All issues / Volume 9 (2015) / Issue 1 (January)
This is an editorial article. It has no abstract.
Polyvinylidene fluoride (PVDF) and polyether sulfone (PES) membranes were activated using low-temperature plasma at atmospheric pressure, and their surface characteristics were investigated. In the plasma-treated PVDF, the XPS data showed that defluorination and oxidation reactions proceeded to 18 and 31%, respectively, at ±4.0 kVp-p for 180 s. Hydroperoxide groups were detected on both the plasma-treated membranes. By decomposing the S2p spectrum, it was proven that the sulfide and sulfo groups were newly formed on the plasma-treated PES. Based on these findings, we proposed an activation mechanism. The SEM images showed that the macrovoid formations were maintained after the plasma treatment. Polyacrylic acid (PAA) was grafted on both of the plasma-treated membranes by thermal treatments. Protein A, originating from Staphylococcus aureus, was immobilized on the membrane grafted with PAA using the EDC/Sulfo-NHS system. Adsorption isotherms with a human immunoglobulin G (IgG) antibody were fitted with the monolayer Langmuir model, and the maximum binding capacity (qm) and equilibrium association constant (Ka) were obtained. The ligand densities of the PVDF (pore size 0.45 and 5.0 µm) and PES (pore size 0.45 µm) membranes were 0.98, 1.42 and 2.06 mg•mL–1, respectively.
In this article, we addressed a feasible and versatile method of the fabrication of porous polyimide microspheres presenting excellent heat resistance. The preparation process consisted of two steps. Firstly, a novel polyimide/nano-silica composite microsphere was prepared via the self-assembly structures of poly(amic acid) (PAA, precursor of PI)/nanosized SiO2 blends after in situ polymerization, following the two-steps imidization. Subsequently, the encapsulated nanoparticles were etched away by hydrofluoric acid treatment, giving rise to the pores. It is found the composite structure of PI/SiO2 is a precondition of the formation of nanoporous structures, furthermore, the morphology of the resultant pore could be relatively tuned by changing the content and initial morphology of silica nano-particles trapped into PI matrix. The thermal properties of the synthesized PI porous spheres were studied, indicating that the introduction of nanopores could not effectively influence the thermal stabilities of PI microspheres. Moreover, the fabrication technique described here may be extended to other porous polymer systems.
Stability of nanostructures of epoxy/acrylic triblock copolymer blends was studied.PMMA-b-PnBA-b-PMMA triblock copolymers (acrylic BCPs) having several compositions on the ratio of the block chains and the molecular weight were initially prepared and were blended with diglycidyl ether of bisphenol-A epoxy thermosets. The blends were cured using phenol novolac with tri phenyl phosphine (TPP) as the catalyst. Several nanostructures, such as spheres, cylinders, curved lamellae, were observed in the cured blends. The nanostructures were controlled by the molecular weight of the immiscible PnBA-block chain and the ratio of the PnBA in the blends. Moreover, the effect of the gel time to the nanostructures was examined by altering the trace amount of the TPP in the blends. The types of the nanostructures were almost kept irrespective of the gel time of the blends when the composition of the blends was maintained. This suggested the stability of the nanostructures of the epoxy/acrylic BCP blends made via the self-assembly mechanism, therefore a phase diagram of the cured blends was proposed.
In this study, lignin-novolac epoxy resin networks were fabricated in the styrene butadiene rubber (SBR) matrix by combination of latex compounding and melt mixing. Firstly, SBR/lignin compounds were co-coagulated by SBR latex and lignin aqueous solution. Then the novolac epoxy resin (F51) was added in the SBR/lignin compounds by melt compounding method. F51 was directly cured by lignin via the ring-opening reaction of epoxy groups of F51 and OH groups (or COOH groups) of lignin during the curing process of rubber compounds, as was particularly evident from Fourier transform infrared spectroscopy (FTIR) studies and maximum torque of the curing analysis. The existence of lignin-F51 networks were also detected by scanning electron microscope (SEM) and dynamic mechanical analysis (DMA). The structure of the SBR/lignin/F51 was also characterized by rubber process analyzer (RPA), thermogravimetric analysis (TGA) and determination of crosslinking density. Due to rigid lignin-F51 networks achieved in SBR/lignin/F51 composites, it was found that the hardness, modulus, tear strength, crosslinking density, the temperature of 5 and 10% weight-loss were significantly enhanced with the loading of F51.
Microfibrous materials with a targeted design based on poly(L-lactic acid) (PLA) and poly(ε-caprolactone) (PCL) were prepared by electrospinning and by combining electrospinning and electrospraying. Several approaches were used: (i) electrospinning of a common solution of the two polymers, (ii) simultaneous electrospinning of two separate solutions of PLA and PCL, (iii) electrospinning of PLA solution in conjunction with electrospraying of PCL solution, and (iv) alternating layer-by-layer deposition by electrospinning of separate PLA and PCL solutions. The mats were heated at the melting temperature of PCL (60°"), thus achieving melting of PCL fibers/particles and thermal sealing of the fibers. The mats subjected to thermal treatment were characterized by greater mean fiber diameters and reduced values of the water contact angle compared to the pristine mats. Heat treatment of the mats affected their thermal stability and led to an increase in the crystallinity degree of PLA incorporated in the mats, whereas that of PCL was reduced. All mats were characterized by enhanced mechanical properties after thermal treatment as compared to the non-treated fibrous materials.
The effect of adding carbon black on the electrical and rheological properties of graphite nanoplatelets/poly(ethylene-butyl acrylate) copolymer composites produced via melt or solution mixing was studied. By adding a small amount of low- or high-structured carbon black to the nanocomposite, the electrical percolation threshold decreased and the final conductivity (at higher filler contents) increased. The effect on the percolation threshold was significantly stronger in case of the high-structured carbon black where replacing 10 wt% of the total filler content with carbon black instead of graphite nanoplatelets reduced the electrical percolation threshold from 6.9 to 4.6 vol%. Finally, the solution mixing process was found to be more efficient leading to a lower percolation threshold. For the composites containing high-structured carbon black, graphite nanoplatelets and their hybrids there was a quite reasonable correlation between the electrical and rheological percolation thresholds.
A ternary system based on blends of poly(vinylidene fluoride)(PVDF) and polycaprolactone (PCL) and made the multi-walled carbon nanotubes (MWNT) selective distribution in PCL phases via melt blending has been studied. The studies on conductivity of MWNT/PCL/PVDF composites with different proportions of PVDF and PCL showed that the conductivity was good in the mass ratio range of PVDF/PCL from 70/30 to 40/60 and that of other matching was poor. The scanning electron microscope (SEM) observation of the composites revealed co-continuous morphologies of PVDF and PCL were formed in composites under suitable proportion of PVDF to PCL. The interfacial tensions of PVDF and PCL melts was tested at mixing temperature of 200°C, the calculated wetting coefficient indicated that MWNT would selectively distribute in PCL phase owing to interfacial effects. Transmission electron microscope (TEM) observation further confirmed that co-continuous morphologies of PVDF and PCL could appear with the increase of PCL content, as indicated by MWNT selective localization in PCL.As the result, the desired structure of double percolation was built in MWNT/PCL/PVDF composites, which have much higher conductivity than that of PVDF or PCL composites with the same MWNT content. Through a strategy of selective localization of MWNT, PVDF based material with low percolation threshold (<0.5 wt%) was acquired which held promise for potential use in large-scale industrial applications.