USF student invents alternative to wood using recycled plastic

When lumber was largely unavailable and prices soared to historic highs during the coronavirus pandemic, a University of South Florida mechanical engineering student was developing a cost-effective alternative. Now funded by the National Science Foundation, doctoral student John Cotter is making a recycled plastic building material that can replace structural lumber.

The ultra-strong recycled material, Recycled Plastic Lumber, is made of composites reinforced with polymers, a reinforced material like concrete. The material will be used as a replacement for wood to create fence posts that can last 30 to 50 years, about three times longer than a wooden fence.

In addition to significantly reducing future costs for customers, recycled plastic lumber will reduce the 10 million acres of forest harvested each year in the United States. Cotter estimates that the green alternative will produce 15 million fence posts per year.

The NSF grant runs until May 2023. Cotter will spend that time refining and perfecting the material. He works alongside PhD student Tia Sayers and Rasim Guldiken, an associate professor of mechanical engineering, to incorporate customer feedback into reviews. From there, it will begin the product approval process to get it to market and into the hands of customers.

Through a previous USF I-Corps grant, the team spent the spring semester conducting interviews with homeowners, farmers, ranchers, and fencing contractors across the country. The data helped identify market demands.

According to the first interviews with customers, wooden fence posts generally last 10 to 20 years. In some locations with extreme weather conditions, such as Florida, customers have reported problems as early as five years after installation. The team learned that customers of wooden fences most often experience rotting due to humidity and severe warping due to heat that requires rework. Both of these issues impact the strength and durability of fences.

Polymer, the main material of recycled plastic wood, is much less affected by environmental factors.

“The goal is to make an effective material for the price based on the resistance provided,” Cotter said. “The secret behind the technology is not necessarily the polymer itself, but the reinforcement method.”

Cotter has developed a reinforcement method that can be used with extrusion processes – where plastic is heated, melted and pressed through a specialized machine tool. Instead of pressing to create a shape, the reinforcement is fed into the tool and coated with polymer.

Cotter intends to devote its future to the exploration and manufacture of low-cost structural materials. He obtained his first patent for recycled plastic lumber in 2021 and has another one pending. Both involve the use of glass as a cost-effective structural material, including as reinforcement for the polymers used in fence posts.

Not only does he plan to explore ways to extend the current concept to other wood applications, such as decking, but he has already started building another fence alternative based on the needs and requests received during the client’s initial discovery – a concrete reinforced and filled with recycled product that can be installed in the same way as wood.

Over the past 14 years teaching mechanical engineering, Guldiken says Cotter’s entrepreneurial spirit stands out. Cotter’s forward thinking mindset led to solutions to real problems and ultimately a bridge between academia and his future career.

“What we do in the classroom and in the lab can have a big impact, even on a global scale,” Guldiken said. “The main goal is not to make money, but to help our citizens.”

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