This is an editorial article. It has no abstract.
A series of polymeric alloying films were prepared from bisphenol A/aniline-based bifunctional benzoxazine resin (BA-a) with three isomeric biphenyltetracarboxylic dianhydrides, i.e., 2,3,'3,4'-biphenyltetra carboxylic dianhydride (a-BPDA), 2,2',3,3'-biphenyltetracarboxylic dianhydride (i-BPDA), and 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) through fully thermal curing. Chemical structure, thermomechanical property and thermal stability of bisphenol A/aniline type polybenzoxazine (PBA-a) copolymers were evaluated. Their chemical structures analyzed via Fourier transform infrared spectroscopy reveal ester carbonyl linkage formation between hydroxyl group of the PBA-a and anhydride group in the isomeric dianhydride. Glass transition temperatures (Tgs) of the dianhydride-modified PBA-a increased with PBA-a"<<"i-BPDA"<"a-BPDA"<"s-BPDA. Degradation temperatures (Td) of the PBA-a copolymers recorded to be in the range of 365–402°C were significantly higher than that of the neat PBA-a i.e. 334°C. Finally, char yield of the PBA-a copolymers was found to be about 54–57% which is about twofold increase from that of the parent PBA-a.
In order to enhance the adhesion between inorganic particles and polymer matrix, in this paper, the mesoporous silica SBA-15 material was synthesized by the sol-gel method. The surface of SBA-15 was modified using γ-glycidyloxypropyltrimethoxysilane (GOTMS) as a coupling agent, and then mesoporous silica/phenolic resin (SBA-15/PF) nanocomposites were prepared via in situ polymerization. The structural parameters and physical properties of SBA-15, SBA-15-GOTMS (SBA-15 surface treated using GOTMS as coupling agents) and E-SBA-15/PF (SBA-15/PF nanocomposites extracted using ethanol as solvent) were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The thermal properties of the nanocomposites were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results demonstrated that the GOTMS were successfully grafted onto the surface of SBA-15, and chemical bonds between PF and SBA-15-GOTMS were formed after in situ polymerization. In addition, it is found that the in situ polymerization method has great effects on the textural parameters of SBA-15. The results also showed that the glass transition temperatures and thermal stability of the PF nanocomposites were obviously enhanced as compared with the pure PF at silica contents between 1–3 wt%, due to the uniform dispersion of the modified SBA-15 in the matrix.
Three techniques including acid hydrolysis (AH), 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation (TMO) and ultrasonication (US) were introduced to isolate nanocellulose from microcrystalline cellulose, in order to reinforce poly(vinyl alcohol) (PVA) films. Important differences were noticed in fiber quality of nanocellulose and film properties of PVA nanocomposite films. The TMO treatment was more efficient in nanocellulose isolation with higher aspect ratio, surface charge (–47 mV) and yields (37%). While AH treatment resulted in higher crystallinity index (88.1%) and better size dispersion. The fracture surface, thermal behavior and mechanical properties of the PVA nanocomposite films were investigated by means of scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile testing. The results showed that both the TMO-derived and AH-derived nanocellulose could be dispersed homogeneously in the PVA matrices. AH/PVA films had higher elongation at break (51.59% at 6 wt% nanocellulose loading) as compared with TMO/PVA, while TMO/PVA films shown superior tensile modulus and strength with increments of 21.5% and 10.2% at 6wt% nanocellulose loading. The thermal behavior of the PVA nanocomposite films was higher improved with TMO-derived nanofibrils addition.
The effects of tool geometry and properties on friction stir spot welding properties of polypropylene sheets were studied. Four different tool pin geometries, with varying pin angles, pin lengths, shoulder diameters and shoulder angles were used for friction stir spot welding. All the welding operations were done at the room temperature. Lap-shear tensile tests were carried out to find the weld static strength. Weld cross section appearance observations were also done. From the experiments the effect of tool geometry on friction stir spot weld formation and weld strength were determined. The optimum tool geometry for 4 mm thick polypropylene sheets were determined. The tapered cylindrical pin gave the biggest and the straight cylindrical pin gave the lowest lap-shear fracture load.
Carbon nanotubes (CNTs) were melt mixed directly or by using an in situ polymerized masterbatch into a matrix polymer, polystyrene (PS) or poly(methyl methacrylate) (PMMA). The mechanical properties of the composites were mostly determined by the amount of CNTs, and not by the use of directly melt mixed CNTs or the use of the masterbatch. In contrast, the electrical resistivity of the composites was dependent on the manner in which the CNTs were added to the matrix polymer. When there was increased interfacial adhesion between the components, as for PS and the CNTs, the use of directly melt mixed CNTs gave better resistivity results. Without strong interactions between the CNTs and the matrix, as with PMMA and CNTs, the use of a tailored masterbatch had a significant effect on properties of the final composites. The molecular weight and viscosity of masterbatches can be varied and when the PMMA-masterbatch had optimized viscosity with respect to the PMMA matrix, electrical resistivity of the final composites decreased noticeably.
The object of this study was to investigate how different decreasing of pH regimes during microencapsulation process with melamine-formaldehyde (MF) resin affects the composition, morphology and thermal stability of microcapsules containing a phase-change material (PCM). Technical butyl stearate was used as PCM. Microencapsulation was carried out at 70°C. For all experiments the starting pH value was 6.0. After one hour of microencapsulation at the starting pH value, the pH value was lowered to final pH value (5.5; 5.0; 4.5) in a stepwise or linear way. The properties of microcapsules were monitored during and after the microencapsulation process. The results showed that pH value decreasing regime was critical for the morphology and stability of microcapsules. During microencapsulations with a stepwise decrease of pH value we observed faster increase of the amount of MF resin in the microencapsulation product compared to the microencapsulations with a linear pH value decrease. However, faster deposition in the case of microencapsulations with stepwise decrease of pH value did not result in thicker MF shells. The shell thickness increased much faster when the pH value was decreased in a linear way or in several smaller steps. It was shown that for the best thermal stability of microcapsules, the pH value during microencapsulation had to be lowered in a linear way or in smaller steps to 5.0 or lower.
Effect of different ligands on the controlled polymerization of monodisperse polystyrene nanospheres by atom transfer radical polymerization in an aqueous emulsion
B. Y. Tian, P. J. Hu, M. Yuan, E. J. Tang, S. J. Liu, X. Y. Zhao, D. S. Zhao
Vol. 6., No.10., Pages 837-846, 2012
Vol. 6., No.10., Pages 837-846, 2012
Polystyrene nanospheres have been synthesized by atom transfer radical polymerization (ATRP) to control the molecular weight distribution in the aqueous system. The crucial factor in such a system is the ligand that adjusts the solubility of the catalyst in different phases to control the concentration of both the activator and the deactivator in reaction phase. The effect of different ligands including ethylenediamine, 1,10-phenanthroline (phen) and 4,4-dinonyl-2, 2-bipyridyl (dNbpy) on the catalytic solubility in the organic and aqueous phase has been investigated. The molecular weight distribution of polymer obtained in this way was analyzed by gel permeation chromatography (GPC). It showed that the obtained polymer particles presented a broad molecular weight distribution (polydispersity index 1.78) with ethylenediamine as the ligand, but the polymerization rate was high and conversion reached 96.8%. The molecular weight distribution of polystyrene was narrowest with dNbpy as ligand, but the conversion was lowest and only achieved to 69%. Possible reasons were the influence of the structure of three different ligands on the control of ATRP reaction. SEM and GPC indicated that the polystyrene nanospheres presented regular sphere with a diameter of about 120 nm and uniform molecular weight distribution, which possessed a significant potentials in drug carrier field.
The nanosheet of graphene was chemically modified by long alkyl chain for enhanced compatibility with polymer matrix and graphene/poly(methyl methacrylate) (PMMA) nanocomposites with homogeneous dispersion of the nanosheets and enhanced nanofiller-matrix interfacial interaction were fabricated via a facile in-situ bulk polymerization. The nanocomposites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy and thermogravimetry. The results showed that the graphene nanosheets were fully exfoliated in PMMA matrix and the thermal and mechanical properties of the nanocomposites were significantly improved at low graphene loadings. Large shifts of 15°C in the glass transition temperature and 27°C improvement of onset thermal degradation temperature were achieved with graphene loading as low as 0.07 wt%. A 67% increase in tensile strength was also observed by the addition of only 0.5 wt% graphene. The method used in this study provided a novel route to other graphene-based polymers.