Manufacturing Bits: Dec. 23

Magnetic glue
Nanyang Technological University (NTU) Singapore has developed a new magnetic-activated glue technology.

Conventional glue or adhesives involve epoxy and related materials. These adhesives are used to bond plastics, ceramics and wood. The adhesives are bonded and cured using moisture, heat or light. The curing temperatures range from room temperature to 80 degrees Celsius.

In one example, heat curing glues are used to make sport shoes. The heat curing process itself is conducted in large industrial ovens, which consume energy and take up space.

In response, NTU has developed a new “magnetocuring” glue. This magnetic glue bonds materials when activated using a magnetic field.

The new magnetocuring adhesives from NTU are made by combining commercially available epoxy adhesives with magnetic nanoparticles. In the process, these materials are applied on a surface. A small electromagnetic device is activated, which then bonds the materials.

This is a remote, wireless, and contactless way to cure the adhesives using so-called alternating magnetic fields. The maximum lap shear adhesion strength exceeded 6.5 MPa, according to NTU.

This process uses less energy than a conventional oven. For example, one gram of magnetocuring adhesive can be cured by a 200-watt electromagnetic device in five minutes. This process consumes 16.6 watt hours, according to researchers.

This is 120 times less energy needed than a traditional 2,000-watt oven. The conventional process takes an hour to cure conventional epoxy, according to researchers.

Magnetocuring could be used for wood, ceramics and plastics. Applications include sports equipment, automotive products, electronics, energy, aerospace and medical. It is an ideal solution when current adhesives do not work well.

“Our key development is a way to cure adhesives within minutes of exposure to a magnetic field, while preventing overheating of the surfaces to which they are applied. This is important as some surfaces that we want to join are extremely heat-sensitive, such as flexible electronics and biodegradable plastics,” said Terry Steele, an associate professor at NTU.

“Our temperature-controlled magnetic nanoparticles are designed to be mixed with existing one-pot adhesive formulations, so many of the epoxy-based adhesives on the market could be converted into magnetic field-activated glue,” said Raju Ramanujan, a professor at NTU. “The speed and temperature of curing can be adjusted, so manufacturers of existing products could redesign or improve their existing manufacturing methods. For example, instead of applying glue and curing it part by part in a conventional assembly line, the new process could be to pre-apply glue on all the parts and then cure them as they move along the conveyor chain. Without ovens, it would lead to much less downtime and more efficient production.”

Turning plastics into adhesives
The University of California at Berkeley has developed a chemical process that converts polyethylene plastic into a valuable adhesive.

Polyethylene materials are used to make single-use plastics, plastic bags and other packaging types. The problem with polyethylene packaging is that it clogs landfills and pollutes rivers and oceans. That’s why some cities have banned them.

Recycling polyethylene is one way to solve the problem. This painstaking process involves chopping up the materials and forming them into generic products. These products are often low-value or environmentally questionable, however.

The University of California at Berkeley has found another solution to the problem. Researchers have developed a process, which keeps many of the original properties of polyethylene. But they also add a chemical group to the polymer, which in turn makes it stick to metal. Researchers have developed oxidized polyethylene, which could stick to water-based latex paint.

To enable this, researchers have developed a new catalytic process, where small chemical units are added to large hydrocarbon chains or polymers. Using a catalyst based on ruthenium, UC Berkeley chemists were able to add specific chemical groups to polyethylene polymer chains, creating an oxidized polyethylene.

“The vision is that you would take a plastic bag that is of no value, and instead of throwing it away, where it ends up in a landfill, you would turn it into something of high value,” said John Hartwig, the Henry Rapoport Chair in Organic Chemistry at UC Berkeley. “You couldn’t take all of this recycled plastic — hundreds of billions of pounds of polyethylene are produced each year — and turn it into a material with adhesive properties, but if you take some fraction of that and turn it into something that is of high value, that can change the economics of turning the rest of it into something that is of lower value.”