Improved Adhesives Containing CNT/SP1 Nano Fillers

Abstract

Carbon nanotubes (CNT) have stimulated research due to their wide range of applications. However, their existence as aggregates and the difficulty in debundling and dispersion limits the improvement of properties when used as fillers. Many techniques have been employed to obtain such dispersions including mechanical, ultrasonic, and solution mixing, resulting in limited effect. Attaching a protein moiety such as SP1 showed promising results. SP1 is a thermally stable protein, originally isolated from poplar trees, which self-assembles to an extremely stable 11-nm ring-shape dodecamer. Linkage of CNT to specific peptides on SP1 N-terminus by genetic engineering resulted in 12 CNT binding sites per ring.

It was demonstrated by us that the CNT/SP1 complex prevents CNT aggregation and allows its homogenous mixing in water at rather low CNT/protein weight ratio (20:1). In order to obtain homogenous CNTs in a polymer matrix, the dehydrated complex was redispersed in epoxy resin. The CNT/SP1 is covalently bound to epoxy groups prior to polymerization with the curing agent. Dispersion and uniformity were improved by using a speed-mixer and a 3-roll mill. CNT/SP1 in epoxy resin exhibited improved mechanical properties compared with pure unfilled epoxy (EPON® 828/Versamide® 140). CNT/SP1 filler in epoxy adhesive at less than 1% wt. improved peel strength by 50% and shear strength by 24%. In addition, HR-SEM images of 0.7% wt. CNT/SP1 nano-filled epoxy adhesive fracture surfaces demonstrates efficient load transfer and crack arrest by the CNT/SP1 particles. Moreover, comparing the thermal properties of neat epoxy with those of 0.35% and 0.7% wt. CNT/SP1 filled nano-composite was tested using three methods: differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA) showed a dramatic improvement increasing T_g by 20°C.

KEYWORDS:

• CNT
• Dispersion
• Epoxy adhesives
• Nano-toughening
• SP1

Notes

*C—cohesive, A—Adhesive, A DIV—Adhesive divided. No deformation of the adherends in SLS was observed.

EXT = exotherm.

*▵W—change in weight.

Presented in part at the 1st International Conference on Structural Adhesive Bonding (AB2011), Porto, Portugal, 7–8 July 2011.