University of South Florida student creates an alternative to wood using recycled plastic

While wood was not widely available and prices were skyrocketing during the coronavirus pandemic, a mechanical engineering student at the University of South Florida was developing a cost-effective alternative. Now funded by the National Science Foundation, doctoral student John Cotter is making recycled plastic building materials that could replace structural wood.

The extremely strong recycled material, recycled plastic lumber, is made of polymer-reinforced composites, a material that is as hardened as concrete. The material will be used as a substitute for wood to create fence posts that can last from 30 to 50 years, about three times longer than a wooden fence.

On top of significantly lowering 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 eco-friendly alternative will produce 15 million fence posts annually.

The NSF scholarship runs through May 2023. Cotter will spend this time improving and perfecting the material. He’s working alongside doctoral student Tia Sayers and Rasim Guldiken, associate professor of mechanical engineering, to incorporate customer feedback into reviews. From there, it will begin the process of approving the product to get it to market and into the hands of customers.

With a previous grant from USF I-Corps, the team spent the spring interviewing homeowners, farmers, ranchers, and fence contractors across the country. The data helped determine market requirements.

Based on initial customer interviews, wooden fence posts usually last 10-20 years. In some locations exposed to severe weather, such as Florida, customers reported problems as soon as five years after installation.

The team learned that wooden fence clients commonly suffer from rot from moisture and severe warping from heat that requires rework. Both problems affect the strength and durability of fences.

Polymer, which is the lead material in recycled plastic lumber, is much less affected by environmental factors.

“The focus is on making a price-effective material based on the strength that is available,” Cotter said. “The secret behind this technology is not necessarily the polymer itself, but the method of reinforcement.”

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

Cotter intends to dedicate his future to exploring and manufacturing low-cost structural materials. He received 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.

He not only plans to explore ways to expand the existing concept for additional wood applications, such as decking, but has already begun building another alternative fencing based on the needs and requests received during the initial client discovery – concrete being reinforced and filled with a recycled product that can be installed similarly to wood.

Guldiken said that for the past 14 years, he has taught mechanical engineering. Cotter’s forward-thinking mindset led to solutions to real-life problems and eventually a bridge from academia to his future career.

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

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