demographic is generating interest in, and demand for, the use of recycled plastics in New Product Development.
A company that responds to this demand will realize some economic benefits:
- Market Differentiator. An increasingly large demographic responds favorably to products that incorporate recycled plastic.
- Production Cost. Recycled plastic is much less expensive than virgin plastic pellets.
Thermoplastic polymers are long chains of atoms arranged in repeating units. Most plastics start life as petroleum* which is refined and mixed with other chemicals, finally processed into solid plastic pellets. Those pellets are then shipped to fabricators who employ different processes to make the thousands of plastic products that you interact with every day.
What those processes have in common is that they melt the solid pellets into a thick liquid, then allow the liquid to resolidify into a useful shape like a spoon, frisbee, or automotive bumper. *16.3 barrels of oil are saved every time 1 ton of plastic is recycled.
The process of making a plastic part generates some scrap; solid bits that cannot be sold. Those bits may be ground up into new pellets called regrind. Regrind is not quite as durable as virgin material. Every time plastic melts and resolidifies it gets a little weaker. For that reason, it is common to allow only 15% to 30% regrind in order to maintain sufficient mechanical properties. The balance is virgin pellets.
What do you think of when you hear “plastic waste?” Most think of plastic straws, packaging, bottles, etc. that are destined for the landfill or the ocean. Add shoes, toys, and carpeting to that list. Some of those items will be taken to a collection center for recycling, and some fraction of what is collected will find its way into new products.
♳ Polyethylene terephthalate (PET) Beverage bottles
♴ High-density polyethylene (HDPE) Milk jugs
♵ Polyvinyl chloride (PVC) Outdoor furniture
♶ Low-density polyethylene (LDPE) Garbage bags
♷ Polypropylene (PP) Bottle caps
♸ Polystyrene (PS) Disposable utensils
♹ Other (ABS, PLA, Nylon) Tupperware
Some products can be made mostly or entirely from recycled plastics because beauty or strength are lower priorities. Carpet backing, barrier-netting, and some children’s toys are common examples.
But suppose we want to make a more sophisticated product that incorporates recycled plastic. We would mix some percentage of ground pre- or post-consumer waste into a plastic part. We expect it to be less robust, and to have some cosmetic imperfections. The Product Development Engineer must compensate for that.
Strength and Stiffness
Parts can be strengthened in many ways. It is a lazy design engineer who relies primarily on material strength. Part geometry and the proximity of mating parts are more important. Imagine a shoebox: without a lid, it is quite flimsy. With a lid installed, it is both strong and stiff.
Many plastic parts are internal to a product or will be covered by labels, printing, etc. These are great candidates for incorporating recycled materials.
Black plastics are great at hiding defects. “Specks” tend to show up in post-consumer material, and it will be very obvious in lighter-colored parts. If it is necessary to use recycled material on light, external parts then we recommend restricting yourself to pre-consumer regrind.
Ductility and Impact Resistance
The design engineer is expected to pay attention to several modes of failure. A part should be impact resistant so that it can be dropped without damage. If overstressed, it should deform rather than fracture into potentially sharp pieces. The way to achieve this is to mix (“alloy”) the recycled plastic with a virgin polymer that is highly ductile and impact-resistant. Achieving the desired results often requires some experimentation.
Using recycled plastics in New Product Development requires diligent engineering. Recycled plastics are less predictable, and their material properties are inevitably diminished compared to the virgin material. Skilled and experienced design engineers can compensate with different strategies:
- Protect a weaker part with a stronger one.
- Design compliance into the system so that force is more evenly distributed.
- Achieve strength or stiffness with geometry instead of inherent material stiffness.
- Take advantage of mating components to achieve system strength and stiffness.
- Select colors or finishes that hide visible imperfections.
- Mix recycled plastic with virgin plastic to achieve the necessary ductility and impact resistance.
Plastic Part Design is one of Porticos’ specialties and we have worked with a diverse set of clients to bring their vision into reality. Any recycled material can be used in plastic part design, but reliably dealing with reduced mechanical properties will require a Systems Engineering mindset and an experienced Product Development team. Porticos is eager to help your company to incorporate recycled plastic into your products. Give us a call to learn more.