Pyeong-Su Shin

Mechanical and electrical properties of electrospun CNT/PVDF nanofiber for micro-actuator applications

Electrospun polyvinylidene fluoride (PVDF)-containing carbon nanotubes (CNT) were prepared for use in fabricating actuator materials. Actuating displacement was measured in an electrochemical environment. The electrospun nanofibers were arranged using a drum-type collector, and morphology was investigated using a field emission-scanning electron microscope. The uniformity of dispersion of CNT in the PVDF nanofibers was monitored by electron probe X-ray micro-analysis. Tensile strength and electrical resistivity results were used as an indication of the state of alignment. The electrospun CNT/PVDF nanofiber sheets exhibited better mechanical and electrical properties in the arranged direction. The efficiency and electrical capacities of electrospun CNT/PVDF nanofiber sheet were compared with those of cast PVDF sheets for use in actuator applications in electrochemical environments. The electrospun CNT/PVDF nanofiber sheets exhibited much better actuator performance than PVDF sheets, which are attributed to their superior electrical properties. Highlights (1) The interfacial durability of CNT/PVDF nanofibers was enhanced to increase contact area by reinforcing CNT. (2) The efficiency of CNT/PVDF actuators was improved due to interfacial properties. (3) Thin thickness drum-type collector was made to enhance nanofiber alignment. (4) The arranged CNT/PVDF nanofibers exhibited better mechanical and actuating displacements.

To improve interfacial and mechanical properties of carbon fiber–modified nano-SiC–epoxy composites using dispersion and wetting control

Significant improvements in mechanical properties (particularly stiffness) result from the appropriate addition of micro-carbon fibers in the nano and heterostructures of modified nano-SiC-filled epoxy matrix composites. The optimum dispersion conditions were found to be significantly dependent upon both the amount of nano-SiC filler and the sonication time. To investigate these dispersion effects, composites were fabricated with five different nano-SiC filler concentrations and compared to the untreated composite. Changes in electrical capacitance were used as a measure of the comparative degree of dispersion in these nano-SiC–epoxy composites. FE-SEM was used to observe the interfacial changes for the different surface conditions, and the mechanical damage was evaluated by inspection of fractured surfaces. Optimal conditions of dispersion, interfacial adhesion, and aspect ratio of the modified nano-SiC fillers were found to improve the composites’ mechanical properties.

Improvement in mechanical properties of recycled GF prepreg with CNT reinforced composites using a spray coating method

Dispersion and shape of nanoparticles, as well as interfacial conditions, add significantly to difficulties in composite manufacture. In the work reported here, an innovative method of recycling composites using out-of-date prepreg was investigated in which the carbon nanotube (CNT) on the prepreg was optimally coated. Nanocomposites utilizing the out-of-date prepreg were coated with CNT and fabricated by a sheet molding method. CNT nanofillers were observed to be uniformly dispersed on epoxy prepreg by spray coating. The mechanical and interfacial properties of these CNT coated nanocomposites were improved over those of more conventionally manufactured carbon fiber/epoxy composites. The CNT nanofillers were embedded at the epoxy and fiber interface, as a result of etching of the epoxy prepreg surface by a CNT dispersion solution which enhanced interfacial reactivity.

Evaluation of optimal dispersion conditions for CNT reinforced epoxy composites using cyclic voltammetry measurements

The optimum dispersion time of nanoparticles is important for obtaining uniform dispersion of fillers or other additives in a matrix. In this study, the optimal dispersion time of carbon nanotube (CNT) in a matrix was investigated using cyclic voltammetry (CV), measurement for different dispersion methods and times. In addition, the mechanical properties of CNT composites manufactured using different dispersion methods were evaluated by tensile and flexural tests. The CV and mechanical test results were correlated to the dispersion condition of CNT in the composites. It was found that tip-type sonication resulted in better dispersion than bath-type sonication. Improved CNT dispersion resulted in composites with both enhanced CV measurements and improved mechanical properties. In the study reported here, improvements in dispersion were generally accompanied by higher electrical currents. This suggests that the CV measurement method is an effective tool for determining optimal dispersion times, for different CNT dispersion processes.

Investigation of Interfacial and Mechanical Properties of Various Thermally-Recycled Carbon Fibers/Recycled PET Composites

The mechanical and interfacial properties were evaluated for carbon fiber reinforced composites (CFRC) manufactured using thermally recycled waste carbon fiber and recycled polyethylene terephthalate (PET). The mechanical properties of the recycled fiber were determined and compared to those of neat fibers using the single-fiber tensile test. The surfaces of the recycled and neat carbon fiber were examined and compared using FE-SEM and dynamic contact angle measurements. A goal of the study was to determine the applicability of industrial use of recycled CF and/or recycled PET in CFRC. Mechanical properties were measured using short beam and tensile tests. These properties were observed to be correlated with crystallinity. The interfacial properties between the recycled carbon fibers and recycled PET were evaluated using the microdroplet test. At low temperature residual resin remained on the recycled CFs surface resulting relatively the low interfacial properties. At excessively high temperatures, oxidation occurred, on the CFs surface, which also resulting in relatively poor low mechanical properties. The optimal treatment condition was 500 °C, where the surface was relatively clean and the reduction in mechanical properties was minimized.

Evaluation of Interfacial and Mechanical Properties of Glass Fiber/Poly-Dicyclopentadiene Composites with Different Post Curing at Ambient and Low Temperatures

Recently new poly-dicyclopentadiene (p-DCPD) has increasing been used for composites in military, aerospace, and transportation applications due to its favorable impact properties. In this work, the cross-linking density of p-DCPD with different post curing conditions was indirectly measured by thermal analysis using differential scanning calorimetry (DSC), weight variation accompanying swelling and density. The effects of the post curing conditions on mechanical properties of p-DCPD and glass fiber (GF)/p-DCPD were determined via tensile, Izod impact, and flexural tests at ambient and low temperatures (-20 °C). Interfacial properties were evaluated by fragmentation and cyclic loading tests. The work of adhesion was determined via Static contact angle using four solvents measurements, to provide the information on the differences in the interfacial properties between GF and p-DCPD. The change of cross-linking density by post curing of p-DCPD affected the mechanical and interfacial properties of GF/p-DCPD composites.

New sensing method of dispersion and damage detection of carbon fiber/polypropylene-polyamide composites via two-dimensional electrical resistance mapping

Evaluation of sensing for electrical conductive composites has been implemented using electrical conductive nano materials such as graphene, CNT and carbon fiber. Electrical resistance (ER) measurement for nondestructive evaluation (NDE) was developed using self-sensing composites because method of damage sensing and crack prediction of composites under external load is possible to use at aerospace, heavy industry, and automobile. In this research, diverse damage sensing from mechanical impact and thermal aging for electrical conductive composites was investigated by using ER method. To have the test, electrical conductive materials such as graphene, CNT and carbon fiber and matrixes such as epoxy and vinyl ester were used for damage sensing and finding optimum materials for improving the bonding force. Two and three dimensional ER mapping was used to sense and predict damages from tensile, compressive, impact and drilling force. The differences in ER from different force were compared to explore their usage for real time monitoring and sensing of damages. Enhance optimum materials and conditions from diverse force were confirmed by ER method.