New Adhesive Expected to Replace Traditional Glue and Hot Melt Adhesive

The application range of adhesives is extremely wide, usually used in many fields such as automobiles, packaging, electronics, solar panels, and construction, thus forming an industry cluster of over 500 billion dollars, supporting the needs of modern life. However, almost all adhesives on the market are petroleum derivatives and non-biodegradable, causing pollution to the environment.

To address this issue, a team comprising Colorado State University, the U.S. National Renewable Energy Laboratory, and the University of California, Berkeley, used the natural polymer poly (3-hydroxybutyrate) (P3HB) for chemical redesign, producing a strong and recyclable adhesive. This adhesive is more robust, easier to degrade, and reusable compared to the commonly used adhesives on the market. The research results were published in the magazine “Science” on January 16.

P3HB is a natural, bio-based, biodegradable polymer that can be produced by microbes under suitable biological conditions. However, the P3HB freshly produced by microbes does not have adhesiveness and requires chemical structure redesign to enable it to adhere properly to various substrates or other objects’ surfaces.

Researchers added P3HB monomers to yttrium, lanthanum, and phosphorus-based catalysts and produced several P3HB polymers with different stereostructures and molecular weights through different heating methods.

In the analysis of these different stereostructures and molecular weight P3HB polymers, researchers found that different temperatures enhance the adhesive tensile strength, fracture toughness, and flexibility of these different stereostructure P3HB polymers. However, once the temperature is elevated to 245°C, P3HB undergoes thermal degradation causing the adhesion to fail.

After a round of experiments, they found that the performance of sr-P3HB structure was the most excellent due to its unique stereostructure, contributing to the required thermal-mechanical and viscoelastic properties. Its adhesive strength surpasses common commercial adhesives like epoxy resins, polyurethanes, and hot melt adhesives and can firmly bond substrates such as aluminum, glass, wood, and steel.

Researchers also compared the strength, durability, and adhesive strength of sr-P3HB with the commercial hot melt adhesive (EVA). The results showed that the adhesive strength of sr-P3HB is 2.5 times that of EVA, and it can withstand over 20 pounds of pull force (about 9 kilograms) when bonded to a steel plate, while EVA’s limit is 15 pounds.

Experiments also revealed that the performance of sr-P3HB does not dramatically change due to molecular weight, reprocessing, and reuse, and it has biodegradable properties.

Although sr-P3HB is an ideal choice for large-scale production and application, further development of more efficient monomers, catalysts, polymer synthesis, and production methods are needed to reduce environmental impact.

Eugene Chen, distinguished professor in the Department of Chemistry at Colorado State University, committed to developing chemically recyclable and biodegradable materials, expressed to the university’s newsroom that petroleum-based thermoset adhesives and thermoplastic hot melt adhesives are generally challenging to recycle and remove. However, “the P3HB we provide can naturally biodegrade in environments like seawater, soil, or landfills. Additionally, it features recyclability, reprocessing, and reusability, along with adjustable adhesive strength, expanding its applications.”

The primary author of the paper, Dr. Ethan C. Quinn, from Colorado State University, stated, “We developed P3HB glue stick samples and tested them alongside commercial hot melt adhesives to evaluate their performance on sealing paperboard boxes and steel plates. The results showed it is stronger than other hot melt adhesives, but what shocked me was its ability to withstand a weight of 20 pounds, higher than other hot melt adhesives that can only bear 15 pounds.”

Currently, the Colorado State University team, along with the U.S. National Renewable Energy Laboratory and other scientists, are researching different methods to advance this polymer into crucial areas for improvement to reduce the overall cost of the product and eliminate environmental impact, thus enabling P3HB to be commercialized.