Jing-hui Yang

A simple strategy to achieve very low percolation threshold via the selective distribution of carbon nanotubes at the interface of polymer blends

Selective distribution of carbon nanotubes (CNTs) at the interface of immiscible polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) is achieved via a combination of adding maleic anhydride grafted ABS (ABS-g-MA) and using an appropriate processing procedure. The composite shows a much lower percolation threshold of 0.05 wt%. The value obtained here is the smallest percolation threshold reported so far, comparing with those in the literature.

Super toughening of the poly(L-lactide)/thermoplastic polyurethane blends by carbon nanotubes

Carbon nanotubes (CNTs) were introduced into the poly(L-lactide)/thermoplastic polyurethane (PLLA/TPU) blend to prepare the ternary nanocomposites. The results showed that CNTs selectively localized in the TPU phase, leading to a morphological change from the sea-island morphology to the quasi-cocontinuous morphology. The high content of the CNTs induced the formation of the percolated network structure. Consequently, super toughened PLLA/TPU/CNTs nanocomposites were prepared successfully. More apparent cavitation of the TPU phase and the intensified local plastic deformation of the PLLA matrix under the impact load were observed on the impact-fractured surface of the ternary nanocomposites. This was believed to be the main toughening mechanisms for the ternary nanocomposites. After being annealed, besides the morphological change of the nanocomposites, PLLA matrix also exhibited a large number of crystalline structures. Furthermore, the impact toughness of the ternary nanocomposites was enhanced further.

Green synthesis of hybrid graphene oxide/microcrystalline cellulose aerogels and their use as superabsorbents

In this work, we developed a green synthesis method to prepare the hybrid aerogels containing graphene oxide (GO) and microcrystalline cellulose (MCC) using lithium bromide (LiBr) aqueous solution as the solvent, which insured the complete dissolution of MCC. The interaction between GO and MCC was investigated through different methods The results demonstrate that there is a strong interaction between GO and MCC molecules, which promotes the exfoliation of GO in the hybrid aerogels. The hybrid GO/MCC aerogels exhibit typical three dimensional porous structure and the pore morphology can be well adjusted by changing the content of GO. The adsorption ability of the hybrid aerogels was measured using methylene blue (MB) as an adsorbate. The results show that the adsorption ability of GO per unit mass is greatly enhanced compared with the pure GO aerogel, especially at relatively low GO content the adsorption amount of GO per unit mass is enhanced up to 2630mg/g. Further results demonstrate that the hybrid GO/MCC aerogels still obey the pseudo-second-order adsorption model, which is similar to that of the pure GO aerogel. The mechanism for the amplified adsorption ability of GO in the hybrid GO/MCC aerogels is then analyzed.

Organic-inorganic hybrid materials 7 : characterization and degradation of polyvinylimidazole-silica hybrids

Abstract Polyvinylimidazole–silica hybrid materials (PVI–SiO 2 ) containing various proportions of covalently bonded silica were prepared from [3-(methacryloxy)propyl]trimethoxysilane modified polyvinylimidazole (PVI), water and tetramethoxysilane (TMOS) via a sol–gel technique. Infrared (IR), 29 Si and 13 C nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to analyse the structures and properties of hybrids with various proportions of TMOS. The apparent activation energies E a for desorption of water and decomposition of PVI chains in hydroxylated hybrids were respectively around 55 and 35 kJ/mol, while the values were increased by about 10 kJ/mol in dehydroxylated hybrids.

Trapping carbon nanotubes at the interface of a polymer blend through adding graphene oxide: a facile strategy to reduce electrical resistivity

Graphene oxide (GO) and carbon nanotubes (CNTs) were simultaneously introduced into an immiscible polymer blend. The dispersion of fillers and the electrical resistivity of the composites were studied. The results first showed that more CNTs were trapped at the blend interface by GO. Consequently, a remarkable decrease of electrical resistivity by about 7 orders of magnitude was achieved even if the concentration of CNTs was only 0.1 wt%. Further results showed that the quaternary composites exhibited much smaller percolation threshold (0.06 wt%) compared with the ternary composites containing only CNTs (0.24 wt%).

Organic-inorganic hybrid materials. II. Chain mobility and stability of polysiloxaneimide-silica hybrids

Polysiloxaneimide-silica hybrid materials (PSI-SiO 2 ) were obtained using the sol-gel technique by polycondensation of tetramethoxysilane (TMOS) in a polyamic acid solution. IR, 29 Si- and 13 C-NMR spectroscopy, and thermogravimetric analysis were used to study hybrids containing various proportions of TMOS and hydrolysis ratios. The morphology, dynamics, and thermal stability of the hybrids were investigated. The chain mobility of the hybrids was investigated by spin-spin relaxation time (T 2 ) measurements. The apparent activation energy (E a ) for degradation of the hybrids in air was studied by the van Krevelen method. The T 2 value was independent of the silica content whereas that of the E a decreased as silica content increased.

Effect of graphene oxides on thermal degradation and crystallization behavior of poly(L-lactide)

Graphene oxides (GO) were introduced into a poly(L-lactide) (PLLA) to prepare the PLLA/GO composites with different concentrations of the GOs. The main attention of the present work was focused on the thermal degradation and crystallization behaviors of a PLLA matrix induced by GOs. The measurements based on gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) clearly proved the thermal degradation of the PLLA matrix during the melt-processing procedure. Consequently, reduced complex viscosity of the composites was achieved. The crystallization behaviors of the PLLA matrix were comparatively investigated under different crystallization conditions including melt-crystallization (nonisothermal or isothermal crystallization occurring from the melt state) and cold-crystallization (crystallization occurring from an amorphous solid state) using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). Largely enhanced crystallization ability of the PLLA matrix was achieved. The crystallization conditions and the GO content are key factors which influence the crystallization behavior of the PLLA matrix. This work proved that the stabilization of the PLLA matrix during the melt-processing procedure must be considered when designing and preparing the PLLA/GO materials.

Super toughened immiscible polycarbonate/poly(L-lactide) blend achieved by simultaneous addition of compatibilizer and carbon nanotubes

Polycarbonate/poly(L-lactide) (PC/PLLA) blend exhibits great potential application in several fields, including package, toy, electronic element and automobile. However, the poor mechanical properties of the immiscible PC/PLLA blend restrict its application. In this work, a compatibilizer maleic anhydride grafted ethylene–octene copolymer (EOR-g-MAH) and functionalized carbon nanotubes (F-CNTs) were introduced into the immiscible PC/PLLA blend by simple melt-compounding processing. Mechanical property measurements showed that even at low environmental temperature (0 °C), the blend composites exhibited excellent fracture toughness, e.g. 40.9 ± 2.1 kJ m−2 at F-CNT content of 2 wt%. To better understand the toughening mechanism, the morphologies of the blend composites and the dispersion of F-CNTs and the rheological properties were systematically investigated. The results showed that with the combined effects of EOR-g-MAH and F-CNTs, the decreased PLLA particles were achieved. Most of F-CNTs selectively located in the PC matrix and some F-CNTs entered into PLLA particles. Specifically, at relatively high content (>2 wt%), F-CNTs formed percolated network structure. Then, the toughening mechanism was proposed on the basis of the morphology evolution, the formation of F-CNT network structure and the impact-fractured surface morphologies. This work demonstrated that even for the immiscible polymer blend, the super toughened blend composites could be achieved by the combined effects of compatibilizer and carbon nanotubes, and therefore it provides an alternative strategy for largely improving the fracture toughness of immiscible polymer blends.

Blend-electrospun poly(vinylidene fluoride)/polydopamine membranes: self-polymerization of dopamine and the excellent adsorption/separation abilities

In this work, a certain amount of dopamine was firstly dissolved into the solution of poly(vinylidene fluoride) (PVDF) and then the fibrillar membranes were prepared through an electrospinning technology. Then, the self-polymerization of polydopamine (PDA) was triggered in a Tris–HCl buffer solution. The self-polymerization of PDA on the fiber surface and the microstructure of the PVDF/PDA membranes were systematically researched. The results demonstrated that the morphologies of the membranes were dependent upon the polymerization time of dopamine in the buffer solution. PDA homogeneously coated on the fiber surface, which greatly enhanced the hydrophilicity of the membranes. The adsorption abilities toward organic dyes and heavy metal ions of the PVDF/PDA membranes were evaluated using methylene blue (MB) and Cu2+ as the probe adsorbates. The results showed that the PVDF/PDA fibrillar membranes exhibited excellent adsorption ability and the experimental saturation adsorption capacities were 172.3 and 26.7 mg g−1 for MB and Cu2+, respectively. Further analysis based on adsorption kinetics, adsorption isotherms and thermodynamic parameters showed that the adsorption of MB follows the pseudo second-order model and the Langmuir adsorption model and the adsorption was a spontaneous process. Further results demonstrated that the PVDF/PDA membrane exhibited good regeneration ability after adsorbing MB. The oil/water separation ability of the PVDF/PDA membranes was also measured. The presence of the PDA coating layer greatly enhanced the separation efficiency of the membranes, and the maximum water flux was increased up to 729.3 L m−2 h−1 according to the measuring method applied in this work. The excellent adsorption and separation abilities endow the electrospun PVDF/PDA fibrillar membranes with great potential applications in wastewater treatment.

Thermal and electroactive shape memory behaviors of poly(L-lactide)/thermoplastic polyurethane blend induced by carbon nanotubes

Poly(L-lactide) (PLLA) based shape memory materials (SMP) recently attracted much attention due to their great potential application in biomedical materials. In this work, we introduced carbon nanotubes (CNTs) into a blend of PLLA/thermoplastic polyurethane (TPU) through a simple melt compounding processing to develop a new kind of PLLA SMP. The effects of CNTs on morphologies of blend composites, the selective location of CNTs, the dynamic mechanical properties of samples and the microstructure of CNTs in the blend composites were characterized using a scanning electron microscope (SEM), a transmission electron microscope (TEM) and rheological measurements, respectively. The results demonstrated that CNTs selectively located in the TPU component and induced apparent change of the blend composite morphology. High content of CNTs also formed the percolated network structure in the material, which resulted in the dramatic decrease of electrical resistivity. The shape memory behaviors of the samples were comparatively investigated in two different conditions, i.e. thermally activated and electrically activated conditions. It was demonstrated that CNTs prevents the thermally activated shape recovery process of the blend composites, especially when CNTs formed the percolated network structure. However, with the aid of electrical actuation, largely accelerated shape recovery process and enhanced degree of shape recovery were achieved for the blend composites containing 5 wt% CNTs, especially at relatively low recovery temperatures. The main mechanism was attributed to the largely enhanced electrical conductivity, which provides more Joule heating in the sample. This work provides an alternative way to develop PLLA-based shape memory materials through a simple melt compounding processing.