Nylon 6,10 is a commercially important thermoplastic polyamide. Recently, researchers have started looking at ways to improve its mechanical and thermal properties by adding multiwalled carbon nanotubes (MWNTs) as "fillers". These efforts have produced composites with a 214% improvement in elastic modulus and a 162% increase in yield strength over pure nylon by incorporating just 2 wt% MWNTs.
Compared to MWNTs, SWNTs have a higher Young's modulus and tensile strength, but making polymer composites with SWNTs is more challenging. Among other things, this is because the high aspect ratio of SWNTs coupled with strong intrinsic van der Waals attractions produces ropes or bundles that are difficult to disperse in solvents and polymer matrices as compared to MWNT bundles.
Karen Winey and colleagues of the University of Pennsylvania, together with co-workers at Rice University, began with a method patented by engineers at Penn called interfacial polymerization. This technique evenly disperses the carbon nanotubes throughout the nylon structure. Next, the researchers fine-tuned the composite material on the molecular level by introducing alkyl segments (or carbon spacers) that act as linking segments, covalently bonding the nanotubes and nylon chains. This breakthrough approach solves the problems encountered in previous attempts to make SWNT-nylon composites that were brittle.
The new nanocomposites, which contain just 1 wt% of SWNTs, have as much as 160% higher modulus, 160% higher strength and 140% higher toughness than nylon itself.
"Nanotechnology is providing new composite materials with tuneable mechanical properties," said Winey. "By adding covalently bonded carbon spacers to the filler–matrix interface in these composites, we have significantly improved their mechanical properties and perhaps demonstrated a broadly applicable approach to nanocomposite design." Winey adds that nanocomposites are likely to be more efficient methods for improving the mechanical, thermal and electrical properties of polymers than starting from scratch and synthesizing completely new ones.
The nanotube-based composites, and others like them, could revolutionize fabrics, structural materials for aerospace, electrical and thermal conductors for energy applications, nano-biotechnology and more.
The researchers published their work in Nano Letters.