NTU Prof Raju holding and bending two pieces of wood glued in the middle of the magnetocurant glue, to demonstrate its strong binding resistance. Credit: NTU Singapore
A potential advantage for organic production, the new adhesive saves energy, time and space.
Scientists at Nanyang University of Technology, Singapore (NTU Singapore), have developed a new way to cure adhesives using a magnetic field.
Conventional adhesives, such as epoxy, that are used to glue plastic, ceramic, and wood are usually designed to heal using moisture, heat, or light. It often requires specific curing temperatures, ranging from room temperature to 80 degrees Celsius.
The curing process is required to cross-bond and glue the adhesive to the two secured surfaces as the adhesive crystallizes and hardens to achieve its final strength.
The new NTU magnetocuring adhesive can be cured by passing it through a magnetic field. This is very useful in certain environmental conditions where current adhesives do not work well. Also, when the adhesive is sandwiched between the insulating material, such as rubber or wood, traditional activators such as heat, light and air cannot easily reach the adhesive.
Products, such as composite frames for bicycles, 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 producers of carbon fiber – thin carbon ribbons glued together layer by layer – and manufacturers of sports equipment involving carbon fiber, their factories use large, high-temperature furnaces to cure the epoxy adhesive for several hours. This energy-intensive curing process is the main reason for the high cost of carbon fiber.
The new ‘magnetocuring’ adhesive is made by combining a typical commercially available epoxy adhesive with specially adapted magnetic nanoparticles made by NTU scientists. It should not be mixed with any hardener or accelerator, unlike bicomponent adhesives (which has two liquids to be mixed before use), making it easy to manufacture and apply.
It binds materials when activated by passing through a magnetic field, which is easily generated by a small electromagnetic device. It uses less energy than a large conventional oven.
Conf. Univ. Steele (left) and Dr. Richa healing the glue on a cotton net using an electromagnetic field. Credit: NTU Singapore
For example, one gram of magnetic-adhesive adhesive can be easily cured by a 200-watt electromagnetic device in five minutes (consuming 16.6 watts-hours). This is 120 times less energy required than a traditional 2000-watt oven that takes an hour (consuming 2000 watts per 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 findings were published in the scientific journal Materials applied today and offers potential applications in a wide range of fields.
This includes state-of-the-art sports equipment, automotive, electronic, energy, aerospace and medical manufacturing processes. Laboratory tests have shown that the new adhesive has a strength of up to 7 megapascals, just like many of the epoxy adhesives on the market.
Conf. Univ. Steele, an expert in various types of advanced adhesives, explained: “Our key development is a way to cure adhesives within minutes of exposure to a magnetic field, while preventing the surfaces on which they are applied from overheating. This is important because some surfaces we want to join are extremely sensitive to heat, such as flexible electronics and biodegradable plastics. “
How does magnetocuring glue work
The new adhesive consists of two main components – a commercially available heat-curing epoxy and oxide nanoparticles made from a chemical combination that includes manganese, zinc and iron (MnxZn1-xFe2O4).
These nanoparticles are designed to heat up when electromagnetic energy is passed through them, activating the curing process. The maximum temperature and heating rate can be controlled by these special nanoparticles, eliminating overheating and hotspot formation.
(From left to right) NTU Assoc. Terry Steele, Prof. Raju V. Ramanujan and Dr. Richa Chaudhary supporting various soft and hard materials related to their new magnetocurant adhesive. Credit: NTU Singapore
Without the need for large industrial furnaces, glue activation has a smaller footprint in terms of space and energy consumption. Energy efficiency in the curing process is crucial for organic production, where products are manufactured 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 because the rubber is a thermal insulator and resists heat transfer to conventional epoxy adhesive. An oven is needed to heat the shoe for a long time before the heat can reach the glue.
The use of magnetically activated glue avoids this difficulty, directly activating the curing process only in the glue.
The alternating magnetic field can also be incorporated into the bottom of conveyor belt systems, so that products with pre-applied adhesive can be cured when they pass through the magnetic field.
Improving production efficiency
Prof. Raju Ramanujan, who is internationally recognized for his advances in magnetic materials, led the project together and predicted that the technology could increase production efficiency where adhesive joints are needed.
“Our temperature-controlled magnetic nanoparticles are designed to be mixed with existing adhesive formulations with a pot, so that many of the epoxy-based adhesives on the market could be turned into magnetic field-activated glue,” said Prof. Ramanujan.
“The curing speed and temperature can be adjusted so that manufacturers of existing products could redesign or improve their existing manufacturing methods. For example, instead of applying glue and hardening side by side in a conventional assembly line, the new process could be to pre-apply the glue to all parts and then cure them as they move along the chain. transporter. Without ovens, this would lead to much less downtime and more efficient production. “
The first author of the study, Dr. Richa Chaudhary said: “The healing of our newly developed magnetocurrent adhesive takes only a few minutes instead of hours and yet is able to provide surfaces with high strength bonds, which is of considerable interest in sports, industry medical, automotive and aerospace industry. This efficient process can also bring 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 on heat-activated adhesive has used an electric current flowing through a coil, known as induction curing, where the adhesive is heated and cured from the outside. However, its disadvantages include overheating of surfaces and uneven gluing due to the formation of the hotspot in the adhesive.
Going further, the team hopes to hire adhesive manufacturers to collaborate in marketing their technology. They filed a patent through NTUitive, the university’s innovation and enterprise company. They have already received interest in their research from sporting goods manufacturers.
Reference: “Magnetocuring of temperature failsafe epoxy adhesives” by Richa Chaudhary, Varun Chaudhary, Raju V. Ramanujan and Terry WJ Steele, 15 September 2020, Materials applied today.
DOI: 10.1016 / j.apmt.2020.100824