Preparation And Properties Of EVOH/Carbon Nanotubes Composite Micro/Nanofibers

In recent years, carbon nanotubes(CNTs) have been excellent inorganic fillers for their great physical and chemical properties. Polyethylene-co-polyvinyl alcohol(EVOH) resin is a polymer matrix with excellent properties because of its high separation, environmental-friendly and good processability. Nowadays there are a lot of preparation methods for nanofibers, such as electro-spinning and interfacial polymerization, however, neither of them is suitable for thermo-plastic polymer nanofibers. In this paper, EVOH/CNTs micro/nanofibers with three different kinds of carbon nanotubes were successfully prepared by melt extrusion of immiscible blends.First, EVOH/CNTs composite masterbatches with 0-12wt% CNTs loadings, as dispersed phases, were prepared by melt extrusion. Then, Celluose acetate butyrate(CAB) with excellent biocompatibility was fully mixed with EVOH/CNTs masterbatches in a twin-screw extruder. The EVOH/CNTs micro-nanofibers with uniform size could be prepared after drawing and removal of CAB matrix by acetone.The CNTs dispersion in EVOH and morphology of three kinds of composites were observed on a transmission electron microscopy (TEM) and a scanning electron microscopy(SEM) respectively. It was indicated that both long multiwalled CNTs(LMWNTs) and aligned multiwalled CNTs(aMWNTs) were well dispersed in EVOH matrix while carboxylation multiwalled CNTs(COOH-MWNTs) was totally agglomerated in EVOH matrix. SEM images showed EVOH/LMWNTs micro/nanofiber was with a favorable surface morphology, and its morphology, fiber size and size distribution were hardly changed with the increase of CNTs loadings. The morphologies of EVOH/aMWNTs and EVOH/COOH-MWNTs micro/nanofibers were rougher as CNTs increased, and the size and size distribution of EVOH/COOH-MWNTs micro/nanofiber were also increased.The composites crystallinity was studied through X-ray diffractometer and differential scanning caborimetry(DSC). DSC data showed crystalline temperature of EVOH/LMWNTs and EVOH/aMWNTs micro/nanofibers was a bit higher than EVOH pure fibers, and their melt temperature and degree of crystallization was a little lower. Both crystalline and melt temperature of EVOH/COOH-MWNTs micro/nanofiber were obviously decreased with increasing CNTs loadings, and there appeared a maximum degree of crystallization when CNTs loading was 6wt%. It was stated by XRD that both EVOH/LMWNTs and EVOH/aMWNTs micro/nanofibers would show an obvious (020) bragg reflection at about 2θ=26°with the increase of CNTs, but EVOH/LMWNTs happened with a lower CNTs loading.The composite thermostability was researched through thermogravimetry(TG) analysis. It was demonstrated that thermostability of EVOH/LMWNTs and EVOH/aMWNTs micro/fibers was improved while EVOH/COOH-MWNTs one dropped after mixing CNTs. This may be relative with dispersion of CNTs in EVOH matrix. However, all these composites'residual weight was increase with increasing CNTs loadings.The viscoelastic and electrical behaviors of composites were studied through dynamic rheology and resistivity measurements. It was showed there were similar viscoelastic and electrical behaviors between EVOH/LMWNTs and EVOH/aMWNTs composites. And the viscoelastic and electrical percolation threshold were nearly equal, which were 8-10wt% CNTs loading. The electrical conductivity were increased by 4-5 orders of magnitude (from 10-11 to 10-7 ohm-cm) on addition of 12 wt% CNTs while that of EVOH/COOH-MWNTs composite was never changed because of destruction of CNTs electrical structure.