Enhanced thermal and mechanical properties of epoxy composites at ultra-low loading of functionalized MoS2 nanosheets

Shahina Riaz,Kyong Y. Rhee,Soo Jin Park 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.41 No.4

In this study, single-step branched polyethyleneimine (PEI)-assisted exfoliation of molybdenum sulfide nanosheets (MoS2-PEI) was carried out. These functionalized MoS2-PEI nanosheets were employed as toughening agents for epoxy composites. The loadings of nanosheets were kept lower than 1 wt.%. The mechanical and thermal properties, and interfacial interactions of epoxy composites were investigated. The epoxy composites have shown ~67% and ~101% enhancements in fracture toughness (KIC) in fracture energy (GIC), respectively, at nanosheets loadings as small as 0.09 wt.% (EP/MoS2-PEI-0.09), KIC has shown a direct linear relationship with the surface free energy and is highest at 52 mJ.m−2 for the EP/MoS2-PEI-0.09 composite. However, the surface free energy values of EP/MoS2-PEI-0.16 and EP/MoS2-PEI-1 composites decreased to 48 mJ.m-2 and 45 mJ.m−2. The overall flexural modulus (E) and strength (σ) were not highly responsive to the addition of the MoS2-PEI nanosheets. Furthermore, the thermal stability and thermomechanical properties of the epoxy composites improved significantly. The optimum MoS2-PEI nanosheet loading was observed to be 0.09 wt.%, beyond this a gradual decrease in thermal stability and mechanical properties was observed. The significant improvement in thermal and mechanical properties of the epoxy composites could be accredited to the good interfacial interaction between the MoS2-PEI nanosheets and epoxy matrix at the interface and the inherent strength, high aspect ratio, and excellent barrier effect of PEI molecules.

Hierarchical structures of CNT@basalt fabric for tribological and electrical applications: Impact of growth temperature and time during synthesis

Mittal, Garima,Rhee, Kyong Y. Elsevier 2018 Composites. Part A, Applied science and manufactur Vol.115 No.-

<P><B>Abstract</B></P> <P>Hierarchical structures are continuously drawing the attention of researchers to replace traditional polymeric structures. Here, hierarchical structures of basalt fabric coated with CNTs (BF-CNTs) were prepared using chemical vapor deposition (CVD). To understand the effects of growth temperature and growth time during chemical vapor deposition on grafting of CNTs on basalt fabric, two cases were considered i.e., grafting at 600, 650, and 700 °C for 30 min and at 650 °C for 30, 60, and 120 min. BF-CNTs were characterized using XRD, HR-Raman, FE-SEM, and DSC. Further, BF-CNTs were sandwiched with epoxy via a hand lay-up method and their effects on the tribological and electrical properties of epoxy composites were analyzed. The results show the composites with BF-CNT prepared at higher growth temperature and for longer time possessed a lower coefficient of friction (CoF), lower wear loss, lower volume resistivity, and improved electromagnetic interference shielding effectiveness (EMI SE).</P>

Reinforcements in multi-scale polymer composites: Processing, properties, and applications

Mittal, Garima,Rhee, Kyong Y.,Miš,ković,-Stanković,, Vesna,Hui, David Elsevier 2018 Composites Part B, Engineering Vol.138 No.-

<P><B>Abstract</B></P> <P>Smart and novel materials require the replacement of conventional composites with superior ones, which requires an advanced class of composites with multi-functionality. Multi-scale composites are advanced composites that are reinforced with nanoscale materials along with macroscale fibers, and these materials have attracted the attention of researchers as well as various industries. Multi-scale composites have potential applications in almost every field due to their remarkable features like extraordinary mechanical, electrical, and optical properties; extremely high aspect ratios of the nanomaterial constituents; and the uniformity, flexibility, and stability of the fibers. To optimize the performance of these kinds of composites, it is crucial to understand the selection of appropriate reinforcements, processing, and utilization of these advanced materials. Most reviews in this area concentrate only on CNTs, while this review considers other nanomaterials too. Additionally, various methods to improve the dispersion of nanomaterials into the matrix are also discussed. Overall, this article focuses on the components of multi-scale composites, key challenges related to their processing, and the multi-functionality of designed multi-scale composites.</P>

Chemical vapor deposition-based grafting of CNTs onto basalt fabric and their reinforcement in epoxy-based composites

Mittal, Garima,Rhee, Kyong Y. Elsevier 2018 Composites science and technology Vol.165 No.-

<P><B>Abstract</B></P> <P>Basalt fiber (BF) is considered to be a green industrial material, exhibiting outstanding environmental stability along with superior mechanical properties compared to E-type glass fiber. It is also less expensive than carbon fiber, making make it perfect for the mass-production of basalt fiber-reinforced polymer (BFRPs) composites. BFRPs are reinforced with nanomaterials to further enhance their performance. However, nanomaterials have the tendency to agglomerate because of their high surface energy, which hinders their efficient dispersion into the matrix. Hence, in this study, we grafted CNTs onto basalt fabric using chemical vapor deposition (CVD). Furthermore, CNT-grafted basalt fabric (BF-CNT) was sandwiched with epoxy via a hand lay-up technique. XRD, HR-RAMAN, FE-SEM, and thermogravimetric analysis (TGA) were performed to characterize BF-CNT. The properties of the fabricated BF-CNT/epoxy composites were also analyzed and compared with CNT-reinforced BF/epoxy composites. Based on our results, we found that the BF-CNT/epoxy composite shows improved properties.</P>

Effects of oil absorption on the wear behaviors of carbon/epoxy woven composites

Jae-H. Lee,Jae-S. Lee,Kyong-Y. Rhee 한국탄소학회 2011 Carbon Letters Vol.12 No.4

Carbon/epoxy woven composites are prominent wear-resistant materials due to the strength, stiffness, and thermal conductivity of carbon fabric. In this study, the effect of oilabsorption on the wear behaviors of carbon/epoxy woven composites was investigated. Wear tests were performed on dry and fully oil-absorbed carbon/epoxy woven composites. The worn surfaces of the test specimens were examined via scanning electron microscopy to investigate the wear mechanisms of oil-absorbed carbon/epoxy woven composites. It was found that the oil absorption rate was 0.14% when the carbon/epoxy woven composites were fully saturated. In addition, the wear properties of the carbon/epoxy woven composites were found to be affected by oilabsorption. Specifically, the friction coefficients of dry and oil-absorbed carbon/epoxy woven composites were 0.25-0.30 and 0.55-0.6, respectively. The wear loss of the oilabsorbed carbon/epoxy woven composites was 3.52×10-2 cm3, while that of the dry carbon/epoxy woven composites was 3.52×10-2 cm3. SEM results revealed that the higher friction coefficient and wear loss of the oil-absorbed carbon/epoxy woven composites can be attributed to the existence of broken and randomly dispersed fibers due to the weak adhesion forces between the carbon fibers and the epoxy matrix.

Analysis of Longitudinal Strains of Cross-ply Composite Laminates using A-EFPI Optical Fiber Sensor

Woo, Sung-Choong,Choi, Nak-Sam,Kwon, Il-Bum,Rhee, Kyong Y. Sage Publications 2007 Journal of composite materials Vol.41 No.7

<P>The longitudinal strains (U03B5;<SUB>x</SUB>) of the core and the skin layers in glass fiber reinforced plastic (GFRP) cross-ply composite laminates are analyzed using embedded optical fiber sensors (OFSs) of absolute extrinsic FabryU2014;Perot interferometer (A-EFPI). Foil-type strain gages (SGs) bonded on both upper and lower surfaces of a specimen are employed for comparison of the strain measurement on the surface. It has been shown that the values of U03B5;<SUB>x</SUB> in the interior of the skin layer and the core layer measured by embedded A-EFPI sensor are lower than those of the specimen surface measured by SGs. Experimental results agree well with those from finite element analysis based on a shear lag model. Optical microscopy observation of the damage behavior around the fiber sensor by the thin-sectioning technique shows that reinforcing glass fibers protect the OFS embedded in the 0<SUP> U00B0;</SUP> skin layer, whereas the formation of transverse cracks in the 90<SUP> U00B0;</SUP> core layer substantially reduces strains at the failure of OFS embedded in the core layer.</P>