This is an editorial article. It has no abstract.
A series of polyurethane nanocomposites were synthesized from thermoplastic polyurethanes (with different hard segment ratios) and two types of organically modified montmorillonites (OMMT) – Cloisite® 10A and Cloisite® 20A. The thermal behavior was examined by non-isothermal thermogravimetry (TG, DTG), Differential Scanning Calorimetry (DSC) and Dynamic-Mechanical Thermal Analysis (DMTA). The results of X-ray analyses showed that the OMMT produced the intercalated polyurethane nanocomposites. It has been proven that the thermal stability and tensile properties of these new systems were higher when the organoclay was present within the polymer matrix. Moreover, these properties depend on both the OMMT loading and the type of gallery cations of the organically modified montmorillonites.
Bioactive guided tissue regeneration (GTR) membrane has had some success for periodontal therapy. In this study, poly(lactic-co-glycolic acid) (PLGA)/multi-walled carbon nanotubes (MWNTs) composite membranes were incubated in three supersaturated calcification solutions (SCS) of different pH values for 21 days to prepare a PLGA/MWNTs/apatite composite. Scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), water contact angle measurement and mechanical testing were used for characterization. It was found that after 21 days incubation, apatite with low crystallite size and crystallinity was formed on the PLGA/MWNTs composite membranes. The Ca-poor carbapatite was similar in morphology and composition to that of natural bone. The size and shape of the apatite crystals immersed in three SCS were different from each other. The hydrophilicity and mechanical properties of the PLGA/MWNTs composite membranes were significantly enhanced after mineralization. This indicated that biomimetic mineralization may be an effective method to improve the biocompatibility and bone inductivity of certain materials. The PLGA/MWNTs/apatite composites may be potentially useful in GTR applications, particularly as GTR membranes for periodontal tissue regeneration.
Poly(ethylene terephthalate) (PET) nanocomposites containing rod-like silicate attapulgite (AT) were prepared via in situ polymerization. It is presented that PET chains identical to the matrix have been successfully grafted onto simple organically pre-modified AT nanorods (MAT) surface during the in situ polymerization process. The covalent bonding at the interface was confirmed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The content of grafted PET polymer on the surface of MAT was about 26 wt%. This high grafting density greatly improved the dispersion of fillers, interfacial adhesion as well as the significant confinement of the segmental motion of PET, as compared to the nanocomposites of PET/pristine AT (PET/AT). Owing to the unique interfacial structure in PET/MAT composites, their thermal and mechanical properties have been greatly improved. Compared with neat PET, the elastic modulus and the yield strength of PET/MAT were significantly improved by about 39.5 and 36.8%, respectively, by incorporating only 2 wt % MAT. Our work provides a novel route to fabricate advanced PET nanocomposites using rod-like attapulgite as fillers, which has great potential for industrial applications.
The effect of different nanoparticles on the geometrical percolation transition of multi-wall carbon nanotubes (CNT) in polypropylene (PP) composites was studied. Our results show that the electrical conductivity of PP/CNT composites (around 2 vol%) can be tuned depending on the characteristic of the third component. Non-conductive layered silica fillers disrupt the CNT percolated network reducing the electrical conductivity of the composite. Spherical nanoparticles otherwise, either copper metal or silica-based, decrease the percolation threshold down to 0.5 vol% of CNT. These results cannot be explained by previous theories about the effect of a second particle on the electrical behaviour of polymer/CNT composites such as the interparticle bridging or the excluded volume. The effect of annealing in the melt was further analyzed and our results show that depending on the concentration and the type of filler, the electrical conductivity of the composites can be increased several orders of magnitude.
A triple-stimuli responsive polymer, poly(3-acrylamidophenylboronic acid)-b-poly(N-isopropylacrylamide) (PAAPBA-b-PNIPAM), has been synthesized by reversible addition-fragmentation chain transfer polymerization. Temperature, pH, and fructose induced micellization and dissociation transition of block copolymer was investigated by a combination of static and dynamic laser light scattering. PAAPBA-b-PNIPAM copolymer self-assembles into micelles with PAAPBA block as core and PNIPAM as shell in lower pH aqueous solution at room temperature. Increasing the temperature causes the micelle to shrink due to the dehydration of PNIPAM segments at pH 6.2. After the elevation of solution pH from 6.2 to 10.0, the increase in the hydrophilicity of PAAPBA block leads to an expulsion of unimers from micelles. In addition, the fructose addition further enhances the dissociation of micelles. Our experiments demonstrate that the micelle to unimer transition process proceeds via the step-by-step sequential expulsion of individual chains.
Samples were produced by injecting Na+-montmorillonite (Na+-MMT) slurry into a co-rotating twin-screw extruder. Na+-MMT was modified inside the extruder, in an in-situ process, and blended with the LDPE/LLDPE in melt state. Three different types of alkyl ammonium salt (ALAMS) were used as modifier to study the effect of chemical composition and chain length of ALAMS on the dispersion of nanoparticles. Also, the effect of nanoclay content on structural, mechanical, and permeability properties of the samples was investigated. To translate the data into intelligible trends, response surface method was utilized to analyze the effects of the factors on the results. Moreover, transmission electron microscopy was implemented to observe the dispersion of nanoclay platelets. The results suggested that the chain length of ALAMS dramatically affects its ability to modify nanoclay platelets. What is more, while nanoclay increase deteriorates nanoparticles dispersion, it brings about better mechanical and gas barrier properties. The improvement in the properties was higher than those of nanocomposites prepared by conventional method. By studying the effects of feeding rate on nanoclay dispersion, we proved that unlike conventional melt intercalation, water-assisted melt intercalation is controlled by diffusion rather than shear stress. In the end, we proposed a mechanism for this process.
Flow conditions are different in the cavity of the injection mould from the capillary flow of a laboratory rheological instrument. An injection moulding slit die rheometer (Rheo-mould) was designed with a series of slit and orifice dies. Four pressure sensors were built in the stationary side of the mould, therefore the pressure could be measured at four different places. A changeable slit die insert was designed in the moving side. The shear stress and the shear rate can be calculated from the pressure gradient and from the flow rate of the melt, respectively. Flow curves of low density polyethylene were determined using Bagley, Rabinowitsch and Mooney corrections. The results were compared to the flow curves determined by Göttfert and Haake capillary equipments. It was found that the agreement between the methods is excellent.
The multistep procedures for preparing novel anionic spherical polyelectrolyte brushes (ASPB) by grafting sodium-p-styrenesulfonate (SSS) from the surface of γ-methacryloxypropyl trimethoxy-silane modified SiO2 nanoparticles were demonstrated. The morphology of ASPB was characterized by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). The core radius Rc and hydrodynamic radius Rh of ASPB measured by Zeta Potential/Particle Sizer (ZLS) were ca. 50nm and (84.5±1) nm respectively. The percentage of grafting (PG%) of polyelectrolyte brushes was 4.3% investigated by Thermo-gravimetric analysis (TGA). Detailed characterizations on ASPB were performed by cleaving the grafts from the anchoring surface. The molecular weight (MW) and polydispersity (MW/Mn) of brushes were 1.788•103 g/mol and 1.6 respectively from Gel Permeation Chromatography (GPC) measurements. Moreover, Rh and ζ-potential of ASPB in the presence of aqueous NaCl solutions of different concentrations were discussed.