NTU Prof Raju holding and folding two pieces of wood glued in the middle by magnetocurant glue, to demonstrate its strong bonding strength. Credit: NTU Singapore
A potential benefit for green manufacturing, the new glue saves energy, time and space.
Scientists at Nanyang Technological University, Singapore (NTU Singapore), have developed a new way to cure adhesives using a magnetic field.
Conventional adhesives such as epoxy, which are used to bond plastic, ceramic and wood, are usually designed to cure using moisture, heat or light. They generally require specific curing temperatures, ranging from room temperature to 80 degrees Celsius.
The curing process is necessary to crosslink and bond the glue with the two fixed surfaces as the glue crystallizes and hardens to reach its final strength.
The new “magnetocure” glue from NTU can cure by passing through a magnetic field. This is very useful in certain environmental conditions where current adhesives do not work well. In addition, when the adhesive is sandwiched between insulating materials such as rubber or wood, traditional activators such as heat, light and air cannot easily reach the adhesive.
Products such as bicycle frames, helmets and golf clubs are currently made with two-part epoxy adhesives, where a resin and a hardener are mixed and the reaction begins immediately.
For carbon fiber manufacturers – thin carbon strips bonded layer by layer – and sports equipment manufacturers involving carbon fiber, their factories use large, high-temperature furnaces to cure epoxy glue for many hours. This energy-consuming curing process is the main reason for the high cost of carbon fiber.
The new “magnetocure” adhesive is made by combining a commercially available epoxy adhesive with magnetic nanoparticles made to measure by NTU scientists. It does not need to be mixed with any hardener or accelerator, unlike bicomponent adhesives (which have two liquids that must be mixed before use), facilitating their manufacture and application.
It unites materials when activated by passing through a magnetic field, which is easily generated by a small electromagnetic device. This uses less energy than a large conventional oven.
Assoc Prof Steele (left) and Dr. Richa curing the magnet-curing glue on a cotton mesh using an electromagnetic field. Credit: NTU Singapore
For example, one gram of magnetocure adhesive can be easily cured by a 200 watt electromagnetic device in five minutes (consuming 16.6 watt-hours). This is 120 times less energy needed than a traditional 2,000 watt oven, which takes an hour (consuming 2,000 watts / hour) to cure conventional epoxy.
Developed by Professor Raju V. Ramanujan, Associate Professor Terry Steele and Dr. Richa Chaudhary of the NTU School of Materials Science and Engineering, the results were published in the scientific journal Materials Applied Today and offer potential application in a wide range of fields.
This includes cutting-edge sports equipment, automotive, electronics, energy, aerospace and medical manufacturing processes. Laboratory tests have shown that the new adhesive has a resistance of up to 7 megapascals, equal to many of the epoxy adhesives on the market.
Assoc Prof Steele, a specialist in several types of advanced adhesives, explained: “Our main development is a way to cure adhesives in minutes of exposure to a magnetic field, preventing overheating of the surfaces on which they are applied. This is important because some surfaces that we want to join are extremely sensitive to heat, such as flexible electronics and biodegradable plastics. “
How “magnetocurante” glue works
The new adhesive is made up of two main components – a commercially available epoxy that is heat cured and oxide nanoparticles made from a chemical combination including manganese, zinc and iron (MnxZn1-xFe2O4).
These nanoparticles are designed to heat up when electromagnetic energy is passed through them, activating the healing process. The maximum temperature and heating rate can be controlled by these special nanoparticles, eliminating overheating and the formation of hot spots.
(From left to right) NTU Assoc Prof Terry Steele, Prof Raju V. Ramanujan and Dr. Richa Chaudhary holding various soft and hard materials joined together by their new magnetocure glue. Credit: NTU Singapore
Without the need for large industrial ovens, the activation of the glue has a smaller footprint in terms of space and energy consumption. Energy efficiency in the curing process is essential for green manufacturing, where products are made at lower temperatures and use less energy for heating and cooling.
For example, sports shoe manufacturers often have difficulty heating the adhesives between the rubber soles and the upper half of the shoe, since rubber is a heat insulator and resists the transmission of heat to conventional epoxy glue. An oven is needed to heat the shoe for a long time before the heat reaches the glue.
The use of glue activated by magnetic field circumvents this difficulty, directly activating the curing process only in the glue.
The alternating magnetic field can also be incorporated into the bottom of the conveyor belt systems, so that products with pre-applied glue can be cured by passing through the magnetic field.
Improving manufacturing efficiency
Prof Raju Ramanujan, who is internationally recognized for his advances in magnetic materials, led the project together and predicts that the technology can increase manufacturing efficiency where adhesive joints are needed.
“Our temperature-controlled magnetic nanoparticles are designed to be mixed with existing container adhesive formulations, so many of the epoxy-based adhesives on the market can be converted into magnetic field-activated glue,” said Prof Ramanujan.
“The curing speed and temperature can be adjusted, so that manufacturers of existing products can redesign or improve their existing manufacturing methods. For example, instead of applying glue and curing part by part on a conventional assembly line, the new process could be to pre-apply glue to all parts and then cure them as they move along the chain shipping company. Without ovens, this would lead to much less downtime and more efficient production. “
The study’s first author, Dr. Richa Chaudhary said: “Curing our newly developed magnetocure adhesive takes just a few minutes instead of hours, and is still able to protect surfaces with high-strength bonds, which is considerable interest in sports, medical, automotive and aerospace. This efficient process can also generate cost savings, as the space and energy required for conventional heat curing are significantly reduced. “
This three-year project was supported by the Agency for Science, Technology and Research (A * STAR).
Previous work with heat-activated glue used an electric current flowing through a coil, known as induction curing, where the glue is heated and cured from outside. However, its disadvantages include overheating of the surfaces and irregular bonding due to the formation of hot spots inside the adhesive.
In the future, the team hopes to involve adhesive manufacturers to collaborate in the commercialization of their technology. They registered a patent through NTUitive, the university’s innovation and enterprise company. They have already received interest in their research from sporting goods manufacturers.
Reference: “Magnetocure of temperature-proof epoxy adhesives” by Richa Chaudhary, Varun Chaudhary, Raju V. Ramanujan and Terry WJ Steele, September 15, 2020, Materials Applied Today.
DOI: 10.1016 / j.apmt.2020.100824