Cellulose fibers are attracting considerable attention within the transportation industry as a class of reinforcing agents for polymer composites owing to their low cost, low density, high mechanical properties, and considerable environmental benefits. The objective of this study was to develop hybrid composites combining cellulose fiber with long glass fiber (LGF), short glass fiber (SGF), or talc in a polypropylene (PP) matrix to optimize the overall composite properties. Tensile, flexural, and notched Izod impact tests revealed that in general the mechanical properties decreased with increasing cellulose content, however, adding an optimum concentration of the cellulose fiber is a promising alternative to reduce or replace the utilization of inorganic fibers. Hybrid composites with 15 wt% LGF and 15 wt% Cellulose A exhibited an increase of 86% and 252% in tensile stress and Young's modulus, respectively, compared to neat PP X. Regarding the impact strength and the temperature at the maximum rate of decomposition, hybrid composites with 15 wt% SGF and 15 wt% Cellulose B exhibited 23% and 17% increase, respectively, compared to neat PP Z. The crystallization temperature (Tc) of all the composites increased compared to neat PP, revealing the fibers ability to act as nucleating agents and speed rate of part production which will result in lowering the manufacturing cost. For applications in automotive “under‐the‐hood” and body interior components, the hybrid cellulose‐inorganic reinforcement composite approach not only leads to superior weight and cost savings, but also environment benefits over the inorganic reinforced composites.
Bamboo fibers (BFs) have high mechanical properties and are candidate reinforcement for epoxy matrix composites. However, to improve performance, good fiber‐matrix interaction is required. In this work, unidirectional long BF reinforced epoxy composites at fiber volume content of 22%, 40%, and 50% were made by compression molding. The 40 v% untreated BF reinforced composites exhibited 107% and 439% increase for flexural strength and modulus, respectively, compared to neat epoxy. Sodium hydroxide (NaOH) treatment was used to modify the surface of the BFs, and then the NaOH modified BFs were coated with graphene oxide (GO). The 40 v% NaOH modified BF composites showed an improvement from 259.9 to 327.5 MPa for flexural strength and from 16.7 to 21.5 GPa for flexural modulus, compared to 40 v% untreated BF composites. Slight improvement in properties up to 334.6 MPa for flexural strength and up to 23.8 GPa for flexural modulus was achieved for composites made of 40 v% NaOH/GO modified BF. Surface modification of BF after the NaOH and NaOH/GO treatment was confirmed by X‐ray photoelectron spectroscopy and by scanning electron microscopy, which showed differences on the fiber surface morphology and on the composite fracture surface. This BF surface modification approach with GO has potential to impart other properties beyond mechanical to produce multifunctional composite and lead to the use of sustainable plant fibers as alternatives to synthetic fibers.
Electrochemical energy storage (EES) and conversion devices (e.g. batteries, supercapacitors, and reactors) are emerging as primary methods for global efforts to shift energy dependence from limited fossil fuels towards sustainable and renewable resources. These electric-based devices, while showing great potential for meeting some key metrics set by conventional technologies, still face significant limitations. For example, an EES device tends to exhibit large energy density (e.g. lithium-ion battery) or power density (e.g. supercapacitor), but not both. This inability of a single device to simultaneously achieve both metrics represents a major obstacle to widespread adoption of EES devices. Improvements in materials, such as the integration of 2D materials (e.g. graphene, dichalcogenides, MXene, etc.) into electrochemical devices has yielded some exciting results towards tackling this issue, but significant improvements are still needed. Our approach to simultaneously achieving high energy and power density is to focus on one of the fundamental processes that occur in these systems: mass (or charge) transport. The efficient transport of ions within EES devices is critical to realizing both large power and energy densities. The pore structure of the electrode is a key factor in determining this transport phenomena, but in many cases, engineering the pore structure in a highly deterministic fashion is not pursued or even possible for many electrode materials. In this work, we explore a number of additive manufacturing methods (e.g. direct ink write, projection microstereolithography, etc.) to engineer the pore structure of device electrodes. We also determine effective electrode geometries using both simple theory and topology optimization techniques. The topology optimization couples the solution of the forward electrochemical problem over the full electrode domain with gradient-based optimization. The output of our code is a three-dimensional CAD representation which optimizes over specific performance metrics and which can be used to print functional electrodes. This work provides a systematic path toward automatic design and fabrication of engineered electrodes with precise control over the fluid and species distribution.
Electrochemical energy storage devices, such as supercapacitors, are essential contributors to the implementation of sustainable energy. Supercapacitors exhibit fast charging/discharging ability and have attracted considerable attention within the automotive, aerospace, and telecommunication industries. Although these devices show great potential to meet power density metrics, they lack in terms of their energy density. To overcome this challenge, we are investigating better materials, architectures, and additive manufacturing techniques to print electrodes that increase the energy density while maintaining their high-power densities. Topology optimization was used to design an electrode with optimum performance. These electrodes were printed by projection micro stereolithography (PµSL) using PR48, a commercially available polymer resin. The printed electrodes were converted to carbon electrodes through pyrolysis at 1050 ֯C and characterized by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrical impedance spectroscopy. The performance of the PR48 optimized electrodes were compared against PR48 electrodes printed as a simple cubic lattice structure previously shown to improve capacitance and rate capability. The results show that our optimized electrodes have higher areal capacitances for all the current densities tested and they perform better in GCD and CV tests. Lastly, to increase the surface area of the electrodes and increase the capacitance further, we developed a resin formulation by combining graphene oxide (GO) into TMPTA polymer. Electrodes printed with 3%GO/TMPTA have improved electrochemical performance compared to PR48 as evidenced by their higher capacitances and their better GCD and CV curves. This work demonstrates the benefits of using topology optimization to design electrodes and materials development to improve the functional properties of 3D printable resins. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC Figure 1
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