Date of Award

Summer 2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering - (Ph.D.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

Lev N. Krasnoperov

Second Advisor

Victor Stepanov

Third Advisor

Rajesh N. Dave

Fourth Advisor

Haim Grebel

Fifth Advisor

Zafar Iqbal

Abstract

Nanoscale composites of hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX) and polymer binders were produced by co-precipitation using rapid expansion of supercritical solutions (RESS). The binders used in this study are poly (vinylidene fluoride-co-hexafluoropropylene) (VDF-HFP22), polystyrene (PS) and 7-amino-4-methyl coumarin (AMC). The RDX/VDF-HFP22 and RDX/PS co-precipitated nanoparticles were characterized by Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM). The average size of produced nanoparticles is ca. 100 nm. TEM analysis of RDX/PS nano-composite shows a core-shell structure with RDX as the core material and the shell consisting of the polymeric binder. X-ray Powder Diffraction (XRPD) analysis indicates polycristalline structure of RDX in the product with a crystallite size of 42 nm. The content of RDX in the composite particles is in the range 70-73% by mass as determined by Gas Chromatography-Mass Spectroscopy (GC-MS) and by XRPD.

Micronized composites of ibuprofen and bio-compatible polymer binders were produced by co-precipitation in rapid expansion of binary supercritical solutions (RESS). The binders used in this study are poly-L-lactic acid (PLLA), poly (lactic-co-glycolic acid) (PLGA), and polyethylene glycol (PEG). The recrystallized particles of pure ibuprofen as well as produced by ibuprofen co-precipitation with a polymer binder were characterized by optical microscopy. The average ibuprofen particle sizes are 1-3 microns depending on the process conditions. The particle size increases proportionally to the cubic root of the solute concentration in the supercritical solution in CO2. The co-precipitated ibuprofen/polymer particle size is in the range of 3-10 microns. In vitro dissolution rates were measured at ambient temperature as well as at 37 °C. Polymer coated ibuprofen particles produced by RESS co-precipitation dissolve in water at ambient temperature from 10 to 20 times faster than the original ibuprofen powder. At 37 °C the dissolution is from 2 to 3 times faster compare to the original powder. The acceleration of the dissolution rate is due to the much smaller particle size as well as the presence of polymer layers which prevent particle agglomeration.

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