Polymer upcycling of frequent plastic provides toughness, recyclability to structural adhesives

Researchers on the Department of Energy’s Oak Ridge National Laboratory used polymer chemistry to remodel a standard family plastic right into a reusable adhesive with a uncommon mixture of power and ductility, making it one of many hardest supplies ever reported.

The research, revealed in Science Advances, essentially advances pathways to design a brand new class of robust adhesives with fascinating options merged right into a single material. The know-how adapts to bear heavy hundreds, tolerate excessive stress and warmth, and reversibly bond to varied surfaces together with glass, aluminum and metal.

“Strong, tough adhesives are difficult to design because they need to incorporate hard and soft features that are not typically compatible,” mentioned ORNL scientist and corresponding writer Tomonori Saito. Structural adhesives similar to epoxy are largely designed for load-bearing power however lack toughness, a property that helps supplies dissipate stress when pulled or stretched to forestall sudden failure.

“The challenge has been to add the toughness you get in flexible materials without sacrificing strength. Our approach uses dynamic chemical bonds to develop a novel adhesive with remarkable properties not seen in current materials,” Saito mentioned.

Researchers geared toward upcycling a commodity thermoplastic, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene, or SEBS, a rubbery polymer materials that’s simple to course of however not engineered for robust adhesion. The purpose of upcycling is so as to add worth to frequent plastics produced in excessive quantity for common and sometimes disposable functions, similar to meals containers, toys and home goods.

The group modified SEBS’ chemical construction with dynamic crosslinking to make it extra sturdy, in addition to to create reuse pathways for plastics, past conventional recycling, that improve their efficiency for brand new and specialised functions.

Crosslinking is a recognized technique for designing supplies with extra steady properties. The method can create a bridge between constructions that aren’t usually appropriate. In the research, boronic esters have been used to couple SEBS with silica nanoparticles, or SiNP, a filler materials used to strengthen polymers. The mixture yields a novel crosslinked boronic ester-SiNP composite materials.

Conventional crosslinking sometimes leads to everlasting bonds that stop adhesives from being eliminated or reprocessed. The research discovered that boronic esters allow “dynamic” or reversible crosslinking and are key to the brand new materials’s robust adhesion in addition to recyclability. These distinctive chemical compounds can create steady bonds that may make and break repeatedly—an uncommon function that makes them enticing for sustainable supplies design.

“A fundamental discovery was that the boronic esters on SEBS can rearrange bonds with hydroxyl groups—oxygen and hydrogen—on SiNP to adapt properties for demanding jobs. We also found the formation of similar reversible boronic ester bonds with a variety of surfaces that have the hydroxyl groups,” mentioned lead writer Md Anisur Rahman, who works with Saito in ORNL’s Chemical Sciences Division.

This two-fold discovering was noticed experimentally and computationally by density practical principle.

Results confirmed crosslinked bonds shift inside the materials to allow particular properties and cling to surfaces so strongly {that a} skinny sq. centimeter can maintain roughly 300 kilos. Shear checks that measure toughness by making an attempt to detach supplies with pressure have been off the charts, extensively exceeding all business adhesives examined within the research. The materials was so robust in adhering to glass, in reality, that tumbler fractured earlier than the pattern debonded. The method additionally enhanced thermal stability to 400 levels Fahrenheit, making the adhesive enticing for ambient and high-temperature functions.

In addition to extraordinary adhesion, a shocking property of the robust materials is that it can be recycled. “It is rare for a high-performance adhesive to be removable, but ours is designed for reuse and recyclability,” Rahman mentioned. “It can be applied and detached with heat and pressure and reused several times.”

The growth widens functions for aerospace, automotive and building adhesives. “There are benefits to industry and the environment to save resources and reduce waste. By design, this adhesive allows you to make repairs or correct costly mistakes and can be reprocessed for new uses in very challenging applications,” Saito mentioned.

The group plans to commercialize the know-how and is exploring dynamic crosslinking with different fillers to develop robust adhesives optimized for particular bonding surfaces and functionalities.