The Effect of Matrix Molecular Weight on the Dispersion of Nanoclay in Unmodified High Density Polyethylene

Type of Document Master's Thesis
Author Chu, David
URN etd-06282006-154608
Title The Effect of Matrix Molecular Weight on the Dispersion of Nanoclay in Unmodified High Density Polyethylene
Degree Master of Science
Department Chemical Engineering
Advisory Committee
Advisor Name Title
Dr. Donald G. Baird Committee Chair
Dr. Aaron S. Goldstein Committee Member
Dr. Richey M. Davis Committee Member
Keywords

* high density polyethylene
* molecular weight
* nanoclay

Date of Defense 2006-06-26
Availability unrestricted
Abstract

The effect of molecular weight on the dispersion of relatively polar montmorillonite (MMT) in non polar, unmodified high density polyethylene (HDPE) was examined. Polymer layered silicate (PLS) nanocomposites were compounded using three unmodified HDPE matrices of differing molecular weight and an organically modified MMT in concentrations ranging from 2 wt% to 8 wt% via single screw extrusion. The weight average molecular weights of the HDPE matrices used in this study ranged from 87,000 g/mol to 460,000 g/mol. X-ray diffraction (XRD), mechanical testing, dynamic mechanical thermal analysis (DMTA), as well as dynamic and capillary rheometry were performed on the nanocomposites. Nanocomposites generated from the high molecular weight (HMW) HDPE matrix exhibited increased intercalation of the MMT as shown by XRD as well as greater improvements in the Young’s modulus compared to nanocomposites generated from both the low (LMW) and middle molecular weight (MMW) matrices. This was attributed to higher shear stress imparted to MMT during compounding from the more viscous matrix facilitating their separation and orientation during injection molding. DMTA showed that the torsional response of the HMW nanocomposites was not as great compared to their LMW and MMW counterparts as observed from a lower percentage enhancement in the storage modulus (G’) and estimated heat distortion temperature (HDT) due to anisotropy in mechanical properties. Dynamic rheology indicated that a percolated network did not exist in any of the nanocomposites as shown by no change in the terminal behavior of G’ upon addition of clay.

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