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School of Materials Science and Engineering

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search.filters.applied.f.advisor: Kumar, Satish × Item Type: Publication × search.filters.applied.f.resourcesubtype: Thesis ×

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Now showing 1 - 10 of 15
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Development of fundamental understanding of the cure kinetics of benzoxazine epoxy blends

2020-01-13 , Maffe, Adam Paul

This study attempts to bridge the gap between the current fundamental understanding of benzoxazines on the monomer level and their macro scale thermo-mechanical properties. Bisphenol-A based benzoxazine (Bz) was blended with di- and tri-functional epoxies to reduce viscosity for processing, and their resulting thermal and mechanical properties were characterized. Additionally, the formation of inter-molecular and intra-molecular hydrogen bonds was investigated within a Bz-epoxy two component system. Activation energy, heat of reaction, degradation temperature, hydrogen bonding characterization and thermo-mechanical characterization were studied using a differential scanning calorimeter, dynamic mechanical analyzer, thermogravimetric analysis, Fourier transform infrared spectroscopy and quasistatic tensile testing. Preliminary results show a synergistic increase in Tg of the blends, for both di- and tri-funcitonal epoxy blends. Surprisingly, while the two components exhibit Tg’s of ~ 150-170 oC, the blended systems consistently exhibited a Tg in the range of 210-250 oC. This work aims to expand upon thermal and mechanical characterization data generated by our collaborator Ehsan Barjasteh for the benzoxazine – di-functional epoxy system, as well as explore a new benzoxazine – tri-functional epoxy-based system. Our underlying motivations in this study are to identify the origins of the synergistic increase in Tg upon blending through various thermo-mechanical characterization methods and in-situ FT-IR analysis of cure kinetics, as well as identifying the compositions and functionality which exhibit the most desirable combination of thermal and mechanical properties.

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Light Scattering Study on Single Wall Carbon Nanotube (SWNT) Dispersions

2004-04-12 , Wang, Tong

Carbon nanotubes, and particularly single wall carbon nanotubes (SWNTs) have attracted much attention for their unique structure, as well as for their excellent mechanical, electrical and thermal properties. Most properties of carbon nanotubs are closely related with its anisotropic structure and geometry factor. Characterization of carbon nanotube length is critical for understanding their behavior in solutions as well as in polymer composites. Microscopy, particularly atomic force microscopy, has been used for their length measurement. Microscopy, though straightforward, is quite laborious, particularly for statistically meaningful sampling. Light scattering can be used to measure particle dimensions. In this study, light scattering has been used to study polyvinyl pyrrolidone (PVP) wrapped SWNTs surfactant assisted aqueous dispersion and SWNT dispersion in oleum. To determine the length of SWNTs, Stokes - Mueller formalism was used, which is a universal model for particles with any size and shape. The Mueller matrix for an ensemble of long, thin cylinders proposed by McClain et al. was used in this study. This Mueller matrix includes the information of size (length and radius) and optical constants (refractive index and extinction coefficient) of cylinders. In this matrix, extinction coefficient, radius and length of SWNTs are unknown. By normalizing scattering intensity I(theta) (theta from 30 to 155 degree) to that at 30degree , the effects of radius and extinction coefficient were cancelled out. Thus, the effect of SWNT length on scattering intensity could be studied independently. A series of curves of normalized scattering intensity of SWNTs (I(theta) /I(30degree)) with varied length as a function of wave vector were predicted. A curve of normalized scattering intensity of SWNT as a function of wave vector was also obtained experimentally. By comparing experimental and predicted curves, average SWNT length in the dispersion has been determined. Scattering intensity at a given angle initially increases with concentration, and then reaches a critical concentration(C*), above which the scattering intensity decreases. This phenomenon has been attributed to the competition between scattering and absorption of light by the presence of SWNT. By using Beer-Lambert law, this phenomenon has been used to determine the molar absorption coefficient of SWNTs.

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Solution studies of soybean protein isolate using circular dichroism and SDS-PAGE

1999-12 , Lambert, Karen A.

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Solution studies on soybean protein for fiber spinning

1996-05 , Zhang, Yi

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Tensile testing and stabilization/carbonization studies of polyacrylonitrile/carbon nanotube composite fibers

2012-11-14 , Lyons, Kevin Mark

This study focuses on the processing, structure and properties of polyacrylonitrile (PAN)/ carbon nanotube (CNT) composite carbon fibers. Small diameter PAN/CNT based carbon fibers have been processed using sheath-core and islands-in-a-sea (INS) fiber spinning technology. These methods resulted in carbon fibers with diameters of ~3.5 μm and ~1 μm (for sheath-core and INS respectively). Poly (methyl methacrylate) has been used as the sheath or the sea component, which has been removed prior to carbonization. These fibers have been stabilized and carbonized using a batch process. The effect of stabilization has been characterized by Fourier Transform Infrared Spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). A non-isothermal extent of cyclization (Mcyc) from the DSC kinetics study was developed in order to obtain an unbiased method for determining the optimal stabilization condition. The results of Mcyc were found to be in good agreement with the experimental FTIR and WAXD observations. The carbon fiber fracture surfaces have been examined using SEM. Various test parameters that affect the tensile properties of the precursor fiber (both PAN and PAN/CNT), as well as carbon fiber have been studied. In an attempt to validate single filament tests, fiber tow testing has also been done using standard test methods. Batch processed carbon fibers obtained via sheath-core geometry exhibited tensile strengths as high as 6.5 GPa, while fibers processed by islands-in-a-sea geometry exhibited strength values as high as 7.7 GPa.

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Solution spinning and characterization of poly(vinyl alcohol)/soybean protein polyblend fibers

2001 , Zhang, Xiefei

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Structure and properties of linear and star-like thermotropic liquid crystalline polymeric fibers

1998-12 , Bai, Yiqun

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Single Wall Carbon Nanotube/Polyacrylonitrile Composite Fiber

2004-11-01 , Liang, Jianghong

Single Wall Carbon Nanotubes (SWNTs), discovered in 1993, have good mechanical, electrical and thermal properties. Polyacrylonitrile (PAN) is an important fiber for textiles as well as a precursor for carbon fibers. PAN has been produced since 1930s. In this study, we have processed SWNT/PAN fibers by dry-jet wet spinning. Purified SWNT, nitric acid treated SWNTs, and benzonitrile functionalized SWNTs have been used. Fiber processing was done in Dimethyl Formamide (DMF) and coagulation was done in DMF/water mixture. The coagulated fibers were drawn (draw ratio of 6) at 95 oC. Structure, orientation, and mechanical properties of these fibers have been studied. The cross-sections for all the fibers are not circular. Incorporation of SWNT in PAN results in improved mechanical properties, tensile modulus increased from 7.9 GPa for control PAN to 13.7 GPa for SWNT/PAN composite fiber, and functionalized SWNTs result in higher improvements with tensile modulus reaching 17.8 GPa for acid treated SWNT/PAN composite fibers. The theoretical analysis suggests that observed moduli of the composite fibers are consistent with the predicted values.

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Fiber spinning, structure and properties of poly(ethylene terephthalate-co-4,4' bibenzoate) copolyester fibers

2001 , Ma, Hongming

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PET/nylon 66 polymer blends and carpet recycling

1996-12 , Parpart, Dawn Allison

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