Self-stick or pressure sensitive adhesives (PSAs) have myriad applications in everyday products including duct tape and sticky notes, but most are derived from petrochemicals. Now, a team of researchers from the POLYMAT Institute at the University of the Basque Country has designed a new PSA made of 71% renewable biological products. The adhesive can be tuned to different strengths using ultraviolet light (ACS Sustainable Chem. Eng. 2019, DOI: 10.1021/acssuschemeng.9b05067).
Researchers already knew that some natural fatty acids could replace petroleum-derived monomers in PSAs, but using fatty acids in polymer-forming reactions isn’t straightforward. “Their high hydrophobicity makes emulsion polymerization difficult,” explains José R. Leiza, who led the new study.
His team instead decided to try 2-octyl acrylate, which is derived from castor oil, and piperonal, found in black pepper. The structure of piperonal suggested it could be easily derivatized in two steps to piperonyl methacrylate, a great substitute for other monomers that are more difficult to prepare. Piperonal is already commercially available and produced on industrial scales. And piperonyl methacrylate “can be readily incorporated in conventional existing production plants,” Leiza says. Between 7-10% of the world production of polymers—around 300 million tons—uses emulsion polymerization for producing adhesives, coatings, paints, latex, and more, including PSAs.
To test their idea, the researchers blended the two raw materials under the same conditions that would be used in emulsion polymerization. They then performed standard adhesive tests on the resulting polymers to determine that the materials worked as well as commercially available PSAs. They also discovered that by exposing the material to UV light, they could tune the material’s strength, stickiness, and shear resistance.
Being able to tune the materials’ properties using UV light could open up a world of possibilities, says Adrián Badía, the study’s first author. Dental materials and other structural adhesives and coatings rely on UV-light curing already, so they would be possible applications.
“This is an important extension of the previous work to develop bio-content PSA,” says Kevin Lewandowski of 3M Corporate Research Materials Laboratory, an adhesives expert not involved with the work. “Researchers have demonstrated the utility of a new bio-based monomer.” The UV-mediated cross-linking mechanism could be useful for further tuning the adhesive properties, he adds. UV curing could change a sticky pressure sensitive adhesive—good for initial tack and repositioning—into a stronger crosslinked adhesive with better bonding performance.”
Alex Lancelot, a postdoctoral researcher at the Universitat Autònoma de Barcelona who collaborates with adhesives maker Henkel, notes that the researchers managed to synthesize the adhesive in water, which minimizes volatile organic compounds, enhances the overall safety of the process, and reduces costs.
Because of a production error, this story was updated on Jan. 15, 2020, to correct the spelling of piperonyl methacrylate in the figure caption and the author's byline.