Effects of ZnO nanoparticles on the mechanical and antibacterial properties of polyurethane coatings

Polyurethane-based coatings reinforced by ZnO nanoparticles (about 27 nm) were prepared via solution blending. The ZnO/PU films and coats were fabricated by a simple method of solution casting and evaporation. The mechanical properties of the films were investigated by a universal material test, and the abrasion resistance of the prepared coats was evaluated by a pencil-abrasion-resistance tester. It was found that significant improvement of the PU films in Young’s modulus and tensile strength was achieved by incorporating ZnO nanoparticles up to 2.0 wt%, and that the abrasion resistance of the PU coats was greatly enhanced due to the addition of ZnO nanoparticles. Moreover, the antibacterial property test was carried out via the agar dilution method and the result indicated that PU films doped with ZnO nanoparticles showed excellent antibacterial activity, especially for Escherichia coli.     

Experimental Study of the Oxidative Degradation of PBX 9501 and its Components

The results of the constituent aging study (CAS) are given, where low‐temperature (T<64 °C) aging experiments were performed on over 1100 closed‐container samples of various combinations of the components of the plastic‐bonded explosive PBX 9501. Experiments were performed on the various combinations both in the absence and presence of free‐radical stabilizers. The product gases were identified and quantified as a function of aging time. The gas data show diverse chemistry between CAS samples and initial linear increases in product gas formation. Temperature analysis of the initial production rates of gas products shows straight Arrhenius plots. The extracted activation energies and frequency factors for the formation of the individual gas products yield a single linear kinetic compensation plot suggesting a common degradation pathway for PBX 9501 and combinations of constituents that contained nitroplasticizer (a eutectic mixture of bis‐2,2‐dintropropyl acetal and bis‐2,2‐dintropropyl formal).     

Synthesis,characterization and dielectric properties of nickel-based polyoxometalate/polyurethane composites

The aim of this study was to synthesis, characterization and investigation of the influence of the polyoxometalate concentrations (1, 3, 5 and 10 wt%) on chemical, thermal, physical and morphological properties of nickel-based polyoxometalate/polyurethane composite (Ni-POM/PU) materials. Firstly, nickel-based polyoxometalate (Ni-POM) compound has been synthesized and characterized through various spectroscopic techniques. Synthesized Ni-POM compounds have been used for preparation of polyurethane composites as a reinforcement. Three different Ni-POM/PU composites containing Ni-POM were prepared by solution mixing and casting techniques. The chemical structure and morphology of prepared Ni-POM/PU composite samples were confirmed by Fourier transform infrared spectroscopy (FTIR), elemental analysis and SEM techniques. Effects of Ni-POM on thermal stability, glass transition temperature, optical transparency, hydrophilicity and physical properties of polyurethane composites were examined. Thermal stabilities and glass temperatures of the materials have been checked by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). The SEM results confirmed the highly porous structure and the formation of Ni-POM structures in the polymer matrix. Synthesized composites showed high chemical stability, good processability, and low Tg values. The dielectric properties of the prepared Ni-POM/polyurethane composites were also investigated at room temperature. These results displayed that the dielectric constant of the POM/polyurethane composites decreased with the increase of the Ni-POM content in polymeric matrix.     

Waterborne polyurethane: the effect of the addition or in situ formation of silica on mechanical properties and adhesion

A series of composites consisting of commercial waterborne polyurethane (PU) and silica were prepared by in situ synthesis (sol-gel method) and compared to those prepared by the addition of commercial silica (blending method). Adhesion resistance, mechanical resistance, small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) measurements were performed in order to evaluate the effect of silica addition. The adhesion resistance reached a maximum at 3 wt.% of added silica. Comparing the sol-gel composites with the analog composites obtained by the addition of commercial nanosilica, it was observed that although the composites containing commercial silica displayed higher mechanical resistance, better adhesion was obtained with the in situ method. The DSC results showed increasing crystallinity with increasing silica addition.     

Studies on corrosion resistant properties of inhibitive primed IPN coating systems in comparison with epoxy-PU systems

Though blending polymers to obtain high performance materials is an old practice, the new trend in such an approach is the emergence of interpenetrating polymer networks (IPNs) as binders for protective coatings with improved properties. In this study, one ambient curing IPN-type polymer alloy developed out of epoxy and acrylic polyurethane systems as a high performing binder was formulated into paints and evaluated in comparison with the currently used conventional epoxy polyamide and polyurethane systems. A three-coat system consisting of a zinc phosphate primer, a micaceous iron oxide (MIO) undercoat, and a topcoat was formulated out of the IPN along with a similar system of epoxy primer, epoxy undercoat, and a PU topcoat. A two-coat system of the same primer with an IPN clear topcoat and a similar system with epoxy has also been studied. All the systems were studied under accelerated laboratory tests and field tests at a corrosive location. The results are reported and conclusions are drawn in this article. An erratum to this article can be found at     

Nanoclay-tethered shape memory polyurethane nanocomposites

The study investigated shape memory properties of nanoclay-tethered polyurethane nanocomposites. Polyurethanes based on polycaprolactone (PCL) diol, methylene diisocyanate, and butane diol and their nanocomposites of reactive nanoclay were prepared by bulk polymerization in an internal mixer and the values of shape fixity and shape recovery stress were determined as function of clay content. The melting point of the crystalline soft segment was used as the transition temperature to actuate the shape memory actions. It was seen that clay particles exfoliated well in the polymer, decreased the crystallinity of the soft segment phase, and promoted phase mixing between the hard and soft segment phases. Nevertheless, the soft segment crystallinity was enough and in some cases increased due to stretching to exhibit excellent shape fixity and shape recovery ratio. A 20% increase in the magnitude of shape recovery stress was obtained with the addition of 1 wt% nanoclay. The room temperature tensile properties were seen to depend on the competing influence of reduced soft segment crystallinity and the clay content. However, the tensile modulus measured at temperatures above the melting point of the soft segment crystals showed continued increases with clay content.     

Controlling nonlinear optical effects of polyurethanes by adjusting isolation spacers through facile postfunctional polymer reactions

With the aim to control nonlinear optical (NLO) effects of polyurethanes, especially to efficiently translate the fixed μβ values of the organic chromophore to possibly higher macroscopic NLO activities of polymers, a facile synthetic strategy, consisting of the postazo coupling and esterification reactions, was developed to prepare a series of second-order nonlinear optical polyurethanes (P2-P5). And in the polymers, different isolation groups were introduced to the sulfonyl-based chromophore moieties at the acceptor side. Thus, polyurethane P1 containing aniline groups was obtained from the copolymerization of 2,4-toluenediisocyanate (TDI) and N,N-2-(2-hydroxyethyl)aniline directly; then a postazo coupling reaction of p-(2-hydroxyethyl)sulfonylbenzenediazonium fluoroborate toward the aniline ring afforded the sulfonyl-based chromphore-functionalized polyurethane P2, which underwent the subsequent esterification reactions between the hydroxyl groups in P2 and different organic acids to link different isolation spacers (changing from small groups to much larger ones such as carbazolyl groups), to the chromophore moieties at the acceptor side, to yield polyurethanes P3, P4 and P5. The polymers exhibit good solubility in common organic solvents and are thermally stable. The maximum absorption appeared at about 436 nm with a cutoff at ca. 570 nm, resulting in a wider transparency window. The tested NLO properties demonstrate that the resonant d₃₃ values of polymers could be improved about 1.5 times by attaching isolation spacers with suitable bulkiness.     

Corrosion protective performances of commercial low-VOC epoxy/urethane coatings on hot-rolled 1010 mild steel

The protective properties of low-VOC epoxy/urethane paint systems of commercial grade have been investigated using a variety of techniques such as electrochemical impedance spectroscopy (EIS). One epoxy-polyamide mastic/urethane, three high-solid epoxy-amine/urethane coatings, one solvent-free epoxy-amine/urethane, one water-based epoxy-amine and one high-VOC alkyd paint system (used as paint reference system) were applied on hot-rolled 1010 mild steel panels and exposed for up to 2000 h in the salt spray cabinet (SSC) or for 1 year at an outdoor marine test site. These paints were tested for their barrier properties, corrosion-induced adhesion loss and visual defects, as well as for their flexibility and resistance to direct impact. The barrier properties increased in the following order: alkyd相似文献   

Synthesis of polyurethanes from solvolysis lignin using a polymerization catalyst: Mechanical and thermal properties

Two methods of synthesis, namely, using a polymerization catalyst versus a non-catalytic route, were investigated to produce lignin-based polyurethanes. The films were characterized with respect to crosslink density, ultimate tensile behavior and glass transition temperature. The results indicated that use of the catalyst for polymerization is an effective way for producing films with consistent properties, even at lignin contents as high as 45 to 50 wt%. To illustrate the catalyst effectiveness, crosslink densities of catalyzed films with 20 wt% of lignin content increased drastically from 0.2-0.3 to 1.7-2.7 mmol/cm 3 when the NCO/OH molar ratio increased from about 1.3 to 3.0, without much increase in the corresponding crosslink densities of the non-catalyzed films. Also, when the NCO/OH molar ratio increased from 1.2 to 3.2, the tensile strength increased from 1.9 MPa to a maximum of 55 MPa (NCO/OH=2.6) before decreasing. Also, for same NCO/OH ratios, ultimate strain decreased drastically from 174.4% to 4.3%, with a corresponding increase in Young's Modulus from 0.03 GPa to 2.8 GPa. The glass transition temperatures of the catalyzed films also increased from 35°C to 89°C. Without the catalyst, only polyurethanes with low NCO/OH ratios, low lignin contents, and inferior mechanical properties, could be synthesized.     

Synthesis, characterization and infrared emissivity property of optically active polyurethane derived from tyrosine

Optically active polyurethanes (LPU and DPU) and racemic polyurethane (RPU) were synthesized by the self-polyaddition of the isocyanate-phenols which derived from the chiral and racemic tyrosine. All of the polymers were characterized by FT-IR, ¹H NMR, GPC, UV-Vis spectroscopy, circular dichroism (CD) spectroscopy, TGA and X-ray diffraction (XRD), and the infrared emissivity values were investigated in addition. LPU and DPU were two enantimorphs, they possessed helical configurations and higher degree of hydrogen bondings compared to the RPU which presented random coiled molecular chain. The crystallinity and thermal decomposition temperature of LPU and DPU were higher than that of the RPU due to the more regular secondary structure which facilitate the formation of a large number of inter-chain hydrogen bonds. Consequently, the LPU and DPU exhibited lower infrared emissivity values (8-14 μm), which came down to 0.611 and 0.625.