Tackling hard-to-recycle plastics from auto windshields, airbags

Denver — Plastics researchers are tackling ways to recycle plastics from automotive applications.

Researchers from materials giant Dow Inc. and from the University of Stuttgart each presented research on that subject at the Society of Plastics Engineers Antec 2023, held March 27-30 in Denver.

Midland, Mich.-based Dow is developing ways to better recycle polyvinyl butyrate (PVB) layers from auto windshields, according to global application technology leader Manoj Nerkar.

"We started the project as a way to help our customers meet their sustainability goals, then we thought we could take it outside and see if others needed the same thing," he said.

The challenge is a large one, according to Nerkar, since 75 million windshields are replaced each year, with each containing 1 kilogram of PVB.

"The glass [from windshields] gets recycled, but a huge volume of PVB ends up in landfills," he said. In many windshields, PVB makes up a middle layer between two layers of glass.

Through research and testing, Dow has found a way to use acrylic additives from its plastic additives business to improve the recycling of PVB. Those additives more typically are used in construction applications and in auto interiors.

Dow's acrylic additives are spray dried into powders before being used in PVB recycling. The resulting formulation has improved the processing and performance of recycled PVB and increased the material's sustainability, said Nerkar, who has more than 20 years of industry experience.

"This has really opened up new avenues for recycled PVB," he added.

At the University of Stuttgart in Stuttgart, Germany, research has been done on recycling of auto airbags, which typically are made of nylon 6/6 fibers and silicone coating.

"A new recycling strategy is needed to optimize mechanical properties of airbags," said scientific associate Sinja Pagel.

Previous methods of airbag recycling included chemical separation, which takes large amounts of solvents and has a high energy demand, and extruding crushed fabric parts into granules, which produces low quality material.

The Stuttgart project found that airbag waste can be compounded with an organofunctional silane liquid to create a better, more usable material. The resulting material has the same tensile strength as the original material, Pagel said.

"One challenge is that silicone content varies a lot in airbags, so you need to use the right amount of additives in recycling them," she added. Future work in that area will include use of different types of silane.