Effects of annealing (solid and melt) on the time evolution of polymorphic structure of PA6/silicate nanocomposites

The effects of annealing including solid-state annealing (190 °C) and melt-state annealing (230 and 250 °C) on the polymorphic behavior and thermal property of polyamide 6 (PA6)/layered-silicate nanocomposites (PA6LSN) have been investigated as a function of annealing time using Modulated Differential Scanning Calorimetry (MDSC) and wide angle X-ray diffraction. For comparison, thermal behavior and polymorphism of pure PA6 were also studied. It was demonstrated that PA6LSN and PA6 exhibited a similar polymorphic behavior when they were annealed in the solid state for different time duration. As the annealing temperature was elevated to 230 and 250 °C, significant differences in thermal behavior and polymorphism between PA6LSN and PA6 could be found. For example, the γ phase became the absolutely dominating for PA6LSN, while the α crystal was the most predominant phase in neat PA6. Moreover, a new endothermic peak is observed around 235 °C in all PA6LSN MDSC scans, which might be related to the melting of PA6 lamellae formed in the confined environment on the surface of the nano-silicate.     

用改性蒙脱石制备聚丙烯纳米复合材料的研究

介绍了用插层改性蒙脱石制备聚丙烯纳米复合材料的方法 ,并对纳米复合材料的力学性能和微观结构进行了分析。结果表明 :采用季胺盐 苯乙烯两步复合插层改性的蒙脱石 ,在双螺杆挤出机中同聚丙烯熔融混合后可达到纳米级分散 ,蒙脱石分散片层厚度 <5 0nm ,制备的蒙脱石 /聚丙烯纳米复合材料拉伸强度 33.9MPa、弯曲强度 4 6 .3MPa、冲击强度 74 .2kJ/m2 、热变型温度 (1.82MPa) 5 6℃ ,分别较纯聚丙烯树脂提高了 5 .78%、2 8.2 5 %、1.6 4%和 2 3.6 2 %。     

Preparation of aqueous dispersion of β-carotene nano-composites through complex formation with starch dextrin

Aqueous dispersions of β-carotene nano-composite were prepared through a blending process with a dextrin of high amylose corn starch in immiscible phases of aqueous dextrin and organic β-carotene solutions and water solubility and stability against oxidation of β-carotene were examined. Gradual evaporation of organic solvent during the mechanical stirring allowed the formation of aqueous solutions in which β-carotene was homogeneously dispersed with dextrin. Proper control of the solid concentrations effectively induced the complex formation between dextrin and β-carotene whereas an excess amount of β-carotene (>8 mg) in a dextrin solution (200 mg in 50 mL) induced crystallization and precipitation of β-carotene. The complex particles showed an irreversible endothermic transition of V-amylose (via DSC). X-ray diffraction analysis, however, revealed that the complex had no typical V-type crystalline arrangement. Hydrodynamic size of the complex particles in the aqueous solution could be decreased to nano-scale (16–30 nm) by a mild ultrasonication. The nano-composite contained β-carotene at approximately 30% on a weight, with improved stabilities against oxidation and enzymatic digestion.     

Tunable green-red luminescence in Ho/Yb/Ce: YF3 nanocrystals embedded transparent glass ceramics

The Ho³⁺/Yb³⁺/Ce³⁺:YF₃ nanocrystals embedded transparent oxyfluoride glass ceramics were successfully synthesized and the emission spectra have been measured. We changed the doped concentrations of ion Ce³⁺ in the glass ceramics and unexpectedly found that the different concentrations brought forth different luminescence wavelengths, a tunable luminescence wave band from green to red, which might be useful to the tunable visible laser or display applications. In addition, excitated with wavelength 975 nm LD, the transitions of Ho³⁺: ⁵G₄ → ⁵I₈ at 390 nm, ⁵G₅ → ⁵I₈ at 420 nm and ⁵F₃ → ⁵I₈ at wavelength 490 nm were observed in the glass ceramic GCCe0, while in samples GCCeJ(J=1,3,5,8), the three peaks disappeared.     

Advanced elastomer nano-composites based on CNT-hybrid filler systems

Different techniques to disperse multiwalled carbon nanotubes (CNT) in elastomers using an internal mixer are applied and physical properties of the composites are evaluated: stress–strain behavior, dynamic-mechanical, thermal diffusivity, dielectric and fracture mechanical properties. The electrical percolation threshold is found to decrease by using ethanol as dispersion agent, compared to “dry” mixing, correlating with improved optical dispersion. The effect of nanoscopic gaps between adjacent CNTs on the electrical and thermal conductivity of the composites and the missing percolation behavior of the thermal conductivity are discussed. We have found some technically promising synergetic effects of the hybrid filler systems. For all systems one observes significantly steeper stress–strain curves by addition of 1.6 vol.% CNT to the systems with conventional fillers. In natural rubber the fatigue crack propagation resistance, tensile strength and electrical conductivity is found to be improved also for dry mixed CNT-silica hybrid systems.     

Synthesis and characterization of flame retardant hyperbranched polyurethanes for nano-composite and nano-coating applications

Flame retardant hyperbranched polyurethanes were prepared by reacting phosphorous containing triol, tris(bisphenol-A) mono phosphate, castor oil, and polyethylene glycol with different diisocyanates like TDI, IPDI and HMDI via A₂+B₃ method. In this method A₂ reactants were diisocyanates along with castor oil and polyethylene glycol whereas phosphorous containing triol was used as B₃ reactant and dibutyltin dilaurate (DBTDL) was used as catalyst. Synthesized polyurethans were characterized by gel-permeation chromatography (GPC), elemental analysis, Fourier transform infrared spectroscopy (FTIR) and ¹H NMR spectroscopic techniques. Neat polyurethanes were used for preparing films. Nano-clay composites were prepared with various concentration of organomodified montmorillionite nano-clay. Flame retardant, Thermal and mechanical properties of these hyperbranched polyurethanes and their nano-composites were found out. The polyurethanes and their formulations with nano-clay were also used for the coating of mild steel panels. Scratch, pencil, and impact hardness, flexibility and adhesion properties of coated panels were also determined. Observations show an increase in the scratch hardness and flexibility with the introduction of clay. All the coatings show excellent chemical resistance properties compare to their linear counterpart.     

Nano-composites derived from melt mixing a thermotropic liquid crystalline polyester and zinc sulfonated polystyrene ionomers

A nano-composite was produced by simply melt mixing a blend of a thermotropic liquid crystalline polyester (LCP) and the zinc salt of a lightly sulfonated polystyrene ionomer at 300 °C. The nano-particles, which were in the form of relatively uniform rectangular prisms of ca. 30 nm×30 nm×200 nm, formed from the LCP phase due to an ester-interchange reaction between the LCP and residual catalytic amounts of zinc acetate that were present from the neutralization step in the preparation of the ionomer. The nano-particles possessed a different crystal pattern and higher melting point than the parent LCP, and they were easily oriented when the blend melt was uniaxially stretched. The nano-particles provided reinforcement of the ionomer comparable to what would be expected of short fibers with a modulus of at least 25 GPa.     

In situ reduction of graphene oxide nanoplatelet during spark plasma sintering of a silica matrix composite

Well dispersed silica-graphene nanoplatelet (GNP) and silica-graphene oxide nanoplatelet (GONP) composites were fabricated by optimising their processing conditions. Different processing methods, including colloidal and powder processing, were investigated using different solvents. High temperature and inert environment during SPS resulted in the reduction of the GONP during sintering. The in situ reduction of GONP in the SPS was investigated for various sintering times and temperatures, and characterised using Raman spectroscopy and XRD analysis. The composite sintered at 1200 °C, 50 MPa pressure and 15 min dwell time confirmed the recovery of the crystalline graphitic phase of GNP after reduction without crystallising the silica matrix. GONP was found to inhibit the crystallisation of the silica matrix at higher sintering times and temperatures possibly due to increased viscosity and reduced mobility of the silica particles bound to GNP.     

Nanoparticle reinforced epoxy gelcoats for fiber-plastic composites under multiple load

Novel surface coatings that are load-adapted and suitable for economical manufacturing are required for fiber-plastic composites subjected to complex loads. They must have good wear and chemical resistance compared to conventional thermoset coatings (paints, gelcoats), and high failure strain and adhesive strength compared to metallic or ceramic protection layers. Polymeric nanocomposites offer particular advantages in this respect. Given this background, the main aim of this work is to characterize and evaluate surface-protection layers made of metal oxide nanoparticle reinforced epoxy gelcoats for mechanical, tribological and media loaded fiber-reinforced plastics (FRP). The focus is set on the property characterization of the heterogeneous gelcoat as a function of particle material and filler content, as well as the adjustment of the required rheological properties of the liquid particle-resin dispersion so that nanoparticle reinforced gelcoats can be applied to the anisotropic FRP substrate by spray processing in an economical and variable-geometry manner.     

Lithium ferrite (LiFe5O8)/polymethyl methacrylate (PMMA) nano-composite used in high dielectric constant capacitor and electromagnetic applications

Poly methyl methacrylate/ Lithium ferrite nano-composites have been prepared by solution mixing process. The electrical conductivity and dielectric properties of these prepared nano-composite have been investigated in the frequency range 10²–10⁶ Hz at different LiFe₅O₈ concentrations from 0 vol% to 25 vol%. The prepared samples are studied by thermal gravimetric analysis (TGA) and X-ray diffraction (XRD). Moreover, the magnetic properties of these nano-composites are investigated through vibrating sample magnetometer studies. XRD spectral investigation revealed that the structural of PMMA and its chemical characterization are appreciably affected by mixed lithium ferrite filler. The thermal stability of the PMMA matrix was found to increase appreciably by LiFe₅O₈ loading. The (I-V) characteristic of these nano-composites are in very good agreement with the non-linearity predicted by Kaiser et al. model. The effective dielectric constant is studied through different proposed models. Saturation magnetization of 10.05 emu/g is achieved for PMMA sample loaded with 25 vol% of LiFe₅O₈ particles.