Whereas most discarded plastic water and beverage bottles (those imprinted with a number 1 within a triangular arrow) can be recycled, the resulting second-generation plastic is generally unusable for making new plastic bottles. This is because the polyethylene terephthalate (PET) thermoplastic polymer used to make the original bottles is often made with the help of metal oxide or metal hydroxide catalysts that linger in the recycled material and weaken it over time.
That means new plastic bottles must be created to keep up with consumers' insatiable thirst for liquid refreshment in disposable containers. Nearly 24 billion plastic beverage cans and bottles have been dumped in landfills, littered and incinerated in the U.S. so far this year, according to the Container Recycling Institute, a Culver City, Calif., nonprofit that tracks container recycling and deposit programs.
A team of IBM and Stanford University researchers report in the most recent issue of Macromolecules, published Wednesday, they have created a new family of organic catalysts that could be used to make plastics that are free of metal and fully recyclable. "The idea is to make a class of polymers that's fully biodegradable," says Spike Narayan, manager for science and technology at IBM's Almaden Research Center in San Jose, Calif. Organic catalysts are those made from carbon, hydrogen, sulfur and other nonmetallic elements.
PET bottles are usually made with the help of heavy metal catalysts that remain in the plastic throughout the life of the bottle and help with the breakdown when the plastic is heated and recycled, Narayan says. But the residual catalyst remains active even after the plastic is recycled, weakening this second-generation plastic and making it impractical to recycle for a third generation. Second-generation PET is often used to make carpets or fiberfill for coats and sleeping bags because less strength is needed for those products. The recycled PET can also be combined with another polymer to make more durable products including car bumpers or rope.
IBM and Stanford report having demonstrated that organic catalysts can rival even highly active metal-based catalysts while being environmentally benign. They also think their research could lead to a new recycling process that can break polymers back down into reusable monomers.
IBM's next step is to launch a pilot PET recycling project with scientists from King Abdulaziz City for Science and Technology (KACST) in Saudi Arabia. This additional research will help determine whether the new organic catalysts can help develop plastic products that are cheaper and more easily recycled. In an interesting twist for Saudi Arabia, greater use of recycled plastics means there will be less demand for petroleum to make new plastics.
Image: Jim Hedrick, a researcher at IBM’s Research facility in San Jose, works on new formulas that could make it easier to recycle the 113 billion plastic bottles disposed of each year globally. Courtesy of Monica M. Davey/Feature Photo Service for IBM