Title

Nano-particle formation in zinc sulfonated polystyrene ionomer/thermotropic liquid crystalline polymer blend by melt-mixing

Date of Completion

January 2005

Keywords

Engineering, Chemical

Degree

Ph.D.

Abstract

A nanocomposite was produced by simply melt mixing a blend of a thermotropic liquid crystalline polyester (LCP) and the zinc salt of a lightly sulfonated polystyrene ionomer at 300°C. The origin and kinetics of the nano-particle formation and the mechanical and rheological properties of these nanocomposites were investigated in this study. ^ Variety of characterization techniques including FTIR, TGA, GC-MS, TEM and WAXD revealed that the nano-particle, which were in the form of relatively uniform rectangular prisms of ca. 30 x 30 x 200 nm, formed from the LCP phase due to the chain modification of the LCP induced by chemical reactions between the LCP and the residual catalytic amounts of zinc-acetate and/or acetic acid that were present from the neutralization step in the preparation of the ionomer. The X-ray diffraction patterns for the blends indicated that chain-packing within nano-particles is largely different compared with that of the LCP or the homopolymers. Based on the positions of the peaks in WAXD patterns of the blend, the orthorhombic unit cell structure with dimensions of a = 0.920, b = 0.648, and c = 1.288 run was proposed for the structure of the nano-particles. ^ The formation of nano-particles and their structure and sizes were highly dependent on the mixing time as revealed by the kinetic, morphological and X-ray diffraction studies on the blend. The rheological study indicated that the increase in complex viscosities of the melt of Zn-SPS/LCP blends can be attributed to the formation of nano-particles. Furthermore, the time sweep experiment at 290°C revealed that some chemical reactions might occur at elevated temperatures in the blends. The mechanical properties of the blends revealed a significant enhancement in stiffness and the modulus of nano-particles is estimated more than 75 GPa based on a composite theory. ^