Localization of MWCNTs in PET/LDPE blends

Abstract

The localization of un-functionalized MWCNTs in immiscible blends of PET and LDPE was investigated as a function of blend ratio and for a 20:80 PET:LDPE blend as a function of MWCNT loading up to 5wt%. Theoretical prediction of wetting coefficients, microscopic examination, electrical conductivity measurements, differential scanning calorimetry (DSC) and oscillatory rheology analysis confirmed the MWCNTs preferentially located to the PET phase. For blends where the blend ratio was varied and the MWCNT content kept constant at 2wt.%, the onset of phase inversion was detected from the formation of a ‘droplet in droplet’ morphology for the 40:60 PET:LDPE blend. This blend was semi-conductive (104Ωcm), but when the LDPE content was increased to 80wt.%, the MWCNTs were confined to isolated PET droplets, the resistivity of the blend increased by 11 orders of magnitude. Crystallization temperature (Tc) and crystalline content (Xc) of the PET component increased, but Tc and Xc for the LDPE phase was unchanged with MWCNT addition. The melt viscosity of the PET:LDPE blend at low frequencies (ω<1rad/s) increased with increasing PET blend content as the MWCNTs were readily dispersed in PET when it was the continuous phase. Evidence from Cole–Cole plots for the 20:80 PET:LDPE blends with increasing MWCNT loading up to 5wt.% showed the MWCNTs had little effect on the rheological response of this LDPE rich blend. However, as more MWCNTs are condensed in the PET phase, the melt viscosity of this blend increased, MWCNT transfer between phases, dispersion and distribution, and, particle coalescence become more difficult. Therefore, at higher MWCNT loadings, some MWCNTs remain in the LDPE phase or at the blend interface and a significant increase in electrical conductivity was obtained.