Yan Qin

Mechanical properties and thermal conductivity of graphene nanoplatelet/epoxy composites

AbstractnNanocomposites of epoxy with 3 and 5xa0wt% graphene nanoplatelets (GnPs) were fabricated with GnP sizes of ~5 and <1xa0μm dispersed within an epoxy resin using a sonication process followed by three-roll milling. The morphology, mechanical, and thermal properties of the composites were investigated. Tensile and flexural properties measurements of these nanocomposites indicated higher modulus and strength with increasing concentration of small GnPs sizes (<1xa0μm, GnP-C750). The incorporation of larger GnPs sizes (~5xa0μm, GnP-5) significantly improved the tensile and flexural modulus but reduced the strength of the resulting composites. At 35xa0°C, the dynamic storage modulus of GnP-5/epoxy composites increased with increasing platelet concentration, and improved by 12xa0% at 3xa0wt% and 23xa0% at 5xa0wt%. The smaller GnP-C750 increased the storage modulus by 5xa0% at 3xa0wt% loading but only 2xa0% at 5xa0wt% loading. The glass transition temperatures of the composites increased with increasing platelet concentration regardless of the GnP particle size. A marked improvement in thermal conductivity was measured with the incorporation of the larger GnP size reaching 115xa0% at 5xa0wt% loading. The effects of different platelet sizes of the GnP reinforcement on the damage mechanisms of these nanocomposites were studied by scanning electron microscopy.

Size effect of graphene nanoplatelets on the morphology and mechanical behavior of glass fiber/epoxy composites

We investigated the effect of graphene nanoplatelets (GnPs) with two different lateral dimensions on the morphology, flexural, and thermo-mechanical properties of multiscale GnPs/glass fiber/epoxy composites. First, 3 and 5xa0wt% of GnP-C750 (<1xa0µm in diameter) and GnP-5 (5xa0µm in diameter) were individually integrated into epoxy suspension through a combination of calendaring and sonication processes. The GnPs/glass fiber/epoxy composites were then fabricated by incorporating glass fibers into the GnPs/epoxy mixture. Results showed that the flexural modulus of the GnPs/glass fiber/epoxy composites was improved by 11.5 and 26.3xa0% with the addition of 5xa0wt% GnP-C750 and GnP-5, respectively. At the same filler content, the storage modulus of the glass/epoxy composites incorporated with GnP-C750 and GnP-5 at 30xa0°C was enhanced by 10.2 and 28.2xa0%, respectively. The flexural strength of the 3xa0wt% GnP-5-reinforced glass fiber/epoxy composite is 16.2xa0% higher than that of the glass fiber/epoxy composite. The dispersion results of GnPs in the composites and the interfacial interactions between fibers and modified matrix were evaluated by scanning electron microscopy.

Effects of functionalized graphene nanoplatelets on the morphology and properties of epoxy resins

Graphene nanoplatelets (GnPs) were successfully functionalized with a liquid rubber, amine-terminated poly(butadiene-co-acrylonitrile) (ATBN), and the functionalized GnPs (ATBN-GnP) were characterized by microscopic and spectroscopic techniques. Different amounts of ATBN-GnP and pristine GnP were individually incorporated into an epoxy resin to fabricate epoxy composites. Compared with the pristine GnP, ATBN-GnP demonstrated stronger ameliorating effects due to an enhanced GnP-epoxy interfacial adhesion. At 5.0 wt% GnP content, the flexural modulus of GnP/epoxy composite increased by 18.1%, whereas the ATBN-GnP improved the flexural modulus by 22.1% at the same fraction. A remarkable enhancement of quasi-static fracture toughness was obtained at 5.0 wt% GnP and 5.0 wt% ATBN-GnP with 76.2% and 92.8% increase, respectively. Incorporation of 5.0 wt% ATBN-GnP improved thermal conductivity of the neat epoxy by 133.6%, and the thermal conductivity of 5.0 wt% ATBN-GnP/epoxy is about 16% higher than that of the pristine GnP/epoxy. The superior reinforcement of ATBN-GnP is attributed to the strong interfacial bonding between ATBN-GnP and epoxy matrix as confirmed by microscopic observations.

Dynamic and mechanical properties of vinyl ester/epoxy interpenetrating polymer networks

A series of vinyl ester (VE)/epoxy (EP) interpenetrating polymer networks (IPNs) were prepared by a simultaneous method. The change in characteristic groups, curing process, mechanical properties, damping properties, morphology, and thermal stability was studied. It was found that the damping ability, mechanical properties, and thermal stability were all enhanced through the introduction of VE into EP to form the IPN structure. Result of the dynamic mechanical analysis showed that glass transition temperature decreased and the tanδ peak shifted to a lower temperature with increased EP content in IPNs. Mechanical measurement revealed that the impact strength of the IPNs was higher than that of the EP matrix, and the tensile strength of the IPNs was impaired when the VE content was beyond 10%. Morphological investigation also proved that the brittle behavior was improved.

Thermal behavior of phenolic-based ceramizable composites modified by nano-aluminum oxide

A novel ceramizable organic composite was prepared by compression molding using silicone-modified phenolic resin (PR) as the matrix, nano-aluminum oxide powder as the filler, glass powder with low melting point as the forming additive, and vitreous silica fiber as the reinforced material. The ablative characteristics were explored in terms of linear/mass ablation rate and microscopic pattern of ablation via the oxyacetylene torch tests. Thermal stability of the investigated composites was estimated by means of thermogravimetric analysis. The final charring yields after pyrolysis increased from 63% to 69% and 74%, respectively. The silicone-modified PR acted as cross-linking adhesive at low-temperature region and tended to convert to bonding layer at high-temperature region. The formation and growth of the ceramic phase after thermal treatment enhanced the thermal stability and ablation performance of the composites at high-temperature region. The morphology and phase composition of the residual chars were studied by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction, respectively. The test results revealed that the modified composite possessed excellent thermal stability and ablation property.

Castor Oil-Based Polyurethane/Epoxy Intercross-linked Polymer Network Adhesives for Metal Substrates

Castor oil based polyurethane (CO-PU) was first synthesized from castor oil and 4, 4’-diphenyl-methane-diisocyanate (MDI). Then, a series of CO-PU/epoxy (EP) intercross-linked polymer network (ICPN) adhesives for metal substrates were prepared by a sequential method. The functional groups, tack -free time, mechanical properties, adhesive properties, and thermal stability were studied. Fourier transform infrared spectroscopy analysis indicated that an ICPN structure was formed through the introduction of CO-PU into EP. Results of adhesive measurements showed that the maximal value of lap shear strength was achieved at the CO-PU content of 20%. Thermogravimetric analysis results indicated that thermal stability of the adhesive film decreased with increased CO-PU content.