Carbon fibers boast excellent mechanical properties, but widespread adoption into everyday composite materials is limited by their high cost. Polyethylene seems like an ideal low-cost precursor based on its high carbon content, low cost, and melt-processability, but as a saturated hydrocarbon it is functionally far removed from the graphitic structure. Here, we report that after crosslinking, the oxidation of polyethylene can be performed in a controlled manner to provide significant yields of oxidized black solid that resembles its original shape and can be subsequently heated under inert atmosphere to yield a carbonaceous solid in 10–30% carbon yield. When oxidation is conducted in the presence of ammonia, nascent carboxylic acids en route to CO2 evolution are intercepted to provide up to 70% carbon yield. This ammoxidation process was characterized by solid-state nuclear magnetic resonance, infrared spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy to contain various nitrogen containing functional groups, including amides, lactams, imides, and pyridines. The resulting carbonaceous structures were characterized by Raman spectroscopy, elemental analysis, high resolution transmission electron microscope and selected area electron diffraction to be consistent with a highly disordered wavy lattice carbon structure.

Chemical reactions on the surface or throughout a thermoplastic fiber present an interesting and challenging reaction engineering problem. This paper presents the design and implementation of a modular multiphase continuous stirred tank reactor for the sulfonation of polyethylene fibers. Polyethylene fiber tows, composed of 1000-6000 filaments, are sulfonated in a series of stirred tank reactors. Fundamental reaction engineering principles are applied to address common batch-to-continuous reactor challenges, such as heat and mass transfer, material balances, and reaction kinetics. The introduction of polymer fibers to a continuous process also requires the solution of practical problems associated with fiber processing. Additional considerations are introduced for designing a reactor system for continuous processing of fiber using liquid with a batch reactor or CSTR contacting pattern in each vessel and containing the effluent gaseous reaction byproducts in a controlled vent stream. The overall sulfonation reaction stoichiometry was determined such that approximate to 1 mol of SO3 reacts per mol of CH2 fed. Additionally, carbon sulfonation selectivity was determined to be 95-99%, depending on the sulfonation conditions.

A practical and user-friendly strategy for the chain-end reduction of halogen terminated polymers that employs hydrogen gas and heterogeneous catalysis (palladium on carbon) is reported. Quantitative dehalogenation of a wide variety of monomer families (polystyrenes, polyacrylates, and polymethacrylates) with either chlorine or bromine chain-ends is observed. The utility of this chain-end reduction is further highlighted by mild reaction conditions, simple purification, and compatibility with a wide range of solvents.

In this work, the crosslinking of various thin polyethylene films via electron beam exposure in an inert environment was studied. Increasing Melt Flow Index and polymer density both decreased the insoluble gel fraction resulting from irradiation at a dosage of 800 kGy. The effect of adding low levels of two different polyfunctional monomers was also examined. Trimethylolpropane triacrylate (TMPTA) was found to decrease the dosage necessary to initiate gel formation, and gave higher gel fractions at lower dosages, but showed little effect at higher dosages. A low molecular weight polybutadiene (PBd) resin showed little effect on gel fraction as compared to the neat resin controls.

Currently, carbon fibers (CFs) from the solution spinning, air oxidation, and carbonization of polyacrylonitrile impose a lower price limit of ≈$10 per lb, limiting the growth in industrial and automotive markets. Polyethylene is a promising precursor to enable a high-volume industrial grade CF as it is low cost, melt spinnable and has high carbon content. However, sulfonated polyethylene (SPE)-derived CFs have thus far fallen short of the 200 GPa tensile modulus threshold for industrial applicability. Here, a graphitization process is presented catalyzed by the addition of boron that produces carbon fiber with >400 GPa tensile modulus at 2400 °C. Wide angle X-ray diffraction collected during carbonization reveals that the presence of boron reduces the onset of graphitization by nearly 400 °C, beginning around 1200 °C. The B-doped SPE-CFs herein attain 200 GPa tensile modulus and 2.4 GPa tensile strength at the practical carbonization temperature of 1800 °C.

Sulfur trioxide (SO3) is a highly reactive oxidant, and its reactions with polyethylene fibers in chlorinated solvents can be used to functionalize and stabilize the polyethylene fibers for subsequent carbonization to produce carbon fiber. In this study, the apparent reaction kinetics between SO3 and polyethylene were investigated in various halogenated solvents using in situ Raman spectroscopy with an immersion Raman probe. This work demonstrates the power of in situ Raman spectroscopy to monitor hazardous reactions, and the results show that both solvent and polyethylene properties have a large influence on the reaction kinetics.

The design, synthesis, and characterization of solution-processable polymers for organic light emitting diode (OLED) applications are presented. Theoretical calculations were employed to identify a carbazole-pyrimidine based building block as an optimized host material for the emissive layer of an idealized OLED stack. Efficient, free radical homopolymerization and copolymerization with a novel methacrylate-based heteroleptic iridium(III) complex leads to a library of nonconjugated polymers with pendant semiconductors. Optoelectronic characterization reveals impressive photoluminescence quantum yield (PLQY) values exceeding 80% and single-layer OLEDs show optimal performance for copolymers containing 6 mol % of iridium comonomer dopant.

This paper presents a structure-property model for carbon fiber derived from a polyethylene (PE) precursor that relates tensile modulus to the elastic properties and angular distribution of constituent graphitic layers, as measured using wide-angle x-ray diffraction of individual carbon fiber filaments. The observed relationship and interpretation of data using a uniform-stress model has revealed fundamental differences in the nature of the microstructure present in carbon fiber produced from polyethylene compared to carbon fiber produced from polyacrylonitrile (PAN) or pitch precursors. Specifically, it was found that the shear modulus, indicative of the shear between adjacent graphitic layers of the carbonized fiber is lower for polyethylene-derived carbon fiber than for PAN- or pitch-derived carbon fiber, suggesting that the covalent CC sp3 crosslink density connecting adjacent graphitic layers in PE-derived carbon fiber is reduced. This structure that is less crosslinked is anticipated to be easier to orient during carbonization and high-temperature graphitization processes, yielding a highly oriented structure necessary for high tensile modulus.

A new high-temperature fibre tensile cell is described, developed for use at the Advanced Photon Source at Argonne National Laboratory to enable the investigation of the carbonization and graphitization processes during carbon fibre production. This cell is used to heat precursor fibre bundles to temperatures up to ∼2300°C in a controlled inert atmosphere, while applying tensile stress to facilitate formation of highly oriented graphitic microstructure; evolution of the microstructure as a function of temperature and time during the carbonization and higher-temperature graphitization processes can then be monitored by collecting real-time wide-angle X-ray diffraction (WAXD) patterns. As an example, the carbonization and graphitization behaviour of an oxidized polyacrylonitrile fibre was studied up to a temperature of ∼1750°C. Real-time WAXD revealed the gradual increase in microstructure alignment with the fibre axis with increasing temperature over the temperature range 600-1100°C. Above 1100°C, no further changes in orientation were observed. The overall magnitude of change increased with increasing applied tensile stress during carbonization. As a second example, the high-temperature graphitizability of PAN- and pitch-derived commercial carbon fibres was studied. Here, the magnitude of graphitic microstructure evolution of the pitch-derived fibre far exceeded that of the PAN-derived fibres at temperatures up to ∼2300°C, indicating its facile graphitizability.

This paper will discuss the structure-property model developed that correlates the tensile modulus to the elastic properties and angular distribution of constituent graphitic layers for carbon fiber derived from a polyethylene precursor. In addition, a high-temperature fiber tensile device was built to enable heating of carbon fiber bundles at a variable rate from 25 °C to greater than ∼2300 °C, while simultaneously applying a tensile stress. This capability combined with synchrotron wide-angle x-ray diffraction (WAXD), enabled observation in situ and in real time of the microstructural transformation from different carbon fiber precursors to high-modulus carbon fiber. Experiments conducted using PAN- and PE-derived fiber precursors reveal stark differences in their carbonization and high-temperature graphitization behavior.

To develop low-cost carbon fiber, The Dow Chemical Company and others have explored the sulfonation of polyethylene fibers as an alternative to the incumbent poly(acrylonitrile) route. Although the process of polyethylene sulfonation and subsequent thermal carbonization in an inert atmosphere has been known to provide carbonaceous material for over 35years, we have found the chemical understanding of this transformation to be insufficient. Herein, we report a series of studies that have led to our current understanding for both the sulfonation and subsequent thermal treatment steps. Sulfonation of hydrocarbon model compounds yields completely conjugated and functionalized products. Spectroscopic data suggest that sulfonated polyethylene is similar; containing extended conjugated systems with sulfonic acids and various other oxygen-containing functional groups. Near-Edge X-ray Absorption Fine Structure data have identified that between 150 and 200°C the polymer undergoes a cross-linking step, while evolved gas analysis has identified concomitant release of SO2 and H2O. Above 600°C, H2 is produced and a graphenic carbon microstructure is obtained.

L'invention concerne des procedes pour preparer des polymeres carbones, tels que des fibres de carbone, consistant a sulfoner un polymere au moyen d'un agent de sulfonation qui renferme un gaz SO 3 afin de former un polymere sulfone ; a traiter le polymere sulfone au moyen d'un solvant chauffe, la temperature du solvant etant d'au moins 95 °C ; et a carboniser le produit resultant en le chauffant a une temperature comprise entre 500 et 3000 °C.