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 SP1N-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.
Bibliographical noteFunding Information:
This work was funded by the Natural Science Foundation of China (31100417 and 31300482), the Jiangsu Province Science Foundation for Youths (BK20130975 and BK20130966), the Doctorate Fellowship Foundation of Nanjing Forestry University, China, the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), China, the Department of Civil and Environmental Engineering of the University of Alberta, Canada, and the Natural Science and Engineering Research Council (NSERC) of Canada. The authors acknowledge the support of infrastructure and instrument grants from the Canada Foundation for Innovation (CFI), NSERC, and Alberta Advanced Education and Technology. The authors also thank the Air Quality Characterization and Control Research Group at the University of Alberta and Dr. Runzhou Huang for suggestions for revising the paper.
- Epoxy adhesives