• Carbon letters
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• v.17 no.1
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• pp.11-17
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• 2016

Recently, with continuous developments in the field of materials science, graphene oxide (GO) has emerged as a promising material with excellent electrical, thermal, mechanical, and optical properties, which play important roles in most fields. Researchers have achieved considerable progress with graphene. Chitosan (CS) is a natural polymer that has been studied intensively owing to its specific formation, high chemical resistance, and excellent physical properties. These outstanding properties have led to its universal use in applications such as textile fabrics, tissue engineering, medicine and health, coatings, and paints. By combining the advantages of GO and CS, different types of promising materials can be obtained. This review discusses the preparation of GO-CS fibers, hydrogel and aerogel, and the applications of GO-CS nanocomposites. In addition, directions for future research on graphene material composites are discussed.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.216-216
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• 2006

A special group of polymers, those from renewable resources, has attracted an increasing amount of attention over the last two decades, due to two major reasons: environmental concerns and the limitations of our finite petroleum resources. Generally, polymers from renewable resources (PFRR) can be classified into three groups: (1) natural polymers, such as starch, protein and cellulose; (2) synthetic polymers from natural monomers, such as polylactic acid (PLA); and (3) polymers from microbial fermentation, such as polyhydroxybutyrate (PHB). Like many other petroleum based polymers, various properties of PFRR are also vastly improved through blending and composites formation.

• Advances in aircraft and spacecraft science
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• v.6 no.2
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• pp.87-103
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• 2019

Recently, natural fibre composites are widely used in aerospace industries due to their good specific mechanical properties, better acoustic properties, light weight, readily availability, biodegradability, recyclability, etc. In this study, the hemp fibre woven fabrics / polypropylene based honeycomb sandwich structure were proposed for aerospace applications. Firstly, the hemp fibre woven fabrics based honeycomb sandwich structures were manufactured and experimental mechanical tests (compressive and flexural) were performed in the laboratory. Numerical simulation was also performed and analysed to validate the proposed methodology. Different complex shaped aircraft part CAD models were created and numerical analysis was carried out in order to have a better understanding about the complex honeycomb sandwich structures.

• Elastomers and Composites
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• v.46 no.3
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• pp.223-230
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• 2011

Considering of utilizing renewable resources and recycled plastics, green composites consisted of recycled polyethylene (PE) as matrix and eco-friendly natural fibers as reinforcement were processed and characterized in the present study. First, the wood flour/recycled polyethylene pellets with different wood flour contents were prepared by twin-screw extrusion processing. Using the pellets, wood flour/recycled polyethylene green composites were fabricated and the effects of wood flour loading on their flexural, tensile, impact properties, heat deflection temperature and fracture behavior were investigated. It was concluded that the flexural strength, flexural modulus, tensile modulus and heat deflection temperature of wood flour/recycled polyethylene green composites were increased with wood flour, whereas the tensile strength and impact strength were decreased. The fracture behavior observed by means of scanning electron microscopy supported qualitatively the tendency of the impact strength with wood flour loading, compared with the ductile fracture pattern of recycled polyethylene.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.123-131
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• 1995

Natural convection in bridgman growth and it's effect on macrosegregation in unidirectionally solidified off-eutectic alloys were examined in this study. AlCu off-eutectic alloys(27.5wt% ~35. 6wt% ) were solidified upward or downward for producing a different natural convection and then Cu concentrations of off-eutectic composites were measured as a function of solidified fraction. Solutal and temperature distributions ahead of the solid/liquid interface were measured on quenched specimen. When hypo-utectic AlCu alloys are directionally solidified with downward growth, considerable macrosegregation occurs due to flow induced by thermal and solutal convection in melt. Soultal convection affects the macrosegregation of hyper-eutectic AlCu alloys more severely than thermal convection. Solute composition at solid/liquid interface of offkutectic composites was eutectic and also temperature was near eutectic point without large undercooling.

• Korean Journal of Ecology and Environment
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• v.46 no.2
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• pp.225-233
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• 2013

We examined the effect of different field temperatures on water quality improvement (WQI) of natural domestic plant-mineral composites (PMCs). This method was previously used by Kim et al. (2011), to monitor the restoration of water quality of a eutrophic lake, Lake Shingal (Korea). Results indicate that PMCs on phytoplankton, BOD and phosphorus showed more than 70% WQI below $20^{\circ}C$, and less than 40% WQI over $25^{\circ}C$, respectively. The WQIs of PMCs on blue-green algae were gradually decreased with the increase of temperature, whilst diatoms exhibited more than 90% higher WQIs, regardless of water temperature. Additionally, the WQIs on bacterial biomass and total nitrogen were low at all temperatures. These results collectively indicate that water quality improvement activity of plant-mineral composites was dependent on the water temperature, and that the field application of above chemical during temperatures over $25^{\circ}C$, would be less effective in treating a cyanobacteria bloom dominated by Microcystis aeruginosa, than by diatoms.

• Advances in aircraft and spacecraft science
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• v.9 no.3
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• pp.169-193
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• 2022

By the present paper, both experimental and analytical models have been proposed to study the vibration behavior of partially bio-sourced sandwich panel with orthogonally stiffened core. For a variable mass fraction of Alfa fibers from 5% to 15%, impregnated in a Medapoxy STR resin, this panel were manufactured by molding the orthogonally stiffened core then attached it with both skins. Using simply supported boundary conditions, a free vibration test was carried out using an impact hammer for predicting the natural frequencies, the mode shapes and the damping coefficient versus the fibers content. In addition, an analytical model based on the Higher order Shear Deformation Theory (HSDT) was developed to predict natural frequencies and the mode shapes according to Navier's solution. From the experimental test, we have found that the frequency increases with the increase in the mass fraction of the fibers until 10%. Beyond this fraction, the frequencies give relatively lower values. For the analytical model, variation of the natural frequencies increased considerably with side-to-thickness ratio (a/H) and equivalent thickness of the core to thickness of the face (h_s/h). We concluded that, the vibration behavior was significantly influenced by geometrical and mechanical properties of the partially bio-sourced sandwich panel.

• Composites Research
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• v.27 no.1
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• pp.19-24
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• 2014

In this study, an investigation on mechanical properties of flax/vinyl ester natural fiber composite was performed as a precedent study on the design of eco-friendly structure using flax/vinyl ester composite. Vacuum Assisted Resin Transfer Molding(VARTM) manufacturing method was adopted for manufacturing the flax fiber composite specimen. The mechanical properties of the manufactured flax composites were compared with flax composite data cited from some references. Based on this, the experimental data showed that the flax/vinyl ester composite has some advantages when it is applied to environment-friendly structure.

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.394-399
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• 1999

As the prosthetic application of natural mineral substituted for chemical reagent, composites and a glass-ceramics containing hydro-xyapatite isolated from tuna bone were prepared by solid state reaction. On x-ray examinations, the major phases of composites were identified as pseudowollastonite(${\alpha}-CaSiO_3$) and ${\beta}$-tricalcium phosphate($\beta$-TCP) and the phase of a glass-ceramics was observed as $\beta$-TCP and fluoroapatite caused by $CaF_2$ respectively. SEM images depict that the microstructures of grain at the composites were a function of temperature. The measured strength of a glass-ceramics prepared at $900^{\circ}C$ for 4 hr in air was 90 MPa as a 4-point bending method and this value was similar to the cortical bone, as 50~150 MPa but it was lower than its maximum strength.

• The Journal of Natural Sciences
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• v.8 no.1
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• pp.53-59
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• 1995

Effects of sintering additives and sintering temperatures on the sintering behavior and mechanical properties of SiC whisker reinforced alumina composites have been investigated in this study. Dense (>95% TD) composites were obtained by using 2 wt% $Y_2O_3$ as liquid phase sintering additive. But only porous composite could be obtained when the sintering additives were MgO and $TiO_2$, which were known as the sintering additives for solid state sintering of alumina. Bending strength and fracture toughness were enhanced by reinforcement of SiC whisker. It is belived from the microstructure investigation that the enhanced by strength and toughness could be attribute to the reinforcing and grain growth inhibition effects of SiC whisker. After HIP treatment, fully dense composites were obtained and further enhanced mechanical properties achieved.