Investigation of Thermal Stability and Flammability of Polyolefin Composites

• Main Author: Kunkel, Bryanna Megan
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2011
• Subjects: Organic chemistry
• ISBN: 9781267194244; 1267194243

Organoclay-polyolefin nanocomposites are often reported to exhibit slightly increased thermal stability and decreased flammability, compared to unfilled polyolefins. In this thesis, we investigate the properties of nanocomposites containing clay that has not been organically-modified. They are less thermally stable but, unexpectedly, also much less flammable. We investigate the mechanistic origins of these surprising effects. Clay-polyolefin nanocomposites free of surfactants were prepared by in situ polymerization of ethylene or propylene, using a tetrabenzylzirconium catalyst adsorbed onto acid-treated montmorillonite. Their thermal decomposition was investigated qualitatively and quantitatively by anaerobic thermogravimetric analysis, pyrolysis-combustion flow calorimetry and volatiles analysis. The results are compared to those for the unfilled polymers, and for microcomposites prepared by melt-blending. Decreased thermal stability is attributed to clay-catalyzed polymer cracking, which has a lower activation barrier than uncatalyzed thermal depolymerization. Decreased flammability arises in part because the acidic clay also catalyzes the formation of a polyaromatic char from olefins trapped in the solid material by the barrier effect of the dispersed nanofiller. Composites containing either carbon black or fullerenes were prepared and their thermal stability was compared to unfilled polyethylene and clay-polyethylene nanocomposites. Fullerenes were found to be more effective than carbon black, achieving similar increases in aerobic thermal stability at much lower concentrations. Polymer composites were also produced in the presence of layered double hydroxides by in situ polymerization of ethylene in toluene and dimethylformamide. Unlike the acidic clay, layered double hydroxides do not exhibit a detrimental effect on the thermal stability of the polymer.