Researchers Developed New Family Of Polymer That Can Self Heal, Have Shape Memory & Recyclable
Nature’s blueprint for the human limb may be a carefully layered structure with stiff bone wrapped in layers of various soft tissue, like muscle and skin, all sure to one another perfectly. Achieving this type of sophistication using synthetic materials to create biologically inspired robotic parts or multicomponent, complex machines has been an engineering challenge.
By tweaking the chemistry of one polymer, researchers at Texas A&M University & therefore the U.S. Army Combat Capabilities Development Command Army Lab have created an entire family of synthetic materials that home in texture from ultra-soft to extremely rigid. The researchers said their materials are 3D printable, self-healing, recyclable and that they naturally adhere to every other in air or underwater.
Their findings are detailed within the May issue of the journal Advanced Functional Materials.
“We have made an exciting group of materials whose properties are often fine-tuned to urge either the softness of rubber or the strength of load-bearing plastics,” said Dr. Svetlana Sukhishvili, professor within the Department of Materials Science and Engineering and a corresponding author on the study. “Their other desirable characteristics, like 3D printability and therefore the ability to self-heal within seconds, make them fitted to not just more realistic prosthetics and soft robotics, but also ideal for broad military applications like agile platforms for air vehicles and futuristic self-healing aircraft wings.”
Synthetic polymers are made from long strings of repeating molecular motifs, like beads on a sequence . In elastomeric polymers, these long chains are lightly crosslinked, giving the materials a rubbery quality. However, these crosslinks also can be wont to make the elastomers more rigid by increasing the amount of crosslinks.
Although previous studies have manipulated the density of crosslinks to form elastomers stiffer, the resulting change in mechanical strength was generally permanent.
“Crosslinks are like stitches during a piece of fabric , the more stitches you’ve got , the stiffer the fabric gets and the other way around ,” said Sukhishvili. “But rather than having these ‘stitches’ be permanent, we wanted to realize dynamic and reversible crosslinking in order that we will create materials that are recyclable.”
So, the researchers focused their attention on the molecules involved within the crosslinking. First, they chose a parent polymer, called pre-polymer, then chemically studded these pre-polymer chains with two sorts of small crosslinking molecules — furan and maleimide. By increasing the amount of those molecules within the pre-polymer, they found that they might create materials stiffer. during this way, the toughest material they created was 1,000 times stronger than the softest.
However, these crosslinks also are reversible. Furan and maleimide participate during a sort of reversible chemical bonding. Put simply, during this reaction, furan and maleimide pairs can “click” and “unclick” counting on temperature. When the temperature is high enough, these molecules break from the polymer chains and therefore the materials soften. At temperature , the materials harden since the molecules quickly click back together, once more forming crosslinks. Thus, if there’s any tear in these materials at ambient temperatures, the researchers showed that furan and maleimide automatically re-click, healing the gap within a couple of seconds.
The researchers noted that the temperatures at which the crosslinkers dissociate or unclick from the pre-polymer chains are relatively an equivalent for various stiffness levels. This property is beneficial for 3D printing with these materials. no matter whether or not they are soft or hard, the materials are often melted at an equivalent temperature then used as printer’s ink .
“By modifying the hardware and processing parameters during a standard 3D printer, we were ready to use our materials to print complex 3D objects layer by layer,” said Dr. Frank Gardea, research engineer within the US Army lab and a corresponding author on the study. “The unique advantage of our materials is that the layers that structure the 3D part are often of vastly different stiffness.”
As the 3D part cools to temperature , he added that the various layers join seamlessly, precluding the necessity for curing or the other chemical processing. Consequently, the 3D-printed parts can easily be melted using high heat then recycled as printer’s ink . The researchers also noted that their materials are reprogrammable. In other words, after being set into one shape, they will be made to vary into various shape using just heat.
In the future, the researchers decide to increase the functionality of their new materials by amplifying its multifaceted properties outlined within the current study.
“Right now, we will easily achieve around 80% self-healing at temperature , but we might wish to reach 100%. Also, we would like to form our materials aware of other stimuli aside from temperature, like light,” said Gardea. “Further down the road, we’d wish to explore introducing some low-level intelligence in order that these materials know to autonomously adapt without having a user to initiate the method .”