Scientists from Nanyang University of Technology, Singapore (NTU Singapore), have developed a new way of treating adhesives using a magnetic field.
Common adhesives such as epoxy used to bond plastics, ceramics, and wood are typically designed to cure with moisture, heat, or light. They often require certain curing temperatures, ranging from room temperature to 80 degrees Celsius.
The curing process is required to crosslink and bond the adhesive to the two secured surfaces while the adhesive crystallizes and cures to achieve final strength.
NTU’s new “magnetically curing” adhesive can be cured by passing it through a magnetic field. This is very useful in certain environmental conditions where instant adhesives do not work well. Also, when glue is placed between insulating materials such as rubber or wood, traditional activators such as heat, light and air cannot easily reach the glue.
Products such as composite bicycle frames, helmets and golf clubs are currently made with two-part epoxy adhesives, where the resin and hardener are mixed and the reaction begins immediately.
For carbon fiber manufacturers – thin strips of carbon glued layer by layer – and manufacturers of sports equipment that includes carbon fiber, their factories use large, high-temperature ovens to harden epoxy glue for many hours. This energy-intensive curing process is the main reason for the high cost of carbon fiber.
The new “magnetically” adhesive is made by combining a typical commercially available epoxy adhesive with specially adapted magnetic nanoparticles made by scientists from NTU. It should not be mixed with any hardener or accelerator, unlike two-component adhesives (which have two liquids that must be mixed before use), which facilitates production and application.
It binds materials when activated by passing through a magnetic field, which is easily generated by a small electromagnetic device. This consumes less energy than a large conventional oven.
For example, one gram of magnetizing glue can be easily cured with a 200 W electromagnetic device in five minutes (consumes 16.6 Watt hours). This takes 120 times less energy than a traditional 2000 W oven, which takes an hour (consumes 2000 Watt hours) to cure conventional epoxy.
The findings, developed by Professor Raju V. Ramanujan, Associate Professor Terry Steele and Dr. Richa Chaudhary of the NTU School of Materials Science and Engineering, were published in the scientific journal Applied Materials Today and offer potential application in a wide range of fields.
This includes state-of-the-art sports equipment, automotive products, electronics, energy, space and medical manufacturing processes. Laboratory tests have shown that the new adhesive has a strength of up to 7 megapascals, just like many epoxy adhesives on the market.
Izv. Prof. Steele, an expert on various types of advanced adhesives, explained: “Our key development is a way for adhesives to heal within minutes of exposure to a magnetic field, while preventing the surfaces to be applied from overheating. This is as important as some surfaces we want to bond they are extremely sensitive to heat, such as flexible electronics and biodegradable plastics. “
How “magnetic hardening” glue works
The new adhesive is made from two main components – commercially available heat-curable epoxy 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 passes through them, activating the curing process. The maximum temperature and heating rate can be controlled with these special nanoparticles, eliminating overheating and the formation of focal points.
Without the need for large industrial ovens, activating the adhesive has less trace in space and energy consumption. Energy efficiency in the curing process is crucial for green production, where products are produced at lower temperatures and consume less energy for heating and cooling.
For example, sports shoe manufacturers often have difficulty heating the adhesive between the rubber soles and the upper half of the shoe because the rubber is a heat insulator and is heat resistant to conventional epoxy adhesive. An oven is needed to warm the shoe for a long time before the heat reaches the glue.
The use of magnetic field activated adhesive circumvents this difficulty by directly activating the curing process in the adhesive only.
The alternating magnetic field can also be installed on the bottom of the conveyor belt system, so that the products with the previously applied glue can harden when they pass through the magnetic field.
Improving production efficiency
Professor Raju Ramanujan, who is internationally recognized for his advances in magnetic materials, co-led the project and predicted that the technology could increase production efficiency where sticky joints are needed.
“Our temperature-controlled magnetic nanoparticles are designed to mix with existing adhesive formulations in a single pot, so many epoxy-based adhesives on the market could be converted into magnetic field-activated adhesives,” said Prof. Ramanujan.
“The curing speed and temperature can be adjusted so that manufacturers of existing products can redesign or improve their existing production methods. For example, instead of applying glue and curing it piece by piece on a conventional assembly line, a new process could be pre-applied glue on all the parts and then cure them as they move along the conveyor chain. Without the furnace this would lead to much less downtime and more efficient production. “
The first author of the study, dr. Richa Chaudhary said, “Curing our newly developed magneto-adhesive takes only minutes, instead of hours, and yet is able to secure surfaces with high-strength bonds, which is of great interest in the sports, medical, automotive and aerospace industries. This efficient the process can also lead to cost savings because 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 (ASTAR).
In previous work on heat-activated adhesive, an electric current passing through a coil, known as induction curing, was used, where the adhesive is heated and cured from the outside. However, its disadvantages include overheating of surfaces and uneven bonding due to the formation of focal points within the adhesive.
Moving forward, the team hopes to hire adhesive manufacturers to work together to commercialize their technology. They applied for a patent through NTUitive, a university innovation company and company. They have already shown interest in their research from sports equipment manufacturers.
Nanyang University of Technology
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