Organizational Unit:

School of Materials Science and Engineering

Permanent Link

https://hdl.handle.net/1853/70762

Parent Organization

Organizational Unit

College of Engineering

ArchiveSpace Name Record

https://finding-aids.library.gatech.edu/agents/corporate_entities/1126

Full item page

Publication Search Results

Now showing 1 - 10 of 11

Processing, structure, and properties of polyacrylonitrile-nanocellulose composite films and fibers

(Georgia Institute of Technology, 2018-07-24) Luo, Jeffrey

Cellulose is the most abundant biopolymer on earth with an estimated production of 1.5 x 1012 tons per year. With the high production, cellulose could be utilized to increase our sustainability and reduce our dependence on synthetic polymers made from oil. Recently nanocellulose in the form of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) as potential fillers have been gaining significant interest. This is due to nanocellulose’s high mechanical properties, high surface area, biodegradability, biorenewability, and low toxicity.Polyacrylonitrile (PAN) is a synthetic polymer and has uses in clothing, home furnishings, and filtration membranes. PAN is also the predominant precursor for carbon materials such as carbon fiber. The effect of CNC loading on the mechanical, thermal, optical, and structural properties of PAN-CNC films was studied. Films were made successfully with up to 40 wt% CNC loading. These composite films demonstrated the same optical transparency, and an increase in mechanical properties when compared to neat PAN. The effect of CNC loading on rheology was also looked at, and it was found that the addition of CNCs increases the viscosity at low shear rates. It was also found that the viscosity of the PAN-CNC suspensions increased with time. The stabilization kinetics of the PAN-CNC films, and structural changes of the films were investigated. It was found that the addition of CNCs reduced the cyclization activation energy. It was also found that the reaction rate of cyclization and oxidation could increase with the addition of CNCs. The thermal stability of CNCs was determined to be higher in the composite films than in neat form, which was examined by wide angle x-ray diffraction and Fourier transform infrared spectroscopy. A method to make sulfonated CNFs that has the same surface chemistry as CNCs made by sulfuric acid hydrolysis is developed. This sulfonation of CNFs improves the dispersibility of CNFs in solvent. The method developed in this study can produce sulfonated CNFs faster the other reported sulfonation method. This technique is also faster than the most common CNF functionalization, TEMPO oxidation. The chemical stability of TEMPO CNFs and sulfonated CNFs in water and dimethylformamide was also investigated. The characterization of PAN-CNF fibers and the effect of processing on the resulting mechanical properties was studied. Two different methods of functionalization were performed on the CNFs, TEMPO oxidation and amination, and the reinforcement effect of the different functionalizations were studied. The aminated CNFs provided more mechanical reinforcement than the TEMPO CNFs. This is attributed to the difference between surface chemistry, and the better interaction between the amine groups on the aminated CNFs and PAN than the carboxylic acid groups on the TEMPO CNFs.
Structure, processing, and properties of carbon nanotube composite with polypropylene

(Georgia Institute of Technology, 2018-01-22) Wang, Po-Hsiang

Having high aspect ratio and structural similarity to the macromolecular building blocks, carbon nanotubes (CNTs) have demonstrated their great potential in tailoring the physical properties, e.g. conformation, crystallization, rheological, electrical and thermal characteristics etc., of the polymers. However, achieving good CNT dispersion, while also achieving good interfacial properties, remains a challenge, especially in non-polar polymers such as polyethylene (PE) and polypropylene (PP). In this study, the CNT modified PP with an engineered interphase was manufactured using a co-solvent process where a homogeneous PP layer was bonded non-covalently on acid functionalized multiwall carbon nanotubes (f-MWNTs). Unlike conventional melt blending, which simply compounds the neat polymer and pristine CNTs, or preparing the nanocomposite with covalently modified CNTs, e.g. via in-situ polymerization of macromolecules, this approach provides a practical way not only to obtain good CNT dispersion but also to alter the polymer physical properties by using small amount of CNTs (less than 1 wt%). This research systematically investigates the polymer-CNT interaction when the interphase is tailored. Three types of interphase were studied: (i) The PP/f-MWNT system using co-solvent process. (ii) The maleic anhydride grafted polypropylene (MA-g-PP)/f-MWNT system using co-solvent process. (iii) The PP/pristine MWNT (p-MWNT) system using melt process. The f-MWNT based systems, termed as master batches, were further melt blended with neat polymers to the target f-MWNT concentrations (0.001 wt% to 1 wt%) followed by injection molding. Mechanical properties, including the tensile and impact testing, as well as rheological, crystallization and the structure of the interphase were studied. It was shown that CNTs serve as a strong nucleating agent for templated polymer crystal growth. With addition of 1 wt % f-MWNT, an 152 % increase in PP impact strength was achieved in the PP/f-MWNT system. On the other hand, addition of pristine (unmodified) MWNTs yielded no statistical difference in the impact strength between the nanocomposite and neat PP. Strong adhesion between PP and f-MWNTs owing to the presence of interphase was verified by Raman spectroscopy as well as SEM and was shown to be absent between PP and p-MWNTs. Also, the structure of this interphase was characterized by thermal analysis and wide-angle X-ray diffraction. It was found that the polymer at the interphase exhibits higher melting temperature, suggesting higher crystal perfection and/or larger crystals, with respect to the bulk polymer. With a designed thermal treatment, the span of this interphase can be further increased as demonstrated by the formation of columnar crystals surrounding CNTs. Abnormal temperature dependence of shear viscosity was observed when temperature of the polymer melt was increased from 190 °C to 220 °C. Overall, this research demonstrates that tailored CNT/polymer interphase is needed for achieving high performance nanocomposites and improving the polymer-CNT interaction.
Studies on polyacrylonitrile/cellulose nanocrystals composite precursor and carbon fibers

(Georgia Institute of Technology, 2017-11-10) Chang, Huibin

In this study, PAN fibers containing up to 40 wt% CNC were spun by gel-spinning technology. The structure, morphology, and mechical properties of PAN/CNC precursor and their carbon fibers have been studied. The results show that the H2O/dimethyl formamide (DMF) co-solvent disperses individual CNCs more effectively than pure H2O or pure DMF, especially at high CNC concentrations. The addition of CNCs improves the tensile modulus of PAN fibers at a low draw ratio. The fully drawn PAN/CNC fibers containing even the 40 wt% CNCs exhibit the same strain to failure as the fully drawn PAN fibers. The high orientation of CNCs in PAN fibers was observed by Raman spectroscopy, in which the 1095 cm−1 Raman band of CNCs shows a two-fold symmetry under vertical/vertical (VV) mode and a four-fold symmetry under vertical/horizontal (VH) mode. With the addition of 40 wt% CNC, the activation energy of cyclization and crosslinking reactions of PAN is reduced by 17.5 and 19%, respectively. The carbon fibers made from PAN containing 20 wt% CNCs show the tensile strength of 2.3 GPa and the tensile modulus of 252 GPa, which are comparable to the PAN based carbon fiber properties (tensile strength of 1.9 GPa and tensile modulus of 251 GPa) processed under the same conditions.
Effect of poly(methyl methacrylate) wrapping on the structure and properties of CNT films, and polymer/CNT films and fibers

(Georgia Institute of Technology, 2017-02-24) Bakhtiary Davijani, Amir Ahmad

Carbon nanotubes (CNTs) exhibit high electrical and thermal conductivity and good mechanical properties, making them suitable fillers for composites. Their effectiveness as a filler is affected by their state of aggregation. Various solvents, surfactants, and processing techniques have been studied to improve CNT dispersion in polymers. However, prior to this work there is no suitable solution for achieving good CNT dispersion. In this study, a novel process has been developed that prevents CNT aggregation. Ordered helical wrapping of poly (methyl methacrylate) (PMMA) has been achieved on single wall carbon nanotubes (SWNTs). PMMA wrapped SWNT dispersions in dimethylformamide (DMF) are found to be stable for over three months at room temperature. Ordered PMMA wrapping has been confirmed by X-ray diffraction, and the wrapping behavior has also been verified using molecular modeling. PMMA only wraps on SWNTs with diameter of ~1 nm and not on larger diameter CNTs, such as few wall and multi wall carbon nanotubes. PMMA wrapped SWNT dispersions have also been characterized using UV-vis and Raman spectroscopy which confirm exfoliation of PMMA wrapped SWNTs. The novel finding has been successfully leveraged for electrical energy storage and mechanical reinforcement. SWNT buckypapers, typically have a surface area of about 650 m2/g. Using PMMA wrapping, SWNT buckypapers with surface area as high as 950 m2/g have been processed. These buckypapers exhibited significantly higher energy storage performance when used as electrodes in electrochemical supercapacitor. At a given power density, the energy density of the high surface electrodes was more than four times higher than the best value reported in the literature to-date for carbon nanotube or graphene electrodes. Wrapping SWNTs with PMMA in buckypaper increased the modulus and tensile strength by a factor of 5.9 and 3.7, respectively, compared to pristine SWNT buckypaper. Stress transfer studies on buckypapers revealed that while non-wrapped SWNTs experienced negligible stress during deformation, PMMA wrapped SWNTs took up to ~1 GPa stress before mechanical failure of the buckypaper. The modulus of composite films with PMMA wrapped SWNTs was 75 % higher than non-wrapped SWNT films. The effect of PMMA wrapping on thermomechanical properties and electrical conductivity of composite films is also reported. PMMA wrapped and non-wrapped SWNTs were incorporated in PAN fibers and the effect of PMMA wrapping on mechanical properties, and stress transfer was characterized. The stress transfer analysis of SWNTs in precursor fiber indicated 45 % higher interfacial shear strength in PMMA wrapped SWNTs compared to non-wrapped SWNTs. PMMA wrapping effectively debundled SWNTs in the PAN fibers as evidenced by Raman spectroscopy of the precursor fiber. SEM images of the carbon fiber fracture surface revealed 60% reduction in fibril size when PMMA wrapped SWNTs were used instead of non-wrapped SWNTs.
Gel spun polyacrylonitrile based carbon fibers containing lignin and carbon nanotubes

(Georgia Institute of Technology, 2017-01-13) Liu, Hsiang-Hao Clive

Forestry bioproduct lignin has been long proposed as an ideal material for carbon fiber precursor due to its abundance, renewability, high carbon yield and cost-effectiveness as the biorefinery by-product. However, little success of lignin based commercial carbon fibers had been reported due to the barriers such as varying chemical structure, complex thermal stabilization process, poor miscibility with other polymers that resulted in unmanageable processing and limited mechanical performance. In this research, systematic investigations are conducted on the lignin/polyacrylonitrile (PAN) blends in solution, fiber structure, and during thermal stabilization and carbonization process to valorize biorefinery waste lignin for its potential towards green manufacturing and renewability of carbon fibers. Dynamic shear rheology study of PAN with various lignin content in solutions was carried out to investigate the potential boundary conditions for lignin incorporation, and to characterize the interactions of PAN and lignin with respect to fiber processing. The findings have shown that increasing incorporation of lignin in the PAN solution promotes fluid-solid transition during coagulation, and reduces solution viscosity, yield stress, relaxation time, and thermo-reversibility. The rheology findings along with gel spinning technology been successfully leveraged to address un-favored porous structure of PAN/lignin blends reported in the literature. Single-component PAN/lignin and PAN/lignin/carbon nanotubes (CNT) blend fibers, as well as PAN-sheath and PAN/lignin-core bi-component fiber are manufactured. The presence of lignin in spinning dope is shown to reduce the fiber maximum draw ratio. Since fibers manufactured with higher draw ratio can render smaller diameter to reduce number of defects per unit volume in the fiber structure, the decrease in maximum draw ratio limits the improvements on the derived carbon fiber mechanical properties. With the aid of bi-component fiber spinning, PAN sheath provides protection and endurance to fibers towards higher draw ratios. The presence of lignin and CNT is shown to affect the precursor fiber structure and to alter the structural reordering process during carbonization. In thermal stabilization process, a critical step in carbon fiber conversion, lignin was shown to reduce PAN cyclization, oxidation, and crosslinking reaction activation energies and increase the corresponding reaction rates. This renders a potential to reduce time and energy consumption during carbon fiber manufacturing. With ≥ 30 wt.% of lignin incorporation, batch-processed PAN/lignin carbon fibers exhibit tensile strength of 2.11 GPa and tensile modulus of 260 GPa, exceeding low-cost carbon fiber performance target (1.72 GPa, 172 GPa) set by the U.S. Department of Energy and the best PAN/APL carbon fiber mechanical performance reported in the literature to-date. With proper processing parameters, PAN sheath, and PAN/APL core bi-component carbon fibers with porous core (translates to ~24% overall porosity) can be manufactured as an approach for low-density carbon fibers.
Gel spun PAN and PAN/CNT based carbon fibers: From viscoelastic solution to elastic fiber

(Georgia Institute of Technology, 2015-04-06) Newcomb, Bradley Allen

This study focuses on the processing, structure, and properties of gel spun polyacrylonitrile (PAN) and polyacrylonitrile/carbon nanotube (PAN/CNT) carbon fibers. Gel spun PAN based carbon fibers are manufactured beginning with a study of PAN dissolution in an organic solvent (dimethylformamide, DMF). Homogeneity of the PAN/DMF solution is determined through dynamic shear rheology, and the slope of the Han Plot (log G’ vs log G’’). Solutions were then extruded into gel spun fibers using a 100 filament fiber spinning apparatus in a class 1000 cleanroom. Fibers were then subjected to fiber drawing, stabilization, and carbonization, to convert the PAN precursor fiber into carbon fiber. Carbon fiber tensile strength was shown to scale with the homogeneity of the PAN/DMF solution, as determined by the slope of the log G’ vs log G’’ plot. After the development of the understanding between the homogeneity of the PAN/DMF solutions on the gel spun PAN based carbon fiber tensile properties, the effect of altering the fiber spinning processing conditions on the gel spun PAN based carbon fiber structure and properties is pursued. Cross-sectional shape of the gel spun PAN precursor fiber, characterized with a stereomicroscope, was found to become more circular in cross-section as the gelation bath temperature was increased, the amount of solvent in the gelation bath was increased, and when the solvent was switched from DMF to dimethylacetamide (DMAc). Gel spun fibers were then subjected to fiber drawing, stabilization, and carbonization to manufacture the carbon fiber. Carbon fibers were characterized to determine single filament tensile properties and fiber structure using wide-angle x-ray diffraction (WAXD) and high resolution transmission electron microscopy (HRTEM). It was found that the carbon fiber tensile properties decreased as the carbon fiber circularity increased, as a result of the differences in microstructure of the carbon fiber that result from differences in fiber spinning conditions. In the second half of this study, the addition of CNT into the PAN precursor and carbon fiber is investigated. CNT addition occurs during the solution processing phase, prior to gel spinning. As a first study, Raman spectroscopy is employed to investigate the bundling behavior of the CNT after gel spinning and drawing of the PAN/CNT fibers. By monitoring the peak intensity of the (12,1) chirality in the as-received CNT powder, and in differently processed PAN/CNT fibers, the quality of CNT dispersion can be quickly monitored. PAN/CNT fibers were then subject to single filament straining, with Raman spectra collected as a function of PAN/CNT filament strain. As a result of the PAN/CNT strain, stress induced G’ Raman band shifts were observed in the CNT, indicating successful stress transfer from the surrounding PAN matrix to the dispersed CNT. Utilization of the shear lag theory allows for the calculation of the interfacial shear strength between the PAN and incorporated CNT, which is found to increase as the quality of CNT (higher aspect ratio, increased graphitic perfection, and reduced impurity content), quality of CNT dispersion, and fiber drawing increase. PAN/CNT fibers were then subjected to stabilization and carbonization for the manufacture of gel spun PAN/CNT based carbon fibers. These fibers were then characterized to investigate the effect of CNT incorporation on the structure and properties of the carbonized fibers. The gel spun PAN/CNT based carbon fibers were compared to commercially produced T300 (Toray) and IM7 (Hexcel) carbon fibers, and gel spun PAN based carbon fiber. Fiber structure was determined from WAXD and HRTEM. Carbon fibers properties investigated include tensile properties, and electrical and thermal conductivity. PAN/CNT based carbon fibers exhibited a 103% increase in room temperature thermal conductivity as compared to commercially available IM7, and a 24% increase in electrical conductivity as compared to IM7. These studies provide a further understanding of the processing, structure, property relationships in PAN and PAN/CNT based carbon fibers, beginning at the solution processing phase. Through the manufacture of more homogeneous PAN/DMF solutions and investigations of the fiber spinning process, gel spun PAN based carbon fibers with a tensile strength and modulus of 5.8 GPa and 375 GPa, respectively, were successfully manufactured in a continuous carbonization facility. Gel spun PAN/CNT based carbon fibers exhibit room temperature electrical and thermal conductivities as high as 74.2 kS/m and 33.5 W/m-K.
Multi-functional PAN based composite fibers

(Georgia Institute of Technology, 2014-11-17) Chien, An-Ting

Various nano-fillers can introduce specific functions into polymer and expand their application areas. Myriad properties, such as mechanical, electrical, thermal, or magnetic properties can be combined with original polymer characteristics, including flexible, light weight, and ease of use. These composites can be used to produce multi-functional fibers as the next generation textile or fabrics. In this research, Polyacrylonitrile (PAN) is adopted as the main polymer with different nano-fillers, such as carbon nanotube (CNT), iron oxide nanoparticle, and graphene oxide nanoribbon (GONR). Using gel-spinning technology, PAN-based composite fibers are fabricated in single- or bi-component fibers. Fibers are also characterized for their structure, morphology, mechanical properties, as well as for their electrical, thermal, or magnetic properties. For example, bi-component fibers with polymer sheath and polymer-CNT core as well as polymer-CNT sheath and polymer core are processed. With electrical and thermal conductivity introduced by CNT, such bi-components fibers can be applied for wearable electronics or for thermal management. Joule-heating effect owing to applied electrical current on single component PAN/CNT fibers is also investigated. With controllable electrical conductivity and fiber temperature, this active functional fiber can be applied for temperature regulation fibers or new carbon fiber manufacturing process. Another example is magnetic fiber with superparamagnetic iron oxide nano-particles. These novel magnetic fibers with high strength can be used for actuator, inductors, EMI shielding, or microwave absorption. GONR is also discussed and used to reinforce PAN-based fibers. Several theoretical models are considered to analyze the observed results.
Tensile testing and stabilization/carbonization studies of polyacrylonitrile/carbon nanotube composite fibers

(Georgia Institute of Technology, 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.
Carbon nanotubes as structural templates within poly(vinyl alcohol) composite fibers

(Georgia Institute of Technology, 2012-11-12) Ford, Ericka N. J.

Because the gel-spinning process has the potential to yield fibers of high strength and high modulus, this technique was employed to process continuous filaments of PVA/CNT, having CNTs at ¡Ü1 weight percent of polymer. A gel aging technique was employed with the goal of increasing the draw ratio for composite fibers and for promoting the development of crystalline PVA. Since residual solvent can lower the mechanical properties of drawn fibers, solvent phases of water and dimethyl sulfoxide (DMSO) within the drawn fibers were also characterized. As embedded SWNTs were uniaxially aligned along the drawn fiber axis, they were found to induce preferential alignment in the PVA side groups as well as for the residual solvent. This was attributed to charge transfer between SWNT and the respective functional groups. This orientation behavior has been characterized using Raman spectroscopy and infra-red dichroism. The behaviors of gel crystallization and solvent freezing within PVA/CNT dispersions were studied using thermal analysis and rheology. Carbon nanotubes were found to nucleate PVA crystallization in the gel state. PVA/CNT gel aging behavior was characterized by structural, thermal, and mechanical, and dynamic mechanical means. Gel aging was shown to increase the draw ratio of PVA/CNT fibers, and the development of the higher temperature melting peak was attributed to the draw induced ordering of PVA along CNTs. The scanning electron micrographs of fractured PVA/CNT fibers showed fibrils having an average diameter of about 22 nm. The storage modulus of aged gel was a function of solvent diffusion, which changed with aging time. CNTs were shown to have stabilized the gel network, as characterized by the dynamic mechanical properties, and to provide nucleation sites for the ordering of PVA chains, as characterized by WAXD.
Stabilization and carbonization studies of polyacrylonitrile /carbon nanotube composite fibers

(Georgia Institute of Technology, 2010-11-15) Liu, Yaodong

Carbon fibers contain more than 90 wt. % carbon. They have low density, high specific strength and modulus, and good temperature and chemical resistance. Therefore, they are important candidate as reinforcement materials. Carbon fiber is made by pyrolysing precursor polymers. Polyacrylonitrile (PAN) which has been used as precursor to produce high strength carbon fiber is used as precursor in this study. The theoretical tensile strength of carbon fibers can reach over 100 GPa. Currently, the best commercial carbon fibers reach only 7.5 GPa. To make good quality carbon fiber and to narrow the gap between theoretical values and currently achieved experimental properties, the entire manufacturing process including fiber spinning, stabilization and carbonization, needs to be improved optimized. In this dissertation, the stabilization processes of gel-spun PAN/carbon nanotubes (CNTs) composite fibers are studied. PAN/CNT (1 wt. % CNT) composite fibers are spun by dry-jet gel-spinning. Three types of CNTs with different number of walls and varying catalyst content are used as additives. The effect of different types of CNTs on the properties of the stabilized fibers was compared. It is found that the CNTs with the highest surface area shows the best reinforcement efficiency on the tensile modulus, and reduces the formation of β-amino nitrile. The residual catalyst in the range of 1 to 4 wt. % shows little effect on the mechanical properties of the stabilized fibers. Stabilization involves complex chemical reactions, including cyclization, oxidation, dehydration, and cross-linking. These complex reactions are separated by using different gas environments during stabilization. The cross-linking reaction has the highest activation energy among all stabilization reactions, and requires a temperature higher than 300 DegC to be completed. The effect of applied tension on the stabilized fiber properties are investigated, and it is found that higher tension leads to better properties for the stabilized fiber, including higher Young's modulus, higher orientation, less formation of β-amino nitrile, and less shrinkage. The relationship between stabilization conditions and the mechanical properties of the carbonized fiber is investigated, and the methods to identify optimum stabilization conditions are proposed. It is observed that the highest tension should be applied during both stabilization and carbonization, and the mechanical properties of the resulting carbon fibers are increased if fibers are further stabilized at a temperature of ~ 320 DegC to improve the cross-linking degree as compared with the fibers only stabilized at 255 DegC. The optimum stabilization time depends on both the stabilization temperature and on the applied tension. A new characterization method by monitoring the dynamic mechanical properties, while stabilization is in progress is used to narrow down the range of the optimum stabilization time. Also, the effect of carbonization temperature on the ultimate carbon fiber properties is studied in the batch process carbonization. Preliminary studies are carried out to find the relationship between the structure and properties of precursor fibers and the tensile strength of carbon fibers, including mechanical properties and co-monomers of precursor fibers.