Shenyuan Fu

Striking multiple synergies created by combining reduced graphene oxides and carbon nanotubes for polymer nanocomposites

The extraordinary properties of carbon nanotubes (CNTs) and graphene stimulate the development of advanced composites. Recently, several studies have reported significant synergies in the mechanical, electrical and thermal conductivity properties of polymer nanocomposites by incorporating their nanohybrids. In this work, we created polypropylene nanocomposites with homogeneous dispersion of CNTs and reduced graphene oxides via a facile polymer-latex-coating plus melt-mixing strategy, and investigated their synergistic effects in their viscoelastic, gas barrier, and flammability properties. Interestingly, the results show remarkable synergies, enhancing their melt modulus and viscosity, O2 barrier, and flame retardancy properties and respectively exhibiting a synergy percentage of 15.9%, 45.3%, and 20.3%. As previously reported, we also observed remarkable synergistic effects in their tensile strength (14.3%) and Youngs modulus (27.1%), electrical conductivity (32.3%) and thermal conductivity (34.6%). These impressive results clearly point towards a new strategy to create advanced materials by adding binary combinations of different types of nanofillers.

Facile fabrication of HDPE-g-MA/nanodiamond nanocomposites via one-step reactive blending

In this letter, nanocomposites based on maleic anhydride grafted high density polyethylene (HDPE-g-MA) and amine-functionalized nanodiamond (ND) were fabricated via one-step reactive melt-blending, generating a homogeneous dispersion of ND, as evidenced by transmission electron microscope observations. Thermal analysis results suggest that addition of ND does not affect significantly thermal stability of polymer matrix in nitrogen. However, it was interestingly found that incorporating pure ND decreases the thermal oxidation degradation stability temperature, but blending amino-functionalized ND via reactive processing significantly enhances it of HDPE in air condition. Most importantly, cone tests revealed that both ND additives and reactive blending greatly reduce the heat release rate of HDPE. The results suggest that ND has a potential application as flame retardant alternative for polymers. Tensile results show that adding ND considerably enhances Young’s modulus, and reactive blending leads to further improvement in Young’s modulus while hardly reducing the elongation at break of HDPE.

Effect of Lignin Incorporation and Reactive Compatibilization on the Morphological, Rheological, and Mechanical Properties of ABS Resin

In order to develop the potential application of industrial alkali lignin, its acrylonitrile-butadiene-styrene (ABS) composites were fabricated via melt blending in the absence/presence of a compatibilizer. The lignin can uniformly disperse in the ABS matrix with number-average dispersed-phase domains of sub-micron scale, ranging from 150–250 nm, as observed by scanning electron microscopy. Infrared spectroscopy reveals that strong intermolecular interactions, mainly hydrogen bonding, were responsible for their good interfacial compatibility. Rheological behaviors show that the presence of lignin restricts to some extent the relaxation of polymer chains without affecting the processing properties of ABS resin. The presence of lignin increases storage modulus and glass transition temperature (T g) of ABS. Incorporating small amounts of lignin, e.g. 5 wt%, can produce ABS composites with enhanced tensile strength and modulus, while higher loading of lignin will reduce mechanical properties. The latter, however, can be improved by reactive compatibilization.

Effect of Carbon Nanotubes on the Mechanical Properties of Polypropylene/Wood Flour Composites: Reinforcement Mechanism

Maleic anhydride grafted polypropylene (PP-g-MA) was employed as the compatibilizer and carbon nanotubes (CNTs) or hydroxylated CNTs as reinforcements for polypropylene/wood flour composites. The results showed that when the PP-g-MA loading level was 10 wt%, the bending strength, tensile strength, Izod notched impact strength, and elongation at break of PP-wood composites were enhanced by 85% (66.3 MPa), 93% (33.7 MPa), 5.8% (2.01 kJ/m2), and 64% (23%), respectively, relative to the uncompatibilized composites. The introduction of pristine CNTs only improved slightly the overall mechanical properties of the compatibilized composites due to poor interfacial compatibility. Unlike CNTs, incorporating hydroxylated CNTs (CNT-OH) could significantly improve all of the mechanical properties; for instance, at 0.5 wt% CNT-OH loading, the flexural strength and tensile strength reached 68.5 MPa, and 40.4 MPa about 6.6% higher than that for the composites with the same CNT loading. Furthermore, CNT-OH also remarkably enhanced the storage modulus. Contact angle and morphology observations indicated that the increases in mechanical properties could be attributed to the improvements of interfacial interactions and adhesions of CNTs with the matrix and fillers.

Thermal and flame retardancy properties of thermoplastics/natural fiber biocomposites

Environmental issues, such as global warming, have been increasing, due to the rapid consumption of petrol-based resources. Therefore green composites based on natural fibers and biodegradable polymers have rapidly developed and have found wide applications as building and transport materials because of their high specific strength and eco-friendliness. However, compared with traditional materials like metal and ceramics, these plant fiber-based biocomposites are less thermally stable and much more flammable, due to their chemical structure features. Thus it is extremely necessary to enhance the thermal stability and flame retardancy to ensure their safe applications. This chapter focuses on discussing types of natural fibers, biopolymers, and currently available flame retardants, the thermal properties and flammability of natural fiber-based biocomposites and possible flame retardancy mechanisms. Although great advances have been made with regards to enhancing thermal stability and flame retardancy of these biocomposites, there are still some challenges to be addressed.

Bioinspired Design of Strong, Tough, and Thermally Stable Polymeric Materials via Nanoconfinement

The combination of high strength, great toughness, and high heat resistance for polymeric materials is a vital factor for their practical applications. Unfortunately, until now it has remained a major challenge to achieve this performance portfolio because the mechanisms of strength and toughness are mutually exclusive. In the natural world, spider silk features the combination of high strength, great toughness, and excellent thermal stability, which are governed by the nanoconfinement of hydrogen-bonded β-sheets. Here, we report a facile bioinspired methodology for fabricating advanced polymer composite films with a high tensile strength of 152.8 MPa, a high stiffness of 4.35 GPa, and a tensile toughness of 30.3 MJ/m3 in addition to high thermal stability (69 °C higher than that of the polymer matrix) only by adding 2.0 wt % of artificial β-sheets. The mechanical and thermostable performance portfolio is superior to that of its counterparts developed to date because of the nanoconfinement and hydrogen-bond cross-linking effects of artificial β-sheets. Our study offers a facile biomimetic strategy for the design of integrated mechanically robust and thermostable polymer materials, which hold promise for many applications in electrical devices and tissue engineering fields.

Nonisothermal crystallization behavior of polypropylene-C60 nanocomposites

The nonisothermal crystallization behavior of polypropylene (PP) and PP-fullerene (C60) nanocomposites was studied by differential scanning calorimetry (DSC). The kinetic models based on the Jeziorny, Ozawa, and Mo methods were used to analyze the nonisothermal crystallization process. The onset crystallization temperature (Tc), half-time for the crystallization (t1/2), kinetic parameter (F(T)) by the Mo method and activation energy (ΔE) estimated by the Kissinger method showed that C60 accelerates the crystallization of PP, implying a nucleating role of C60. Furthermore, due to the reduced viscosity of PP by adding 5% C60, the parameters of crystallization kinetics for the PP-5%C60 nanocomposites changed remarkably relative to that of neat PP and when lower contents of C60 were added to PP.