Synthesis and testing of soy-based polyols : phosphate and glycerolysis oligomers

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 15, 2010).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Dissertation advisor: Dr. Galen J. SuppesVita.Ph. D. University of Missouri--Columbia 2009.Soy-based polyols are important industrial prepolymeric materials that use renewable resource. They react with isocyanates to produce polyurethanes (PU) and can be produced at costs less than polyols derived from petrochemicals. This project proposes new soy-based polyols with high hydroxy equivalent weights that produce significant reactivity with isocyanate in flexible and rigid polyurethane foams and bioelastomers. Biocatalytic, transesterification and polymerization processes were evaluated to increase equivalent weights and hydroxyl functionality of soy-based polyols used in polyurethane formulations. Oligomeric soy-based polyols were synthesized using the following chemistries: 1) acidolysis of epoxidized soybean oil with phosphoric acid, 2) glycerol transesterification of bodied soybean oil, 3) ethylene glycol alcoholysis of epoxidized soybean oil, and 4) enzymatic polymerization. Soy-based polyol products described in this study have physicochemical properties comparable to both commercial triglyceride-based and petroleum-based polyols with relatively significant reactivity with isocyanate to produce polyurethane products that include rigid and flexible polyurethane foams, and bioelastomers.Includes bibliographical reference

Supercritical CO2 extraction of porogen phase: An alternative route to nanoporous dielectrics

DOI: 10.1557/JMR.2004.0413We present a supercritical CO2 (SCCO2) process for the preparation of nanoporous organosilicate thin films for ultralow dielectric constant materials. The porous structure was generated by SCCO2 extraction of a sacrificial poly(propylene glycol) (PPG) from a nanohybrid film, where the nanoscopic domains of PPG porogen are entrapped within the crosslinked poly(methylsilsesquioxane) (PMSSQ) matrix. As a comparison, porous structures generated by both the usual thermal decomposition (at approximately 450 °C) and by a SCCO2 process for 25 and 55 wt% porogen loadings were evaluated. It is found that the SCCO2 process is effective in removing the porogen phase at relatively low temperatures (<200 °C) through diffusion of the supercritical fluid into the phase-separated nanohybrids and selective extraction of the porogen phase. Pore morphologies generated from the two methods are compared from representative three-dimensional (3D) images built from small-angle x-ray scattering (SAXS) data.Professor Gangopadhyay and Professor Simon acknowledge the financial support of this work from the Semiconductor Research Corporation and from the National Science Foundation Grant No. CMS-0210230. The authors would also like to acknowledge initial support provided by the State of Texas Advanced Technology Program (ATP Grant No. 003644-0229-1999). The SAXS experiments were performed at the Advanced Photon Source at Argonne National Laboratory, which is supported by the United States Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38. Portions of this research were carried out at the Stanford Synchrotron Radiation Laboratory, a national user facility operated by Stanford University on behalf of the United States Department of Energy, Office of Basic Energy Sciences

Electric field and temperature-induced removal of moisture in nanoporous organosilicate films

doi:10.1063/1.1757019The effects of bias-temperature-stress (BTS) or simply temperature-stress (TS) on nanoporous low-k methylsilsesquioxane films are studied. Initially, the as-given and O2 ashed/etched films exhibit physical adsorption of moisture as revealed from the electrical behavior of the samples after 15 days. The temperature stressing at 170 °C volatilized the adsorbed water but is unable to remove chemisorb and hydrophillic Si-OH groups. As a result, the TS films remain susceptible to moisture. BTS at 170 °C also removes adsorbed water. More important, the surfaces under the metal-insulator structure were dehydroxylated by breaking the chemisorb Si-OH group facilitating the formation of siloxane bonds that prevents adsorption of moisture even after 60 days.The authors would like to acknowledge Dorel Toma of TEL for providing the samples, and SRC and NSF for funding this research

Effect of cellulose-based fibers extracted from pineapple (Ananas comosus) leaf in the formation of polyurethane foam

New polyurethane foams were fabricated utilizing cellulose-based fibers extracted from pineapple (Ananas comosus) leaf as raw material. The pineapple leaf fibers (PALF) were treated with alkali and subsequently bleached to enhance its fiber-matrix adhesion. Polyurethane composites have been prepared by incorporating 10% cellulose-based fibers extracted from PALF during polyurethane synthesis. The Fourier transform infrared (FTIR) spectra revealed that increase in the C-H and C-O vibrational modes absorption were observed when cellulose-based fibers were incorporated which might be attributed to the successful bonding of high purity cellulose-based fibers in the matrix of polyurethane foam. The physico-chemical, spectral and thermal properties of the polyurethane foam and the cellulose-based fibers reinforced polyurethane composites have been studied.Keywords: Cellulose-based fibers; Pineapple leaf fibers; Polyurethane foa

Characterization of porous low-k films using variable angle spectroscopic ellipsometry

doi:10.1063/1.2189018Variable angle spectroscopic ellipsometry (VASE™) is used as a tool to characterize properties such as optical constant, thickness, refractive index depth profile, and pore volume fraction of single and bilayer porous low-k films. The porous films were prepared using sacrificial pore generator (porogen) approach. Two sets of porous films with open- and closed-pore geometries were measured. Three models were used for data analysis: Cauchy, Bruggeman effective medium approximation (BEMA), and graded layer. Cauchy, a well-known model for transparent films, was used to obtain thickness and optical constant, whereas BEMA was utilized to calculate the pore volume fraction from the ellipsometric data. The Cauchy or BEMA models were then modified as graded layers, resulting in a better fit and a better understanding of the porous film. The depth profile of the porous film implied a more porous layer at the substrate-film interface. We found 3%-4% more porosity at the interface compared with the bulk for both films. This work shows that VASE™, a nondestructive measurement tool, can be used to characterize single- and multigraded layer porous films quickly and effectively.The authors would like to acknowledge the financial support of Semiconductor Research Corporation (SRC)

Electrochemical properties of carbon nanoparticles entrapped in silica matrix

Carbon-based electrode materials have been widely used for many years for electrochemical charge storage, energy generation, and catalysis. We have developed an electrode material with high specific capacitance by entrapping graphite nanoparticles into a sol gel network. Films from the resulting colloidal suspensions were highly porous due to the removal of the entrapped organic solvents from sol-gel matrix giving rise to high Brunauer-Emmett-Teller (BET) specific surface areas (654 m2/g)and a high capacitance density (∼37 F/g). An exponential increase of capacitance was observed with decreasing scan rates in cyclic voltammetry studies on these films suggesting the presence of pores ranging from micro (< 2 nm) to mesopores. BET surface analysis and scanning electron microscope images of these films also confirmed the presence of the micropores as well as mesopores. A steep drop in the double layer capacitance with polar electrolytes was observed when the films were rendered hydrophilic upon exposure to a mild oxygen plasma. We propose a model whereby the microporous hydrophobic sol-gel matrix perturbs the hydration of ions which moves ions closer to the graphite nanoparticles and consequently increase the capacitance of the film.This work was supported by the National Institutes of Health grant NS048826

Isocyanate Reduction by Epoxide Substitution of Alcohols for Polyurethane Bioelastomer Synthesis

A phosphate ester-forming reaction was carried out by mixing epoxidized soybean oil with up to 1.5% o-phosphoric acid. In situ oligomerization took effect almost instantly producing a clear, homogeneous, highly viscous, and a low-acid product with a high average functionality. The resulting epoxide was used as a reactant for urethane bioelastomer synthesis and evaluated for rigid foam formulation. Results have shown that with a number of catalysts tested phosphoric acid significantly enhances a solvent-free oxirane ring cleavage and polymerization of the epoxidized soybean oil via phosphate-ester formation at room temperature. The resulting phosphoric acid-catalyzed epoxide-based bioelastomer showed an 80% decrease in extractable content and increased tensile strength at the same isocyanate loading relative to the noncatalyzed epoxide. The oligomerized epoxidized soybean oil materials exhibited ASTM hydroxyl values 40% less than the nonoligomerized starting material which translates to reduced isocyanate loadings in urethane applications

Resistance distance in some composition of graphs

In graph theory, the resistance distance between any two vertices of a simple connected graph G is equal to the e ective resistance between two corresponding nodes on an electrical network, constructed so as to correspond to G, with each edge being replaced by a unit resistor or a 1 ohm resistance. This resistance is known to be a metric on a graph. This paper aims to nd an explicit expression for the resistance distance between any pair of vertices in some composition of graphs. Speci cally, the e ective resis- tance between any two vertices in each graph of Pn[Km] Tn[Km] Cn[Km] Pn[Km] Tn[Km] Cn[Km] are determined. The relationship between the resistance distance between two vertices in a graph and its complement will be investigated

In Silico Investigation of the Impact of Reaction Kinetics on the Physico-Mechanical Properties of Coconut-Oil-Based Rigid Polyurethane Foam

Conventionally, designing rigid polyurethane foams (RPUFs) with improved physico-mechanical properties from new, bio-based polyols is performed by modifying foam formulations via experimentation. However, experimental endeavors are very resource-dependent, costly, cumbersome, time-intensive, waste-producing, and present higher health risks. In this study, an RPUF formulation utilizing a coconut-oil (CO)-based polyol with improved physico-mechanical properties was approximated through a computational alternative in the lens of the gel time of the RPUF formation. In the RPUF formation of most bio-based polyols, their very fast gel times negatively impact foam robustness. The computational alternative functioned by finding a CO-based RPUF formulation with a gel time in good agreement with a formulation based on commercial petroleum-derived polyol (control). The CO-based RPUF formulation with the best-fit catalyst loading was approximated by simulating temperature profiles using a range of formulations with modified catalyst loadings iteratively. The computational approach in designing RPUF with improved properties was found to effectively negate foam collapse (with a shrinkage decrease of >60%) and enhance foam strength (with a compressive strength increase of >300%). This study presents an economically and environmentally sustainable approach to designing RPUFs by enabling minimized utilization of material sources for experimentation and analysis and minimized dependence on waste-producing methods

Analysis and Simulation of Blood Cells Separation in a Polymeric Serpentine Microchannel under Dielectrophoresis Effect

The current work presents a novel microfluidic approach, allowing a full separation of blood cells. The approach relies on using a polydimethylsiloxane serpentine microchannel equipped with a series of electrodes, providing two separation zones. The proposed design exploits the unique configuration of the channel along with the inherent difference in dielectric properties of the three kinds of blood cells to achieve a size-based sorting. The platelets (PLTs) are subjected to a larger dielectrophoretic force than red blood cells (RBCs) and white blood cells (WBCs), forcing them to be separated in the first zone. This leaves RBCs and WBCs to be separated in the second zone. The model developed in this work has been used intensively to examine the feasibility of the proposed approach. The model results showed a full separation of blood content can be achieved over a range of phase flow rates and AC frequencies