Researchers from the Polytechnique Montreal have produced an ultra-tough polymer fiber inspired by spider silk that could be up to ten times tougher than steel or Kevlar.
Sespite its lightness, spider silk has such remarkable elongation and stretch-resistance properties that humans have long sought to replicate. In large part, the silk owes its strength to the particular molecular structure of the protein chain of which it's composed. The mechanical origin of this strength drew the interest of the researchers at the Laboratory for Multiscale Mechanics in the polytechnic’s department of mechanical engineering.
‘The silk protein coils upon itself like a spring. Each loop of the spring is attached to its neighbours with sacrificial bonds, chemical connections that break before the main molecular structural chain tears,’ said Professor Gosselin, who, along with his colleague Daniel Therriault, is co-supervising the master's research work of student Renaud Passieux. ‘To break the protein by stretching it, you need to uncoil the spring and break each of the sacrificial bonds one by one, which takes a lot of energy. This is the mechanism we're seeking to reproduce in laboratory.’
The project involves making micrometric-sized microstructured fibers that have mechanical properties similar to those of spider silk. ‘It consists in pouring a filament of viscous solution toward a sub-layer that moves at a certain speed. So we create an instability,’ said Passieux. ‘The filament forms a series of loops or coils, kind of like when you pour a thread of honey onto a piece of toast. Depending on the instability determined by the way the fluid runs, the fiber presents a particular geometry. It forms regular periodic patterns, which we call instability patterns.’
The fiber then solidifies as the solvent evaporates. Some instability patterns feature the formation of sacrificial bonds when the filament makes a loop and bonds to itself. At that point, it takes a pull with a strong energy output on the resulting fiber to succeed in breaking the sacrificial bonds, as they behave like protein-based spider silk.
Multiphysical process
‘This project aims to understand how the instability used in making the substance influences the loops' geometry and, as a result, the mechanical properties of the fibers we obtain,’ explained Professor Therriault. ‘Our challenge is that the manufacturing process is multiphysical. It draws on concepts from numerous fields: fluid mechanics, microfabrication, strength of materials, polymer rheology and more.’
These researchers think that one day they could make composites obtained by weaving together tough fibers of the type they're currently developing. Such composites could, for example, make it possible to manufacture new safer and lighter casings for aircraft engines, which would prevent debris from dispersing in case of explosion.
An article about the research was recently published in the journal Advanced Materials.
This story is reprinted from material from the Polytechnique Montreal, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.
