丙烯酰胺聚合物自由基聚合引发体系研究进展

丙烯酰胺类聚合物是应用较为广泛的水溶性高分子化合物,自由基聚合是大规模生产聚丙烯酰胺的有效方法。文章对自由基聚合偶氮类引发剂、氧化还原引发体系、复合引发体系的特点和研究应用进行了讨论,认为采用水溶性偶氮引发剂、含胺的氧化还原引发体系、含胺基功能性单体类引发剂等新型引发剂能制备高分子量的聚合物,合理设计新型复合引发体系可利于聚丙烯酰胺相对分子质量的进一步提高。     

Structural Optimization and Improved Discharged Energy Density for Niobate Glass‐Ceramics by La2O3 Addition

The structural and dielectric properties were investigated in the La₂O₃ added glass‐ceramics based on complex niobates. With the addition of La₂O₃, the optimization of microstructure was observed which resulted in the improvement of breakdown strength for the glass‐ceramics. Besides, the dielectric constant was drastically enhanced because of the doping effect of La³⁺ in the A‐sites of both crystallographic structures. Due to the combined effects of both high breakdown strength and polarization difference, the maximum discharged energy density of 1.2 J/cm³ was achieved in the niobate glass‐ceramics with 2 mol% La₂O₃, suggesting dielectric glass‐ceramics of this composition could be the most attractive candidate for high‐energy density capacitors.     

Reinforcing and Flame-Retardant Effects of Halloysite Nanotubes on LLDPE

Halloysite nanotubes (HNTs) were used to compound with linear low density polyethylene (LLDPE) to prepare composites with better mechanical properties and higher flame retardancy. The PE graft was used as interfacial modifier in the LLDPE/HNTs composites. HNTs were showed to be a promising reinforcing and flame retardant nano-filler for LLDPE. The mechanical properties and flame retardancy as well as thermal stability of the composites can be further enhanced by the addition of the graft copolymer. Morphological observation revealed that the graft copolymer could facilitate the dispersion of HNTs in LLDPE matrix and enhance the interfacial bonding.     

Synthesis and Properties of a Novel Intumescent Flame Retardant (IFR) and Its Application in Halogen-Free Flame Retardant Ethylene Propylene Diene Terpolymer (EPDM)

The PDP, a novel intumescent flame retardant (IFR) with high charred residue of 40.8% in N2 at 700°C by TGA was synthesized successfully for preparing halogen-free flame-retardant EPDM composites. The UL-94 V-0 rating was achieved for EPDM composites with 20 phrs carbon black at the same time by using only 60 phrs PDP. In situ FTIR spectroscopy reveals that P–N rich charred residues are formed through the interaction between hydrogen atom in weak base of P–NH–C and phosphate. SEM characterizes the formation of intumescent chars during burning. The mechanical properties of composites are also discussed.     

New heat-resistant polytriazole adhesives: investigation of adhesion of polytriazole resins to metals

Crosslinkable polytriazole resins (CPTs) were synthesized by 1,3-dipolar cycloaddition reaction between azide and alkyne monomers. Adhesion properties of CPTs and an epoxy resin to different metal substrates (copper, iron and aluminium) were evaluated in terms of the tensile lap shear strength. CPTs to aluminium and iron substrates have higher adhesion strength than those to copper substrates. The effect of temperature and humidity on adhesion strength has been investigated. The resin CPT-3 has the best heat resistance among CPTs, whose retentions of adhesion strength are approximate 80% at 150?°C and 70% at 180?°C to all the substrates. CPTs have high adhesion properties at high temperature and humidity as compared with an epoxy resin.     

Simulation and experiment study on adhesive ejection behavior in jetting dispenser

In this paper, fundamental equations for jetting dispenser are presented to express the influence of adhesive pressure, nozzle diameter, and needle movement law, and the equations are then verified by flow behavior simulation. Subsequently, a novel jetting dispenser system is built to finish experiments about the mentioned influence parameters, and simulation results verify the regularities from experiment are correct. Flow velocity in the central nozzle will be faster and radius of the droplet will be bigger if the pressure in the chamber became higher, flow velocity in the central nozzle will be constant and the radius of the droplet will be bigger if the dead time became longer, and bigger nozzle diameter can lead to faster flow velocity in the central nozzle and bigger droplet. Besides, these mentioned works prove that our designed jetting dispenser is practical and useful for adhesive jetting.     

Viscoelastic and adhesive properties of polystyrene-hydrogenated (3,4-polyisoprene and 1,4-polyisoprene)-polystyrene and polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate-based HMPSA

In the current study, hot melt pressure sensitive adhesives (HMPSA) were prepared by blending polystyrene-hydrogenated (3,4-polyisoprene and 1,4-polyisoprene)-polystyrene (HYBRAR7311), polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (LA2250), tackifier, and other additives in an internal mixer. The compatibility of LA2250, HYBRAR7311, and glycerol rosin ester was investigated on the basis of transparency, differential scanning calorimeter, and scanning electron microscope. The results indicated that glycerol rosin ester was compatible with HYBRAR7311 and LA2250, while HYBRAR7311 was only partly compatible with LA2250. Besides, styrene-ethylene-butene-styrene block copolymers grafted MALEIC ANLYDRIDE was used as compatibilizer added into HMPSA. Although it increased the compatibility and shear strength yet the tack and peel strength were sharply decreased. Simple variable method was used to study the effect of main components on the tack, peel strength, and shear strength of HMPSA. The relationship between adhesive properties and viscoelastic properties of HMPSA was studied via dynamic mechanical analysis. The investigation showed that the smaller storage modulus at low frequency (0.01–0.1?1/s), the larger the tack. Peel strength was found proportional to G′′(f₁)/G′(f₂)(f₁?=?32.03?1/s, f₂?=?0.07?1/s). Similarly, the effect of this blend on damping performance and substrate on peel strength of HMPSA was investigated which was found excellent in this case. The peel strength of polypropylene was larger when HYBRAR7311 content was more than LA2250. However, the peel strength of polycarbonate and polyethylene glycol terephthalate was larger when LA2250 content was more than HYBRAR7311. Furthermore, the mechanical properties of HYBRAR7311/LA2250 HMPSA were found to be superior to the one-polymer HMPSA.     

Synthesis,calcination and characterization of Nanosized ceria powders by self-propagating room temperature method

Nanometric ceria powders with fluorite-type structure were obtained by applying self-propagating room temperature method. The obtained powders were subsequently thermally treated (calcined) at different temperatures for different times. Powder properties such as specific surface area, crystallite size, particle size and lattice parameter have been studied. Roentgen diffraction analysis (XRD), BET and Raman scattering measurements were used to characterize the as-obtained (uncalcined) powder as well as powders calcined at different temperatures.It was found that the average diameter of the as-obtained crystallites is in the range of 3–5 nm whereas the specific surface area is about 70 m²/g. The subsequent, 15 min long, calcination of as-obtained powder at different temperatures gradually increased crystallite size up to ～60 nm and reduced specific surface down to 6 m²/g. Raman spectra of synthesized CeO_2?y depicts a strong red shift of active triply degenerate F_2 g mode as well as additional peak at 600 cm^?1. The frequency of F_2 g mode increased while its line width decreased with an increase in calcination temperature. Such a behavior is considered to be the result of particle size increase and agglomeration during the calcination. After the heat treatment at 800 °C crystallite size reached value larger than 50 nm. Second order Raman mode, which originates from intrinsic oxygen vacancies, disappeared after calcination.     

Enhanced light scattering and photovoltaic performance for dye-sensitized solar cells by embedding submicron SiO2/TiO2 core/shell particles in photoanode

The introduction of light scattering in the photoanodes of dye-sensitized solar cells is one of the most effective approaches to enhance their photovoltaic performance. In this work, we prepared submicron SiO₂/TiO₂ core/shell particles and embedded these particles in the nanostructured TiO₂ photoanodes for light to scatter in the dye-sensitized solar cells. Due to the large difference in the refractive index between the SiO₂ core and the TiO₂ shell, the embedded submicron SiO₂/TiO₂ core/shell particles showed strong light scattering effect. Light absorbance of the dyed photoanode with the embedded SiO₂/TiO₂ particles for light scattering was found to be three times stronger than the one without light scattering particles over a wide wavelength range. The power conversion efficiency of dye-sensitized solar cells was increased by about 50% after the introduction of light scattering SiO₂/TiO₂ core/shell particles in the photoanode. This work will provide a base for further enhancement in the photovoltaic performance of dye-sensitized solar cells by optimizing the submicron SiO₂/TiO₂ core/shell particles and the photoanodes.     

Electrochemical fabrication of polyaniline/MnO2/graphite felt as free‐standing,flexible electrode for supercapacitors

Polyaniline/MnO₂/graphite felt (PMGF) composite, which can be used as a novel free‐standing, flexible electrode for supercapacitors, was fabricated via a facile electrochemical method. Polyaniline/graphite felt (PANI/GF) electrode was prepared by electropolymerization of PANI onto the GF. Subsequently, manganese dioxide (MnO₂) was electrodeposited on the surface of the PANI/GF electrode to prepare PMGF electrode. The microstructure and morphology of the as‐prepared samples were characterized by Fourier transform infrared spectra, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. Specific surface area was examined using N₂ adsorption/desorption test. Cyclic voltammogram, chronopotentiometry techniques and electrochemical impedance spectroscopy were introduced to investigate the electrochemical performance of the composites. The PMGF electrode exhibited specific capacitance as high as about 630 F g⁻¹ at the current density of 0.5 A g⁻¹, which is much higher than that of PANI/MnO₂ composites reported previously. The high specific capacitance of PMGF may be attributed to the fact that the porous GF is a good conductive matrix for the dispersion of PANI/MnO₂ and it can facilitate easy access of electrolytes to the electrode, which results in enhancement of the electrochemical performance of the composite. Moreover, the specific capacitance of PMGF is much larger than that of MnO₂/GF (MGF), which may be ascribed to the participant of PANI, which contributes additional pseudocapacitance and electron transport path. POLYM. COMPOS., 34:819–824, 2013. © 2013 Society of Plastics Engineers