Characterization of thermoplastic nonwovens of copolyamide hot melt adhesives filled with carbon nanotubes produced by melt-blowing method

Abstract

Thermoplastic nonwovens containing 2.5 wt% of multi-walled carbon nanotubes were manufactured by half-industrial melt-blowing process from two copolyamides belonging to the group of hot melt adhesives having different melt-viscosities. The initial masterbatches have been analyzed by their rheological and thermal properties to adjust the appropriate conditions of melt-blowing process which allowed to manufacture the nonwovens without structural defects. It was found using a scanning electron microscope that in 10 wt% masterbatches fewer agglomerates of the multi-walled carbon nanotubes occurred in less viscous coPA2 and their average diameter measured by ImageJ was 60 µm. For more viscous coPA1 some oval agglomerates with even 270 µm diameters have been detected but during the extrusion they were destroyed. Microstructural observations of the nonwovens showed that fibers occur in the entangled state and their average diameter is around 45 µm for each type of the copolyamides. Analysis of the electrostatic properties of the nonwovens with low and high areal weight showed that electrical surface resistivity is slightly higher for the nonwovens based on coPA2 and those with higher areal weight. Using high-resolution microscope, it was possible to ascertain that in the nonwovens made of coPA1 + 2.5 wt% the carbon nanotubes are well-dispersed with their visible alignment along the fiber axis, unlike those in the nonwovens made of coPA2 + 2.5 wt% which occur mainly as lightly connected bundles without any specific orientation. The developed nonwovens can be used as interlayers to increase the electrical and mechanical properties of composite structures in the aerospace and automotive sectors.