Multiwalled carbon nanotubes grafted with polyhedral oligomeric silsesquioxane and its dispersion in poly(l-lactide) matrix

Multiwalled carbon nanotubes (MWNTs) were functionalized with polyhedral oligomeric silsesquioxane (POSS) via amide linkages. The oxidized MWNT (MWNT–COOH) was converted to the acyl chloride-functionalized MWNT (MWNT–COCl) by treating them with thionyl chloride (SOCl2), and then MWNT–COCl was reacted with aminopropylisooctyl-POSS to prepare aminopropylisooctyl polyhedral oligomeric silsesquioxane modified MWNT (MWNT-g-POSS). Energy-filtering TEM, FTIR, and Raman spectroscopy revealed that the POSS was covalently attached to the MWNT and the weight gain due to the functionalization was determined by the thermogravimetric analyses (TGA). PLLA/MWNT and PLLA/MWNT-g-POSS composites with different MWNT loadings were first prepared by the simple solvent casting approach. A fine dispersion of MWNT-g-POSS throughout PLLA matrix was observed by SEM. Moreover, the composites were also prepared by using melt compounding under the different shearing speed of extruder via our custom-built high-shear extruder. A special feedback-type screw was used in this extruder to realize a high shearing flow field. Using this new technique, a uniform dispersion of the neat MWNTs in the PLLA matrix was found under higher screw rotation speed (≥1500 rpm) while poor dispersion was observed under low speed (<1500 rpm). The homogeneous dispersion of MWNTs throughout the PLLA/MWNT-g-POSS composites without any aggregation was observed at full range of screw rotation speed. The fractured surface of the composites showed not only a uniform dispersion of MWNTs but also a strong interfacial adhesion with the matrix, as evidenced by the presence of many broken but strongly embedded MWNTs in the matrix in the absence of debonding of MWNTs from the matrix. Incorporation of MWNTs improved the mechanical properties.