International. A team of researchers from Japan, led by Associate Professor Daisuke Suzuki of Shinshu University, develops an innovative way to produce latex films based on hard, crack-resistant elastic nanoparticles without using harmful additives.
It is a new class of latex films composed of acrylic nanoparticles cross-linked with rotaxane. These films exhibit remarkable mechanical properties, including excellent resistance to crack propagation without additives and are easily recyclable, paving the way for more environmentally friendly materials.
Synthetic latex films, a type of nanoparticle-based films, are widely used in many fields, but they usually contain harmful additives, which are also expensive, to improve their strength. It is essential to ensure that they are safe, durable and sustainable. This is especially true for synthetic latex films, which are widely used in packaging, biomedicine and electronics.
Key to the researchers' approach was a new molecular structure known as rotaxane, which consists of two main components; a ring-shaped molecule and a linear axis molecule. The ring-shaped molecule is threaded through the shaft molecule, which is mechanically trapped due to the shape of the shaft terminations.
The researchers took advantage of this interconnecting mechanism in the rotaxane by making the ring-shaped molecule chemically bind to one polymer chain and the shaft molecule to another chain. They then prepared mixtures of water and polymeric nanoparticles by standard ultrasonication and subsequent polymerization which, in turn, served to produce latex films.
Stretching experiments conducted on these films revealed that the rhotaxane-based strategy resulted in some remarkable properties.
"Unlike conventional nanoparticle-based elastic polymers, latex films composed of rhotaxane-crosslinked nanoparticles exhibited unusual crack propagation behavior," explained Dr. Suzuki.
"The direction of propagation of the crack changed from being parallel to the crack to one perpendicular to the crack, resulting in increased tear resistance," he said.
The new approach to making latex films offers many advantages over conventional methods. Most importantly, no toxic additives are needed to achieve reasonable film hardness. In addition, since only a small amount of rotaxane is needed, the overall weight of the films can be kept low while maintaining flexibility. The proposed latex films are also sustainable.
"They are degradable and can be easily disassembled into individual nanoparticles simply by immersing them in an environmentally friendly organic solvent, such as an aqueous solution of ethanol," Dr. Suzuki said. "These nanoparticles can form a film again after evaporation of the solution. The findings of this research can help create highly durable and recyclable materials."
The team hopes their work will expand the scope of designing new additive-free polymer films. Therefore, such materials could become biocompatible, with potential applications in biotechnology and medicine, in addition to packaging, industrial coatings and adhesives.
