Master of Science, University of Akron, 2018, Polymer Engineering

Silicone rubber is widely used as an elastomer. This thesis investigates the fabrication and material properties of silicone rubber blended with some inexpensive fillers. The section of this thesis focuses on cornstarch-silicone rubber blends. In acetoxy cured silicone rubber, cornstarch has good compatibility and is able to blend well with the silicone resin. Samples were prepared by simple physical mixing. The crosslinking degree and other mechanical abilities can be investigated as a function of the weight percent of cornstarch and water. The second section of this thesis focuses on shape memory polymers. Shape memory polymers were fabricated by mixing acetoxy silicone with crystalline small molecules. The solid-liquid transition of the small molecule is able to generate reversible solid networks, which enable the shape memory effect. The shape memory effect properties tested as a function of the weight percent of the small molecule in samples. With increasing weight percent of the small molecule, the fixity is increased to ca. 99% and the recovery decreased to ca. 87%. Based on these tests, an optimum blend formulation is found, which shows the best shape memory performance can be found and repeatability through several test cycles. Due to the differences in the interaction degree between the small molecule and the silicone rubber, the choice of the small molecule is also an important factor to influence the shape memory effect.

Committee: Kevin Cavicchi (Advisor); Nicole Zacharia (Committee Chair); Erol Sancaktar (Committee Member) Subjects: Polymer Chemistry; Polymers

PhD, University of Cincinnati, 2018, Pharmacy: Pharmaceutical Sciences/Biopharmaceutics

Controlled release oral dosage form offers great advantages over conventional dosage form by providing steady drug plasma concentration, decreasing the frequency of administration, and providing enhanced patient compliance. However, orally ingested tablet is exposed to varying pH conditions and fluctuating mechanical agitations during its travel through the gastrointestinal tract (GIT). Selection of materials that provide controlled release mechanism to the oral dosage form is important as they can a) minimize drug release rate fluctuations for ionizable drugs during its travel along the changing pH environment of the GIT and b) maintain the release rate mechanism even when subjected to the physiological mechanical agitation forces. To examine these two important requirements, matrix tablets prepared using low glass transition temperature (Tg) silicone pressure sensitive adhesive (PSA) were evaluated and compared with matrix tablets prepared using high Tg ethyl cellulose (EC). Specifically, the effect of dissolution medium pH on drug release from binary tablets consisting of the polymer and ionizable model drugs verapamil hydrochloride and diclofenac sodium was studied using USP dissolution apparatus (without mechanical stress). The effect of simulated physiological mechanical stress agitation on drug release was studied using dissolution stress test apparatus for non-ionizable model drug acetaminophen. Mechanical properties, physical structures, electrical resistance, water uptake, and contact angle of pure polymer films and of matrix tablets were studied to understand the relationships of these factors to drug release. Our study indicated that increasing polymer amount decreased drug release rate from both silicone PSA and EC tablets using USP dissolution apparatus. However, silicone PSA tablets showed lower friability compared to EC tablets. The application of physiological simulated mechanical stress affected drug release from high Tg EC tablets that resulte (open full item for complete abstract)

Committee: Kevin Li Ph.D. (Committee Chair); Pankaj Desai Ph.D. (Committee Member); Sergey Grinshpun Ph.D. (Committee Member); Gerald Kasting Ph.D. (Committee Member); Gary Kelm Ph.D. (Committee Member); R. Randall Wickett Ph.D. (Committee Member) Subjects: Pharmaceuticals

PhD, University of Cincinnati, 2010, Engineering : Materials Science

Lipases have been proven to be versatile and efficient biocatalysts which can be used in a broad variety of esterification, transesterification, and ester hydrolysis reactions. Due to the high chemo-, regio-, and stereo-selectivity and the mild conditions of lipase-catalyzed reactions, the vast potential of these biocatalysts for use in industrial applications has been increasingly recognized. Polysiloxanes (silicones) are well known for their unique physico-chemical properties and can be prepared in the form of fluids, elastomers, gels and resins for a wide variety of applications. However, the enzymatic synthesis of silicone polyesters and copolymers is largely unexplored.In the present investigations, an immobilized Candida antarctica lipase B (CALB) on macroporous acrylic resin beads (Novozym-435®) has been successfully employed as a catalyst to synthesize silicone polyesters and copolymers under mild reaction conditions. The silicone aliphatic polyesters and the poly(dimethylsiloxane)–poly(ethylene glycol) (PDMS-PEG) copolymers were synthesized in the bulk (without using a solvent), while the silicone aromatic polyesters, the silicone aromatic polyamides and the poly(ε-caprolactone)–poly(dimethylsiloxane)–poly(ε-caprolactone) (PCL-PDMS-PCL) triblock copolymers were synthesized in toluene. The synthesized silicone polyesters and copolymers were characterized by Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Wide Angle X-ray Diffraction (WAXD). This dissertation also describes a methodology for physical immobilization of the enzyme pepsin from Porcine stomach mucosa in silicone elastomers utilizing condensation-cure room temperature vulcanization (RTV) of silanol-terminated poly(dimethylsiloxane) (PDMS). The activity and the stability of free pepsin and pepsin immobilized in silicone elastomers were studied with respect to pH, temperature, cross-lin (open full item for complete abstract)

Committee: Stephen Clarson PhD (Committee Chair); Jude Iroh PhD (Committee Member); Gregory Beaucage PhD (Committee Member); James Mark PhD (Committee Member) Subjects: Materials Science

MS, University of Cincinnati, 2005, Engineering : Materials Science

Elastomers usually require the incorporation of reinforcing fillers in order to improve their mechanical properties. The resulting properties are very much dependent on the volume fraction, size and shape of the reinforcing agent. For commercial silicone systems silica and titania are typically used as fillers. Fumed and precipitated silica are made on an industrial scale for many applications however it was shown recently that biological and synthetic macromolecules can generate new silica structures using a bioinspired route. The morphology of these new silica structures being different than conventional silica fillers gives a wide scope for new synthetic composites and their study. Herein we have incorporated bioinspired silica fillers into poly(dimethylsiloxane) (PDMS) elastomers and investigated their mechanical, morphological and thermal properties as a function of filler loading. The equilibrium stress-strain characteristics of the elastomers were determined as a function of bioinspired filler loading and the Mooney-Rivlin constants (2C1 and 2C2) were calculated from the stress-strain isotherms. The thermal characteristics, in particular the glass transition temperature (Tg) and the melting point (Tm) of the elastomers were characterized using differential scanning calorimetry (DSC). We have also synthesized poly(propyleneoxide) (PPO) hybrid networks by incorporating bioinspired silica as a filler. The high temperature thermal stability of PDMS networks and PPO networks were investigated and compared using thermogravimetric analysis (TGA). In previous studies a mechanism was proposed explaining the formation of these new silica structures which is based on the silica incorporating the (bio)macromolecule. The results obtained from thermogravimetric analysis strengthen the “proposed mechanism” of formation of these new bioinspired silica structures. The morphology of the samples and the filler dispersion were characterized using Scanning Electron Microscopy (SE (open full item for complete abstract)

Committee: Dr. Stephen Clarson (Advisor) Subjects: Engineering, Materials Science