Seawater Effects on Thermally Aged Ambient Cured Carbon/Epoxy Composites: Moisture Kinetics and Uptake Characteristics.

Carbon fiber-reinforced epoxy matrix composites using ambient- and moderate-temperature curing non-autoclave processes have broad applicability in marine, offshore, and naval applications. This research focuses on the characterization of moisture kinetics of ambient cured carbon/epoxy composites subject to immersion in seawater for up to 72 weeks after prior periods of extended thermal aging. A two-stage model is shown to best describe the overall kinetics and response. The level of maximum moisture uptake shows an increasing trend with the temperature and time of prior thermal aging, reaching asymptotic levels at the highest levels. The transition point is seen to represent a shift between the diffusion and relaxation-/deterioration-based dominant regimes, and the ratio of uptake at the transition point to the maximum uptake can be correlated to the relaxation coefficient. Diffusivity, as expected, generally increases with the temperature of prior aging and shows changes based on the level of post-curing and network changes with time. Moisture uptake kinetics and characteristics developed through the sequence of exposures provide a better understanding of phenomena towards the development of a future comprehensive model capable of long-term prediction based on the sequential prior history of exposure to elevated temperatures and immersion in seawater.

Effect of Thermal Exposure on Residual Properties of Wet Layup Carbon Fiber Reinforced Epoxy Composites.

Ambient cured wet layup carbon fiber reinforced epoxy composites used extensively in the rehabilitation of infrastructure and in structural components can be exposed to elevated temperature regimes for extended periods of time of hours to a few days due to thermal excursions. These may be severe enough to cause a significant temperature rise without deep charring as through fires at a small distance and even high-temperature industrial processes. In such cases, it is critical to have information related to the post-event residual mechanical properties and damage states. In this paper, composites are subjected to a range of elevated temperatures up to 260 °C over periods of time up to 72 h. Exposure to elevated temperature regimes is noted to result in a competition between the mechanisms of post-cure that can increase the levels of mechanical characteristics, and the deterioration of the resin and the bond between the fibers and resin that can reduce them. Mechanical tests indicate that tensile and short beam shear properties are not affected negatively until the highest temperatures of exposure considered in this investigation. In contrast, all elevated temperature conditions cause deterioration in resin-dominated characteristics such as shear and flexure, emphasizing the weakness of this mode in layered composites formed from unidirectional fabric architectures due to resin deterioration. Transitions in failure modes are correlated through microscopy to damage progression both at the level of fiber-matrix interface integrity and through the bulk resin, especially at the inter-layer level. The changes in glass transition temperature determined through differential scanning calorimetry can be related to thresholds that indicate changes in the mechanisms of damage.

A Novel Strategy for Creating an Antibacterial Surface Using a Highly Efficient Electrospray-Based Method for Silica Deposition.

Adhesion of bacteria on biomedical implant surfaces is a prerequisite for biofilm formation, which may increase the chances of infection and chronic inflammation. In this study, we employed a novel electrospray-based technique to develop an antibacterial surface by efficiently depositing silica homogeneously onto polyethylene terephthalate (PET) film to achieve hydrophobic and anti-adhesive properties. We evaluated its potential application in inhibiting bacterial adhesion using both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) bacteria. These silica-deposited PET surfaces could provide hydrophobic surfaces with a water contact angle greater than 120° as well as increased surface roughness (root mean square roughness value of 82.50 ± 16.22 nm and average roughness value of 65.15 ± 15.26 nm) that could significantly reduce bacterial adhesion by approximately 66.30% and 64.09% for E. coli and S. aureus, respectively, compared with those on plain PET surfaces. Furthermore, we observed that silica-deposited PET surfaces showed no detrimental effects on cell viability in human dermal fibroblasts, as confirmed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide and live/dead assays. Taken together, such approaches that are easy to synthesize, cost effective, and efficient, and could provide innovative strategies for preventing bacterial adhesion on biomedical implant surfaces in the clinical setting.

Flexible Carbon Nanotube/Polydimethylsiloxane Composite for the De-Icing of Airplane Wings.

In the aviation industry, the process of de-icing is critical for stable flying because of the occurrence of airplane icing. To solve the icing problem, an electrical heating system is applied for airplane de-icing. Among the materials used in the electrical heating system, carbon-nanotube polymer composites are appropriate for an ice-prevention system owing to their rapid heating properties and flexibility. In this study, we fabricated a flexible carbon-nanotube/polydimethylsiloxane composite with a high content of carbon nanotube (20 wt%) for airplane de-icing. The high-load carbon nanotube composite was fabricated using a three-roll milling method, resulting in uniform dispersion of carbon nanotubes in the polymer matrix. The carbon nanotube/polydimethylsiloxane composites exhibited uniform and stable heating performance (from room temperature to 100 °C for 25 s without thermal aggregation). In addition, the carbon nanotube/polydimethylsiloxane composite is suitable for application to the curved surface of airfoils. For the de-icing experiments, a small airplane wing consisting of carbon nanotube/polydimethylsiloxane composite as a heating unit was fabricated with a scale ratio of 15:1. We conducted electrical heating and de-icing experiments using the developed airplane-wing system for actual anti-icing/de-icing applications.

Effect of Filler Alignment on Piezo-Resistive and Mechanical Properties of Carbon Nanotube Composites.

Highly aligned multi-walled carbon nanotube (MWCNT) polymer composites were fabricated via a roll-to-roll milling process; the alignment of the MWCNTs could be controlled by varying the speed of the rotating rolls. The effect of MWCNT alignment on the polymer matrix was morphologically observed and quantitatively characterized using polarized Raman spectroscopy. To provide a more detailed comparison, MWCNT composites with alignment in the transverse direction and random alignment were fabricated and tested. Enhanced mechanical and electrical properties were obtained for the aligned MWCNT composite, which can be attributed to the efficient electrical network and load transfer, respectively. In addition, a cyclic stretching test was conducted to evaluate the piezo-resistive characteristics of the aligned MWCNT composites. The composites with an aligned filler configuration showed an exceptionally high degree of strain sensitivity compared to the other composites.

Development of Multi-Functional Graphene Polymer Composites Having Electromagnetic Interference Shielding and De-Icing Properties.

We developed a multi-functional graphene composite with electromagnetic interference (EMI) shielding and de-icing properties. Two-dimensional graphene fillers were homogeneously dispersed in a polymer by three-roll milling. The electrical properties and percolation threshold of the graphene composites were measured with various graphene contents. The variation in the EMI shielding properties of the graphene composites with respect to the filler content was measured. The shielding efficiency improved with increasing graphene filler content. Furthermore, we conducted electrical heating tests on the graphene composites. The composites could be heated rapidly to 200 °C by electrical Joule heating with low electric power because of the high electrical conductivity of the composite. Moreover, the composite film was suitable for application in a de-icing unit because of its rapid and homogenous heating performance.

Adsorption of Nitrate and Phosphate on Basalt Based Nanostructured Zeolite 13X.

In this work, we prepared basalt based nanostructured zeolite 13X by alkali fusion and hydrothermal synthesis process. The sample prepared was characterized using XRD, SEM, and low-temperature nitrogen analysis. The adsorption equilibrium and kinetic characteristics of ammonia nitrogen (NH+4-N) and phosphate phosphorus (PO3-4-P) were investigated. It was found that the basalt based nanostructured zeolite 13X showed high adsorption capacities for NH+4-N (75 mg/g) and PO3-4-P (25 mg/g) under the experimental conditions used. Our results demonstrate that basalt based zeolite 13X can be a good alternative adsorbent for the simultaneously removal of NH+4-N and PO3-4-P from aqueous solution.

Synthesis of zeolitic material from basalt rock and its adsorption properties for carbon dioxide.

A zeolitic 4A type material was successfully prepared from natural basalt rock by applying an alkali fusion process and hydrothermal synthesis. In particular, the optimum synthetic conditions were examined at different crystallization times. Several methods such as XRD, SEM, EDX, and N2 and CO2 adsorption analysis were used to characterize the synthesized 4A type zeolite. In addition, CO2 adsorption equilibrium capacities for this basalt base zeolite were measured over temperature ranges from 283 to 303 K and pressure ranges from 0.1 to 1500 kPa in a volumetric adsorption apparatus. Then the results were compared to those of commercial zeolite. Moreover, to further investigate the surface energetic heterogeneity of the prepared zeolite, the isosteric heat of adsorption and adsorption energy distribution was determined. We found that basalt based zeolite 4A shows a CO2 adsorption equilibrium capacity of 5.9 mmol g-1 (at 293 K and 1500 kPa) which is much higher than the 3.6 mmol g-1 of the commercial zeolite as its micro-pore surface area, micro-pore volume and surface heterogeneity indicate.