Date of Award

Winter 12-13-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Dr. Jeanne Norton, jnorton@pittstate.edu

Second Advisor

Paul Herring, pherring@pittstate.edu

Third Advisor

Dr. Charles-Jody Neef, cneef@pittstate.edu

Keywords

Polysiloxane, Tan delt, vulcanization, twin-screw extrusion, platinum, filler

Abstract

Polysiloxanes are a class of high-performance polymeric materials that are used in a wide variety of applications, including O-rings, gaskets, sealants, coatings, and adhesives. These materials have high temperature resistances as well as flexibility at low temperatures. This is due to the bond between the oxygen and silicon atom, a bond that requires a high dissociation energy to break. However, their elastomers, which can be obtained by crosslinking linear precursors using various crosslinkers, generally exhibit low strength and have poor mechanical properties unless reinforced. Therefore, fillers, additives, UV-stabilizers, and anti-oxidants are often incorporated in order to improve the resulting properties.

The process of compounding incorporates additives into polysiloxane formulations, with one approach being twin-screw extrusion which vigorously mixes the additives into the polymer matrix. In this work, a lab-scale co-rotating twin-screw extruder was used to compound a commercially available reinforcing silica filler, Hi-Sil-233D, and a commercial polysiloxane, vinyl-terminated diphenyl-dimethyl siloxane copolymer (Gelest PDV-0535), to determine a filler ceiling loading. These copolymers were then compounded with two crosslinkers, trimethylsiloxane-terminated methylhydro-dimethyl siloxane copolymer (HMS-082 & HMS-151). The crosslinking reactions were initiated with two separate catalysts, platinum acetylacetonate in 1,3-dioxolane (Pt(acac)2) and trimethyl(methylcyclopentadienyl) platinum IV in 1,3-dioxolane ((MeCp)Pt(Me)3). In addition, diethyl azodicarboxylate (DEAD) in dry toluene was used as a catalytic inhibitor. Finally, PDV-0535 with the Pt(acac)2) catalyst is compounded in varied formulations and cured to analyze the shelf life and mechanical properties of the fully formulated system.

Thermogravimetric analysis (TGA) was used to determine the consistency of the additive content by analyzing the percent residue. Oscillatory rheometry was used to determine yield stress; and flow rheology was used to evaluate the thixotropy of the compounded samples. Rheometric analysis also helped determine the shelf-life of the polysiloxane system before becoming fully crosslinked. Soxhlet extraction was used to determine the gel content of the crosslinked systems. Dynamic mechanical analysis (DMA) was used to measure the mechanical properties of the fully cured polysiloxane formulations.

Comments

Formulation study using various platinum catalysts, catalysts amounts and inhibitor ratios in filled polysiloxanes.

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